. . . and here's why.
Our ears use three different methods to
determine the position of objects that are producing sounds we hear,
each involving the differential response between one ear and the
other. With bass frequencies, it is the relative phase along the
wavelength; with midrange, relative sound pressure; with high;
relative time of arrival. In effect, our ears are performing a
constant real-time analysis of what is taking place in one ear
compared to the other.
Imagine you are sitting in a small
concert hall, being careful not to make the foolish mistake of
sitting dead center. (This would be difficult in a good hall because
the designers would know better than to make that possible.) Then,
let's imagine an oboe player is seated 15o to your left.
While you enjoy a short selection, imagine an absolutely perfect
2-channel recording is made of the performance, flawlessly storing
exactly what both your ears heard, one in each channel. Then, you
return home where you have assembled a playback system capable of
reproducing exactly what each of your ears heard in the actual hall
during the performance, the left speaker recreating exactly what
your left ear heard, and likewise the right. Naturally, these last
two things are impossible, but for the moment, pretend it's
happening. You may think this would allow you to enjoy the exact
same sonic experience as the live performance. If you do, you are
mistaken; the experience will be quite unlike the original. The
reason is this: while the left speaker is delivering to your left
ear exactly what you heard in the hall, it is also delivering it to
your right ear, and likewise the right delivering its information to
the left. The result is that both ears are hearing, with some degree
of distortion caused by our directional sensing mechanism, what the
other ear is hearing. Remember, in the original performance, there
was only one oboe player – now, there are two, one in each speaker.
This combination of factors results in the destruction of the
spatial clues that create the three-dimensional sense that natural
hearing creates. In the concert hall, you could tell not only that
the oboist was to your left, but that she was at a higher elevation
as well as some distance away. Typically, in your living room, the only method
used for creating a positioning effect is to play one speaker louder than
the other. You are left only with sufficient information to determine
left-to-right positioning.
Superior audio equipment will allow you
to resolve the relative height of the instruments to some degree due
to careful crossover design and driver selection, but this can do
nothing to overcome the fundamental problem that both ears are
hearing information that was only intended for one. The result is a
collapsed, two-dimensional sound stage that extends no father than
the vertical plane created by the front of the speakers. It is a
very frustrating way to have to listen to music, and is the primary
reason why recordings can never carry the emotional impact of a live
performance, even though recordings typically “sound” much better
than the real thing. Your ears know better . . .
So what can we do to fix the problem,
apart from building a sound-proof wall that extends from the front of
the room, through your head, and all the way to the back of the room?
Well, one method has been the use of
binary recordings, made with two microphones positioned in the same
way our ears are, and then listening to the results with headphones.
This completely isolates one ear from another, eliminating the
fundamental problem of cross-hearing. Such recordings are quite
amazing, but they have rarely been applied to anything other than
novelty recordings, such as the sound of sitting in a rain forest or
some such thing. When attempted with normal stereo recordings, the
result is an image located inside your head instead of out in front
of you where it belongs, and once again, your ears know better.
Another attempt was made by Matthew
Polk way back who-knows-when with his SRS series of speakers. He
attempted to cancel out the cross-hearing effect by mechanically
manipulating the phase information with additional speakers in each
cabinet that delivered out-of-phase information from the other
cabinet. I heard it once - for about 7 seconds. I'm very sensitive
to phasing information, and that sound had me jumping out of the
chair in seconds.
It wasn't until the early '90s when
Lexicon released its first digital processors, the CP-1 and CP-2,
that I heard an effective solution to the problem. For many years,
each of their successive surround processors have provided an effect
called “Panorama”. The processor electronically manipulates both
channels of stereo information in such a way that causes each speaker
to carry a mixture of both channels of sound. By altering the phase
as it comes out of the “wrong” speaker, it cancels the waveform
coming from the “correct” speaker, with the result that, once
properly adjusted, your left ear can literally only hear the left
speaker, even though both are playing, and the same for the right
speaker.
The trouble – and of course, there's
always some price to be paid – is that the effect is very sensitive
to external factors. The speakers themselves must be operate as a
point source, something relatively uncommon. The farther away the
speaker's characteristic dispersion pattern is from a point source,
the less effective the process is. Another is the listener position;
the placement of the listeners head relative to the two speakers is
critical. A movement to the left or right of an inch will
drastically reduce the effect of the process. As a result, every
time you sit down to listen like this, you have to engage the
calibration tones to make sure you're in the right place, and then
you have to be careful to remain still. Then there's the fact that
Lexicon processors can be pricey if you find one with the remote and
in good working condition. And of course, because it is a processor,
you'll need a separate multi-channel power amp, or multiple stereo
amps, to take advantage of everything they will do. The only reason
I have such a rig is because I upgraded an old client's theater, and
claiming the old equipment is part of the deal.
A lot of trouble? Well, yeah. But is
it worth it?
Absolutely, definitely, positively yes.
The effect is uncanny, hypnotizing. The image is no longer
seemingly trapped behind a piece of plexiglass that is resting on the
front of the speakers, preventing it from getting out to where you're
sitting. You hear a smoothly fading image from front to back, the
natural decay in sound pressure as it travels from the source of the
sound toward the back of the room finally back where it belongs
instead of falling on the floor between the speakers. Instead of the
guitar player sounding like a cardboard cutout looks, he and his
instrument are three-dimensional, allowing you to hear the tone of
the instrument changing as the notes decay the farther they get from
the speaker. You are, acoustically, a factor in the experience,
instead of an observer. Toggling back and forth between having
Panorama turned on and then off is jarring. The Panorama effect
instantly makes what you're hearing sound “normal” - when you hit
the Bypass button to turn it off, the sound field collapses; it's as
if the entire room in front of the speakers no longer exists.
I treasure the freedom to listen to
music this way. It was many years between the time I first heard the
effect and the time when I actually owned the stuff that does it.
It's been well worth the wait.
Fact is, Bob Carver was right –
stereo is fundamentally wrong, but it can be fixed.
