solarbird: (pingsearch)

In an audio device with a tone knob, and an on/off switch by that tone knob, which “ON” makes more UI sense?

What does "ON" mean?

  • [ ] ON: TONE KNOB is on, knob has effect on sound
  • [ ] ON: BYPASS is on, knob has NO effect on sound.

CLICK HERE TO ANSWER

This is an honest question. I mean, I’m going to wire it up so that “ON” means “tone knob on,” because that’s how I roll, but I see this go the other way a lot.

(Also in this case “tone knob” means “low pass filter” which means “removes high frequencies” because AND THERE YOU GO. See? SEE?)

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solarbird: (made her from parts)

Remember a long time ago – like, a little over three years ago – I built a ribbon microphone? I had all kinds of problems chasing radio interference ghosts and stuff, it was strange and messy but came out with a neat sound in the end.

Except… even after fixing the RF problems, it was kind of noisy. Not unusably so, not for direct-miking, which is how I’ve used it, but still… kinda noisy. Noisier than it should’ve been.

I rediscovered this when trying to use it in a “mid-side” type mic setup with the new RK-47, which I was doing just to see how that would work. (Tony of Vixy & Tony has been after me to try that for a while.) And because it involves playing towards a figure-eight microphone from the side – the point of least sensitivity – it required enough extra gain that the noisiness became a problem.

Since the special preamp (also a kit) was the entry point for the RF noise, and since said amp works with dynamic microphones, I tested that for noise, using an SM-58 as input. Dead silent, cranked all the way up. Result: it wasn’t the microphone preamp’s fault.

Then I remembered how the RK-47/990B build manual talked so much about making damn sure you had no solder rosin or finger oils at the high-impedence connection points in the circuit, and to just scrub those connections with isopropyl alcohol. So I took apart the ribbon microphone, redid those solder connections while I was in there, and then scrubbed the hell out of them. A downright confusing amount of old solder rosin came up when I did so.

Result? Problem sorted. Huge drop in noise. There’s still a little at the high end at probably more gain than I even need here – this may be an “only elves can hear this” moment, at least in part – but a little -3db cut starting at 14-15kHz sorts it. It might not even be true noise, it could be something like air movement – ribbons will pick that up in ways nothing else will, and I didn’t turn off the HVAC, etc.

So, yeah! Turns out that finicky bit about solder rosin and flux is real important, kind of generically, at high impedance. Good to know. (And is why I’m posting this, and why I’ll link to it from the old microphone buildout writeups.)

I still have not the vaguest idea why so much rosin ended up on those connection points. Seriously, it’s weird. That was my old stock of Radio Shack silver solder, which I’d had since I Don’t Even Know When, and not the BenzOMatic solder that gave me so many problems. I never noticed it doing that before – but then again, I wasn’t really looking. ¯\(ツ)/¯

Anyway, have a test recording I made at 1:30 yesterday morning trying out that configuration, with the Micparts RK-47/990B kit mic being used as the “mid” and the above-mentioned Austin OTA-1 ribbon microphone as the “side.” It’s intermixed with a recording made simultaneously using a pair of M-Audio Novas in a spread X-Y configuration. Both versions are mixed directly to mono, rather than spread-stereo, which is not what you usually do, but does allow maximum left-right placement in a mix.

(This may be called “T” rather than “mid-side” since mid-side includes a kind of subtractive mixing not used here? I dunno. But this is, again, just a straight mix to mono.)

The recording starts with the RK47/990B plus OTA 1 pair, then switches back and forth between that and the Novas. Remember: all of this is mono.

Kinda neat, eh?

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solarbird: (made her from parts)

Build reports are nice enough. (I wrote up a little errata post yesterday, by the by.) But the real question, of course, is how does the RK-47/990B kit mic sound?

Early impressions are surprisingly good. Even with only the single microphone, there’s a sense of presence and space – even with a purely mono signal path – that I normally have to dual-mic to attain. Also, it has tremendous precision – this is a mic capable of great subtlety. And the amount of gain built into the microphone itself is crazy – this is one spicy meatball of a microphone. That’s something you won’t hear in recordings, but it results in a lower noise floor, which is always good.

Let’s start with some unsubtle differences, ones that’ll show up on laptop speakers. Because while I’ve never liked the MXL-990, they sell a zillion of ’em, and we should make a couple of direct comparisons.

Here’s a snippet of chords from “Lukey,” alternating between the MXL-990 (unaltered factory) and the RK-47/990B. It starts with the MXL-990, then transitions in-song to the RK-47, then back and forth. It ends with the RK-47. It’s a pure mono signal path until prepped for uploading to Soundcloud.

And here’s a short melody, on zouk – again, starting on MXL-990 (factory stock), then RK-47, then back to MXL-990. The last phrase is repeated to allow us to end on the RK-47; also, I wanted that ending bit to be presented on both microphones. The glissando really highlights some of the differences.

But that’s shooting fish in a barrel, as it were. The MXL-990, while popular, is not a good microphone. We should do comparisons to microphones I actually like – let’s say, the M-Audio Nova. At about twice the price of the MXL-990, it’s still a cheap microphone, just one I consider entry-level competent. But it has issues – not the least of which being it’s kind of a noisy beast as these categories of microphones go.

So let’s take the easy swing – here’s a sharply boosted noise level comparison of the RK-47 to the M-Audio Nova, at equivalent gain levels. This is not the noise you’d actually hear; I recorded a silent room at gain appropriate on each microphone for instrument recording, then cranked that recording up 32db for easy noise levels comparison.

Unfortunately, this really requires headphones, because it’s RK-47 on left, Nova on right:

NOT SUBTLE. But also, an easy shot. The Nova is noisy and everybody knows it. There are some mods out there to improve that, but they change the sound a bit in ways I don’t like, so I work with it.

comparison of waveformsSo let’s dig down a bit. Pictured here is a snippet of waveform from a bit of music played, in mono, over my studio monitors, into identically positioned microphones relative to those speakers. These two recordings were made simultaneously.

You’ll note in this highly-zoomed-in render how the RK47 waveform remains clear and unmuddled in these extremely rapid changes, while the Nova’s blurs into a bit of a mush. That’s the sort of thing I’m talking about, and also, the sort of thing you can hear in these very short snippets of horns from a jazz track. This comparison requires headphones, possibly good ones:

They’re short because they must be uncompressed for best comparison – sorry about that – but listen to them a few times and compare. Note how the edges of detail – bits which add flavour – are blurred in the Nova, but retained in the RK-47. Neat, eh?

That out of the way, let’s step up a level in comparator microphones. Oktava 012s are considered very good affordable microphones, particularly strong in their price ranges, and street for a new 012 and one pickup is comparable to the cost of this kit. With a second head (to add a second pickup pattern, as this mic has), it’s a bit more. They’re small-can capacitor instrument mics, rather than large-can, but we’re doing instrument recording, so that’s fair. The components inside – particularly older ones picked up used – can be a bit dodgy, but the design is great and the pickups are great, and you can upgrade the iffy capacitors and the suspect transistor if necessary. I have, of course, done this with mine.

Here’s the intro to “King of Elfland’s Daughter,” on the Oktava 012 (upgraded components) and the RK-47/990B kit. This recording repeats phrases, with the Oktava 012 first, then the RK-47/990B. Pure mono signal path, identical recording setup made within a few minutes of each other, but not simultaneously, as you can’t put two microphones in exactly the same place and I wanted the most equal comparison I could, modulo performance limitations. This probably also requires headphones, as the 012 is a pretty darned precise microphone itself:

44.1khz/16-bit uncompressed WAV file version here.

Once again, I’m finding that the RK-47 has a real staging advantage. There’s a sense of in-the-room presence with the RK-47 that I can make happen by dual-miking with my other microphones and mixing down, but not directly in mono.

Now, I don’t want to leave the impression that it is BEST AT ALL THINGS, because it’s not. These aren’t the only recordings I made – they’re just ones that show differences best. The first example I found was mandolin – the Nova likes my mandolin better than the RK-47 does. The specific response behaviour and foibles of the Nova work in its favour; a single RK-47 may have more presence and precision than a single Nova, but the Nova recording sounded more musical just the same. I’m sure there will be other examples as well.

In the end, I think this will probably become a heavy-use microphone in my kit. It may even become my go-to mic on the zouk – I need to do some stereo and multi-distance comparisons before I will know that for sure, but it’s looking very good. I also like what it does with piccolo and flute. I haven’t done any playing around with fiddle or drums, and one thing I want to play with is a two-mic setup with the ribbon kit mic I built, to see how those behave together – it’s a mic placement technique I’ve wanted to try for a while, but have never got round to testing. Now is probably the time.

I kind of wish I’d ordered the matched-pair version of this microphone kit. But it would’ve cost twice as much and I couldn’t know in advance I’d like it this much, so.

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solarbird: (made her from parts)

A bit of errata on the micparts rk-47/990B kit microphone build report yesterday:

First, I didn’t mention that the board kit includes extra capacitors, to be used either for different capsules than I chose, or to tailor the response curve of the microphone. I went for flattest response, but I could’ve had more or less high-end responsiveness by choosing which included tone capacitors to use.

Second, I said that the “omni” switch setting probably wasn’t really going to be actually “omni,” but was more likely to be figure-eight or the like. This was in response to both the capsule design, grille design, and older pictures of the circuit board which appeared to indicate that. In testing, I discovered that I was mistaken – as you can see here, levels as seen in waveforms made by holding a tone generator at the four cardinal directions remain constant. But read on, after the graphs, because there’s a catch:


rk-47 set to omni, against tone generator at 30cm, front, right, rear, left positions

And here’s the same test, with the mic set to cardioid:


rk-47 set to cardioid, against tone generator at 30cm, front, right, rear, left positions

And here’s an M-Audio Nova, same conditions, for comparison:


nova, cardioid, against tone generator at 30cm, front, right, rear, left positions

The total pickup is certainly omnidirectional. But this is not a true basket head on this thing, there are support brackets on the left and right sides, and that does affect tone! High-end harmonics definitely fall off on the left and right sides.

So while it does qualify as an omnidirectional microphone in “omni” mode, I’d have to call it flawed in that mode, and use something else – like an Oktava 012 with the omnidirectional head, which is built for true omnidirectional pickup and does not exhibit this behaviour.

Alternately, I suppose it might be usable in that mode if you’re recording someone who is a tad screechy – aim the wrong side at the performer and presto, fewer high harmonics. EVERYBODY WINS XD

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solarbird: (made her from parts)

After a few suggestions that I do so, I finally went ahead and splurged for another kit microphone – the micparts RK-47 capsule and amplifier circuit board, both sized to use the dirt-common MXL-990 microphone case.

The MXL-990 is kind of a go-to microphone for people just starting at home recording. I don’t recommend it, even in that role; I think it’s a nasty piece of kit and sounds terrible. Even at $50 – the used price, roughly – you’re better off spending another $40 and getting a low-end AKG or Nova. But it is about the cheapest condenser microphone with XLR out that you could pretend to treat like a real mic, and that has meant a thriving mod community.

Here are the basic parts included with the kit. I didn’t have the capsule out – the actual thing that vibrates to sound – because it needed to stay in its protective box until installation.

This is technically an MXL-990 mod, one wherein nothing is kept but the case and socket. It’s also a nontrivial assembly, so I’m going to talk about building in this one, and have some sound samples in the next.

You can see the instruction booklet over on the right. It’s quite clear, and has some important commentary, about extra care being needed not to touch certain components any more than you have to, and which parts are particularly sensitive to heat. It does not say up front that about 25 pages in it will suggest that you use a couple of chemical products if you have them, so I ended up having to order some purple loctite and conformance coating.

If I had it to do again, I probably wouldn’t order the conformance coating, because the MDA sheet on that is not attractive. But now that I have it, I might as well use it. If anyone local needs some, let me know.

As you can see, the board is clearly labelled:

For the most part, this is one of those insert-and-solder projects. The tolerances are reasonable, though they were emphatic about working at a meaningfully lower iron temperature than I prefer. If you use 60/40 lead solder, their temperature would be fine.

(I ran at 350°C, which is a little hotter than they recommend, but I use silver solder, and it seemed to work out. In these cases, I solder only one leg from each component, then cycle back to the start, and do the second leg, then cycle around again for the third if necessary. This lets the heat that is building up in the component itself dissipate, reducing peak temperature inside the component. This is most important with semiconductors, usually – particularly transistors.)

They also have you cleaning the board with isopropyl alcohol regularly, and suggest cleaning your iron between each solder point. I don’t know if they just meant wiping the tip or actually using the sal ammoniac, so I kind of compromised. (Though for the most sensitive components, I did do a complete sal ammoniac cleaning between each point.)

This is the board essentially complete:

The process is a bit fiddly, I have to say. They’re quite strict in the manual about flux cleanup and so on, so you’ll end up using tweezers and foam swabs and lint-free cloth and and and. Still, with kits this expensive, it’s best not to take chances.

You might note that the connections on the switch are not made yet; that’s because you’re wiring two of the leads from the pickup to the circuit at these points directly. Those connections are where they’re most persnickety about how things are to be done – but I followed their directions precisely and it worked out.

Here’s the new RK-47 pickup canister in its mount:

I’m liking this canister already, at this point. I know, I know, “good feel” is silly, but this capacitor pickup has a good materials feel to it. The mounting system you see in use is also partly a replacement – the original was a ring mount system; this is a saddle, larger, and is also where you need the threadlocker. I’m not convinced MXL used a threadlocker on that post, but I see how the larger, heavier pickup does kind of call for it.

Once the board is mounted back into the bracket and grille, you end up with this:

And once you’ve wired the three leads from the pickup and the three from the XLR connector, you’re pretty much ready to test.

I did have an initially-worrying test result: voltage at the primary test point – the one you conduct before any audio checks – was running high. The manual had a lot to say about what you’ve probably done wrong if it runs low, and further tests to isolate your mistake, and spends a couple of pages going on making sure you’ve got a bare minimum of 45V going to the exciter, with a preferred minimum of 50v, and an “operating range” of 50-62v, where 60v is optimal.

The range on mine ran from a low of 62.45v to a high of around 68v, so I was concerned. But it turns out the actual operating range is 50v-70v – they just don’t expect anybody to be able to get to the upper end. Support even said that if I was mostly recording quiet material I could safely crank it up to 65v full-time for an even hotter pickup, but, heh, that’s not what I generally do, so I’ll leave it where it is. XD

As for the sticker – I put “MP-SVS” over the “MXL” logo because at this point, it’s not an MXL microphone in any way, so why would I keep that? It’s just silly. MP-SVS is MicParts-Supervillain Studios, naturally. I also changed the model number to RK-47, after the canister number.

I did not mention before that this is a switch-selectable dual-pickup-pattern microphone:

That will let me try an instrument miking style I’ve wanted to try for a while anyway. The only downside of using an existing microphone housing is that the switch has to live on the inside, and you have to unscrew the bottom of the housing to get to it. But it’s just twist-open, so not really an issue.

Regardless, as you can see, the switch says “cart” (for cartioid) and “omni” (for omnidirectional), but I think I’m pretty sure it’s really more figure-eight, given the construction of everything and what the switch does. And pictures in the manual actually agree with that – the printing on the board is different in the photos.

An optional modification to the case involves coating the lower half with silicate caulk (or a couple of other listed materials). I, of course, did that too:

The idea is that this reduces case resonance. Does it? I dunno, I just went ahead and did it because silicon caulk is dirt cheap – the local hardware store down the hill had a small tube for three dollars. The lack of silicon at the top is necessary – the upper part of the case scrapes into the lower half quite tightly, and any added material would be scraped off right away. As you can probably see, it’s even scraping off its own coating.

This is what it looks like all put together, and put in the standard MXL-990 shock mount:

As always, larger versions of the photos are at my Flickr account.

All in all, I’d call it a straightforward well-documented build. It’s far from the most difficult I’ve done. Not a good starter project, but if you’re reasonably good with a soldering iron, you’re going to be fine.

And this is already a long post, so I’ve decided to make it Part 1 of 2, and will talk about the important part – what the result sounds like – next time. Spoiler: a whole hell of a lot better than an MXL-990. But it also has audibly (and visibly, in the waveform) finer and more precise pickup than, say, my Novas.

I’m also going to see if I can’t do some comparisons to my Oktava 319 and possibly the (already-improved via mods) Oktava 012s as well before next time. That, too, might be interesting.

Have a good weekend, everybody!

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solarbird: (made her from parts)

I thought I was going to be posting about a new microphone I built today! I was pretty sure I could get the kit construction finished and even make a couple of recordings.

And I could’ve, but no, I had to have one of these moments:

…wherein on page 24 of the assembly instructions it talks about connection sealing material and special kinds of thread-locking fluid which aren’t strictly necessary but are definitely good to use, if, you know, you just happen to have them around, and if you don’t, well, you can add them later but EVERYTHING WILL EXPLODE.

Particularly the connection sealing material. Apparently.

None of this was in the components and tools list up front. Of course. So thanks, now I get to order all that stuff, which I already have, and it’ll get here Wednesday. (No, it’s not at the local hardware. I did check!)

Anyway, this is how far I got, and where it’ll be until Wednesday:

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solarbird: (molly-oooooh)

I wanted to post about the cool second-generation crystal microphone today BUT NO IT’S ALL STUPID AND NOISY AND I DON’T KNOW WHY but it sounds like either a really bad cold solder joint (please be that) or a bad transistor (@&*$&!!! special orders please don’t be that) and I don’t know which.

It’s too bad because I came up with a nice little jury-rig jig (say that five times fast) and so the backplate of the housing came out really well and I was looking forward to showing that off. Fingers crossed this is some sort of Surprise It’s Easy! fix – that would indeed be a surprise, to be honest about it, but a pleasant one.

In the meantime, enjoy this video of Overwatch players in custom game mode making some genuinely gorgeous Genji Beams. These are effects created by lining up opposing teams of Genji players opposite each other, in continuous-shot-deflection mode, and hitting them with various weapons. The shots bounce back and forth between the teams, and you get some really neat graphics interactions. It’s pretty cool and occasionally hilarious. Enjoy:

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solarbird: (pindar-most-unpleasant)

i was going to post the more than vaguely punchdrunk tweetstorm from my 13-hours-and-counting marathon run-in with Microsoft technical support about why windows hadn’t been letting me install security updates since AUGUST directly into the blog, because some of it is pretty funny

and i’m gonna do that anyway

but the seventh (7th!) tech sport did something i specifically said we cannot and must not do and destroyed my desktop machine, which drives all my audio software

(seriously, completely levelled it, i’ve got partition recovery running right now)

(broken boot table, no more linux system partition, no more swap partition, can’t even get to windows loader because grub2 is 100% made of “wot?”)

so i just storified the twitter rant instead of making a fake collection here (it’s pretty ragehappy) and then played the hilariously stupid current special brawl in overwatch, which is all pharah and mercy (phamercy brawl! <3) and double TriplQUADRUPLE kill Play of the Game until i felt better.

because it turns out i get pretty good at smashy brawls when i’m, like, really mad and have rocket launchers.

so, yeah. fun? enjoy my ranty goodness while I’m rebuilding my machine, again.

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solarbird: (music)

Oktava has some great microphone designs. But the quality of the components can be pretty random, particularly in the used market, since a nontrival number of those were made in the early post-Soviet era. My two 012s sounded pretty different – one in particular rather unpleasantly harsh – so I implemented Recording Magazine’s recommended component upgrade* on the harsh one, which we’ll call Nr. 1.

Nr. 1 may have been modded a bit before. It’s certainly been opened before; one of the three screws was stripped and useless, the other was jammed badly. I had to drill both out, so I’m hoping I can order replacements. The third was fine.

As soon as I had the microphone open, I saw what Recording meant by random components. The key transistor was a make so old that it had a metal shield ground cap, and separate lead to that cap, something I haven’t seen in gear made after about, I don’t even know, 1978? I also saw what they meant by “fragile circuit board,” because wow, you could lift these circuit board traces with an overly-aggressive hair dryer. Take care!


Comrade!

Still, it was mostly a matter of being methodical and not rushing things, and in good time, I had the key components upgraded, with no surprises other than the transistor’s extra lead.

These are three unmodified before/after snippets in one recording – recorded under identical conditions other than the internal microphone electronics – of Oktava mk-012/mc-012 nr. 1 in my studio. Even on laptop speakers, I can hear the harshness, particularly in the first sample. In all cases, it’s pre-modification first, then post-modification after:

Oktava MC-012 nr. 2 sounded very different to nr. 1, before; opening it, I could see that the components used were of a significantly more modern variety. It may well have been made later, which would be part of that. Now, the two microphones sound much more like each other, indicating that nr. 1 really was meaningfully different in component quality.

Here is a recorded comparison of nr. 2 (still factory) and nr. 1 (upgraded). These recordings were made simultaneously, with the two microphones right next to each other. The differences are much subtler, but I think the upgraded nr. 1 has a bit more presence – or maybe sense of stage – than the factory nr. 2. Despite being mono recordings, it’s almost like there’s a slightly better stereo image in the modified nr. 1… but give a listen and hear for yourself, see what you think.

You’ll definitely need headphones to have any chance of hearing anything interesting here. Factory nr. 2 comes first in all cases:

So, all in all, very glad I did this to nr. 1; pretty sure I’m going to go ahead and do it with nr. 2 as well, though I expect a much less dramatic change.

The only thing I’m thinking about now is – there’s a bank of capacitors in back. They’re good ones – Philips, not generic, which have a good durability and spec-compliance record. (I don’t know whether they’re original; some Oktava 012s shipped with quality caps already in place, and their track record has improved with time.) So I shouldn’t need to upgrade them – and the article at Recording Magazine says not to bother if you already have “improved” capacitors.

But I don’t know how old these are, and electrolytics have a lifespan. That’s measured both in calendar time (years), and in use – tho’ the latter is in tens of thousands of hours, and these mics are certainly nowhere near that.

The small downside is time spent, the large downside is the possibility of circuit board damage, which wow I don’t want. The upsides would be 1. possible sound improvement if they are aging already, and 2. Never having to think about it again, in practical terms.

So I dunno. Get it out of the way, or leave sleeping caps lie? Hm.
 
 


*: errata for the linked article: Capacitor “C6” in the parts list is actually capacitor C1; there is no “C6” in the build description or circuit diagramme; I assume this is a typo.

Also, some of the items in their parts list are no longer made, but they have exact replacements. R1/R2 exact replacement part number as per my October 2016 Digi-Key invoice: MOX200J-1000ME-ND. Capacitor C1 (listed as “C6” in parts list, see previous paragraph) current part number: 445-4737-ND. Capacitor C2 current part number: 399-1418-ND. Capacitors C3 and C4: 4073PHCT-ND. Capacitor C5: 4047PHCT-ND. Mostly, the substitutions are lead-free versions replacing earlier versions with lead.

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solarbird: (made her from parts)

I made a thing! It’s called a focus knob. It’s quite simple and normally you’d built it into an electric guitar as a guitar mod, but since I don’t have an electric guitar, I built it as a pluggable external box.

Basically a mild high-pass filter that serves to pull out ‘boominess’ from instruments, it puts a bit more of an edge on an instrument’s sound – the more you turn it up, the greater the change. As effects go – on my zouk, anyway – it’s pretty subtle. But it’s also the kind of shift that is multiplied by later effects added in, and changes how later-in-chain boxes like distortion pedals work.

As you can see from the instructions here, the wiring takes all of about 20 minutes’ time. But it’s good warmup for making a bunch of component upgrades to my Oktava 012s, and I already had all the parts from the Great Radio Shack Lootfest of 2014. Plus, hey, cool hard candy tin!

So I have a a HARD CANDY knob now. It goes from Hard to Candy. Yum. 😀

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solarbird: (pingsearch)

So the new iPhone is out, and as predicted, it does away with the standard, unencumbered, unrestricted-by-patent 3.5mm audio connector. You can read about the release on BuzzFeed’s pretty decent writeup if you like. And this matters, even if you have an older phone, or an Android phone, because Apple is the kind of 10,000-pound-gorilla that can shape markets in this area. Even if you’re not an Apple user, this throws expectations around for the future.

There is an adaptor – really, a mini-interface-card disguised as a cable adaptor – to let you use 3.5mm devices with the lightning port. It has to contain a D/A converter and a small amplifier. One will be included with the new phones, and it costs $9 and doesn’t make your cable weird – it’s not some big block like the previous 30-pin to Lighting interface, and it’s not $30.

I have concerns about how good a job a $9-retail D/A converter and amp unit is doing to do at rendering quality audio. It will be very tempting to make it deliver “meh” quality output, and push people to new gear. That’s short-sighted, but let’s not pretend that stops anyone.

Countering that concern is the fact that at least at one point, Apple required a specific D/A converter for the Lightning audio standard: this one. I have no idea whether that’s still a requirement. But if it is, I’m willing to assume a baseline of competence for it – anything else would’ve been suicidal for the spec right out the gate.

I’ve heard a lot of people talking about whether the new interface is built for digital rights management (DRM) as the long goal. I genuinely don’t think so, because it doesn’t really add much capability they don’t already have. Sooner or later, you have to go to analogue, and unless they want to remove the capability to connect to high-end audio equipment – and Bluetooth does not cut it for audiophiles, or necessarily even mid-philes – there has to be a way to hook up to standard, not-Apple gear.

You can’t get around that. Lest people forget, an Apple-provided solution for this already exists in the form of the dock – shown on the iPhone 7 front page, too. It’s not going away. And the reason it won’t go away is that while audiophiles are not a big market, they are exactly the kind of lifestyle market Apple wants and needs in order to support its brand, and more importantly, its markup. That’s not tech; that’s image management. Even without Steve, Apple knows its image.

Similarly, they can’t cut off concert musicians and DJs from plain old analogue output. There are too many audio pros out there using phones now, and while that market isn’t actually large, it’s a market Apple still invokes in image, and it’s too perceived as cool for Apple to throw overboard without throwing another serious wrench into its branding.

And frankly, with the recording industry betting what’s left of the farm on streaming, they don’t really don’t seem to care much about DRM on plain audio anymore. The RIAA destroyed the value of owning music, so from their point of view, who cares? Music is the billboard, not the product. I just really can’t see this as “HDMI for audio.”

So from a consumer standpoint, mostly I see “Apple has made your headphone cable annoying.” Even that’s assuming you’ve got your own headset and aren’t using the one Apple included, which most people do and will continue to do.

Now, this does get more complicated for musicians and DJs. Even if the included little cable adaptor is good – and let’s say it is straight up great – then you can’t trivially run the new devices on power and interface directly to performance gear anymore. That’s a headache. “Oh shit, I forgot to charge my phone” becomes a critical failure. Best case is you get a new device for that – and the dock is not suitable, you need something you can’t knock over or drop – which means one more damn thing to buy and carry around and/or lose.

Let’s also say you’re using some sort of audio software on the phone, and it doesn’t have a way to save files that you can transfer to other devices. (Even the software I have which does this doesn’t do it easily or well, it’s kind of a pain in the ass and I don’t do it. I use the headphone jack.) And a lot of software – like 8-bit emulator sequencers, and like Animoog, which I have actually used on multiple released tracks – just doesn’t do it. So that just got more annoying on newer hardware too. Another dock or another cable or another whatever. It’s one more step.

But, interestingly, not on the iPad. So far, I’ve heard no rumours that the iPad will drop the 3.5mm connector. And the iPad – particularly the iPad Pro – has very un-phonelike things like a keyboard case and special connector, and art stylus/pencil, and so on.

So what I’m thinking – particularly with the Pro – is that Apple is seeing a differentiation opportunity between “phone” and “pad,” and that they’re pushing “iPhone” to “purely consumption device,” paralleling their attempt to push “iPad” towards “creation device.” That’s not the actual usage out there – lots of people use the iPhone to make things – but it’s coherent market segmentation, and marketroids love their market segmentation.

Also, the iPad isn’t nearly as space-constrained as the iPhone. It’s just not comparable. On the iPhone, replacing that jack space with bigger battery and camera means vastly improved camera and about an hour extra battery life. On the iPad, it’s not a big enough percentage of space to care.

If the next generation of iPad keeps the 3.5mm analogue headphone jack – while adding support for the new Apple wireless headphone specs, of course – I’ll take that to be pretty solid supporting evidence. We’ll see.

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solarbird: (molly-oooooh)

In yesterday’s post, I posed a question: do USB chipsets matter in the 2.0 environment? I had reason to suspect they might.

The answer is holy crap yes they matter they matter so much it is unbelievable.

First, let me talk about what prompted this research, so you’ll know why this matters.

On my old sound interfaces I had live monitoring in hardware, so I didn’t have a lot of need to care about latency. Since that won’t mean much to most people, I’ll explain; when recording, it’s good if you can hear yourself, in headphones. If you’re multitracking, it’s critical.

My old audio interfaces did this with direct connections in the hardware. Whatever came in the microphones also went out the headset. There are advantages to this method, but also disadvantages, in that you aren’t actually hearing what’s being recorded, just what’s being sent in the microphone jack.

But now, I have this shiny new 1818vsl, which doesn’t do hardware monitoring under Linux. Higher-level kit generally doesn’t provide that; they’re assuming you have enough computer that your computer can send back what is actually being recorded, effects and all, and that you’ll do that instead.

This means I now have to care about latency in my system. Latency is basically delay, between mic and computer, and computer and headset. And if the computer is feeding my monitor headphones, that delay matters. You want to hear yourself live, or close to it, not with, oh, a quarter second of delay or something horrible like that.

Now, the good news was that straight out of the box on Ubuntu 16.04 (the latest long-term support version), I had better, lower latency numbers on my new 1818vsl than on my old hardware, when I was using that on 12.04. I could get down to a buffer size of 256 samples, and three frames, which gave me about 30ms basic latency – roughly half what I had with my old hardware and old install. I could use it as-was.

But I couldn’t go any lower on those buffers. One more setting down, and even playback would lag. It’d be okay until the system had to do anything else, then you’d get a playback pause, or a skip, or if recording – presumably, I didn’t bother trying – lost sound. That’s unacceptable, so 30ms was the lower limit, and I wasn’t sure it was a safe lower limit.

And that’s what got me doing all that chipset research I talked about yesterday, and I ordered a new USB card (plugs into PCI sockets) based on that research. I was hoping for a couple fewer milliseconds of latency, that I wouldn’t actually even use; I just wanted a safety margin.

So that new card arrived on Sunday, with its OHCI-compliant chipset made by NEC, and I popped it into the machine and started things up with normal settings.

At first, I was disappointed, because I only saw about half a millisecond less lag, instead of the 1-2ms drop I’d hoped to see. But across tests, it was more consistent – it was always at that same number, which meant I could rely on that 30ms latency in ways I wasn’t sure I could before.

They I decided to see what would happen moving the sample buffer setting one level lower, into what had been failure mode. And the result was 1) it actually worked just fine, where it hadn’t before, and 2) when running analysis, tests showed much lower latency at that setting than with the previous USB ports.

That was an ‘oh ho‘ moment, because it implied that the 256-sample run rate was basically the spot at which the on-motherboard USB could just keep up, and trying to run faster wouldn’t actually produce any actual processing improvement. It’d try, but fail, and time out.

So I did a couple of recordings on that, and they all worked. Then I dropped it another level, until finally, I just said hell with it, let’s just set it as far down as the software will allow and see how hilariously we explode.

I just successfully recorded test tracks four times with these settings, on the new card:

0.7 milliseconds isn’t even something you think about on USB 2.0. 2.8ms, maybe, okay. I’ve seen that managed a few times before, and that’s genuinely indistinguishable from realtime/hardware monitoring. But 0.7ms?

Seriously, this is well into “…is that actually possible?” territory. I’ve never even heard of someone running over USB 2.0 at latencies this low.

So, I guess it looks like the chipset matters a whole lot. Maybe not for most applications, and maybe not in the same way as in USB 3.0 or in FireWire, were there are serious compatibility issues. But in the 2.0 world, in realtime audio, it appears that the chipset makes all the difference in the world.

And yet, I can find this nowhere online. I’m beginning to think nobody bothered until now. Certainly when I’ve asked about it, the response has “why are you on USB get firewire” or “why are you on USB get PCI” because sure I want to throw out all this hardware and start over THANKS NO.

I think USB users have been trained just to accept it and deal. But surprise! You don’t have to! You can actually get a better USB card, if your system allows it, and it’s $30 instead of $1300!

So, HELLO, OTHER SMALL-STUDIO MUSICIANS! You want a chipset that uses OHCI on the USB 1.1 level even if it’s a USB 2.0 card or later because the 1.1 layer still matters, and still gets invoked by the higher-order drivers for card management. See previous post for why that’s important.

This means avoid Intel and VIA chipsets, and look for NEC or SiS – or anything else that loads OHCI drivers and not UHCI. If you’re on Linux, you want to:

cat /proc/interrupts | grep usb

If you see “uhci_hcd” in there, you have a UHCI chipset running your USB port and getting a new USB card with an OHCI-compatible chipset (and disabling whatever’s already installed) might help you with your latency issues.

Good luck!

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solarbird: (pingsearch)

I’ve been trying to find out whether there’s any sort of difference between USB 2.0 cards, specifically as addresses the needs of digital audio workstations on Linux.

Very few people in linux communities seem to have addressed this question at all, and none I can find on the audio side. (Firewire, oh my gods yes – huge lists. Just not USB.)

But I did a lot (a lot) of digging, and discovered via the Linux USB kernel driver dev mailing list(!) that while there’s not much difference on the USB 2.0 side, there are important differences on the 1.1 side. These difference manifest in two different driver models. That still matters at least a little bit in 2.0, because those 1.1 drivers still get loaded.

Anyway, that difference is that there are two very different driver interface models. One is UHCI, created by Intel and used by Intel and Via, mostly. The other is OHCI, which Compaq pushed when it was still around, and Microsoft preferred; it has less intellectual-property load, and NEC, SiS, and some other makers use it. If you see a “Mac compatible” card? It’s going to be OHCI.

The OHCI model puts a lot more of the business of doing USB into hardware on the card. UHCI has the processor do that work. And while that isn’t a heavy load, it is a nonzero load, and more importantly means that UHCI chipsets require more CPU attention than OHCI chipsets, on a recurring basis. And that is something we don’t need in a digital audio workstation; there are only so many board interrupt opportunities; I want them for moving data, not servicing USB mechanics.

Once I knew that, I did more searching and found people saying how switching to a NEC chipset card had (in one case in particular) ‘saved their bacon’ specifically on their digital audio workstation. They were using ProTools on Windows, not Linux, but it was still with a USB audio interface.

The chipset used by my on-motherboard USB ports is, of course, Intel, and therefore UHCI. (And UHCI drivers are actually loaded, I checked.) There’s also an on-motherboard hub between the outside world and the one true root device; that doesn’t help anything either. So there’s a nonzero chance I’ll see improvement both from changing from UHCI to OHCI, and from moving to a true root USB device instead of a hub device. It won’t be much, but I’m only looking for a few milliseconds of latency here. And even that’s more for… reliability buffer, I suppose? Yeah. Reliability buffer, rather than pure necessity.

I’m mostly posting this 1) so I remember it and 2) so other people looking for this data can find it. HI! I can’t be the only one!

I’ll update this post if I get interesting results.

eta: INTERESTING RESULTS AHOY: CHIPSETS MATTER SO MUCH OMG. I’ll write up a post with details, post it tomorrow.

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solarbird: (banzai institute)

I’ve been playing with that ‘added pressure adds bass response’ idea, for use with these piezo pickups. I made a little wooden chamber that would let me add light pressure, as with the bridge pickup design. It would be held down with a clamp for testing, but would isolate that pressure from the piezo itself.

Anyway, I made a bunch of recordings, two for control, and eight with a range of pressure in the chamber. The controls were made with the pickup taped to the front of my zouk with double-sided tape (standard attachment), and with the pickup directly clamped to the front (also a standard attachment) and come first and second in the recording. The other eight were with the pickup in the test chamber, with increasing amounts of pressure on the crystal, applied by inserting paper as seen here:


With thin cardboard and two sheets of paper

Note again that the clamp is not adding pressure to the disc in any way.

Audio samples in a single mp3, here. There is some extra noise in these recordings; I was trying the modular approach again and that’s the result. I think the TRS connectors are inherently noisy. But that’s a separate matter.

I also ran spectrographic analysis on each recording, and combined those into a single animated gif that cycles through the recordings in order. Here’s the key for both. The gif is repeating, so each frame is labelled in the upper left.

 1: taped to top
 2: clamped directly to top
 3: in chamber, no paper
 4: in chamber, thin cardboard (0.46mm)
 5: in chamber, cb+1 sheet  (+0.11mm)
 6: in chamber, cb+2 sheets (+0.21mm)
 7: in chamber, cb+3 sheets (+0.31mm)
 8: in chamber, cb+4 sheets (+0.42mm)
 9: in chamber, cb+5 sheets (+0.52mm)
10: in chamber, cb+6 sheets (+0.63mm)

You’ll note in both the graphs and the audio that bringing in the chamber at all, even with no additional crystal pressure, caused a big drop in high-end oversensitivity, and boosted the low-end. That was interesting; I have suspected for a while that the crystal side of the disc would actually be better as a source-facing element, but there are physical issues to doing that, since the wires have to attach on that side.

Adding pressure continued to boost low-end response through test 7, without inhibiting high-end response. After that, I think additional pressure began to overcome the benefits, and you see a return to a more midrange-heavy sound – though in all cases, I think it’s better than either traditional mount.

This is consistent with tests made in the bridge pickup from last week, and reminds me of a diagramme I saw of a period crystal microphone that implied the crystals themselves would be set up forward-facing.

Anyway, data! And lots of it, for lots of your crystal/piezo experimental needs.

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solarbird: (asumanga-yay)

A couple of months ago, I tried making a Cortado-based bridge pickup for the octave mandolin. It worked okay – better than the ad-hoc clamp arrangement I’d bodged together for last January’s Conflikt show, but not what I’d hoped. It was a lot more stable, but still needed lots of equalisation help.

I’ve built a new one, with a new design! It’s much better. Here’s an mp3 of the previous design alternated with the new design, on octave mandolin – no eq of any kind, no effects, just raw output from the old design vs. the new. (Old design is first.)

While working with the previous attempts, I’d figured out what really improved things was the right kind of pressure on the piezo disc itself. My thumb was pretty optimal, but you can’t exactly do that and play at the same time. The clamp wasn’t bad, but it was slippery and awkward and actually came off on me during rehearsal, so I didn’t trust it. Most piezo-style pickups live under the bridge of an instrument, but you can’t do that the usual way with this one, it’d be destroyed by the pressure.

So I went about trying to fix that.

First was to take the bridge plate and add a wide, flat channel – one wide enough specifically to contain the entirety of the Cortado piezo element. I made it by wrapping sandpaper around a flat piece of metal, and scrubbing back and forth to excavate out the wood I needed removed.


This is actually a new bridge plate.
But it’s made of the same material, so no real diff.

You need to sand away enough wood to make room for the piezo and all the tape wrappings, and some extra. But you do not need to sand away enough for the wires soldered to the disc – you want to avoid those entirely.

Keep sanding away wood until the bridge slides freely over both the new channel and the piezo, like so:

What this makes is basically a wide clamping chamber around the pickup element itself. It doesn’t do any clamping yet; it just creates a space for it. At this stage, in fact, if you hook it up and try it, there’ll no change in sound from the previous version.

(In fact, the “old design” recording I used in the sample is actually this version at this point in the process. I verified that it sounded exactly the same as the previous version, as predicted, which means I’d re-established the old baseline. Important for science!)

But now, of course, I have a clamping chamber! We just need something to apply pressure.

So what’s our clamp? Pieces of paper. Post-it notes, to be specific, just because they were handy. The right number of sheets in this exact case turned out to be four.

Five also worked, and did not feel like too much pressure inserting the papers under the bridge. But it did sound like a bit much compression, tonally, so I went back to four.

(Here’s that sample track again, alternating old design and new, old first.)

The beauty of this is that since it takes several thicknesses of paper, and since that paper be changed out without taking apart the pickup, you can use any number you like. You could even adjust the tone on the fly.

Interestingly, the pickup didn’t even get quieter with more paper. I’d worried about that, but didn’t need to. In fact, adding more sheets made it louder, meaning that the pressure is not so much “damping down treble” as it is pulling up bass. Which, in turn, makes me wonder if it’s not so much “resonating better” as moving the zero/no-vibration point of the crystals’ charge state from all-electrons-in or all-electrons out (doesn’t matter which) to a more middle-range position, which…

…hm. Actually, that’s interesting. No, that’s really interesting. That would explain why the pickup got louder with more clamping, rather than muffled or…

…huh. This is an hypothesis. If I’m right, I can make my next crystal mic substantially more modern sounding, by enclosing the piezo in a small clamping chamber, which is, like this, attached to the resonating disc of the microphone, and possibly…

…possibly I should take my SRMD meds now or I’m going to be up until 5am next Thursday playing with crystals and possibly taking over the moon again, aren’t I? Yeah. I am. Okay. BRB.

So. Yeah! I’m super-pleased with this result. I’m also thinking that maybe this could be used on other items that have flat surfaces which need pickups – like, a piano, maybe – and instead of the bridge, as here, you use a weighted flat bar of some sort across the pickup plate to create the clamping chamber. Then you’re off with tonal control via paper again. I have no need for this functionality at the moment, but it strikes me as legitimate nonetheless.

And most importantly for me, I now have a much more conventional DIY pickup for the octave mandolin. Here y’go, doc – just plug ‘er in, and we’re off.

Much better.

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solarbird: (banzai institute)

I have some mics that react badly to phantom power, so I made a phantom power blocking took. I had an old Smarties block handy, so I made it out of that.


It seemed appropriate. ^_^

I also went at improving an effects box I built a while ago called the Trash-o-Matic 68000. You would have heard it on Daleks Behaving Badly (Dalek Boy), a joke track that really needs a shorter edit, because it takes way too long to build up.

The best part of this box is the Berthold Ray effect circuit that I legit invented. That must have happened in a pretty heavy Science-Related Memetic Disorder attack (or spark hyperfocus, if you’re a Girl Genius reader), because I was trying to figure out how the hell it worked and I am here to tell you that this is some serious-business Oscillation Overthruster bullshit right here.

It’s basically a multi-store self-reducing sampler feedback effect with frequency shift that’s using the device’s amplifier as a delay loop and sending the amplified samples back to the input via a combination of the internal system ground and negative phase of a balanced signal lead. Both matter. I… don’t entirely know why.

Anyway, the whole thing is noisy as hell, and much of that is the platform I was building onto, and I was hoping to fix that. I was able to reduce noise levels somewhat – no, that’s unfair, meaningfully, it’ll be easier to gate out noise now – but it’s still buzzy as hell.

I’m kind of interested in seeing if I can re-implement the Berthold Rays in a less trashy environment. Sure, it’s fun in this mess of noise and grind and crunch, but it’d be nice to have in a cleaner box as well. Maybe I’d use it more then.

I’ve never used it for music before, but here’s a little bit of noodling I call “Broken Music Box, Found After a Fire,” played on Irish Bouzouki and run through Trash-O-Matic voice 6, with full Berthold Ray attack:

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solarbird: (Lecturing)

Building microphones is fun and seems to be of interest to readers, so here’s a collection post for posts about that! These posts discuss building both microphones, and, when applicable, their matching microphone driver circuits and/or pre-amplifiers.

Building a Carbon Microphone:

Related posts:

Building a Crystal Microphone:

Building a Ribbon Microphone:

Building a Large-Diaphragm Condenser Micrphone:

Other microphone and preamp customisation/modification posts:

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solarbird: (korra-excited)

The last parts for the carbon microphone arrived yesterday! And once I got back to the Lair, I set about adding them to the circuit and building out the final version. Here’s a quick sample recording I’ll talk about more later.

I’m starting with the previously-discussed circuit, now taken out of the test harness and reassembled on one of the small breadboards. The new isolation transformer on the left – basically the outputs of the original circuit are attached to one side, and new outputs picked up off the other. This serves two purposes: first, it eliminates some kinds of hum noise if they start to crop up, and second, combined with 2K of resistance on the other side, brings the line-level(ish) output down to microphone level.

(These are standards which matter in a studio and … not many other places. XD )

The zig-zag in the resistors doesn’t serve any function purpose other than fitting into a smaller space – ideally, I guess I wouldn’t’ve been making needed values out of collections of other values? But I had what I had.

Signal flow is right to left in this photo. Underneath, at the top and bottom of the board, I’ve built wire rails to connect the components. That probably means I’m not really using the breadboard entirely as intended? I don’t even know. It holds everything in place and that’s definitely what I intended. XD

To house all this, I’m using an “experimenter’s case,” which is basically old-radio-speak for a metal box. XD It has soft metal on two sides, easily drillable and workable, and a hard case. I’m using one side for input, the power lamp, and the on/off switch; the other side is for output, or, as it turned out, outputs.

The carbon element (in the can) is connected to the driver/amplifier circuit via a 1/4″ TRS phone jack – like an old large headphone jack – with the two leads to the carbon element being on tip and ring, and the shielding ground being on the sleeve. (Tip, Ring, Sleeve: T R S.) That socket is on the left in the above photo; the middle component is a small LED, to indicate power on/off, and the right is a BIG CHUNKY POWER SWITCH. I love big chunky power switches. CHONK

For output, I quickly realised that I could have both balanced XLR output at microphone level, and line-level output on a phone plug, if I could find a way to isolate the chassis ground from the phone socket’s sleeve connector.

Normally, both being grounds on the same circuit, they’re connected automatically. Finding one that isn’t already connected is actively difficult! But careful use of electric tape did the job; I drilled the mounting hole larger than it needed to be, and basically lined anyplace the case and the socket would touch. Isolation achieved!

If you look for the blue and white wires, you can see where the TS (mono) phone plug is tapping the raw (line-level) amplified mic signal, just before it’s fed into the isolation transformer.

The transformer is really pretty optional – powered carbon circuit signals are pretty high as microphone signals go, and as I mentioned above, we’re actually reducing that signal to create the balanced XLR output on the other side of the transformer. But it’s nice to have the option of using line level, since it already exists. That’s what built-in sound inputs like on your laptop want, too, so there’s a point to it.

And here’s the whole driver/amplifier circuit, with a battery holder made of velcro.

Is that cheating? Holding the battery down with velcro, I mean. totally cheating I’m hoping it works out – I didn’t have a 9v battery case and it seemed excessive to try ordering one.

That LED power indicator? It’s warm white, left over from another project. I was planning on putting in your typical red LED, but realised that if they’d had a power indicator on one of these in 1932 or whenever, it most certainly would’ve been a little incandescent bulb, and it may and may not have had a colour lens. So I went with warm white, because period accuracy! Sort of.

The neat thing about the way this circuit works – and all carbon microphone driver circuits work – is how it points you right at vacuum tubes, and from there transistors, conceptually. It really, really does.

See, in tubes and transistors – which are both signal amplifiers – the input signal is used to create an amplified copy by controlling how much raw input power is let through, from another source. That’s why tubes were called “valves” originally; it’s because they are valves, electrically controlled, and regulating the flow of electricity from an input, just like the valve on your faucet controls the flow of water from the plumbing.

In this case, exactly the same thing happens yet again. But the input signal is sound pressure (how loud the sound is), which is controlling how much electricity is let through from the battery. And those changes in sound pressure – and therefore electrical flow – make the electrical copy of the sound waves.

Neat, huh?

Anyway, that’s the inside. Let’s look at the case!

I really like how chunky and primitive it looks. This is an old experimenter’s case; I’ve had a box of random cases in which I can build things for a while, and I don’t even know where I got this one, or when. If you saw it on the set of a 1950s television SF show, nobody would give it a second glance.

Always document your builds! You never know what might confuse people later. And by people, I mean yourself, after you’ve come down from the science-related memetic disorder high. I want at least the theoretical possibility of using this amp with other carbon elements, so writing down how the interface works is pretty important!

Except for the glare from the power light, I think this would be the Radio Shack Catalogue photo from, say, 1975:


Good, Better, or Best? Probably “Good.” It is just carbon, after all!


Or maybe this is the catalogue shot? Not sure.

Finally, here’s a test recording I made, using both outputs (phone/line level and XLR/balanced mic level) at once, hooked up to two different inputs on my board. I put both recordings in the same mp3; one’s on the left channel, the other’s on the right. The two tracks should be pretty much identical – being the same signal picked up at two different places on the board – and I wanted to see if that actually happened. Fortunately, it did!

Well, eventually it did. This is actually the second time I tried this, because the first time, I discovered that I’d managed to wire the two outputs up as electrical inverses of each other. Playing the two tracks back at the same time resulted in massive waveform cancellation. Which was hilarious, but also a good indicator; they wouldn’t’ve cancelled so well if they weren’t really similar. 😀


EXTREME WAVEFORM CLOSEUP

So that’s about it for this project! I’ll most likely do something to the ring to control the elastic better. And I’ll probably build a case for the whole kit, like I’ve done before – mics should have cases for protection! – but that’s a separate project.

This has been such a fun build, you have no idea. If you have any interest in this kind of DIY audio, I totally recommend this as a fun, easy project. Particularly if you don’t have studio gear, because you can look up the line level part of the output to damn near anything (including a PA system, I might mention) and it’ll work.

As always, more and bigger pictures on my Flickr account. And if you’re out of work, that’s a great time to listen to the new (NSFW lyrics) single! It’s awesome.

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solarbird: (Lecturing)

My carbon microphone is actually in a can now! I’m super happy with it, and yes, it works, even if most of the circuit is still in a test harness. The can itself does not contain anything important in the way of circuitry, though it does contain quite a bit of grounded shielding which is very important, and that shielding is carried forward out the cable, which is a TRS phone plug.

I made the decision to put the support circuitry in a separate box for a couple of reasons. First, the signal level is pretty high, so a decently-shielded cable should prevent most issues from being actual issues. Second, the support circuitry for these things tended to be external in the originals, so it’s period-accurate. Third, opening the can to replace a battery every 15 hours of use or so was going to be annoying; much easier to do it an an external experimenter’s cabinet.

And yeah, one of the downsides of this mic is the high power consumption. I thought about trying to tap phantom power, but from what I can tell reading up on it, the amount of power actually supplied – voltage aside – is dramatically lower than a battery’s supply and is not well defined, by which I mean is not defined, so… yeah. Batteries it is.

Anyway! I decided to make it look like a vintage carbon-element microphone of its era, only using elastic instead of springs. Springs look cool, but they’re also noisy as hell and create other issues, and it’s easy to tell that they would’ve used elastic if they’d had it just by how quickly they changed to using elastics as soon as they had elastics to use.

BUT SOLARBIRD, HOW DID YOU DO IT?

Well, first, let’s ask the eternal question: ah, junk shop, is there any build problem you can’t solve?


No. No, there is not.

If you’re wondering, that’s a vaguely-20s-looking kind of drink can holder in the middle, and I believe a hand towel holder designed to hang from the top of a door.

My only worry was whether the towel ring assembly was just screwed into the plate, or bolted to it; most excellently, it turned out to have been attached with a screw. So I just separated the ring from the existing base, sanded the attachment point down a bit to make it nice and flat, and attached it to a small metal L, using a rubber plumbing washer to make up the extra space.

Attaching to a standard microphone stand attachment is just as easy; unscrew one of those infinite number of cheap mic clips that are floating around every studio ever, toss the bit that holds the mic, drill out the hole in the L metal to be large enough, and pad with more plumbing washers.


Result!

Now the ring is ready to attach to any standard microphone stand.

Now, the can itself was a little more of a trick. This is all mechanical construction, not circuitry, since all that will be in an external box. But! There is some electrics, because given my particular… affinity… with RF (and radiating it, hi, it’s solarbird for a reason), I wanted a good heavily-shielded pickup enclosure.

Did you know you can buy adhesive tape made of copper? With conductive adhesive? It’s made exactly for this purpose. I love it. I started by lining the back, and peeling excess up the sides a bit intentionally. You want a good amount of overlap with this tape.

Lining the sides involves another ring of copper metal tape, with – again – overlapping tabs made of the excess height. Getting the height right is really simple – just put the tape in and cut inwards, using any common scissors – this may be metal tape, but it’s pretty thin, and no special tools are required.

After I took that photo, I realised I needed smaller tabs, so I went through and made another set of cuts, halfway between each existing cut.

Once you’ve fiddled around with it a bit, you’ll end up with something that looks like this:

Make sure the copper is well rubbed down against each other, so the conductive adhesive can really carry current without adding any resistance. Again, no special tools, a fingernail is fine – but make sure it’s well stuck down.

You might also notice in that photo, a small black line – I broke the tape, and fixed it with just a small piece to cover the gap. As long as you have well-connected metal throughout, you’ll be fine. We’re talking very low power with RF noise, in most circumstances, so you don’t have to worry about carrying power or anything like that.

Unless you have a tesla coil, maybe. That’s different.

Now, I also needed a grill for the microphone, and – importantly – it had to be a conductive grill, because I need that RF blocking all around the carbon element. I know, I know, some of you are going, “it’s a carbon element how are you doing anything to it?!” and all I can say is I have recordings and I have to ground myself with a wrist strap if I’m using AKG microphones, and again, supervillain.

Fortunately, a material that serves this purpose quite well is common and cheap: aluminium window screening! I’m kind of annoyed with myself, because I threw away a bunch two weeks ago – used but still clean and good – because I had no thoughts I’d need it. What was wrong with me? I can’t even tell you. Moods. So I had to stealbuy some. Fortunately, it’s pretty much dirt cheap.

I got a ring of heavy flexible rubberised foam to make a structural ring, and measured the right size just by pushing the screening into the bottom of the can until I had good edges. Since it is window screening, it has a lot of room to compress, and that helped. You want that excess screening material, for reasons which should be obvious momentarily.

In the above photo, I’ve sized the screening material, and am getting ready to make a ring of copper tape to surround both the inner and outer layers of the support ring. This is partly structural – you can see that my support ring is not a single loop, but a bent straight piece – and partly to help make sure of good, solid contact between the metal screening, through copper tape, to the interior copper shielding of the can. Make this part a little too large, if anything, and you end up with a solid pressure-contact connection.


Swaaaaank

Holding the carbon element in place is also a job for foam. In this case, I have some high-density impact-absorbing foam left over from my case making projects earlier, so I just used that. It can be a very rough cut, as long as it’s just a tad bigger than the ring it’s going into. It’ll compress, and that provides a little more outward pressure to make the grounding contact between the grille and the interior shielding better.

You’ll also note inside the can, against the back, I’ve placed a spacer ring. This keeps the grille’s support ring from going too far into the can; it’s just a physical element, since you want the carbon element nice and forward, and not sinking into the can where sound would get echoey.

What you can’t see is an important step I … didn’t remember to photograph. Sorry! And that’s drilling a hole for the cable. The cable is three-conductor; two signal leads (which connect to the two contact points of the carbon element) and one shield ground. The shield ground gets soldered directly to the copper tape, which is why you use copper metal tape instead of some other metal. This is a little tricker than you might expect, mechanically; I had to use higher temperature on the soldering iron. I think it mostly has to do with soldering wire (physically complex, wicks well) to a flat surface (physically simple, does not wick well). Just take that part as read.


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Some of you might be looking at this picture and going, “…wait. The carbon element is right up against the grill. It’s touching, and metal, and isn’t that a problem?”

Well spotted, you! It would indeed be a problem! I solved it by cutting out a couple more layers of plastic window screening – also left from another project – to provide an insulation barrier between the metal screening and the actual pickup element. If you don’t have any of that, hosary would do fine – the same material used in pop filters. Acoustic transparency is important here, of course, but to be frank – less so than usual.

“That’s not like you.” Yes. But think about it, I mean, what’s a telephone use? Oh yeah, THICK PLASTIC WITH SOME HOLES IN. Does it hurt the sound? NOT VERY MUCH, because it’s a carbon element with a range of around 300hz to 3500hz, maybe. So you can afford some loss in the high end, because what you don’t lose, the mic will lose for you. And this screen material is plenty acoustically transparent for these circumstances. So would be hosary, or the right foam, or all sorts of other things. Just, you know, use good judgement.

Anyway, the build stuck on hold – ON HOLD! HA! – for a couple of days as I wait for the 600ohm isolation transformers to arrive. They aren’t essential, necessarily, but do reduce RF noise and hum in some circumstances, so I’m going to use one. I’ll post more when I’ve got more done. I’m really pleased with how it’s coming along; this is fun.

Bigger pictures on Flickr, as usual.

ps: People were asking for a sound sample. This is from the test harness, before I built the ‘can.’ New recording sample next time.

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solarbird: (made her from parts)

I have a waveform! I did a bunch of testing of various parts and such, discovering that the carbon transmitter (microphone) I had was indeed fully functional, and really, it came down to “not enough voltage.” 1.5v is pretty borderline for carbon microphone power, so that’s fine.

The waveform is kind of lopsided, but that’s because this test harness doesn’t have the balanced output yet; I’ve ordered the balanced transformer, and that should help. It’s also a bit noisy – here’s a sample – which is partly related to SHIELDING WHAT IS SHIELDING because it’s a test harness.

Talking of, here’s what version one looked like:

This is a direct implementation of the first half of the circuit described in this instructable, which runs off a 9V battery. Once the rest of the circuit is added, it’ll have balanced output, which is pretty snazzy.

This is a closer view, and also after I added an LED, because hey, LEDs!

After that, I tried a smaller capacitor, and that’s working fine – mostly, I’m just picking from what I’ve got, which goes along with what the circuit designer described.

I’m going to play more with the circuit a bit, pending getting the matching transformer. And some shielding.

And, of course, the can. 😀

ps: this harmonica “bullet mic” looks pretty cool too.

Mirrored from Crime and the Blog of Evil. Come check out our music at:
Bandcamp (full album streaming) | Videos | iTunes | Amazon | CD Baby

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