Acoustical
Spaces and Why I Don't Use Reverb
(much)
by John
McKay
Acoustical Space is
the term used to describe the apparent
environment that a sound "appears" in.
That is to say, the sound of the room, the
reverb, the materials, etc. A vocal bathed
in short bright reverb sounds like it was
recorded in a bathroom. The sound of the
bathroom is the Acoustical Space we're
talking about (whether the vocals actually
were recorded in a bathroom is, to the end
listener, not relevant.)
There are two differing philosophies when
it comes to acoustical spaces:
One says that a mix engineer should try to
put each element of the recording
(instruments, vocals, etc.) into its own
acoustical space. For example, having a
fair amount of reverb on the snare drum,
but very little or none on the vocals. The
theory being that since our ears can
discriminate between the spaces, it makes
a mix less cluttered, and gives definition
to the elements. While this may have some
truth to it, most recordings use this
theory far too aggressively, resulting in
a mix that doesn't stick together, and
sounds like 5 or 10 recordings layered one
on top of the other.
The other philosophy, which I adhere to,
is that there should exist a common
acoustical space, and that all of the
elements should appear within that space.
That is, it should sound like a really
great recording of the best live
performance the band has ever done. I'm
not opposed to special effects and
theatrical use of effects, but I think
they should be just that, effects.
Elements can be brought to the forefront
through eq, volume, compression, and the
manipulation of "room tone."
Room tone is simply the sound of the room
while no one is playing (start recording
your vocal mic, with no one singing, and
you can hear the room tone.) Once the
musicians are playing, room tone is the
sound of the instrument in the room, to an
observer, not the player. A mic in a
corner of the room, 15 feet from the drum
set is going to capture the way the drums
sound in that space, for example.
Of course, if you're relying on real room
tone to give you the acoustical space, you
may run into problems with synthetic
instruments. In this category, you'll find
drum machines, keyboards, guitar and bass
amp emulators (Like Line 6 Pods, Amp Farm,
etc.). One of the biggest flaws I hear on
many recordings is the use of Pods. If
your drums and vocals are in an acoustical
space that sounds like a mid size,
semi-live room, and the guitar is using
some emulated Marshall stack in an arena,
guess what? It doesn't work. It sounds
fake and cheap. Similar problems occur
with drum machines and keys. So what do
you do?
One solution is to "reamp" the drum
machine or keyboard through an actual amp,
and mic it up. It you want a good guitar
tone, play through a good amp, and mic it
properly. This is the method I would
advocate, generally speaking. Now, if the
instrument in question is the bass guitar,
you may be able to get away with a Pod or
DI. Bass is pretty non-directional, and we
don't get a lot of spacial information
from it. But a mic'ed bass cab will sound
more authentic than a DI bass.
The other solution to the problem is
synthetic reverb. Using a plug-in or an
outboard unit to add reverb to a sound is
tricky. Sure, it'll sound really cool all
by itself. But when you mix those reverbed
out vocals in with the other dry
instruments, it's going to stick out like
a sore thumb. So, you need to understand
how reverb works, if you're going to pull
it off. Two tricks help a lot. One is to
set up a stereo reverb on a send, then run
a bit of each instrument through it. You
can run more of the snare or drum
overheads and less of the guitars and
bass. But even if you just add a tiny bit,
the listener's brain puts it together and
says "ok, that sounds right."
The other trick with reverb is to use a
pre-delay. Most of the time, when we hear
reverb in real life, it is preceded by a
space of silence. Like this:
sound>> (space)>>
echo>>reverb
The space can be short. (A rule of thumb
is this: Sound travels at about 1100 feet
per second. We can round this off, and say
that sound travels at 1ft per
millisecond.) If you're in the center of a
room that is 20x20, then a predelay of 20
milliseconds will sound pretty natural.
This is because the sound would leave you,
travel 10 feet to the wall, then travel 10
feet back to you, 20 feet round trip. You
can use this knowledge to do some funky
reverb things, too. Split the signal, and
send one through a 10 millisecond delay,
and the other through a 20 millisecond
delay, then send both to the reverb.
You'll get the illusion of being closer to
one wall, particularly if you use hard
panning.
In general, though, I like to use a real
room mic or two. These will be mixed in
very low, and probably compressed pretty
heavily. Compression is generally used to
"even out" the performance, making the
louder parts closer in volume to the
quieter parts. An interesting side effect
of this, though, is that the room tone
gets louder and more audible as you
compress the signal. Before adding reverb
to the drums, try compressing the
overheads a bit. This opens up the sound,
without muddying things. Of course, if the
room sounds bad, you'll want to close mic
everything (vocals included), and use
compression very conservatively.
This technique of compressing a room mic
and bringing it into the mix is often said
to "Glue" the mix together. It makes it
sound more like a real performance, and
less like it was crafted together one bit
at a time (I've even heard of engineers
running the entire mix out to an amp,
mic'ing it at a distance, and mixing that
signal back into the mix.) Of course,
different genres will have different
aesthetics in this regard. While room tone
is valued in classical and jazz, it is
less treasured in metal and pop. And some
genres even value the disparateness of
isolated acoustical spaces, hip-hop and
some dance genres being an example.
For my money, though, nothing sounds as
good as a real band playing in a real
room. Close mic everything, and set up a
room mic or two. Mix and season to
taste!
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