The Stereo Mystique
Someone recently asked my advice about his audio setup,
adding "I prefer to listen to music in two-channel sound." My initial (unspoken)
reaction was that that was like saying "I prefer to listen to music with no
bass."
That was probably unfair. For more than four decades, most
of us have done our music listening -- critical listening, anyway -- in two-channel
stereo, and there is a definite appeal to the familiar. Somehow, two channels just seem to
feel right. The argument, "I only have two ears, so why do I need more than two
speakers?" which was often trotted out in the days when quadraphonic sound was
struggling to survive in the 1970s, was quoted recently in a major hi-fi mag as an
argument that needed serious refutation. Still.
Back in the 1930s, researchers determined that the minimum
number of channels for realistic reproduction of sound was three. The two on the sides
were necessary for creating a sense of space and for spreading the orchestra out across
the imaginary sound stage, but the most important material was in the middle. That's where
the singer or solo instrumentalist would be, and that deserved its own speaker.
The problem was that no one could figure out how to cram
more than two channels on a record, so the only solution was to use those for the width
and take advantage of the phenomenon of "imaging" to replace the missing center
speaker. Two sounds coming from two sources will seem to originate halfway between them as
long as they are identical in level and phase. The success of a pair of speakers in
creating this phantom image was long considered a hallmark of audio quality.
And, to tell the truth, the effect can be magical. I had my
first taste of stereo when a buddy's father brought home the first stereo on the block. It
was one of those single-unit console jobs, with the works under a hatch in the middle and
the speakers mounted on either side, about four feet apart. To hear the effect, you
literally had to sit on the floor directly in front of the cabinet, about a foot and a
half away, but as a teenager I didn't mind doing that. Sit on the couch across the room,
however, and it was mono again.
Since many early stereos were of this form, they gave rise
to an aberration called "ping-pong" recording, in which sounds were routed to
the extreme left and right, with virtually nothing in between, mainly to demonstrate that
there was different information coming out of the two speakers.
This disappeared quite quickly, fortunately, and engineers
began to create more realistic mixes, especially when the most common sort of stereo
system came to include separate, widely spaced speakers. They were stuck with two channels
for the final product, but it's significant that many of the early stereo recordings were
originally made as three-channel tapes, the center information only being distributed to
the left and right tracks in the final transfer.
Those original three-track tapes would now be ideal for
remastering in the new multichannel formats, which offer a discrete center track, but many
of them have disappeared. For those that remain, there are only a handful of machines
equipped to play the half-inch tape with its distinctive track configuration.
In my own early listening days, I often preferred mono. I
was rarely interested in sitting stock-still in the "sweet spot" (the only place
that imaging works at all), trying to identify exactly where the oboe or second viola was.
I was more interested in how the musical elements worked together than where they were in
relation to each other, and the seating requirements of two-channel stereo were too
confining. The moment you got a bit closer to one speaker, the singer disconcertingly
popped into that speaker; at least in mono the image stayed put.
In two-channel stereo, the aim is to spread the music out
across the front of the listening room. That's not always a realistic rendering of a live
experience, however. In the live environment of a concert hall, once you get a certain
distance back in the auditorium, the music is mono; what washes over you and gives you a
sense of depth are the reverberations bouncing off the interior surfaces. Most listening
rooms can't duplicate that, but some can: I've known several large, irregularly shaped
rooms that have had enough of their own ambiance that it was impossible to tell from the
listening position whether the sound was mono or stereo. It still sounded great.
Most people don't have the luxury of such listening spaces,
and most aren't content to sit immobile in one spot in order to have the psychoacoustic
process create a center image. The most dramatic advances the multichannel revolution has
brought have been the creation of credible acoustic environments through extra channels of
sound, and the abolition of the sweet spot.
The latter is far from complete, however. It seems old
prejudices die hard, and there is apparently a body of recording engineers who are
prepared to use the various surround-sound formats to create realistic acoustic spaces,
but are still wedded to the old notion of imaging. According to one recent report, a lot
of music recordings remixed to surround simply don't use the center channel, distributing
the soloist to the left and right, to be heard only in phantom form.
One explanation is apparently that giving the soloist a
separate channel is too likely to reveal flaws that would otherwise be lost in the musical
"soup." Another is that the center speaker in most systems is inferior to the
others, and that the phantom image will thus sound better than a discrete center speaker.
Those arguments seem to me to be unfair to the musicians
and to the speakers. Both should be good enough to stand up to today's technology.
...Ian G. Masters
ian@mastersonaudio.com
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