Creating Custom Reverbs (Impulse Responses) in my Living Room!
I was getting new flooring installed in my house recently. I walked in the door after work and was greeted with my concrete slab foundation and all of the furniture moved out of my living room. I took one step and heard the natural reverb of the space. It was an instantaneous lightbulb moment. I needed to take an impulse response of this space.
What Is an Impulse Response?
An impulse response, or “IR” for short, captures the behavior of a dynamic system over time when a brief signal or “impulse” is presented to it. In the audio world, it’s a snapshot of the acoustic characteristics of a location. In other words, we can capture the reverb of a specific room and duplicate it within the world of audio production software — specifically, using convulsion reverbs.
The Recording Process
I knew I had to act quickly and capture an IR of the space before the flooring installer came back with more materials that would change the sound of the room. So, I dove right into it. I grabbed my Shure MV88 iPhone mic (to save time), set it on my fireplace mantel, walked into the center of the room, and clapped as loud as I could. I waited for the reverb to decay, held my breath, and clapped again. I did this a few times, changing a couple of variables, such as turning off the heat to eliminate extra noise, clapping in different areas of the room, and making sure no cars were driving by when capturing the IR. After about 20 minutes and a pair of slightly sore hands, I had captured what I needed. I emailed the files to myself.
Cleaning Up the Impulse
I imported the files into Pro Tools and got to work scanning the files for the best impulse. I was looking for one that had a nice decay and minimal outside noise. Once I located a file I felt was sufficient, I ran it through iZotope RX7 Spectral De-noise to remove as much extraneous noise as possible from the file. Then, using the Tab to Transient function, I cut the file to the very start of the clap. I listened through the decay and let it go a half second past the point where I could no longer hear the reverb of the space. I then added a small fade. I also applied an EQ with a highpass filter to remove any rumble and give the top end a slight lift to bring out some sheen to the sound. Finally, I exported the file as a WAV.
Creating the Preset
I needed a convolution reverb to import the file into — I chose Altiverb 7 by Audio Ease. I went to the IR Import tab and dragged and dropped the exported impulse into the plug-in window. Once the impulse is dropped, Altiverb looks at the file and gathers the information it needs in order to accurately re-create the reverb heard in the recording. Altiverb has a couple of preset post-processing options that allow it to more accurately re-create the reverb. These include treating the dropped audio as a slate from a movie set, a starter pistol, or one of Audio Ease’s sweeps, which can be played back through a speaker in a space. I tried a couple of the slates but ultimately decided to move forward without any preset.
From there, I imported a vocal from a previous session I had worked on and applied some of my living room reverb to it. Right off the bat, I noticed it was a little darker and shorter than I wanted, so I adjusted the Bright, Size, and Reverb Time controls to my liking. I noticed a boxy tone in it as well, so I opened the EQ-Curve tab and cut approximately 600Hz out. I added a bit of pre-delay and dampened the lows and mids, and I ended up with a very pleasant-sounding reverb that was generated from my empty living room. Since I was happy with the reverb tone I had achieved, I saved the preset to use on future sessions.
I know what you’re thinking: this is some super-audio-nerd-type stuff. But I can honestly say that the process of creating a custom reverb was quite fun and informative. This will definitely be something I keep in the back of my mind when I am out and about and stumble upon a space that has a really fun or unique sound to it.