Convolution Reverb for iOS

Ever heard of a critter called a “convolution reverb”? If you’re a musician who does stuff using computers, you may have. Otherwise, you may be hearing about it for the first time here. A short and rather technical description can be found on Wikipedia.

Most folks know what a “reverb” is when it comes to music and  audio work: it’s a box you plug into your equipment that simulates what the sound would be if you were playing inside of a larger space. It’s used to give “depth” and “ambience” to musical tracks.

If you’ve ever gone into an empty house, garage, or building, you’ve probably noticed that when you talk or clap your hands that you hear some echos that trail off after a second or two. That’s called a “reverberation tail”. It’s caused by the sounds bouncing back and forth off the surfaces in the enclosed space — walls, floor, and ceiling.

The harder and more flat the surfaces are, the sharper and longer the reverberation continues.

I play Native American flutes, and adding reverb to flute music makes it sound a lot “richer” and more hypnotic. Unfortunately, the acoustical properties of most typical bedrooms (where I record myself) isn’t ideal for producing the kind of reverb tails you’d want for this sort of music. To get what you want, you need to record a very “dry” signal, then add reverb into the mix later on using the computer.

There are lots of reverbs in the world, both hardware plugins and software models of them. And most of them allow you to tweak the various settings to alter their sonic characterists in different ways. That’s all well and good, unless there’s a specific place you’ve found that has really terrific acoustics. When that happens, you wish there was some way to take that space home with you so you could reproduce the acoustical properties whenever you wanted.  But that can be problematic.

Suppose you’re inside the Great Pyramid at Giza, and you love how it sounds when you play. What do you do? It’s not like you can take it home with you, right?

Well, that’s where convolution reverbs come into the picture. A convolution reverb (CR) is basically a mathematical acoustical model of a particular space that can be applied to any sound recording and make it seem like it was played and captured inside of that space. Is that cool, or what?! So with a model made from, say, the Great Pyramid, I can apply it to my flute music recorded at home and viola! It sounds almost identical to what it would sound like if I had played it there, inside that space, and recorded it directly.

Now, if you’re familiar with reverb boxes, convolution reverbs aren’t quite the same. For one thing, there’s no “box”. They exist in software. In fact, from a technical standpoint, they’re not even “reverbs”. They’re really just software that applies some fancy mathematical processing to a sound recording, and the result is as if you made that recording inside of the space that you selected. Like the Taj Mahal, or an airplane hanger, or Carnagie Hall.

Anyway, CR software tends to be rather expensive. Standalone products cost several hundred dollars, and folks charge big bucks for the impulse response (IR) files needed to model new spaces. Some of these products require another product to create the IR files, which is a few hundred bucks more.

Well, I just found a new app that runs on the newest iOS devices called AltiSpace. It can be purchased on Apple’s AppStore here for $6.99. That’s a far cry from other software that costs about 100x as much! Here are some screenshots of it:

AltiSpace-1 AltiSpace-2

I got this app because I’ve been looking for a simple way to add some reverb to my sound when I’m playing my flutes live, without having to haul a bunch of equipment around with me. This lets me plug a mic into my iPad Air or iPod Touch (5th gen), then feed the headphone output  into a small amplifier.

I picked up a little Audio-Technica ATR3350iS Lav mic to use with my flutes. (As I write this, the wireless mic that I usually use is still up in storage in Reno, along with most of the rest of my stuff.) I also ordered a wireless audio transmitter/receiver from some supplier in China and am waiting for it to arrive. This combination of goodies might actually end up working better than the wireless mic because I’ll plug the mic into the iPod and the iPod into the wireless transmitter. Everything I need to control the sound is on me, leaving me free to move around.

Here’s what the ATR3350iS looks like:

One thing worth noting is that doohickey at the top. That’s a splitter that plugs into your mobile device and splits it into two plugs — one for the mic, and one for headphones. Usually they cost $20-$30 by themselves, but they include one with this mic kit! These mic kits go for $25-$50, but Amazon has them for around $30. (Click the image for more info at Amazon. )

As I get time to mess with this stuff, I’ll post more about it, as well as snippets of some flute songs.

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