# Sony SL-2700 Betamax

W

#### William Sommerwerck

Jan 1, 1970
0
You do know that Ampex started the development of VHS before they
sold out to a consortium of japanese companies to raise much needed
funds for their financial survival? Ampex wanted to make a cheap,
scaled down version of their existing 1% 2" tape systems, to sell at
an affordable price for consumers but ran into cash flow problems.

That's new to me. I don't see why Japanese companies aren't capable of
designing poor-quality products on their own. (RCA had been working on a
consumer video recorder for years, but felt it wouldn't be marketable until it
hit the same price point as color TV -- $500.) The Betamax machines I worked on treated the tape a lot worse than VHS. That's not altogether surprising. Beta pulled the tape into an elongated loop around the drum, to isolate its motion -- which is why Beta has less line jitter. Some had the tape sliding against itself to simplify the loading and unloading. I'm not sure I understand. Having seen both in use in a broadcast station, the cheap VHS was much better than any Beta, other than the overpriced ENG version that only got 20 minutes per tape. All Sony machines needed a TBC to meet FCC requirements, but I could feed a$79
VHS tape into our Vital Industries Squeezezoom and get a picture
that was stable enough to broadcast.

You are one of the most-knowledgeable people (about anything) I've ever met,
but here I have to say "No way, José." VHS has serious time-base problems.

I first noticed this the early 80s when I was scanning a late-night show I'd
recorded * -- why was the picture visibly sharper than in normal play? I
looked closely and saw the reason -- severe line jitter. When scanning, there
was either less of it (for the same reason analog recorders have less flutter
at higher speeds), or the eye did a better job of averaging the errors.

Just as I judge audio equipment by what I hear, I judge video equipment by
what I see. When VHS recordings have obvious time-base problems -- what am I
supposed to conclude?

* The machine was a high-end RCA-branded Panasonic.

W

#### William Sommerwerck

Jan 1, 1970
0
"Bruce Esquibel" wrote in message
The problem with you "beta was better" guys is you never admit that during
the great VHS vs. Beta wars, 99% of the people who bought them had crap
televisions that probably couldn't produce 280 lines of resolution.

I owned an NAD MR-20A at one time, and my SuperBeta HiFi machine made
recordings that were //almost// indistinguishable from the broadcast.
Obviously, if they were played on modern displays, the loss of quality would
be more visible.

The simple fact of the matter was, most people simply could not tell the
difference from one to the other. People with trained eyes, possibly.

You don't need trained eyes to see the difference. It isn't at all subtle.

There was no day and night difference between them. There couldn't
have been because few people owned any kind of set to watch them
on, to notice the difference.

You're kidding, of course. One of the most-noticeable problems with VHS is the
lousy color. Not only are hues sometimes off, but the chrominance doesn't
always fill the luminance!

I can't speak for or against the quality of Beta transports. They were
more-complex than VHS, so, in principle, they should have been less reliable.
I never had trouble with my SL-HF900 deck. It still works.

C

Jan 1, 1970
0
William Sommerwerck said:

That might be true. But I've spent many years listening to orchestral
recordings enhanced with surround -- either from the recording itself, or a
hall synthesizer -- and the improvement is huge.

They probably do those recordings correctly, and the audience for such
recording will care.

I've seen pretty recent movies where the surround sound effects are
completely random and pointless. One movie has surround sound for a bird
flying around, and it had nothing to do with the scene at all. It's like
there was a budget for 30 seconds of surround sound and somebody played
some canned sound effects to meet a quota.

Then or couse when people were being chased around in the woods and
murdered there was no surround sound. That would have been the perfect
time for such effects- hearing some twigs snap over here or there.
Circa 1980, I had a really high-quality quad system, with Lux electronics and
Infinity speakers. People -- including a hi-fi dealer -- said "I don't like

How were those extra channels added and extracted from the regular two
channel recordings, other than with one of those boxes?

W

#### William Sommerwerck

Jan 1, 1970
0
William Sommerwerck said:
They probably do those recordings correctly, and the audience for such
recording will care.
Absolutely.

Then, of course, when people were being chased around in the woods and
murdered there was no surround sound. That would have been the perfect
time for such effects -- hearing some twigs snap over here or there.

Point well-taken. Movies often miss the opportunity to create a truly
immersive experience.

How were those extra channels added and extracted from the regular two
channel recordings, other than with one of those boxes?

I had a variety of sources and processors. At the top was discrete open-reel
tape, which produced the most-spectacular consumer sound, until multi-ch SACD
came along. (I still have the tapes and an Otari quad deck.) It is unfortunate
that Sony has refused to reissue its huge library of Columbia surround
recordings on SACD.

For quad phonograph records, there was the Audionics Space & Image Composer,
an advanced SQ decoder that could wrap stereo recordings around you, often to
great effect. I also had an Ambisonic decoder for Ambisonic recordings. It
could do things similar to the Audionics, without requiring logic circuitry,
and did a superb job of ambience extraction.

For stereo recordings, I had an audio/pulse Model One, the first consumer
digital ambience device. It didn't generate high echo density, but used
tastefully, it could greatly enhance the sense of space. (I later replaced it
with the improved audio/pulse 1000.)

My current system includes the JVC XP-A1000 and Yamaha DSP-3000 hall
synthesizers. These are modeled on real halls (such as the Concertgebouw). You
can pick an appropriate hall (concert, recital, cathedral, opera, stadium),
then tweak the settings (if you wish) to fine-tune the sound to match the
recording's ambience. These devices are so natural-sounding, you cannot hear
them working until you shut them off.

I have a 6.1 system (no center speaker) with Apogee speakers and Curl
amplification.

There is no excuse to listen in two channels. Stereo is technically and
aesthetically obsolete.

S

#### Smarty

Jan 1, 1970
0

Point well-taken. Movies often miss the opportunity to create a truly
immersive experience.

I had a variety of sources and processors. At the top was discrete
open-reel tape, which produced the most-spectacular consumer sound,
until multi-ch SACD came along. (I still have the tapes and an Otari
quad deck.) It is unfortunate that Sony has refused to reissue its
huge library of Columbia surround recordings on SACD.

Open reel was the best. JVC CD4 discrete disks were the worst......
Pre-recorded open reel tapes were few and expensive, but boy did they
sound wonderful.
For quad phonograph records, there was the Audionics Space & Image
Composer, an advanced SQ decoder that could wrap stereo recordings
around you, often to great effect. I also had an Ambisonic decoder for
Ambisonic recordings. It could do things similar to the Audionics,
without requiring logic circuitry, and did a superb job of ambience
extraction.

For stereo recordings, I had an audio/pulse Model One, the first
consumer digital ambience device. It didn't generate high echo
density, but used tastefully, it could greatly enhance the sense of
space. (I later replaced it with the improved audio/pulse 1000.)

My Audio Pulse hissed and made a lot of background noise. The pushbutton
switch array also got intolerably noisey. The Advent SoundSpace was a
huge improvement.

S

#### Smarty

Jan 1, 1970
0

Point well-taken. Movies often miss the opportunity to create a truly
immersive experience.

I had a variety of sources and processors. At the top was discrete
open-reel tape, which produced the most-spectacular consumer sound,
until multi-ch SACD came along. (I still have the tapes and an Otari
quad deck.) It is unfortunate that Sony has refused to reissue its
huge library of Columbia surround recordings on SACD.

For quad phonograph records, there was the Audionics Space & Image
Composer, an advanced SQ decoder that could wrap stereo recordings
around you, often to great effect. I also had an Ambisonic decoder for
Ambisonic recordings. It could do things similar to the Audionics,
without requiring logic circuitry, and did a superb job of ambience
extraction.

For stereo recordings, I had an audio/pulse Model One, the first
consumer digital ambience device. It didn't generate high echo
density, but used tastefully, it could greatly enhance the sense of
space. (I later replaced it with the improved audio/pulse 1000.)

My current system includes the JVC XP-A1000 and Yamaha DSP-3000 hall
synthesizers. These are modeled on real halls (such as the
Concertgebouw). You can pick an appropriate hall (concert, recital,
cathedral, opera, stadium), then tweak the settings (if you wish) to
fine-tune the sound to match the recording's ambience. These devices
are so natural-sounding, you cannot hear them working until you shut
them off.

I have a 6.1 system (no center speaker) with Apogee speakers and Curl
amplification.

I had Dayton Wrights, some Quad ESLs, now totally Martin Logan except
for subs.

W

#### William Sommerwerck

Jan 1, 1970
0

I owned Dayton Wright //dynamic speakers// (trade name: Watson). Quite good.
Had unbelievable subwoofers that got 15Hz -- solid -- out of a tiny box filled
with SF6. (Sound familiar?) Why no one has "stolen" Wright's long-expired
patents is beyond me.

...some Quad ESLs, now totally Martin-Logan except for subs.

If ever I sell a screenplay, I will replace my belovéd Apogees with the big
Martin-Logans.

I don't know who you are, "Smarty", but its rare to meet an audiophile who
understands the significance of surround.

J

#### [email protected]

Jan 1, 1970
0
"How were those extra channels added and extracted from the regular two
channel recordings, other than with one of those boxes?
"
By summing the left and right channels and sending them to OP AMPS on the inverting inputs, resuling in the attenuation of the L+R component of both channels. By careful mixing, an audio engineer could do alot with that. A system called SQ came out which standardized the process somewhat and only nulled the mid to high ranges, leavng the bass relatively intact for the rearspeakers which were ususally identical to the front speakers, unlike today.. Today, usually nothing under 100 Hz is sent to the rear. Those little satellite speakers couldn't reproduce it anyway.

The standardization was simply the time constant of the feedback network and the actual amount of L+R attenuation. It was sort of licensed, and you could buy recording supposedly in "SQ", which meant that they were mixed in away to take advantage of the standards.

W

#### William Sommerwerck

Jan 1, 1970
0
"How were those extra channels added and extracted from
the regular two channel recordings, other than with one of
those boxes?"

SQ was a full-range system without any frequency discrimination. The encoding
and decoding were more-complex than simply adding and subtracting signals.

S

#### Smarty

Jan 1, 1970
0
I owned Dayton Wright //dynamic speakers// (trade name: Watson). Quite
good. Had unbelievable subwoofers that got 15Hz -- solid -- out of a
tiny box filled with SF6. (Sound familiar?) Why no one has "stolen"
Wright's long-expired patents is beyond me.

I am not familiar with those subs but you certainly have evoked my
curiosity! Tiny boxes and 15 Hz --solid-- are not likely
companions......... My brief flirtation with tiny box subs, ala Carver /
Sunfire True Subs, was disappointing in that regard, although they did
make a lot of subsonic energy considering their size. Now I am wondering
what Wright's sub approach actually was. I still have a remaining
Sunfire True Sub and some Carver Amazings here with quite an arsenal of
low frequency drivers, but they have not been turned on in over a year.
My Logan subs have been from Hsu Research, perhaps a bit pedestrian but
very nice to listen to.

If ever I sell a screenplay, I will replace my belovéd Apogees with
the big Martin-Logans.

If you are dreaming of owning the Logan Statement, I totally understand.
The Apogees will be hard to improve upon.
I don't know who you are, "Smarty", but its rare to meet an audiophile
who understands the significance of surround.
My vocation and avocation since the 1950s has been electrical
engineering, all things electronic, ham radio, audio, video, computers,
and the nearly endless array of gadgets which rely on electronics. A CES
I attended in the 1960s exposed me to the first quad systems then
emerging, and I had a small hand in working with a Toronto company to
develop a gated 4 channel decoder using logic to steer rear channel
content based on primitive rules from left and right amplitudes. Its
intended market was movie theaters.

It was very clear to me right from the start that reconstructing some
information behind the listener had tremendous potential to improve the
listening experience. "True" quad open reel was a joy to behold, and
well miked and properly mastered content was just a quantum leap beyond
anything I had ever heard. Even relatively small speakers allowed a
credible and extremely engaging sound field. I think I was using AR or
Rectilinear boxes at that time. There was a collection of open reel
releases including Joni Mitchell from Verve or some similarly named
company that were among my favorites. Carly Simon and James Taylor,
married at the time, did a spectacular rendition of "Mocking Bird" in
true 4 channel open reel that was another spectacular demonstration of
the potential of surround. The classical releases were, for the most
part, wonderful as well.

As an old geezer, I can attribute my original surround passion to a
Motorola "Vibrasonic" spring delay reverb installed in my 1962 Stingray.
Other than the occasional microphonics which arose from the inevitable
bumps in the road, it created a very satisfying presence and bloom which
filled the passenger compartment.

To this day I bemoan the absence of a really rich multichannel format
for distribution of recorded music. The trend to mediocrity, especially
mp3, is ironic given the low costs of analog to digital and digital to
analog converters, storage, etc. If anything, the bar should be rising,
but instead has been lowering. Was it PT Barnum who said that 'Nobody
has ever gone broke underestimating the taste of the American public'?

S

#### Smarty

Jan 1, 1970
0
SQ was a full-range system without any frequency discrimination. The
encoding and decoding were more-complex than simply adding and
subtracting signals.

The more advanced systems essentially used voltage controlled amplifiers
to synthesize the rear channels using amplitude and phase relationships
from the front left and front right to make somewhat sensible decisions
about when and where to steer energy into the rear channels. The notion
of a "matrix" to construct the coefficients for the steering logic was
developed, in which the VCAs and their control voltages had weighted,
time-dependent control signals. Choosing appropriate time constants for
the attack, release, etc. was artistic and musically dependent, and the
eventually winning techniques such as Columbia SQ were noted for being
comparatively gentle / subtle and without noticeable pumping or breathing.

W

#### William Sommerwerck

Jan 1, 1970
0
"Smarty" wrote in message
Now I am wondering what Wright's sub approach actually was.

Sulfur hexafluoride, same as the 'stats. The woofers had a volume of about 2
cubic feet. When I put 15Hz into them, nothing was audible -- except for
everything loose in the room rattling. These woofers had extremely low
distortion -- around 2% at 20Hz.

If you are dreaming of owning the Logan Statement, I totally understand. The
Apogees will be hard to improve upon.

Hard, but not impossible. There's an Australian company that makes a version
with a true-ribbon titanium midrange.

To this day I bemoan the absence of a really rich multichannel format for
distribution of recorded music. The trend to mediocrity, especially mp3, is
ironic given the low costs of analog to digital and digital to analog
converters, storage, etc. If anything, the bar should be rising, It instead
has been lowering. Was it PT Barnum who said that 'Nobody has ever gone
broke underestimating the taste of the American public'?

If by "rich", you mean "supporting a wide range of formats" (such as
Ambisonics in addition to quadrifontal formats), I agree. But we have at least
two high-quality uncompressed formats that aren't likely to go away --
multi-ch SACD and Blu-ray audio.

W

#### William Sommerwerck

Jan 1, 1970
0
The more advanced systems essentially used voltage controlled amplifiers to
synthesize the rear channels using amplitude and phase relationships from
the front left and front right to make somewhat sensible decisions about
when and where to steer energy into the rear channels.

The correct term is "isolate" or "extract", not synthesize. The rear channels
are always present. Advanced decoders (such as Tate SQ and VarioMatrix QS)
selectively cancel the interfering crosstalk, based on which channel is
momentarily dominant.

S

#### Smarty

Jan 1, 1970
0
The correct term is "isolate" or "extract", not synthesize. The rear
channels are always present. Advanced decoders (such as Tate SQ and
VarioMatrix QS) selectively cancel the interfering crosstalk, based on
which channel is momentarily dominant.

I would perhaps resort to semantic quibbling in this case, since the
'isolation' or 'extraction' of a left or right rear channel would
presume that they had been encoded into the mix in some explicit way to
begin with, and could thus be extracted using some reciprocal process or
decoding scheme. The original front channels did not possess the
bandwidth nor the dynamic range to permit separate channels to be
encoded, and any scheme which claims to fold 4 channels into two and
then magically permits the original 4 to be regenerated would need to
use alternate modulation schemes, thereby rendering downward
compatibility with existing stereo to be none existent. Fundamentally,
you cannot take two channels of 20 KHz bandwidth and (let's say) 70 dB
of dynamic range such as may be found in a standard LP record and
somehow encode anything additional without either spoiling the original
stereo L and R pair, eliminating conventional stereo playback, or
creating a new and different encoding scheme from scratch. JVC
approached the problem with adding an ultrasonic subcarrier and then
(in much the same manner as FM monaural added FM stereo with its similar
pilot and subcarrier multiplexor). Sadly, the JVC ultrasonic subcarrier
imposed on the vinyl, groove, was both extremely fragile and very
susceptible to noise, despite the specially shaped and designed stylus
by Shibata which knew how to deal with it.

My distinction between 'synthesize' and 'extract' really goes beyond
mere semantics, and is quite explicit in communications theory in terms
of signalling and channels, in that uncorrelated content in the 4 quad
channels demands more than mere phase shift nulls, cancellations, or
gated VCAs which temporarily steer energy from one place to another. The
original 2 stereo channels could have encoded 4 true channels had
engineers been allowed to sacrifice backward compatibility and trade
bandwidth for dynamic range, for example. Or they could have
incorporated some in-phase and quadrature method to modulate sidebands
of a suppressed carrier or exalted carrier encoder (such as NTSC color)
or used some (1960's vintage) TDMA mux approach. Or as a partial
compromise, they could have put control tones / signals in the
ultrasonic band above (let's say) 15 KHz and done some low pass
filtering on the front channels and used the control tones to steer some
rear VCAs.

They opted to preserve quality and compatibility, and in doing so
created a two channel mix from which extra channels could be
synthesized, but the isolation / extraction of true rear channel could
at best transpose out of phase information into rear channel output as
if it were somehow supposed to be there in the first place.

W

#### William Sommerwerck

Jan 1, 1970
0
The correct term is "isolate" or "extract", not synthesize. The rear
I would perhaps resort to semantic quibbling in this case, since the
'isolation' or 'extraction' of a left or right rear channel would
presume that they had been encoded into the mix in some explicit way to
begin with, and could thus be extracted using some reciprocal process or
decoding scheme. The original front channels did not possess the
bandwidth nor the dynamic range to permit separate channels to be
encoded, and any scheme which claims to fold 4 channels into two and
then magically permits the original 4 to be regenerated would need to
use alternate modulation schemes, thereby rendering downward
compatibility with existing stereo to be none existent.

This is absolutely true mathematically -- but it is not true
psycoacoustically. The ear can be tricked.

It is possible to have significant material on all four channels at the same
time, with the resulting effect seeming fully "discrete".

Actually, the "alternate modulation schemes" you refer to, do allow full
backward compatibility, just as stereo FM broadcasts can be heard in mono
without losing anything.

Fundamentally,
you cannot take two channels of 20 KHz bandwidth and (let's say) 70 dB
of dynamic range such as may be found in a standard LP record and
somehow encode anything additional without either spoiling the original
stereo L and R pair, eliminating conventional stereo playback, or
creating a new and different encoding scheme from scratch.

Again, yes and no. SQ encodes the front left and front right channels as if
they were conventional stereo, so they sound pretty much the same as they
would on a stereo record -- or when an SQ disk is played in stereo.

It is worth noting that Ambisonic UHJ encoding allows psychoacoustically
correct playback without logic circuits.

Of course, the availability of "discrete" delivery systems largely eliminates
the issues of compatibility.

S

#### Smarty

Jan 1, 1970
0
'isolation' or 'extraction' of a left or right rear channel would
presume that they had been encoded into the mix in some explicit way to
begin with, and could thus be extracted using some reciprocal process or
decoding scheme. The original front channels did not possess the
bandwidth nor the dynamic range to permit separate channels to be
encoded, and any scheme which claims to fold 4 channels into two and
then magically permits the original 4 to be regenerated would need to
use alternate modulation schemes, thereby rendering downward
compatibility with existing stereo to be none existent.

This is absolutely true mathematically -- but it is not true
psycoacoustically. The ear can be tricked.

Indeed it can. I was talking in the parlance of an electrical engineer,
ultimately predicated upon the underlying mathematics of communications
theory and its vocabulary.
It is possible to have significant material on all four channels at
the same time, with the resulting effect seeming fully "discrete".

Yes, this is true, but this ear/brain trickery comes at a price.
Engineers would not call this a discrete system since the effect is
artificially created, aka 'synthetic'.
Actually, the "alternate modulation schemes" you refer to, do allow
full backward compatibility, just as stereo FM broadcasts can be heard
in mono without losing anything.

Only one alternate modulation schemes I mentioned does offer backwards
compatibility, which is why JVC chose it for their CD4 vinyl LP system,
at the expense of rapid wear-out and very noisy rear channels, mitigated
somewhat by companding and severe filtering of highs in the rear. The
other modulation schemes I described do not offer backwards
compatibility unless the original front left and right channel
you cannot take two channels of 20 KHz bandwidth and (let's say) 70 dB
of dynamic range such as may be found in a standard LP record and
somehow encode anything additional without either spoiling the original
stereo L and R pair, eliminating conventional stereo playback, or
creating a new and different encoding scheme from scratch.

Again, yes and no. SQ encodes the front left and front right channels
as if they were conventional stereo, so they sound pretty much the
same as they would on a stereo record -- or when an SQ disk is played
in stereo.

It is worth noting that Ambisonic UHJ encoding allows
psychoacoustically correct playback without logic circuits.

Of course, the availability of "discrete" delivery systems largely
eliminates the issues of compatibility.

The kernel of your semantic distinction in that we are dealing with
extraction and isolation of rear channel information which has been
encoded and added into 2 standard front audio channels, ostensibly
without compromise to the original front channel pair.

I entirely agree that psychoacoustic techniques permit the illusion of 4
(or more) channels to be constructed in the listener's mind. The brain
has a lot of adaptive power, and mp3 recordings with less than 15% of
the originally encoded music are generally accepted as reasonable
approximations to the original recording as well. Perhaps we hear what
we want to hear or what we choose to hear.

To the engineer however, the distinction between extracting an isolated
signal which is independently signaled versus the synthesis of a derived
signal which is not explicitly and discretely separable are two entirely
different methods. The fact that the human brain can be fooled to think
that the more complex discrete version can be adequately imitated by the
less complex derived version really doesn't change the technical
distinction between real versus synthetic.

W

#### William Sommerwerck

Jan 1, 1970
0
To the engineer however, the distinction between extracting an isolated
signal which is independently signaled versus the synthesis of a derived
signal which is not explicitly and discretely separable are two entirely
different methods. The fact that the human brain can be fooled to think
that the more complex discrete version can be adequately imitated by the
less complex derived version really doesn't change the technical
distinction between real versus synthetic.

I never said it did. I object to the term "synthetic".

S

#### Smarty

Jan 1, 1970
0
To the engineer however, the distinction between extracting an
isolated signal which is independently signaled versus the synthesis
of a derived signal which is not explicitly and discretely separable
are two entirely different methods. The fact that the human brain can
be fooled to think that the more complex discrete version can be
adequately imitated by the less complex derived version really doesn't
change the technical distinction between real versus synthetic.

I never said it did. I object to the term "synthetic".
The word "synthetic" is not in any way used in a negative or derogatory
fashion in the engineering context. Synthesis, analysis, and other such
engineering terminology are understood to mean rather concrete things
which may offend those who tend to thing of them in a more informal or
colloquial way. The rear channel information in such systems as Columbia
SQ is synthetic, having not been discretely processed as it would be in
a system explicitly designed to capture and then reproduce such rear
channel information. In fact, an SQ system could not localize a left
rear only signal nor a right rear only signal without producing some
artifacts in the front channels, given the non discrete nature of the
method employed. It is an implementation distinction which may be
noticed or may not, but it not at all like you make be thinking of if
your objection views synthetic = "ersatz", unrealistic, etc.

W

#### William Sommerwerck

Jan 1, 1970
0
The rear channel information in such systems as Columbia SQ
is synthetic, having not been discretely processed as it would
be in a system explicitly designed to capture and then reproduce
such rear-channel information.

That is absolutely incorrect.

In all four-channel matrix systems, there are four inputs and four outputs. A
logic-directed, phase-cancellation decoder is capable of dynamically
"separating" the front and back information.

In fact, an SQ system could not localize a left-rear-only signal nor a
right-rear-only signal without producing some artifacts
in the front channels, given the non-discrete nature of the method employed.

Of course it can, as assuredly as it can simultaneously localize left-front
and right-front signals, without any artifacts in the rear channels.

It can do this for //any two// isolated channels. The decoder cancels out
their crosstalk in the other two channels. This breaks no laws of math or
physics.

It is an implementation distinction which may be noticed or may
not, but it not at all like you make be thinking of if your objection
views synthetic = "ersatz", unrealistic, etc.

I own two hall synthesizers, which produce synthetic ambience -- which happens
to sound very natural.

S

#### Smarty

Jan 1, 1970
0
That is absolutely incorrect.

In all four-channel matrix systems, there are four inputs and four
outputs. A logic-directed, phase-cancellation decoder is capable of
dynamically "separating" the front and back information.

Of course it can, as assuredly as it can simultaneously localize
left-front and right-front signals, without any artifacts in the rear
channels.

It can do this for //any two// isolated channels. The decoder cancels
out their crosstalk in the other two channels. This breaks no laws of
math or physics.

I own two hall synthesizers, which produce synthetic ambience -- which
happens to sound very natural.

I have several hall synthesizers presently including a relatively
elaborate Audyssey processor in my main system, and I have owned many
going back to the AudioPulse 35 years ago (and its annoying hiss and
pushbutton intermittents) and many, many since then. Many if not most of
them sounded and presently sound extremely natural. And this discussion
has absolutely NOTHING to do with their ability to create a convincing
and natural and wonderful sound. I entirely and totally share your
opinion and do not have any disagreement with your assessment of their
performance from a psychoacoustics point of view whatsoever!! Had I been
a critical reviewer of this equipment and been asked my opinion of how
they sounded, I would totally express my vote of approval and
confidence, and have, indeed voted many thousands of my dollars directly
over quite a few decades supporting this very belief. Even my small
audio system in a tiny small home office has a \$2K Denon receiver with
an Audyssey X32 processor because I totally enjoy the perceived effects
of its natural surround sound.

However........

I am now (and have been) exclusively talking from a technical,
engineering viewpoint, and as one who is very qualified in this area.
The various systems which do not provide separate and discrete
independent channels for each of the 4 original channels cannot, do not,
and will not separate and maintain independent information for each of
the four channels unless each has its own distinct, isolated, channel. A
channel has a very specific and very defined meaning to a communications
engineer not only based on bandwidth and SNR but also its time domain /
frequency domain characteristics, a snapshot of which can be portrayed
in its transfer function, and measured entirely using both time and
frequency domain techniques including Fourier and Laplace analysis. I
spent 2 years in a Masters program learning this topic quite fully on
top of the (4 courses of) required undergraduate electrical engineering
course work required for this area.

You might be convinced that some matrixed scheme of putting 4 audio
channels into a 2 channel stereo medium can somehow permit the originals
to be faithfully extracted, but I am here to tell you that you are
entirely wrong.

The more advanced version of SQ used gated, voltage controlled
amplifiers not unlike the more recent Dolby ProLogic scheme to move out
of phase information selectively to the rear. The encoder can and
certainly does encode the rear channels to be out of phase so as to
emphasize their rear presentation, BUT..............and this is the
killer issue...........the original stereo mix already has out of phase
information which itself conveys time differences attributable to front
separation alone.

The lack of separate and independent channels forces the scheme to
"guess" at which elements of the signal structure represent true rear
data, which represent original left to right phase differences, and how
to use some form of demodulation to portray them. The appearance of
multiple approaches using several competing matrixing, AGC, companding,
and steering techniques and competing ways to trick the ear clearly
illustrated the absence of a single correct solution, since the 4 into 2
back to 4 channel process is inherently very inexact.

The decoder has no way to "cancel out crosstalk". The 2 channel phase
information does not contain identifiable crosstalk since the front and
rear are not orthogonal, and have no clock or other time reference to
independently serve to distinguish front from back out of phase content
versus left to right out of phase content. Were an ultrasonic clock to
have been recorded (an approach considered as one potential solution
versus an ultrasonic subcarrier used by JVC), and this clock used to
time mux the analog stream, then there could indeed be a way to
explicitly isolate separate channels, but at the expense of front
channel bandwidth and signal to noise. In the subsequent digital era,
these problems disappear, and bit pooling and TDMA or other muxing and
sampling allow streams to be created where time can be used as a
reliable reference to sort things out. In the early 1960s when these
systems were being deployed (and I was in my graduate EE program) this
was not an option.

Try to imagine what a stereo capable LP would contain in order to create
a left rear only output:

If you had only left energy recorded, it would show up in the left
channel regardless of phase. Left energy alone would have no phase
difference to reference, and its absolute phase would either cause the
left front speaker to move its cone first forward then back, or, if 180
degrees reversed, would move the cone in the opposite sense. Any phase
angle you choose for conveying "front to back" for this simple example
fails.

If you want to build an encoder / decoder to use phase as a way to
convey front / rear directionality, you can ***SYNTHESIZE*** an
artificial reference frame, exaggerate the effect with VCAs and gating
logic, and treat shorter phase shifts as if they belong to the front and
longer phase shifts as if they belong to the rear. The ear can indeed be
fooled, and this is fundamentally the way it was done.

Lets go one step further and make an even more drastic engineering
assumption. We are going to assume that the front speakers are spaced
much closer to one another than the rear pair are spaced with respect to
the front. We will then "guess" that phase shifts / time delays longer
than the presumed short left to right delay are entirely attributable to
rear delayed energy. We will choose an arbitrary cut off and declare
that all delays longer than "X" degrees of phase shift are the result of
rear channel content. This might even work were it not that 361 degrees
of phase shift is entirely and totally indistinguishable from 1 degree
of phase shift as far as analog processing is concerned. Phase only
offers a brief impartial piece of evidence as encoded in this analog system.

Could an advanced DSP be used to build an FFT waterfall and distinguish
early and late energy more exactly. Yes, of course. But this has nothing
to do with the way SQ, QS, Dolby ProLogic or any such primitive scheme
worked in the 1960s.

Did I ever say that SQ or other techniques of its ilk were bad,
unnatural, or otherwise flawed. Not at all. I ask you please to not
conflate how things work with how things sound. I am an engineer talking

Replies
8
Views
415
Replies
20
Views
937
Replies
1
Views
321
Replies
0
Views
308
Replies
3
Views
801