WRITTEN BY BRAD MEYER, SOUND EFFECTS EDITOR AT BOOM BOX POST

Introduction BY KATE FINAN, CO-OWNER OF BOOM BOX POST

Ever since we shared our Boom Box Post approach to encouraging a creative workplace with René Coronado and Timothy Muirhead on their Tonebenders podcast, we have received countless requests to publish our monthly Lunch & Learn sessions.  At Boom Box Post, we believe in letting each member of our team be both teacher and student.  As part of that ideology, we hold monthly meetings where we choose one team member to teach us something that we may not already know.  The topic is their choice.  It can be something on which they are already an expert, or it can be something that they themselves have always wanted to learn but have never had the time to investigate further.  In doing this, we encourage our crew to be continuous learners themselves (and to get comfortable being an "expert" amongst their peers), and to understand the idea that when we share our knowledge with each other, we all become better at what we do.  

We toyed with the idea of presenting videos of these Lunch & Learns, or perhaps audio podcasts.  But, in the end, we settled on blog posts.  Why?  Because we're working, and you're working. And we know that you probably don't have an hour to invest in the middle of your day to watch us at work.  Instead, we invite you to take 15 minutes during you lunch break each month to read a condensed version of what made this month's Lunch & Learn so special.  You are now part of the team! So grab your soup and get ready to learn something! And don't forget to be on the look out for these L&L posts each month from now on.  

-Kate Finan


Here at Boom Box Post, we conduct monthly Lunch and Learn meetings where a rotating member of the team teaches a lesson to the rest of the studio.  Whenever it is my turn to teach a Lunch and Learn lesson, I always try to rack my brain for a topic that I either don’t use on an everyday basis, or would personally like to learn more about. This month I chose Impulse Responses and Convolution Reverb. 

I find this particular topic very interesting for a few reasons. First, it requires getting up out of that office chair! I’m always down for active and interactive audio experiences. Second, I love customizable audio options. It isn’t often that you find EXACTLY what you’re looking for, so the ability to create custom reverbs is always very useful. And lastly, it is a topic that I always knew about but have never personally done, so I figured diving right in was the best way to get a proper hands-on Convolution Reverb and Impulse Response experience. 

Most of what you read online or in books about Impulse Responses and Convolution Reverb can get very technical very quickly, and I really wanted to share our experience with the subject in an easy to understand way. 

WHAT ARE CONVOLUTION REVERB AND IMPULSE RESPONSES?

  • Convolution reverb is a process used for simulating the reverb of a physical or virtual space through the use of software or algorithms that creates a simulation of an audio environment.  The most popular Convolution Reverb plug-ins on the market are Altiverb, Waves IR-1, and Logic, which has a built in convolution reverb software. In our case, we used AVID SPACE.
  • An impulse response is how a space or room responds to measuring for a convolution reverb.

HOW DO YOU MEASURE AN IMPULSE RESPONSE?

The most common way to measure the Impulse Response of a space is to play back a frequency sine sweep (often from 20Hz to 20KHz) in the space while recording it back at the same time. Once recorded, you can take the dry sweep and the recorded one and compare the two to calculate the difference, which is how most softwares can calculate the reverb of a particular space.

However, the alternative way of measuring for an Impulse response is to use a sound with a hard attack and long tail like a clap, balloon pop, or gunshot. This method is what AVID SPACE prefers and it worked quite well when we gave it a go.

HOW OUR LUNCH AND LEARN WORKED

Directly next door to Boom Box Post is a large warehouse that I’ve always wanted to try measuring Impulse Responses with, so when it came time to conduct the lesson, I figured the warehouse was the perfect option. But for the sake of variety, I wanted to try another more unusual “space” to compare, and we ended up using an old, metal barrel.

I began by going into the warehouse and clapping as hard as I could while our dialogue editor recorded it back. You can hear the clap in the warehouse below.

After we measured the warehouse, we then took our operation inside and clapped inside the metal barrel and recorded that back. The barrel gave our reverb a more metallic, tinny sound, and we began to realize the true design capabilities of convolution reverb. 

We took it one step further after this and instead of clapping in the barrel, we hit the side of it and let it ring out. This created a significantly longer tail because the attack was much more aggressive than a clap. We recorded this just like the previous examples.

AVID 

Once the “dry” claps and hits were recorded, I simply made a folder with the three recordings in it and loaded it into the AVID SPACE plugin on a record track in Protools. It’s as simple as selecting the .WAV file of myself clapping in the warehouse, and I can apply that particular reverb to anything I want. The way AVID SPACE calculates this is by using the tail of the loud sound we recorded, in our case a clap and impact on the side of the metal barrel. It then applies those same properties to whatever sound you choose. 

For the sake of example, the dry recording that I used to apply these reverbs to is co-owner of Boom Box Post, Jeff Shiffman, exclaiming “Boom Box Post” (How fitting!). You can hear the dry version, before any of our custom reverbs have been applied, below:

I can take this recording of Jeff’s voice and “place” it in different spaces with these Convolution Reverbs. Of course you can do this with any reverb, but now I can theoretically place Jeff in the EXACT warehouse that we have next door. Or for fun, pretend like we shrunk him down and put him in our metal barrel! You can hear these examples below. First is the warehouse, second is the clap inside the metal barrel, and third is hitting the side of the metal barrel.

Especially working in animation, it is pretty fascinating the capabilities of convolution reverb. We often have some whacky spaces that our characters are in and the ability to customize our reverbs creates so many more options. Take for example our series Ask The StoryBots. The StoryBots travel through tunnels and metal tubing to get from their animated world to the outside world, and we can easily get our hands on a piece of metal tubing to record an impulse response and recreate that space. Or take when our Teenage Mutant Ninja Turtles went to space at the beginning of season 4. We can record an impulse response in a space similar to the inside of a space suit helmet (motorcycle helmet, for example) and apply that to whenever we are “inside” a character space suit. The sound of the inside of Iron Man’s helmet uses the exact same principle.

This creates a whole new set of design possibilities for any sound designer and can give your edit or mix that extra signature sound it may need, especially if stock reverbs just aren’t cutting it for the space you are trying to create.

Next time, I’d definitely like to try breaking the rules when it comes to convolution reverb and impulse responses, and use something other than a sine frequency sweep, clap, balloon pop, or gunshot. For example, I’d love to play back some telemetry or synthesized drones into a space and record that back to see what sort whacky effects it has. 

In what unique way would you use Impulse Responses and Convulsion reverb?  We’d love to hear how you think!

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