In Quest of Reverb,erb,erb
When DSP -- digital signal processing
-- first became reasonably common in consumer audio equipment, providing the
ambience-enhancement modes in surround receivers and decoders, designers of the more
elaborate DSP chips actually measured the reverberant characteristics of real acoustic
environments -- concert halls, cathedrals, jazz clubs and the like -- and created
algorithms that mimicked them and fed them to the surround-sound speakers.
But lots of recordings, especially live concerts and
classical music, already have a lot of ambient material mixed in with the music and, since
a lot of that is out of phase, it can be readily extracted by even a first-generation
Dolby Pro Logic decoder. Thus it was possible to do a comparison of the artificial
ambience created by the DSP circuits and something like the real ambience extracted by Pro
Logic.
The phony stuff almost always sounded better. That's not
really surprising because, except in the relatively rare instances of music recordings
specifically meant for Dolby decoding, the ambient material was uncontrolled, an
accidental byproduct of recording in a live venue. Sometimes the decoded product sounded
fine, sometimes not, but at least the DSP-produced reverberation usually sounded pretty
much as the designers intended.
Extracting fortuitous surround information is especially
strange if you're listening to FM. Radio stations process their signals in various ways,
and some of the techniques result in wildly exaggerated rear-channel output. Using the DSP
modes can be much more natural, but that can sound pretty strange when the music stops and
the news begins, sounding like it's being read from a pulpit. It's best to have a quick
finger on the remote when listening to radio.
But it still astonishes me that switching such acoustic
effects in and out is so simple. I spent a considerable portion of my early audio
tinkering trying to achieve something -- anything -- that sounded like reverberation.
At one time it was the preserve of professional audio,
which achieved it by means of an "echo chamber." This was a room with very hard
and, ideally, non-parallel walls, in which sounds could bounce around for quite a long
time. The main program was fed to a speaker in one corner and the resultant prolonged
sound picked up by a microphone in a far corner and mixed into the primary signal.
At first, the effect was used mainly in radio dramas to
indicate the sound of a cave or a cathedral, or simply to add dramatic effect to
announcements.
Record companies picked up on the spaciousness of
reverberant sound in the 1950s, and began adding it to virtually every pop recording. It
became so familiar that older "dry" recordings began to sound peculiar, and when
Jimmy Clanton recorded "Just a Dream" with no reverb in 1958, it sounded very
strange indeed, and nobody tried it again.
Almost as odd was the "slap-back" echo used on
Elvis Presley's early RCA discs. Instead of a gradually dying reverberation, this
consisted of one repeat of the original sound immediately afterwards, and no decay. The
effect was like singing in a box.
Once echo chambers gave way to electromechanical reverb
devices using spring and metal plates -- still expensive, but not requiring devoting a
whole room to the effect -- radio stations took to it with a vengeance. One station that
used to come booming in at night in the summer, WABC in New York, put everything through a
reverb processor: music, news, traffic reports, everything.
Ultimately, reverb became so overused that at least one
radio station I know of banned it entirely. I was involved in making commercials for a
hi-fi show at the time, and we had to produce dry versions for that station and reverb-y
ones for everyone else.
Long before that, when I was still becoming familiar with
tape production techniques, I longed to find some way to simulate reverb. I thought of
using a discarded heating-oil tank as an echo chamber, but my parents weren't keen on
having it in the house. So I turned to the electronics magazines, and attempted some of
their projects.
The first involved gluing the end of a long, coiled door
spring to half a ping-pong ball and gluing that to the center of a speaker, which
reproduced the original signal. The other end was straightened out and the metal inserted
into an old-style phono cartridge designed to use steel needles. The sound playing through
the speaker would travel back and forth along the spring, being picked up by the
cartridge. The result was a decidedly boingy effect, and if anything bumped the
table this contraption was on, it made the sort of noise you'd expect from tossing a grand
piano out a third-floor window.
My next attempt involved, as I recall, a length of garden
hose, and sounded like it. I finally was able to get something plausible when I bought my
Revox A77 open-reel tape recorder, whose three heads let you create reverb by tape delay,
which is how many pros did it by then. But the machine made you go through the hoops to
get the effect; it's the one thing I always had to go back to the owner's manual to do.
The notion of simply pushing a button on a receiver to do the same would have been
preposterous.
That's just one more thing that digital does better.
...Ian G. Masters
ian@mastersonaudio.com
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