DIY Reverb Impulses

Have you ever wished you could make your music sound like it was recorded in an awesome Cathedral in Europe? Tired of feeling like a demi-god when you sing in the shower and being sadly disappointed by your vocal stylings anywhere else? Do you love the acoustics inside a spooky cave you found in the mysterious mists of the Himalayas, but do not have the time, resources, or upper body strength to muscle your 18 piece drum kit into it? Well, my sonically frustrated friend, you can CAPTURE that space and use it whenever you want with an impulse response and convolution reverb!

An impulse response is a recording of the reverberation of an acoustic space when an ideal impulse is played. Convolution reverb plugins use pre-recorded impulse samples of real rooms and spaces to build custom reverbs that very closely match an actual space. Convolution reverb plugins simulate real spaces more accurately than most other digital reverbs-- algorithmic reverbs-- which are based on hypothetical spaces. Impulses can be used to capture response of not only physical spaces, but also of speakers, radios, outboard audio equipment, and amplifiers.

So if you record an impulse response in your shower, process it, and apply it to a sample, it sounds like that sample is IN your shower! Woah! Upon completion of this tutorial you too will be able to harness the awesome power of Convolution Reverb!

DIY Fancy:

• Party balloons
• Pushpins
• 2 microphones (either cardioid or omni, you should try both. I use a pair of tube condenser microphones. If you have a flash recorder with build in condenser microphones, like the Zoom H4N, that will also work.
• 2 microphone stands or 1 microphone stand and a Stereo T-Bar
• 2 XLR cables
• A flash recorder or audio interface (such as a Zoom H4N recorder)
• Computer with audio editing software and convolution reverb plugin

DIY Cheap and Simple**:

• Hands to clap together
• Laptop or smart phone with microphone and recording ability
• Computer with audio editing software and convolution reverb plugin

*There are many free or inexpensive audio editing programs and convolution reverb plugins.

** Results with the simple form may vary, but Lo-Fi is better than No-Fi

For the purpose of this tutorial, we will be generating impulse responses in the most basic way available, by either clapping or popping balloons. This is an ideal and accessible impulse that we can reasonably create in an imperfect physical world that doesn't abide by mathematical rules all the time.

Sine sweeps can be used to generate an impulse response for a more accurate result with a little more work, because they must first be 'deconvolved' in order to be usable. Some Convolution Reverb plugins have a deconvolution plugin built in, but there are also plugins dedicated specifically to deconvolving sine sweep impulse responses.

• Microphone placement is up to your judgement, so experiment! I achieved the best results by placing 2 tube condenser microphones in omnidirectional mode in an ORTF formation, plugged into the two outboard microphone inputs of my flash recorder. This setup worked well both in the center of the room and in the back of the room. You can also use the onboard microphones on your flash recorder, your smartphone's microphone, laptop microphone, or whatever other means of recording you are working with.
• Set your microphone's input volume low enough that it does not clip (exceeding the maximum volume, resulting in a crackling sound and loss of wave form information) when you create your impulse.
• Begin recording
• Blow up your balloon, and stand wherever you choose (directly in front of the microphones is ideal, depending on placement). Allow the room to become as silent as possible. Pop the balloon with a swift motion of the pin, and don't move until the reverberation of your impulse is complete and the room returns to its normal noise floor. Or clap your hands, again, waiting until the room returns to silence.
• Repeat. Try to be consistent with your impulse generation.

For a visual explanation, here I am creating an impulse in an igloo I built in my yard a few years ago. The microphones are EV 635A Omni microphones, in a spaced pair. I am using a yard stick with a pin taped to it, as my body inside the igloo dampened the sound too much:

Cut your impulse down to size. You'll need your initial impulse and the entire reverberation that follows. To make this tutorial as widely accessible as possible, I will be using Reaper and Reverberate (Reaper is free and fully functional in demo version and can be licensed for a very nominal fee, and Reverberate is free in demo mode). I am working on a Mac, but will also demo and screen cap on my PC when I have a chance.

• Import the audio file of your impulse response recording onto your computer
• Create a new track in Reaper and import your impulse response recording audio
• Trim sample down so that it begins when you popped your balloon, and ends right as the room returned to silence
• Export or bounce your impulse response
• Create an audio track of whatever it is you want to apply your reverb to in Reaper
• Open Reverberate and drag and drop your impulse response file

It's really that easy! From there, try adjusting the different parameters inside of the plugin. I found that the gain was a little too high, and I had to notch it down to about -30dB in order to achieve the best sound. The impulse I was using was from a very reverberant space (inside a large metal tank), so there was a lot of reflection going on. In addition to that, the layered vocal track I was applying the reverb to was already pretty loud.

You can now apply convolution reverb based on any space in which you capture an impulse response! Shower singers and cave drummers rejoice!

Here is a sample so you can here what actually happened when I applied convolution reverb featuring my very own impulse response.

Before and After.

The effect is fairly subtle, but it definitely does sound like I am singing inside of the space I recorded my impulse (a large metal tank).

There are variety of plugins that facilitate convolution reverb processing. Some are bundled with audio editing software, while others are available separately. Protools and Logic have Space Designer Convolution Reverb, and Digital Performer has Proverb. These range in price, some cost a pretty penny. Here are a few of my personal favorites:

• SIR <---- Free for Windows!
• HybridReverb2 <---- Free for Mac and Windows!
• SIR V2
• Waves IR
• Audioease Altiverb
• LV2 (IR)
• Voxengo Pristine Space
• Revolver

Resources:
http://cnx.org/content/m10059/latest/

http://en.wikipedia.org/wiki/Convolution_reverb

http://cnx.org/content/m10059/latest/

FREE IMPULSE RESPONSES! :

http://www.xs4all.nl/~fokkie/IR.htm

http://www.audioease.com/IR/VenuePages/reverbgear....

http://www.voxengo.com/impulses/

http://www.audioease.com/IR/VenuePages/reverbgear....