furui_suterioo
Quad & 70s Enthusiast
I've also sern a similar "Victor 4 Channel Stereo" clip, would've got both but the Victor has no logo, can't seem to find it now..
The Legacy of Dr Bauer
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Well...I thought there was a very good discussion regarding SQ and "The SQ Position Encoder", but to perhaps sum up it's use as an encoder I thought I'd supply this explanation.
From Ken Sessions "4CHANNEL STEREO ..From Source To Sound" TAB BOOKS 2nd edition
"SQ POSITION ENCODER
-----The SQ matrix code (fig 7-12) may be optimized through the use of an SQ Position Encoder.
-----A Position Encoder produces signal pairs LT a d RT so designed as to provide optimum SQ modulations for the side(as well as the front and back) quadrants. Referring to fig 7-13 , the eight pairs of arrows surrounding the vector diagram represent the LT and RT phasers corresponding to "panning" a unity strength signal to the assigned directions . The LF, CF , RF , LB , CB , and RB phasers and the resulting modulation vectors are exactly the same as those obtained with the straight SQ Encoder. However, the CL and CR phasers result in two elliptical motions coaxial with LT and RT . Their projections on the horizontal line are the same length as those for LF, RF , LB , and RB , with the consequent improvement in monophonic compatibility which now extends to the total "horseshoe" Space surrounding the listeners. The center back is allowed to carry incidental and reverberant sounds which (1) are reproduced in phase and with full accuracy in the quadraphonic mode , (2) tend to become antiphase in the stereophonic mode , and (3) are diminished in amplitude or disappear in the monophonic mode . This at times is desirable , because the clarity of monophonic performance is often improved by removal of excessive reverberant sounds . "
sorry but thats the best schematic of the position encoder as provided.
From Ken Sessions "4CHANNEL STEREO ..From Source To Sound" TAB BOOKS 2nd edition
"SQ POSITION ENCODER
-----The SQ matrix code (fig 7-12) may be optimized through the use of an SQ Position Encoder.
-----A Position Encoder produces signal pairs LT a d RT so designed as to provide optimum SQ modulations for the side(as well as the front and back) quadrants. Referring to fig 7-13 , the eight pairs of arrows surrounding the vector diagram represent the LT and RT phasers corresponding to "panning" a unity strength signal to the assigned directions . The LF, CF , RF , LB , CB , and RB phasers and the resulting modulation vectors are exactly the same as those obtained with the straight SQ Encoder. However, the CL and CR phasers result in two elliptical motions coaxial with LT and RT . Their projections on the horizontal line are the same length as those for LF, RF , LB , and RB , with the consequent improvement in monophonic compatibility which now extends to the total "horseshoe" Space surrounding the listeners. The center back is allowed to carry incidental and reverberant sounds which (1) are reproduced in phase and with full accuracy in the quadraphonic mode , (2) tend to become antiphase in the stereophonic mode , and (3) are diminished in amplitude or disappear in the monophonic mode . This at times is desirable , because the clarity of monophonic performance is often improved by removal of excessive reverberant sounds . "
Just wondering if the Surround Master SQ decoder places CL and CR in the same place upon decoding, regardless of whether a 4 corner SQ encoder or SQ position encoder was used to encode content at CL and/or CR?
Kirk Bayne
Kirk Bayne
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Excellent article.First let's accept that the mind interprets what we hear (and see) in ways we might not expect. we see a white box - take a photograph of it and it looks like an orange box. We put two speakers in front of us, play a record, and hear sounds behind us (as well as centered between the speakers). The photograph's color shift happens because we do not see objects - we see light reflected by objects - the sun provides a light source outside and along the Kelvin scale (or the scale by which we measure the relative temperature of light) it is quite cool. Indoor light can be provided by a number of sources, each with their own temperature. Incandescent light is very warm, thus the orange cast. Film, or the photographic process in any form, does not adjust for the temperature of light sources - so on digital cameras you use the white balance, and with film you use filters, or film specifically created for the light source. The brain - the human brain, takes the reflected light in and instantly adjusts for the temperature of the source. This is why you can pick up that white box in your bedroom, illuminated with florescent lights, take it into the kitchen with all the light being incandescent and outside - and you always see it as white. And it remains white if the sun is shining or if its deeply overcast. - Amazing thing this brain. But what does this all have to do with Australia?
Well, just as the brain takes in visual stimuli and allows, well, itself to interpret it in wondrous, though predictable ways. It does quite the same thing with sound. How we interpret sound relies on many elements - starting with anatomy. While our ears are on the side of our heads, they are cupped in such a way as to favor sounds coming from in front of us.
There are 127 (or more) elements that impact our mind's dealings with sound. For example; sounds that come from behind us, that are reflected - that is, echoes of the sound coming from in front, reach us "out of phase". This is why we can listen to a two channel recording, that has some information not "in Phase" - and think those elements are coming from behind us - the brain is used to telling itself; “out of phase sounds come from behind”.
When I'm ready to write my "History of Quadraphonic Sound in the Modern World" - I'll detail the development of recorded sound from the tin foil sheets of Edison's cylinder to the Super Audio Compact Disc (none of those French experiments from the 1860s). There will be a chapter on the thought behind quadraphonic sound from 2 channel sources, and a chapter on each system developed to accomplish stuffing 4 signals onto a stereo LP, and reconstituting it. Until that time I'll assume you know all of that, or at least the relevant portions, and we can jump right into CBS's SQ system.
At its simplest - the front channels are untouched, the rear channels, 90 degrees out of phase, are mixed into the front, 3 decibels lower in amplitude. They sound to the stereo listener and vaguely mono, somewhere in the center, between the two speakers. Because the signals intended for the rear ARE out of phase, the brain will place them there - particularly when listening through stereo headphones. The SQ system relies on that - simple decoders reverse the "mix" - the front are untouched - the rear now has those signals meant to be in front - 90 degrees out of phase, mixed 3 decibels lower in amplitude (all this, while the sounds meant for the rear are now restored to the left and right). That 3db is a bit of an issue - it is the “threshold of perception” - this means with 3db of "separation" between front and rear - is just enough to perceive, but only just. The problem it introduces - is noise. In order to make the rear channels balanced with the front (ie; as loud as) - you need to increase the levels by 3db - when you do that, you increase the noise as well (basically lowering the signal to noise ratio by, you guessed it - 3db).
So the problem before us - and the engineers from the 70's onward - has been to extract the 4 channels back out from the "encoded" two channels.
Whether SQ was the best of the 1/2 dozen or so (matrix) encoding systems is for another day - it does not impact us here (you'll see these discussions in chapters 8 & 9 of my book).Further, we won't agonize over the evolution of the SQ decoder (that will be chapter 6). Today we look at two systems. One, long considered the state of the art, but no longer in production - the other in production, not as widely known.
The first system, the one no longer in production, but highly thought of and sought after - is the Fosgate Tate II 101a.At the heart of this was the DES (The Directional Enhancement System), also known as the Tate. DES, was an advanced decoder for SQ and enhanced the directionality of the basic SQ matrix. It first performed a straight SQ decode – and took the four outputs of the SQ decoder to derive additional signals, then compared their envelopes to detect the predominant direction and degree of dominance.
A processor section, implemented outside of the Tate IC chips, applied variable attack/decay timing to the control signals and determined the coefficients of the "B" (Blend) matrices needed to enhance the directionality. These were acted upon by true analog multipliers in the Matrix Multiplier IC's, to multiply the incoming matrix by the "B" matrices and produce outputs in which the directionality of all predominant sounds were enhanced.
Since the DES could recognize all three directions of the Energy Sphere simultaneously, and enhance the separation, it had a very open and 'discrete' sounding sound-field. While there were two consumer decoders that employed these chips; the Audionics Space & Image Composer and the Fosgate Tate II 101A, The Fosgate used a faster, updated version of the IC, called the Tate II, and additional circuitry that provided for separation enhancement around the full 360° sound-field, using the Haas effect.
In order to maintain the highest quality levels, Fosgate used hand-sorted ICs and 1% -tolerance components, and each decoder was hand-optimized. Unlike the earlier Full Wave-matching Logic decoders for SQ, that varied the output levels to enhance directionality, the Tate DES cancelled SQ signal crosstalk as a function of the predominant directionality, keeping non-dominant sounds and reverberation in their proper spatial locations at their correct level. In addition, the enhancement was done with sufficient additional complexity that all non-dominant sounds were kept at their proper levels.
All seems pretty impressive, no? In fact up until 1986 or so, it was the fosgate DES that was the core engine used in Dolby Surround. - but now I'm skipping ahead to chapter 9. The fosgate remains impressive - not only for it's ability to separate out the SQ encoded signals into 4 - but it's ability to simulate surround (or quad) from stereo sources with it's cinema setting - something very closely resembling RM/QS.
If you've read my stuff, you know I'm not about measurements - for me it's all about the sound - yet you need to start somewhere. For my tests I've created my own SQ files. I used wide spectrum pink noise (or white noise if you prefer) and then a series of single tones. The sequence wasall 0db VU) - left front, right front, left rear, right rear, front center, rear center, left center, right center, center channel (all 4 channels at equal volume). It should be noted that the last one there - didn't amount to much. Actually - it amounted to nothing at all, you see in SQ there can be no center channel. Because of the phase shifts for a signal to exist in all for channels at equal volume - it would need to exist 180 degrees out of phase with itself - which it can not do. I took VU readings of all four channels during decode, for each signal. The Tate provided at least 24db of separation. This means that when a signal was played - it was at least at -24db in the corresponding channel(s). A 0db signal in Left Front was between -24 and -30 in the left rear. I picked -24 as this was the worst reading (-32 being the best) - different frequencies provided different levels of separation. There was no perceivable "pumping" as the decodes "kicked - in". The next was a music test - the results are purely subjective but in an attempt to be comprehensive - I used a rock track, an orchestral track, a jazz track, a vocal (all with fixed placements) and an opera track with stage movement and a novelty track with surround movement.
For straight listening - they were all very good, in a roughly square room the speakers were in each corner - with the listener 2/3 of the way toward the back of the room. I was not looking to compare the Fosgate's output to that of discrete playback of the same material. Nor was I checking speaker by speaker to judge the crosstalk between channels - simply, how good a listening experience it provided.
Next up, the unit that remains in production, created by a little company from "down-under" called Involve Audio. This device is humbly called The Surround Master. It should be pointed out that SQ decoding is not what the company, or device, is all about. They have created a system of encoding that is very similar to the Regular Matrix (RM/QS) system - and they have produced a decoder to go along with it. I've covered these encoder/decoders extensively in chapter 2-3 but suffice it to say that the surround master basic decoder does a heart stopping job with QS material - and their own encoded programs. But if you want the engineering that went into that unit applied to the sq system - it's gonna cost you extra. Further, there is no SQ encoder available from that outfit. Guess they figure, if you're gonna encode - do it with their system, and, as it's compatible with QS and Dolby PLII - it seems fair. Now - if all you want to do is decode your old SQ records, and you want the best - do you go the on-line auction route and grab yourself a Tate, or do you send some coins to the land of the walkabouts? Well now we come to the reason for this tome. I ran the SM/QS circuit through the same paces as with the tate, and the results kind-of surprised me; on two levels. First - the measurements. The SM produced results within a DB of the tate. - not enough of a difference to make more exacting measurements needed. Then the sound tests - and damn! - if the SM didn't sound better,,,,quite noticeably better. And yes, I do not put much faith in measurements vs listening - soooo there just had to be something I was missing.
I sent about 20 recordings to 18 fellow quad enthusiasts - and 15 picked the SM as producing a better experience - the other 3 said they could hear a difference, but didn't have a preference. How could this be? Well it seemed to come down to what we call the “precision of imaging” and smears (plus a fair bit of cross bandwidth pumping at a micro level). The Tate remains a single band unit. This means for example that low frequency information (with no real directionality) can dominate the math's of the resultant decode and you can get conflict situations where the very high frequencies want one direction yet the midrange wants another direction and the bass – well it just sits there like the .1 it was meant to be, but hampering the decode of the upper frequencies.
This creates poor imaging and smear. The SM is a true tri-band circuit and thus is, in effect, 3 parallel decoders working independently. Involve also spent a lot of time massaging the attack and decay time constants for each band to ensure instruments were picked up as a whole and not smeared elsewhere. So in effect - they made the SM "listen" to music in the same way the ear/brain does - adjusting all mathematics for the logarithmic nature of hearing and allowing for the Fletcher Munsen sensitivity (frequency curve).
This ensures that the direction of steering is not dominated disproportionately by signals that may be higher in magnitude but lower in apparent level. For example in pink noise and music a 100 Hz noise has a way higher magnitude than a 3 kHz tone yet it is the 3 kHz tone that will greatly dominate.
The complexity to do all this is significant and is not easily accomplished with conventional analogue circuitry (due to tolerance drift in components etc). Of course Involve did cheat - some of the software, and circuit designs simply didn't exist in 1979.
At the end of day, it's difficult to find fault with the SM unit. If you already have a Tate would I suggest the SM be your next purchase - no - especially as there is no new SQ material being produced, and the Fosgate/Tate II is really beyond reproach (it even has a joystick type remote ---- it's a guy thing) - but if you’re just getting into surround and are picking up some old vinyl - the surround master with the sq option - well - that's the way to go. If that box had existed in 1972, quad would never have died out - but then the queen would be king if...well, you know the rest.
<note: all spelling errors due to line noise>
So much great information here on SQ and some of the Quad
audio history. We are lucky to have this site and it's members who
lived times and are highly knowledgeable of these facts.
audio history. We are lucky to have this site and it's members who
lived times and are highly knowledgeable of these facts.
That was the purpose of all matrix encoders in the beginning.
The position encoder allowed positioning of sound anywhere.
The SQ Position Encoder also increased the channel separation from LF/RB and RF/LB from ~3dB to ~8dB (IMHO, probably more important than accurately placing sounds at CL and CR).
One thing I wish CBS had done was to strongly encourage monitoring of the decoded SQ using a Sony SQD-1000, modified to only blend LB and RB to enhance the separation of CF as the baseline SQ decoder.
IIRC, it was the 2nd half of the 1970s before a good variable matrix only SQ logic decoder was developed so something was needed from ~1971 till then (for matrix decoder separation enhancement, I favor variable matrix [includes variable blend] decoding only, no gain riding).
Kirk Bayne
One thing I wish CBS had done was to strongly encourage monitoring of the decoded SQ using a Sony SQD-1000, modified to only blend LB and RB to enhance the separation of CF as the baseline SQ decoder.
IIRC, it was the 2nd half of the 1970s before a good variable matrix only SQ logic decoder was developed so something was needed from ~1971 till then (for matrix decoder separation enhancement, I favor variable matrix [includes variable blend] decoding only, no gain riding).
Kirk Bayne
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The SQD-1000 sounds good because it uses a small amount of front and rear blend together. Too much blending the action becomes audible. Some people were unaware that it had any form of "logic" at all. The Pioneer QD-210 uses rear blending only and it is very audible.
I think that it made sense to monitor mixes via a full logic decoder to get the most out of the (then) latest decoders. Latter still SQ mixes (no longer CBS, but rather Wesley Ruggles and Martin Wilcox), were monitored by the Fosgate Tate II.
Has anyone familiar with CBS SQ Decoders , ever heard of the new line of decoders they announced back in 1975 ??
As reported in Billboard, they introduced 3 new ones ...
L1A , L2A , and the L3A ?....along with the TATE DES .
All at the CBS Demonstration Show , in January 1975 (or December 1974 CES )
Reported in Billboard January 11,75 page 51.
As reported in Billboard, they introduced 3 new ones ...
L1A , L2A , and the L3A ?....along with the TATE DES .
All at the CBS Demonstration Show , in January 1975 (or December 1974 CES )
Reported in Billboard January 11,75 page 51.
Soundfield
1K Club - QQ Shooting Star
The three CBS logic decoders (L1, L2 & L3) were suggested designs based on the Motorola chipset described in the CBS technical note of March 1974 -
MidiMagic
2K Club - QQ Super Nova
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I agree. Gain riding destroyed the ambience.
SQ decoders using gain riding were the best that we had in the mid seventies. That technology has long been eclipsed by Tate. Now we have the modern alternative "Surround Master".
I've used the S&IC since the very early eighties. It is the best surround decode system yet devised! Stereo mixes are pulled apart around the room in Stereo Enhance mode (control fully clockwise). Nothing is removed or missing. It's like listening to stereo through a magnifying glass! All the ambience is there.
Now when I go back and listen to a full logic decoder the first thing that I notice is the fixed rear blend. The back speakers image closer together than they should. The biggest benefit of SQ is thrown away in doing that. It was done as a cheap alternative to vari-blend or along side of vari-blend to make the blending action less audible. The SQD-1000 uses vari-blend on both front and rear. A much better solution than using it on the rear alone.
If a full logic (gain riding) decoder is set up properly (less is more) you should not normally notice any pumping. Gain riding was also used in Dolby and Circle Surround decoders as well, as well it was a feature of Peter Schreiber's original patent.
First I've heard about Dolby Surround decoding using gain riding - I believe one decoder (Aphex AVM-8000) used gain riding based SQ decoding in the mid-1980s (Stereophile 1986-03).
Kirk Bayne
This from Wikipedia
In 1987 the decoding technology was updated and renamed Dolby Pro Logic.
A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center, and a single limited frequency-range (7 kHz low-pass filtered[2]) mono rear channel.
A Pro Logic decoder also uses 'Steering Logic', which drives amplifiers, to raise or lower the output volume of each channel based on the current dominant sound direction. For example, while a mono signal is played, the strong correlation to the center channel triggers the output volume of the left, right and surround channels to be lowered. This increases the channel separation achievable, to around 30 decibels between channels. By careful tuning of the response of the amplifiers, the total amount of signal energy remains constant and is unaffected by the operation of the channel steering. Additionally, the response time of the system to changes in sound direction is important as too fast a response results in a twitchy feel, while too slow a response leaves sounds coming from an inappropriate direction.[2]
In addition to 5db of noise processing, the surround channel is slightly delayed, so that any front channel sounds that leak into the surround channel arrive at the listener after the front channels. This takes advantage of the Haas effect - audio that is present in the front speakers but delayed in the surround speakers will have the psychoacoustic effect of emanating from the front of the sound stage.
I don't have a ready reference, but I thought that the QS variomatrix was used by Dolby Labs for Pro-Logic decoders in the theatrical systems.
Kirk Bayne
Kirk Bayne
Owen Smith
1K Club - QQ Shooting Star
Unlikely given people have been pulling Tate chips out of old Dolby cinema processors for years to repair broken Tates and S&IC.
Sansui Variomatrix chips preceded Tate DES by several years. If you saw Star Wars: A New Hope first run at theters in surround it was by Sansui Variomatrix with mods to comply with Dolby analog surround encoding. Later they did switch to Tate DES circuitry. The consumer version, original Dolby surround & Pro-Logic decoding were never used in cinemas. The reason being it transitioned from analog Variomatrix to analog Tate DES to Dolby Digital Surround.
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More interesting is the AVM 6000 described as "Shadow Vector Directional Enhancement System", I don't think that it actually used that technology. Did a struggling Audionics sell the rights to the name?
https://www.quadraphonicquad.com/fo...-3-surround-sound-decoders.31481/#post-598572
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