Steve Strout – comics guy and promoter out on the Olympic Peninsula – asked me last week to write a guest post on Clallam Bay ComiCon for his blog; it went up last night. No pictures, but I have lots of those, here.
Hey, DIYers! Today we have something special for you.
This series has always been about sharing information and people doing things. It’s part of the punk aesthetic, it’s part of particpatory culture, it’s part of maker culture, it’s part of the filk aesthetic – and a part I really like.
So I’m really pleased to feature this post by Jeff Bohnhoff, who will be writing about room conditioning. I’ll let Tony Fabris of the band Vixy & Tony introduce him for you, since he does such a good job of it:
Jeff and his wife Maya have been in rock and folk music all their lives, and have been producing record albums for more than 30 years, so they know a thing or two about both home studio and pro studio recording. Jeff works at Apple as part of the support team for their flagship pro audio recording product, “Logic,” so he knows a thing or two about audio recording software.
He’s produced dozens of amazing-sounding albums, both for himself and for others, so he knows how to get good sound. He also happens to be a brilliant parodist, and Jeff & Maya’s parody albums are characterized by hyper-accurate reconstructions of classic pop songs. He also taught me how to play guitar.
Now, without further ado: Jeff Bohnhoff.
The Sound of Your Studio
by Jeff Bohnhoff, Mystic Fig Studios
So, the topic du jour is acoustics. Specifically, the sound of your studio.
We recording engineers have a natural tendency to geek out over gear – whether we purchase it, make it, or improvise it from inexpensive bits and pieces. Gear is fun, and it’s an important part of making good recordings, but it’s only part of the picture, and not even the most important part.
In fact, better mics, preamps, etc. may lead to worse sounding recordings. “What?!” you say, “how can that possibly be? That Jeff, he’s CRAZY!” Well, okay, guilty as charged, but I stand by the statement. Here’s my reasoning:
When you put a microphone into a room and record something, the acoustic signature of the room is like a fingerprint that covers everything you record. It cannot be removed with any amount of EQ or processing – believe me, I’ve tried. Sound recorded in a bad room is like a white napkin handled by your mechanic after he’s swapped out the oil pan on a ’62 Rambler. The fingerprints are greasy, and will not wash out. Period.
The sad truth is, that your room probably sounds bad. Probably really bad. Most bedrooms, garages, dens, etc simply were not designed to be acoustically pleasing. With the availability of relatively inexpensive, good quality recording gear, this is the main difference between most home studios and commercial facilities. Good facilities have rooms that are designed from the ground up to sound good; everything from the dimensions of the room, the construction methods, to the materials and treatments on the floor, walls and ceiling are designed to eliminate room resonances, slap-back, bass build up, and so on.
So, assuming you are recording in your spare bedroom, why does using better gear – especially a better mic – often lead to worse sounding recordings? A better (i.e. more sensitive) mic “hears” more detail, and picks up more spatial information from the room it’s in. It’s typically more accurate, and does a better job of revealing everything about the source you’re recording and the room it’s in, flaws and all – sort of like the way your HD TV lets you see every pore and blemish on the face of your favorite reality star on Lifestyles of the Vacuous and Incredibly Boring.
Okay – we’ve established the problem, now what’s the solution? Unfortunately, there is no easy, complete solution or panacea. However, there are some practical steps you can take to improve things. First some ideas that involve no modification to the room:
- Understand the pick up patterns of your microphones and how positioning affects the sound.
Most mics have a cardioid pattern. This means they are most sensitive directly in front of the mic, with lobes that extend part way around the back, and almost no pick up directly behind the mic. The shape somewhat resembles a heart, which is where the “cardio” in the word cardioid comes from.
Cardioid pick up pattern. You’ll see this on many microphone spec sheets.
The advantage of this pick up pattern is that it hears less of the room than most other patterns, and so can be more useful in challenging acoustical environments. The downside is that cardioid mics exhibit “proximity effect,” which a bass and low mid frequency emphasis when the source is closer to the mic.
This can be a problem because many small rooms sound very congested and bassy to start with, so even though getting closer to the mic means the source ls louder relative to the room sound (taking the room more out of the sonic picture), the closer you get to the mic, the more low and low-mid cruft you have to deal with.
Hypercardioid mics (not terribly common) pick up even less sound from the side (but slightly more directly from the rear), but exhibit an even stronger proximity effect than cardioid mics. Omnidirectional mics, as the name implies, pick up equally well in all directions. This means they “hear” the room very well. On the plus side, they have no proximity effect at all. Mics with a figure-8 pick up pattern hear from the from and back equally well, or close to it, with little or no pick up on either side. In my opinion, these are the hardest to use in a challenging room. They “hear” a lot of the room, and they exhibit a fairly strong proximity effect.
The key here is to experiment with your mics, and find the best pattern and distance from the mic to minimize the problems with your room. This will vary from room to room, mic to mic and even song to song. You may find that singing a foot or more away from a cardioid mic works best for you, or perhaps singing a few inches from an omni mic will work better in other cases. Just remember that the closer you are to the mic, the more source and less room will be recorded. Likewise, the narrower the pick up pattern, the more source and less room, but getting too close may result in too much low mid and bass. Experiment!
- Understand your room.
Rooms do not sound uniform at all positions. If you set your mics up, and just can’t get a sound you like, try other positions in the room. You just may find a location that sounds good, or at least better. If that means contorting yourself into the corner by the bookshelf while standing on one foot, well this is for art, buddy, so suck it up!
- Isolate yourself from the room.
Get some heavy quilts or drapes and some mic stands, and make a tent. Set your mics up inside the tent. This will certainly not give a very lively sound, but it may be better than the sound of the room, and you can have a friend over and tell scary stories in your tent. My favorite is the one about the recording engineer with a hook for a hand, but I digress…
If you can’t tame your room with mic choice or positioning, then you may want to treat it, to make it sound better. This is a complex issue, and before I say anything more, I feel compelled to offer a huge disclaimer.
I am not an expert on this subject, and may well be full of crap. Debates on how to properly treat a room rage in many corners of the internet, among real, trained acoustic engineers, so-called experts, and people who have no idea what they’re talking about, but have access to a working keyboard and an internet connection. I make no pretense at being an acoustician, so I will not be offering pat solutions and miracle cures. Quite honestly, just raising awareness that this is an issue at all is my main goal here.
With all those caveats in mind, I would like to mention some of the issues that many rooms exhibit, and will offer some general ideas on how a home recording engineer might deal with them, and links to some resources for further, more authoritative, information. I’ll be looking at two basic strategies for dealing with acoustic problems: absorption and diffusion.
The principle of absorption is that you mechanically trap sound waves, usually with some sort of material that causes friction, and converts the energy of the sound wave into heat. Absorption is great if the room is just too live. You usually want to avoid overdoing it though, or your room will sound as dead as the annual Christmas party at the office of Q.R. Fishwell, CPA.
Bass absorption panels for Mystic Fig Studios, unmounted
Diffusion, on the other hand, works by breaking up the waveform and dispersing it non-linearly back into the room. This can deal with phase issues, room modes and comb filtering, without overly deadening the room. The downside is that diffusors are relatively expensive to buy, and are generally harder to build than absorbers.
As with absorbers, the lower the effective frequency you want to deal with with, the larger the diffusor needs to be. One of the common types you will see is a “skyline” diffusor. These use “wells” of various heights (based on prime number sequences) to break up waveforms. They are also known as “primitive root diffusors.”
This page has a calculator that lets you plug in a frequency range you want to control, and a number of columns and rows of wells, which are 2″ x 2″ wood, cut to various heights.
The calculator gives you a grid that shows what height each 2″ x 2″ block (in reality 1.5″ x 1.5″, because lumber and math apparently had a disagreement at some point in the past) should be in each position to diffuse the range of frequencies you entered into the formula.
This page has some images of diffusers built using this method. These things don’t take a huge amount of skill to build, but it’s a bit tedious and time consuming.
One possibly easy to get source of diffusion is bookshelves. (But they have to be full of books – you do read, don’t you?) It works especially well if the depths of the books are different, sort of a faux skyline diffusor. Place the shelves opposite the sound source for most effect.
Let’s look at some of the problems a typical room might exhibit:
Bass buildup: Bass frequencies tend to collect in corners, and where the walls meet the ceiling and floor. It’s especially problematic in smaller rooms, because you just don’t have the space to get the mics or speakers all that far away from the corners and edges where the bass is being accentuated.
This problem can be treated with bass traps, which are treatments designed to absorb low frequencies. Here’s the thing: when it comes to bass, physics is working against us. Because bass frequencies are long, it takes a lot of thickness to properly absorb them. Most of the foam based treatments you can buy are pretty much useless below 250 Hz or so.
However, it’s not that hard to build some good bass traps yourself. I built a bunch for my studio using instructions from a video I found on Youtube. These traps use Corning 703 rigid fiberglass insulation as the basic material. You won’t find it at your local mega-lumber yard / home store. The best place is from a commercial insulation supplier. Chances are you won’t be the first studio or home theater DIY’er to darken their door, and they’ll be happy to help you.
Rigid fiberglass comes in 24″ by 48″ by 2″ sheets. Each trap uses two sheets, for a thickness of 4″. The fiberglass is laid over a frame built of 1″x 2″ pine that’s covered with a sheet of cheap fabric. You then cover the fiberglass with some nice fabric (something that tastefully matches your studio decor). You end up with something that sort of looks like a very firm mattress. I mounted mine straddling the joint where the ceiling meets the wall behind my monitors and straddling the joints from floor to ceiling in the room’s corners.
Flutter echoes: These are “sproingy” metallic sounding echoes, especially noticeable with sounds that have sharp transients, like hand claps. These are generally caused by reflections between the floor and ceiling. The cure is to put some absorbers and/or diffusors on the ceiling.
One approach to absorbers would be to build something like the bass traps, but using Corning 701, which is less dense than the 703, and perhaps only using one 2″ sheet. Unless the flutter is really bad, you probably would aim to cover only 40-50% of the ceiling, in a checkerboard pattern. (I know they’re rectangles, but you get the picture.)
If you want to buy something, then the commercial studio foam from the usual suspects is pretty good for dealing with flutter echoes. Note that when I say foam, I don’t mean the stuff that keeps the shipment of vintage Superman comic books you just bought on eBay safe. Sound waves just laugh at that stuff as they pass effortlessly through it. If you have outfitted your studio walls with egg cartons, take 30 seconds to hang your head in shame, and then go immediately and take it down. Go ahead, I’ll wait…
My point is that if you use foam, there is simply no substitute for the stuff that is designed specifically for sound treatment. If you want to go the DIY route, then rigid fiberglass is your friend.
Excessive ambience: By this I mean general undesirable reverberation from the sound bouncing around the room in a broad range of frequencies. Unless your room is tiled, or has very dense wood paneling, this is probably not your main problem, but even a small room may have excessive amounts of bad reverberation – the kind that makes what you record sound boxy and indistinct.
A bit of absorption and/or diffusion on the walls is a cure for this. Again, homemade absorbers and/or diffusors as described above will probably take care of it, or if you like, some commercial studio foam.
Comb filtering: a hollow sound caused by some frequencies being canceled and others being emphasized as the sound bounces around a room. If you graph the frequency response, it shows closely spaced peaks and valleys, and looks like a comb.
Frequency buildup and cancellation in a comb-filtered pattern
Comb filtering was the bane of my audio life for years.
By necessity, I track vocals and acoustic instruments in an isolation booth. (I live on the flight path for a large airport, I’m only about 500 yards from a railroad line, there’s a busy road nearby, and I have neighbors who like to use lawnmowers and other loud tools at the most inconvenient times.) My booth does an excellent job of keeping all those external noises out of my recordings.
Unfortunately, it also has a very boxy, unpleasant acoustic signature, caused to a great extent by the comb filtering that results from non-random reflections causing narrow bands of frequency cancellation and emphasis. It’s impossible to fully deal with the frequency imbalance with EQ, because there are narrow peaks and valleys all up and down the spectrum. I have spent many happy hours playing “whack-a-mole” with comb filtered vocals recorded in that booth. As soon as I thought I had dealt with one problem frequency, another would pop up.
I have to confess that I never found a completely satisfactory DIY solution to this. Getting the room as dead as possible seemed to be the most effective solution for me. In a typical booth, diffusors are problematic, because effective ones eat up too much space. Finally, I ended up purchasing a set of eight stand-mounted tube traps, that flood the area with random reflections that completely eliminate the comb filtering. This is not a cheap solution by any means, but it really does work.
Room modes: based on the geometry of the room, it may resonate at certain frequencies. The smaller the room, the higher the frequencies tend to be, and therefore more apparent. Room modes are fairly predictable based on the dimensions of a given room. This site and this site both show how to calculate the modes for a room. Once you know what frequencies your room wants to reunite at, you can build absorbers and diffusors that cover that range.
Keep in mind that the above is a simplification. But if you take some basic steps to treat your recording space scientifically – i.e. not by gluing random stuff to your walls – you will certainly improve the quality of your recordings a lot.
Here are some links to information from people who know way more about this than I do:
- Acoustic Treatment and Design for Recording Studios and Listening Rooms, by Ethan Winer
- Room Acoustics: Audio’s Final Frontier, from Absolute Sound Magazine, October/November 2004.
- Trapping Bass in Your Project Studio, by Arthur M. Noxon
- How To Setup a Listening Room, by Ethan Winer
- Creating a Reflection-Free Zone
- Everything you need to measure a room, by Ethan Winer of RealTraps, and Nyal Mellor
Jeff Bohnhoff is a musician, audio engineer, and record producer from California. His and Maya Bohnhoff’s latest CD is Grated Hits; their albums can be purchased online at CD Baby. Follow them on Twitter or on Facebook.
I’m handing over today’s entry to Anna, so she can signal boost a few items, particularly S.L. Gray’s Kickstarter project to get her backlisted novel back in print. We were all part of the big Willowholt Elfquest RP group which has spawned several published writers and one musician (hiya!). But for more, here’s Anna:
Hello! I’m Angela Korra’ti, a writer and a geek, and every so often I like to plug things being done by my fellow authors!
First up, for those of you who’re on Goodreads, my fellow formerly-Drollerie author Gary Inbinder is running a two-week ad on the Goodreads site to plug his books Confessions of the Creature and The Flower to the Painter. If you happen to see this ad, please clickie! And even if you don’t see the ad, please consider adding Gary’s books to your Goodreads To Read shelves. I’ve read Confessions of the Creature and quite liked it as a followup to Frankenstein; The Flower to the Painter is on my queue.
Second, S.L. Gray, who I am pleased to note as one of the several writers who’ve come out of the Willowholt Tribe I ran way back in the day, has a Kickstarter going to resurrect an old novel of hers, The Dragon Undone. Go check her out and give her some support love, people! As you may guess, Kickstarters are currently Highly Relevant to My Interests, but so is supporting writers of my Tribe. Tell her I sent you!
Third, if you’re a fan of the work of Francesca Lia Block, you might want to be aware that she’s in danger of losing her home. Looks like she’s yet another American whose home has gone underwater and her bank’s not playing nice. Click over on the link to read up more about her situation, and if you’re so inclined, sign the petition they’ve set up on Change.org on Ms. Block’s behalf.
Give those some thoughts, won’t you?
Oh, also, tonight, I’ll be doing another one of those Google Hangout online events. Normally there won’t be so many in a row, but Leannan Sidhe are trying to figure out what times are best, so I’m making all the ones I can. We had like 20 participants last time, so it was fun once we got past the technical hurdles. Watch here for the hangout link, sometime around 6pm Cascadian/Pacific, 9pm Eastern time. Hope to see you there!