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SQ Shadow Vector Soundfield Mapping

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Sonik Wiz

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I'm puzzled by this line: "My issue with SQ is the heavy bias of frontal left / right information making the detail of the rear information hidden within a few dB."

If the Involve decoder doesn't use pairs of 0 and 90-degree phase shifters, no L/R separation in the two rear channels can be extracted from (ideal) SQ at all. The standard 4 -> 2 CBS encoders had some phase drift in the sidewall locations, which could translate into some L/R separation for a QS/EV4 style of decoder (which don't rely on pairs of 0 and 90-degree phase shifters to extract F/R information). An ideal SQ encoder, though, will give zero L/R separation in the rear channels for a QS/EV4 style of decoder.

On the other hand, if the decoder is an actual SQ decoder with the mandatory pairs of 0 and 90-degree phase shifters, and uses full-logic gain-riding, TATE cancellation methods, or a Shadow Vector dynamic matrix, there's 25 to 35 dB of separation in the rear channels ... from each other, from the adjacent front channel, or from the opposing front channel. I've measured it myself, it's not an illusion. Separation in the SQ system is mostly limited by the precision of the phase shifters; with each degree of departure from 90 degrees eating up several dB. If the phase shifters are accurate to 1 degree, 40 dB is available in all the cardinal points.

The Shadow Vector retains this separation as the signal is swept across the intermediate locations; I don't know if the TATE does this or not, since I can't unravel the math in the TATE patent. I think it might not, but I don't really know.

I think the shared CB localization in both QS and SQ can give the illusion the two systems are partially compatible. Center Back is actually the only place in the back quadrant of the Scheiber sphere where the two systems overlap. From the point of view of an ideal QS or EV4 decoder, the SQ Left Back and Right Back encodings are in never-never land, with 90-degree phase shifts between the channels. A QS or EV4 decoder, whether dynamic or not, interprets either condition as a 4-speaker sum, with no localization at all, and an odd phase relationship between the 4 channels.

The best description of SQ would be a "phase matrix", and in a deeper sense than QS or EV4. In QS or EV4, the Z axis is represented by the proportion of in-phase to out-of-phase content. The 90-degree phase shifters on the encode end of QS let the recording engineer make an overhead pan from front to back with no sudden jumps in phase. (EV4 does not use 90-degree phase shifters for either encode or decode.)

SQ uses phases all the way from -90 degrees to 180 degrees to +90 degrees to accomplish a pan from LB -> CB -> RB. Remarkably, as this pan happens, there is NO change in L/R ratios; both channels stay exactly equal throughout the pan. A pan across one of the sidewalls, from back to front, gradually reduces the level of the opposing channel to zero (the phase angle no longer has meaning when only one channel is present). A pan across the front is simply a conventional L/R pan in stereo, with the phase angle between the two channels now at 0 degrees.

I agree, this is a screwy matrix, when you look at all the crazy things happening in the sidewalls and rear. That's why Shadow Vector is several times as complex as a Vario-Matrix, but ultimately similar in operation. However, Vario-Matrix could get away with opto-couplers doing the blend functions, but this is too inaccurate for Shadow Vector. Precision VCA's are required to get the phase angles where they should be. I wasn't thrilled with Cliff Moulton designing switching FETs to do the VCA function, but he wanted reasonable distortion combined with precision and speed, which can't be done with opto-couplers. No problem in the digital era, so long as 32-bit precision, combined with independent dither for each VCA, is employed.

But ... if the Involve decoder doesn't have the required set of four allpass phase shifters, with a precision of 3 degrees or better across the audio band, the SQ decoding will be an artifact of encoder errors, which I grant are abundant in the standard CBS encoder. The standard 4 -> 2 CBS encoder isn't "wrong" per se, it just mis-encodes the sidewall signals. The corners are exact, and a pan across the rear is accurate. The "forward-looking" SQ encoder (widely used by EMI) was quite a bit more accurate, the Ghent microphone pretty much spot-on, and the "Position Encoder" right on the money, although it couldn't do a smooth pan, just click-stops at certain locations.

I'll be honest; although the control signals in a Shadow Vector can be skewed to offset the standard encoder errors, I never did this. First, too damn complex when you do this in an all-analog environment, and also, the decoding was accurate enough so the skew was audible for what it was, simply a mis-location of the signal as it traversed the sidewalls. In that sense, it was a good tool for the studio, since you could easily hear when the decoder was mis-locating things a little bit. If the encoding was 100% accurate, the signal stayed pinned to the sidewall, and if the decoder was off a bit, the signal drifted into the room (a little) as it was panned from front to back. I think Malcolm has probably noticed this with his prototype; you can hear the encoder errors as slight mislocations during pans.

I also admit I never built a multi-system SQ/QS version of the Shadow Vector. If it had gone to production, absolutely, QS would have been in there. In QS mode, the -90/+90 sensing axis is not used, the signals going into the VCA's are simpler, and only a pair of VCA's are needed for each decoded channel. The extra precision of VCA's, combined with higher speed, would give a more precise and stable image than the Vario-Matrix.
I think it is interesting that the most compatible matrix quad format for playback in stereo was SQ, but the most adaptable format for playing back stereo into quad was QS.

I don't get the TATE stuff either no matter how much coffee I drink & how many times I read the patent. I am lost at "matrix multiplier"....
However the TATE DES patent also shows it is applicable to Regular Matrix enhancement such as QS. In that approach the QS circuitry is far simpler. In fact any time you compare equivalent function circuits between SQ/QS the latter is always simpler. There was even a Sony patent that used variable mixing between decoded channels for SQ/QS (yes just think: Sony QS decoding) that never made it into production. Functionally it used FET's to mix the 4 channels in pairs with the proper phase. For QS this only meant 4 inverters to mix as needed. For SQ the same thing except those inverter boxes are replaced by 90 deg phase shifts. Yikes!

And Sansui always said that phase shifting the decoded outputs for QS was desirable but optional. The piddly 1 transistor with R/C is token at best. Ambisonics UHJ was even more 90 deg phase shift dependent than SQ in decoding. I liked the way they implemented the phase shift circuits using IC's instead of XSTR/R/C combos. Take a look at here on page 71.

As it has been mentioned two times before that Vario-Matrix used opto-coupled photo resistors I would like to clarify that. In the earliest units such as the QS-1, QS-100, QS-500 they did use photo-couplers. This was not a vario-matrix unit. The photo-couples were used only in the rear channels in an R/C combo to produce variable & out of phase info. The input to the photo-coupler was modulated by sine wave at 8Hz. Supposedly to give a more open sense of spaciousness. In the QSD-1/D2/D1000 and QRX receivers they used an FET chip the HD3103 to accomplish a VCA effect. Other receivers used a combo of type A/B QS decoding and various combos of discrete or IC implementation.

FET's are not great for VCA operation but certainly better than using the OTA chips of the time. And I like how Sansui actually used them in the circuit. If you talk about variably mixing signals to enhance separation it's all about dB relationships not absolute value. For example if both front chs are represented by L+R and you want to increase the separation you can do by adding L-R or having L-R at a fixed value and lowering L+R. Sansui did it this way, by shunting to ground the signal as needed. What you actually heard was what didn't go through the FET. Pretty cool.
 

Sonik Wiz

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meant HDMI to RCA:

Remember all we want is the stereo then we deal with it
Thank you but that's pretty much the opposite of what I thought you were referring to & I was asking about. What happens after decoding in the SM? How does someone with HDMI only inputs get the 4 or chs into his reciever? GOS has this situation where he has analog 2 ch out on his receiver but only HDMI in.
 
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fredblue

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Thank you but that's pretty much the opposite of what I thought you were referring to & I was asking about. What happens after decoding in the SM? How does someone with HDMI only inputs get the 4 or chs into his reciever? GOS has this situation where he has analog 2 ch out on his receiver but only HDMI in.
the only way i could get this working on my Receiver with no 6-ch analogue input was somewhat convoluted and involved ("if you'll pardon the pun!") and may not be viable for some users in that it requires a computer in the chain up and running in order to make it work.

in a nutshell, i run the MultiCh analogue outs from the Surround Master into a Motu MultiCh audio interface connected to the computer and use "Loopback" software to 'virtually' route the Motu's MultiCh analogue inputs back out through the computer's HDMI output into an HDMI input on the Receiver.
 

Lynn Olson

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In the audiophile world, there is much dissatisfaction with S/PDIF not only because of jitter (which directly translates into distortion), but because the ideal location for an ultra low noise clock is about 1 cm from the converter chip. Unfortunately, this means an external DAC has no way of communicating with the CD transport, since S/PDIF is a one-way data transport, and the transport clock eventually gets out of sync with the internal clock of the DAC. So the not entirely satisfactory solution used in most high-end external DACs is a slow-acting phase-lock-loop that slowly synchronizes with the embedded clock of the S/PDIF transport stream. This is not really ideal because the PPL has jitter issues of its own, and the embedded clock architecture of S/PDIF means the jitter of the embedded clock is modulated by the audio data channels (this is real, measurable, and audible). So S/PDIF, although widely used, has issues for the highest quality playback. And the professional AES standard is actually no better, unfortunately, just more robust for longer distances.

One workaround that's come up in the last few years is using the internal I2S signal that is used to transport data inside the digital circuit board ... for example, I2S is the usual data format that goes right into the converter chip. It's kind of a no-no to use this signal off the board, since it's not designed for off-chassis use, but it is a workaround for the problems with S/PDIF. It's a bidirectional data protocol, and the clock has its own signal lines, in both directions. So the master clock sits close to the converter chip (as it should for lowest jitter) and sends out the clock signal back to the transport, so the transport is synchronized to the master clock, rather than the external DAC tagging along after the transport.

Anyway, using I2S format between two data devices has recently become a thing in audiophile circles, although not really authorized by the chip manufacturers. It does work, it does reduce jitter substantially by removing the need for a PLL circuit in the DAC, and the vendors choosing this route have amusingly used either RJ45 or HDMI physical connectors, although the signals going through the cable have nothing to do with Ethernet or HDMI. They're just using the connectors and the standard (very short) cables associated with these connectors ... but the signal is actually in I2S format. It might not survive 3 meters of cable, but 30 cm is fine, since the two components are usually placed right next to each other.

Anyhoo, it did occur to me that a very simple external box with nothing more than the stupid HDMI encoder, and a minimal power supply regulator for the chip, could sit outside the Involve unit and the two interconnected via I2S protocol, the chip-to-chip protocol that is usually confined to the circuit board of more conventional home-theater receivers or 2-channel DACs. The actual physical connection, following the lead of high-end DACs, could be an RJ45 jack, with a short piece of Cat 5e or Cat 6 Ethernet wire connecting the two devices. This has the merit of decoupling the gyrations of the HDMI market from the DSP and complex analog circuitry of the Involve decoder.

Hmm .. maybe forget all that I2S crap and just have a very simple daughterboard with the HDMI chip on it. That way the circuitry on the main board is isolated from the gyrations of the HDMI market, and the daughterboard, it's pricey chip, and digital-out are extra-cost options for those who want it.
 
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Lynn Olson

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Forget everything I said about the S/PDIF digital input for the Involve decoder. I thought it was all-digital, with the expensive phase shifters part of the DSP functions. I didn't know it was hybrid, with the phase shifting in the analog domain. I'm guessing the Involve unit has a pair of input buffers for the L and R inputs, a 0 and 90 pair of phase shifters for the L input, another pair of 0 and 90 degree phase shifters for the R input, and either a 4 or 6-channel ADC for the DSP section (6-input if there's a direct, non-phase-shifted signal path for EV4 or similar decoding).

I'm guessing Malcolm is doing his Shadow Vector decoder entirely in DSP ... those phase shifters are expensive to implement in the physical world, thanks to the array of 1% capacitors and 1% resistors.
 

chucky3042

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Yes we use a TAS 3204 DSP and we do the phase shifty stuff in analogue. The a/d and D/A is internal to to the DSP. Re Sonik Wiz I really hate modern receivers nearly as much as I hate 5.1 / 7.1.....etc and I personally think the whole multiplicity of connecting formats has got out of control. I had no interest in following the pack and really wanted to keep things RCA (yes the Y4 has HDMI/ Bluetooth). What I am getting at is the great advantage of matrix decode from stero is a huge simplification of connections. Just have a look at page 7 of our user manual:

 

Lynn Olson

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Well, AVR's are kind of crappy, I'd be the first to admit that, but the Marantz ones are sonically pretty decent and not insanely expensive. And they have one set of analog multichannel inputs, which is where external devices come in. So interfacing with the wretched world of home theater is not out of the question.

I am gradually migrating towards the world of (high-res) streaming audio, thanks to Tidal and possibly a Qobuz subscription. I'm paying for Netflix, Hulu, and Amazon Prime Video, so Tidal is just more of the same, only for music. The Internet gizmo I'll probably be connecting pretty soon is a Bluesound Node 2 streamer, which has Ethernet-in, RCA and S/PDIF outs, and is controlled from a tablet. It can drive either the high-quality DAC for the big 2-channel rig (with 300B triode amplifiers), or the Marantz AVR, depending on whether I want surround or not.
 

Lynn Olson

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Hi all, if I understand what's currently up and running, Malcolm's Shadow Vector is an all-software approach (including the notorious 0 and 90-degree phase shifters required for LB and RB decoding), while the Surround Master V2 has a 10-pole cascade of analog 0 and 90-degree phase shifters for L and R channels (4 analog cascades in total), which drive the 4 discrete ADCs of the TAS 3204 DSP, which also has 4 discrete DAC outputs.

The DSP in Malcolm's device is a refinement and development of the original Shadow Vector variable-matrix approach (multiband with lookahead), while the Surround Master V2 has some TATE DES influence. (I can understand why Chuck's engineer nearly lost his mind ... the matrix equations in the TATE patent are intentionally opaque, and I strongly suspect there was a lot that was intentionally omitted.)

What I'm listening to here in snowy Colorado (yes, we got snow yesterday) is a several-year-old Marantz AV8003 in DTS Neo:6 mode, which seems to do a better job than the very poor quality Dolby Pro-Logic II (music mode), which seems to combine the worst aspects of detenting with slow, vague and indecisive localization. The DTS Neo:6 is occasionally spitty, and can't seem to make up its mind on a lot of material, but that's better than the dim impression of surround offered by DPL-II.

What feels a little weird is that I'm going on 70 years old, and the other folks in quadraphonic development in the early 1970's were 10 to 20 years older than me. I imagine some of them are no longer with us. I'm healthy enough, but I'm not sure I'll be doing any more inventing. If there's anything I can do to help either of you, Malcolm and Chuck, just let me know. I want high-quality quadraphonic, or even good 5.1, to be heard by more people. At its best, there's nothing like it.

As mentioned earlier, the two men behind the TATE DES system, Wesley Ruggles and Martin Willcocks, had very little communication with me, and as far as I know, there's no Shadow Vector technology in their device. All I can see in their patent are comments about matrix multiplication used to cancel the outputs of a static SQ decoder ... those cancellation signals could be anything as far as I can tell. If anyone has the patience at this date (certainly not me), working out the math for near-cardinal points (a few degrees away from LB or RB) should tell the story of how the TATE really works. If there's a "forcing" function, then the TATE is favoring the cardinal points so the separation spec looks better on paper. In a way, that's how the original CBS "full-logic" decoder worked, and the TATE team may have gotten their cues from CBS.

The Shadow Vector is an LSD-inspired, higher-order version of the Sansui Vario-Matrix, and has nothing to do with the CBS team. In fact, CBS was annoyed with the marketing materials I wrote for Audionics, which to be honest, didn't cast the existing CBS decoders in a very favorable light. My background is a combination of perceptual psychology, various Buddhist meditation techniques (I grew up in Asia), and the college-hippie environment of late-Sixties Los Angeles. I still design loudspeakers and amplifiers to be as spacious and as natural-sounding as possible; that's part of the Shadow Vector heritage that stayed with me.

As for decoding stereo records, to be honest, I now feel that a non-phase-shifted dynamic EV4 matrix is best. The phase shifters are required for SQ, optional for QS, and not needed at all for stereo or EV4 decoding. For these recordings, the only thing given up with the absence of phase shifters is a hard CB localization, and frankly, that's no loss with 99% of the music out there. Both Shadow Vector (UK) and the Surround Master V2 offer superior stereo -> surround conversion in QS or EV4 mode, and there are plenty of stereo recordings that sound pretty spectacular in this format. I was listening to Groove Armada's "At the River" in DTS Neo:6 the other night and was thrilled at the sudden expansion from mono to full-width surround in the early minutes of the recording ... an effect that is largely lost in 2-speaker stereo. Rainsford's "S.I.D." track is full-blown quadraphonic, with all kinds of action on the sidewalls and rear. There are lots and lots of recording with hidden thrills in them, so why not enjoy?

P.S. I've paid my dues with the exotic 2-channel ultra-high-end crowd, designing the Ariel loudspeaker and Amity and Karna 300B all-triode, zero-feedback amplifiers. I know what these guys obsess about ... and I'm kind of sympathetic to it myself. My initial introduction to stereo was hearing "Ben Hur" at a movie theater on Osaka, Japan on a 70mm wide screen and 5-channel discrete magnetic-track all-analog, all-vacuum-tube electronics. Later that same year, I heard stereo in the home on an Ampex tape deck ... again, all-analog, all-vacuum-tube electronics. So that's what I expect stereo to sound like. AVR's are a pale shadow of that, but the Marantz has a bit of that richness and depth dialed in.

A little discussed aspect of all-vacuum-tube sound is the stereo is much richer, more dimensional, and more tonally vivid than all-transistor stereo. So the transition from table-radio mono to full high-fidelity stereo was much more dramatic than the hard, dry "surround sound" we hear in contemporary movie theaters.
 
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scharfis_brain

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I am listening everything 2.0 (music, TV and movies) with DSU upmixing. This is the successor of DPL-II and all of its variants.

It sounds pretty transparent to me. No pumping, no center collapse and the like.
One day I watched a movie with the wrong audio track selected (2.0 instead 5.1): I wasn't really able to tell. That was astonishing. I didn't expected that it was that good. DPL-II and DTS-NEO always are intransparent to me.
 

chucky3042

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Sometimes it only becomes apparent on instant A/ B comparisons
 

Lynn Olson

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My article about the Shadow Vector, the tale of how it got invented, what happened afterward, and current thoughts about the marketing gulf between high-end 2-channel audio and the home theater market:

https://positive-feedback.com/audio-discourse/shadow-vector-emerges-from-the-shadows/

Once again, I want to give the warmest of thanks to Malcolm Lear in the UK, along with Chuck in Oz, for working so hard to bring multichannel music and 2 -> 4 synthesis to the world. I may have invented Shadow Vector, but that was a very long time ago, in the all-analog era, with only LP's and FM stereo as music sources (music cassettes were still a niche format at the time).

As you might tell from the tone of the article, I'm looking forward to surround, or multichannel, music emerging from the shadows of home theater as a medium in its own right. That was my hope back in 1973 when I first started in audio, and it still is.
 

bmoura

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My article about the Shadow Vector, the tale of how it got invented, what happened afterward, and current thoughts about the marketing gulf between high-end 2-channel audio and the home theater market.

And for modern content, whether PCM or DSD, there's the 8-channel exaSound e38 DAC. This approach bypasses the AVR pre/pro completely, since the exaSound e38 has a built-in volume control (with no loss of resolution or quality at reduced volumes, a built-in feature of the ESS Sabre converters). There is a surprising amount of modern PCM and DSD surround content available as downloads (which is where the USB input of the exaSound comes in). I already own an exaSound e20 DAC, and they are pretty impressive DACs that sound like DACs at double or triple their price point.

https://positive-feedback.com/audio-discourse/shadow-vector-emerges-from-the-shadows/
We have a discussion about the exaSound e38 Multichannel DSD 256 DAC here at QQ.
George Klissarov from exaSound has dropped by from time to time to participate in the discussions.
 

Lynn Olson

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David, my editor at Positive Feedback Online, informs me that an exaSound e38 is on its way to me (I very occasionally review products for PFO). The big downside of writing a review for PFO is I will probably be very unwilling to send the e38 back, so I'll end up blowing my budget for audio gear this year. I already own a secondhand e20, and it's a superb implementation of the ESS Sabre 9018, so I pretty much expect the e38 will be as good or better (and in 8 channels!)

And then there's the temptation of the exaSound PlayPoint for streaming TIDAL and Qobuz, with an optional Roon interface and a built-in HQPlayer. Oh well, there's worse ways to spend my money. Besides, I'm not in the market for speakers ... still quite content with the Ariels I designed in 1993 or so.

Switching between all these gadgets is going to take some thought. The Marantz AV8003 has one set of analog inputs, like most AVRs (and some have none), and the music sources will vary between iTunes from my AppleTV (optical output), TIDAL and Qobuz from a Bluesound Node 2 (optical and S/PDIF), and USB from my MacBook Pro using HQPlayer to up and downsample from other sources. In principle, the Marantz MM8003 amplifier has switching between the XLR and RCA inputs ... but the input switching is on the back of the amplifier, and not really convenient.

I think I'm going to have to write a flowchart to figure out all the possible ways this stuff can be connected.
 
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bmoura

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David, my editor at Positive Feedback Online, informs me that an exaSound e38 is on its way to me (I very occasionally review products for PFO). The big downside of writing a review for PFO is I will probably be very unwilling to send the e38 back, so I'll end up blowing my budget for audio gear this year. I already own a secondhand e20, and it's a superb implementation of the ESS Sabre 9018, so I pretty much expect the e38 will be as good or better (and in 8 channels!)
That is a problem.
George at exaSound tells me they rarely get an exaSound DAC returned once it gets sent to a home! :)

Speaking of streaming audio, be sure to check out the PrimeSeat streaming audio service from Japan.
They are streaming audio at DSD 256 Stereo for some performances! Beyond what Tidal and Qobuz have to offer.
PrimeSeat DSD streaming works very nicely with the exaSound DACs.



 

Lynn Olson

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I mentioned the possible price of the e38 DAC to the wife this morning, and she didn't think it was any big deal. Halfway there.

She's heard the e20 connected to the Big Triode System, and approves of the exaSound sound.
 

Lynn Olson

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With the spouse-approval-factor presumably out of the way, I'm now curious about which streaming gizmo (there are three) in the exaSound family makes the most sense for e38. Guess I should drop in over at the e38 forum and ask George K his thoughts on the matter. My desire is letting Roon handle the interface to the outside world, along with indexing what's on the local hard disk, and enough leftover computing horsepower to have HQPlayer handle sample conversion duties. I use HQPlayer on my 2015 MacBook Pro and it does a first-class job transcoding between DSD and PCM and sample-rate conversion. (The exaSound likes to be run at high rates, so an external upsampler is a good way to extract the best sound out of 44.1/16 Red Book content.)

Just took at peek at the Marantz AV8003 manual, along with other paperwork. I didn't realize I bought in 2010, so although it was not cheap at $1500 (refurb price), it has given excellent service over the last nine years. (As AVR's go, that's a long time.) The AV8003 has an 8-channel analog input, and conveniently, when that input is selected, all the internal digital stuff is turned off, so the analog signal only goes through the volume control on its way to the MM8003 amplifier. That also implies the subwoofer will be silent, since there's no bass management in that signal path.

As for disc spinning, I have a Marantz UD7007 universal player, which supports multi-channel DSD over HDMI ... although I'm not sure the AV8003 supports that mode of DSD over HDMI. The Marantz is basically a fancy OPPO, with smoother sound than the OPPO equivalent, according to folks who've done the comparison. I've only been using the UD7007 as a transport for my two different DACs, so it should be interesting connecting it to the AV8003 for the first time.
 

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What an absolute delight it was to read this thread, especially for those of us who were wildly spending every spare penny to achieve the “virtually discrete” nirvana that was always promised back in those early days of quad and multi-channel sound for the home. Malcolm, best of luck with your endeavor to bring the legend that was SHADOW VECTOR to our ears, and Lynn Olson, as creator of that legend, thank you for opening up here on QQ about those crazy early days. You provide insight as to the nature of competitive business which always can extinguish the brightest lights and at the same time bring a glimpse of the absolute audio miracles that are made possible by force of will, or drugs...LOL! It was wonderful to see our present Australian audio archangels chime in with their observations too, and we here at QQ know how lucky we are to have been graced by their talents. I doubt that there were any members of this forum who thought that a small, affordable state of the art unit for both SQ and QS would actually become a reality to fulfill our greedy multi-channel needs. We are so lucky today! Oh, and Jon...Thank You!
Dwight
 

Old Quad Guy

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Thank you for the information in this Thread. Fascinating read.

One question I've been dying to ask for years:

Is it possible for 100% matrix decoding (or something close), at least in theory? Or are matrix recordings forever stuck together, like sonic flypaper? If that's the right analogy.

I've always liked SQ records for whatever reasons. But the bottom line concern is that these matrix recordings might be all that is left to get Quadraphonic if the original Master tapes are gone forever. Thanks.
 
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