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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