Recording - September 2016 - 63

Sampling space
Partly in response to the demanding nature of conventional, or algorithmic reverbs, the techs in white lab coats developed a different
approach. Instead of simulating an artificial room, they would take an
impulse response (IR) of a real room, by creating a loud, short, sudden
sound (an impulse) in that room, typically with a starter's pistol, and
recording the result, then deriving a transfer function which defines
how that room reverberated to the impulse. This transfer function could
then be applied during mixdown (or afterwards, to a full mix) to create
a remarkably accurate simulation of how the recorded musicians
would sound if they were playing in, say, the Concertgebouw auditorium, without the expense of flying them to Amsterdam.
This new approach was called convolution reverb, and manufacturers will happily sell you IRs for all sorts of rooms, ranging from
famously excellent concert venues to more mundane locations. One
manufacturer, for example, offers soundprints for the famous jazz club
Birdland, or for Nashville's Ryman Auditorium (home of the Grand
Old Opry); another offers a recreation of the sonics of an empty parking garage (useful if you're making a noir film).
Once you have a convolution reverb plug-in installed, there are plenty
of IRs you can download; Google "convolution reverb plug-in" to find out
about them. Or you can make your own, though you'll need to get permission from the venue's owners, clear the room of visitors, and wear ear
protection (remember that Ronald Reagan famously lost the hearing in one
ear from being too close to a blank cartridge fired on a movie set).
It's also possible to run impulse signals through various audio
devices, and get IRs from them; for example, this might be a good
way to simulate real slapback from a 1950s-vintage Ampex tape
recorder. Some IR libraries feature phone booths, megaphones, and
even famous reverb boxes (sampling a fake reverb for a realistic fake
reverb... contemplate that for a moment).
The Ottoman Underground session
As I mentioned, I didn't use any of these reverb emulations when I
was mixing the track that Ottoman Underground recorded. Instead, I
mixed dry with no reverb devices; I did think about adding slapback
to Will's vocal, but decided against it. Instead, I mixed with the
expectation that I would add reverb later, in post-production; as it
turned out, I wound up doing exactly what I'd planned to do.
I opened the dry mix in the DAW I use at home, Adobe Audition.
Before I did anything I saved copies in a couple of places, including
a thumb drive, so I would have something to go back to in case of
disaster. (I've lived through computer crashes in the middle of work
sessions, and they're not pretty.)
Next I edited the track down to the short clip I planned to use as an
accompaniment to these articles. Note that I did the editing before I
added any reverb; if I'd done it afterwards, I'd have risked chopping
off some of the reverb's tail.
Then I started playing. I opened Audition's Reverb plug-in, and
called up a preset that they call "Warm Room". It's worked for me in
the past-it's one of the least artificial-sounding digital reverb settings
I've used, and it just plain sounds right to my ears, which like things
on the natural side.
Here are the default settings for this preset. I present them with
some hesitation; I know they won't work for another reverb, since the
nomenclature is different for every reverb out there. Still, I wanted to
give you some idea of what worked for me (and has worked on several other occasions):
Total reverb time: 589 ms
Attack time: 43 ms
HF absorption time: 872 ms
Perception: 2
Dry level: 120%
Wet level: 28%

There are a couple of mysterious-sounding parameters.
"Attack level" describes how long it takes the multiple
bounces to build to their full level. And what's this
"Perception" thing, which is set low in this preset (the
scale runs from 0-200, with no units provided)? Audition
defines it as the level of discrete echoes audible within
the reverberation, noting that low settings sound
"smooth" whereas high settings sound "echoey". Parsing
what the designers mean by these words, and turning
them into a gut-level sense of what to expect, soundwise,
is one of the chief reasons for my strategy of learning
about particular settings by playing with them. In the
long run, that's really the only way to turn the designers'
fanciful metaphors into something you can use.
I followed the Iron Law of Reverb (see the sidebar): initially I set the levels at 120% dry, 56% wet. Then I lowered the wet percentage to 28%, and when I came back
to the reverberated mix the next day, it sounded just right.
Audition also gave me the choice of summing my dry
track down to mono. This simulates the early chambers
and plate reverbs, which took mono signals as their inputs.
I didn't want to do this; when playing with this reverb, I've
always preferred the sounds I got when I didn't check the
"sum-to-mono" box. So I left the signal stereo.
After all my twiddling, I was rewarded with a reverb
sound that my ears called right; it didn't swamp the
recording, or place it in a metallic cave, but it buoyed
up the music on a clean-sounding pedestal of reverb
which added the body the mix needed. I was happy,
and so were the members of Ottoman Underground.
Now that the track was finished, the next step would
be combining it with other tracks into a CD, which is
part of the job of a mastering engineer. We'll talk
about that next month-stay tuned!
Paul J. Stamler (stamler@recordingmag.com) is a
recording musician, engineer, educator, and collector
of bizarre vintage recordings, living in St. Louis.

The Iron Law of Reverb
How much reverb should you add to a mix or, in the
case of our clip, a finished track? This way to decide
has been useful to so many people over the years I've
been teaching it, that I've come to call it the Iron Law of
Reverb.
1. Start with a dry mix, with no reverb.
2. Bring up the reverb until it sounds right.
3. Then turn the reverb down by 6 dB. When the plugin presents the wet level as a percentage, as Audition
does, divide the "sounds right" wet level by two, which
is the equivalent.
Why does this work? Why not simply set the level to
where it sounds right?
The problem is that your ears acclimate almost
instantly to a given level of reverb-they don't hear it
any more. The temptation, therefore, is to add reverb
until you can hear it, then decide that's right. Very
often, when you come back the next day, it sounds like
you recorded in Carlsbad Caverns.
The Iron Law is a way to get around your ears' misperceptions. It sounds counter-intuitive to change a setting that sounds right, but it works! Really.-PJS
RECORDING SEPTEMBER 2016

Table of Contents for the Digital Edition of Recording - September 2016