Surround Master Decode - SQ and QS Encodes of Same Album

[fredblue]

I have tried it and there is almost no leakage, the input signals have to be properly balanced though. Every SQ decoder should have an input balance control!

i have tried it too, many times, with L&R properly balanced and the SM decodes QS better than it does SQ with regard to Front to Back leakage.

it is particularly noticeable with CBS mixes, some CF content always gets bled back into the Rears on SM SQ decodes. it is one aspect where the Tate is better at handling SQ than the SM.

 

[Sonik Wiz]

I have tried it and there is almost no leakage, the input signals have to be properly balanced though. Every SQ decoder should have an input balance control! QS requires proper balance as well it's just not nearly as critical.

@fredblue seems a little obsessed with the SQ center front leakage to the rears. Technically he is right as QS center front to rears is over -50dB. The same for SQ is "only" -16dB. So there is more leakage. My point is that amount is truly a non-issue, quite unable to hear unless you are listening to just the rear speakers. We do have forward oriented hearing and any front to back leakage is completely masked under normal conditions.

https://www.quadraphonicquad.com/forums/threads/2020-sm-v2-testing.29536/

 

[par4ken]

@fredblue seems a little obsessed with the SQ center front leakage to the rears. Technically he is right as QS center front to rears is over -50dB. The same for SQ is "only" -16dB. So there is more leakage. My point is that amount is truly a non-issue, quite unable to hear unless you are listening to just the rear speakers. We do have forward oriented hearing and any front to back leakage is completely masked under normal conditions.

https://www.quadraphonicquad.com/forums/threads/2020-sm-v2-testing.29536/

My testing (subjective) would indicate much better separation than -16dB (with Involve). Use of "Axial Tilt", while a pain to set up improves SQ separation all around. It seemed to make the biggest (most noticable) difference with the Sony decoder. The improvement in left to right front separation is pretty much unnoticeable but the rear separation was noticeably improved using Axial Tilt. There is no technical reason (using test signals at least) that the SQ decoding would have any less separation than the QS. I agree with you that under normal listening conditions any leakage is mostly unnoticeable.

I did some listening comparisons with the RM decoder in the Sony and The Involve (Evaluation Module) and was amazed by how similar they sounded. But when listening to the back channels only there was almost no leakage with the Involve but a considerable amount with the Sony. Subjectively the difference was not nearly as great, I don't think that the RM decoder in the Sony uses any form of logic either.

 

[Sonik Wiz]

My testing (subjective) would indicate much better separation than -16dB (with Involve).

Yep, well, I guess that's the difference between subjective vs objective testing. Both have their good points. As you mentioned earlier SQ is pretty sensitive to input level balance & errant phase shifts. Just a little input balance to left or right could really alter the rear output. I used pure test tones and I think real world play back of, say, analog LP's could only go down hill from there.

How balanced was my input for QS/SQ center front to center back separation test? I used a single channel with a Y splitter to the SM input. The only potential imbalance would be the tracking between the sections in the dual gang input pot.

Use of "Axial Tilt", while a pain to set up improves SQ separation all around. It seemed to make the biggest (most noticable) difference with the Sony decoder.

The concept of Axial Tilt has always appealed to me. A project I'm working on has an RIAA preamp built in & I might add an Axial Tilt circuit for that. Anyway, the Tilt circuit is built into your Space & Image Composer, right? Does it output also to be used with your Sony & SM?

There is no technical reason (using test signals at least) that the SQ decoding would have any less separation than the QS.

In the QSD-2, QRX and other Sansui units with SQ decoding alterations were made to the direction sensing Phase Discriminator chips as well as the Matrix chip. This was a way to conform SQ more to the format of QS and the result was not quite as good as the QS format. Essentially it was a basic SQ decoder with complimentary front/back blending. Where as SQ VariBlend only worked in the rear chs to decrease center front bleed to the rear. Again, subjectively, the Sansui SQ decoding was considered by many superior to Full Logic because of the smoothness of decoding.

Now in regard to the SM SQ decoding, it was a generous after thought by Involve after much pleading from QQ members. Whether that accomplishment is a band aid like Sansui's implementation, only Chucky could say.

Myself, a three band high separation SQ decoder with no audible artifacts? Pretty friggin' cool!!

 

[par4ken]

The concept of Axial Tilt has always appealed to me. A project I'm working on has an RIAA preamp built in & I might add an Axial Tilt circuit for that. Anyway, the Tilt circuit is built into your Space & Image Composer, right? Does it output also to be used with your Sony & SM?

I now always use Axial Tilt when I make a vinyl rip. So my digital files have all been tilt corrected, that is what I play through all the other decoders. For years I didn't bother as it is such a pain to set up. Most test records have test tones that are much too short in duration and the adjustment pots are on the back of the Composer. The Audionics preamp (I forget which model) is rather nice with the tilt adjustments on the front. It is easiest to use an oscilloscope while adjusting, rather than by ear. Improving separation from 20 dB to 30 or 35 dB has little or no noticeable subjective effect on stereo listening. But it does effect SQ decoding. The crosstalk from a phono cartridge, especially if not perfectly aligned could be either in phase or out of phase, and can vary from one channel to the other. By trimming each stereo output to minimize that unwanted crosstalk our SQ encode signal will be that much more accurate. Oddly I found the more accurate encode made the biggest audible difference on the lesser decoders, I guess that they need all the help that they can get.

As I recall I tested both Involve and Involve SQ evaluation modules on the bench with test tones generated by Adobe Audition and found near perfect results with both.

Edit: It just occurred to me that Involve SQ was altered to provide better subjective decoding of SQ vinyl, rather than by the book decoding. That might of increased bleed through in rear. I don't know. I might just have to run tests again. In any case subjectively bleed through is very low.

 

[jaybird100]

Buying used ones these days with no shrink wrap and no sticker makes it a bit more complicated.
I usually just play those Project Records in QS mode if I'm not sure what format it's in.

Remember, QD suffix plays as QS. You can't miss that way.

 

[chucky3042]

@fredblue seems a little obsessed with the SQ center front leakage to the rears. Technically he is right as QS center front to rears is over -50dB. The same for SQ is "only" -16dB. So there is more leakage. My point is that amount is truly a non-issue, quite unable to hear unless you are listening to just the rear speakers. We do have forward oriented hearing and any front to back leakage is completely masked under normal conditions.

https://www.quadraphonicquad.com/forums/threads/2020-sm-v2-testing.29536/

Yes my 12 dB rule

 

[chucky3042]

Yep, well, I guess that's the difference between subjective vs objective testing. Both have their good points. As you mentioned earlier SQ is pretty sensitive to input level balance & errant phase shifts. Just a little input balance to left or right could really alter the rear output. I used pure test tones and I think real world play back of, say, analog LP's could only go down hill from there.

How balanced was my input for QS/SQ center front to center back separation test? I used a single channel with a Y splitter to the SM input. The only potential imbalance would be the tracking between the sections in the dual gang input pot.



The concept of Axial Tilt has always appealed to me. A project I'm working on has an RIAA preamp built in & I might add an Axial Tilt circuit for that. Anyway, the Tilt circuit is built into your Space & Image Composer, right? Does it output also to be used with your Sony & SM?



In the QSD-2, QRX and other Sansui units with SQ decoding alterations were made to the direction sensing Phase Discriminator chips as well as the Matrix chip. This was a way to conform SQ more to the format of QS and the result was not quite as good as the QS format. Essentially it was a basic SQ decoder with complimentary front/back blending. Where as SQ VariBlend only worked in the rear chs to decrease center front bleed to the rear. Again, subjectively, the Sansui SQ decoding was considered by many superior to Full Logic because of the smoothness of decoding.

Now in regard to the SM SQ decoding, it was a generous after thought by Involve after much pleading from QQ members. Whether that accomplishment is a band aid like Sansui's implementation, only Chucky could say.

Myself, a three band high separation SQ decoder with no audible artifacts? Pretty friggin' cool!!

Precisely. We absolutely will never do "bandaid"

 

[gvl_guy]

Remember, QD suffix plays as QS. You can't miss that way.

Ah! So I'm assuming the ones where it says "Quadraphonic" on the cover and doesn't have a QD, SQ, or CD-4 as the stuffed to their number, it's EV4?
Like this one?
PR-M4C 900
https://www.discogs.com/release/10520408-Enoch-Light-4-Channel-Stereo

 

[jaybird100]

Ah! So I'm assuming the ones where it says "Quadraphonic" on the cover and doesn't have a QD, SQ, or CD-4 as the stuffed to their number, it's EV4?
Like this one?
PR-M4C 900
https://www.discogs.com/release/10520408-Enoch-Light-4-Channel-Stereo

Yes, the two quad sampler LP's are EV-encoded. Play them as QS.

 

[MidiMagic]

Hold it!

There is no way to tell a QS from an SQ recording by listening to a CF signal from the album.

CF is encoded in exactly the same way in both QS and SQ. There is no difference at all in the signal. So we can't tell which format with this signal.

The differences in leakage you are noticing are in the decoding of the CF signal, not the encoding of the CF.

You could play a mono record and get the same results.

 

[par4ken]

@fredblue seems a little obsessed with the SQ center front leakage to the rears. Technically he is right as QS center front to rears is over -50dB. The same for SQ is "only" -16dB. So there is more leakage. My point is that amount is truly a non-issue, quite unable to hear unless you are listening to just the rear speakers. We do have forward oriented hearing and any front to back leakage is completely masked under normal conditions.

https://www.quadraphonicquad.com/forums/threads/2020-sm-v2-testing.29536/

Well Sonic I tested the Involve SQ and can confirm your finding of about 16 dB Cf to Cb. I also checked with a L only and R only signal and could notice no rear leakage at all ( just a bit of noise on the scope display). With + and -90° test signals (to simulate back left and right) the results were similar to that with a centre front signal. So the Involve seems to decodes the front L and R perfectly while other directions about produce something a bit less. Again that must be due to the way Involve set it up for SQ vinyl, no technical reason front to back separation can't be much higher. The tests you did are likely a bit more accurate than mine.

I ran the same test with one of the Composers and got about 25 dB separation Cf to Cb.

 

[Sonik Wiz]

Well Sonic I tested the Involve SQ and can confirm your finding of about 16 dB Cf to Cb. I also checked with a L only and R only signal and could notice no rear leakage at all ( just a bit of noise on the scope display). With + and -90° test signals (to simulate back left and right) the results were similar to that with a centre front signal. So the Involve seems to decodes the front L and R perfectly while other directions about produce something a bit less. Again that must be due to the way Involve set it up for SQ vinyl, no technical reason front to back separation can't be much higher. The tests you did are likely a bit more accurate than mine.

I ran the same test with one of the Composers and got about 25 dB separation Cf to Cb.

Thanks for the come back and verifying my tests. Prior to posting the separation specs I sent them to Chucky to make sure there weren't any glaring mistakes. It got his nod of approval.

Despite the bit of leakage, another aspect I like about the SM decoding, SQ or QS, is very good symmetry. Now there might be, say, a few dB difference of crosstalk between different directions but when the separation is that high to begin with it's truly negligible. I doubt quality vintage decoders could do that good. And as you mentioned the front soundstage SQ decodes perfectly in the SM, and certainly accurate front L/R was one of the goals from the beginning with SQ technology.

Considering the high separation between left back & right back in SQ, maybe some blending would do some good with minimal noticeable harm. But I would want to do some careful listening before I baked it into the circuit.

 

[kfbkfb]

Of course, there's another way to test the SM w/SQ and QS decode of same content - select one of your discrete quad music segments and encode it (if possible w/all digital SQ and QS encoders) and compare the resulting decode w/discrete original, SM SQ and SM QS decodes.

The advantage is that the Lt and Rt levels can be matched so as to give the SM decoder the best possible signal to work with.


Kirk Bayne

 

[fizzywiggs41]

That's exactly what I'd do for an objective listening test between SQ vs QS.

Try a few music tracks known for their discreet display in matrix
Encode these 3 HI Rez tracks in QS and SQ for demo purposes.

You could try "Black Water" from The Doobie Brothers Blu-ray.
Next up give "Riders On The Storm" from The Doors ,Blu-ray.
And also the song "Beginnings" from Chicago's Blu-ray.

I think in practice they should provide excellent quad demonstration qualities. Besides being 3 distinctly quad tracks for quadraphonic demonstration ,via matrix once encoded. They are all 192/24 hi rez.






RE : Quadraphile Test Record(CD-4 ,UD-4 ,QS ,SQ)
FWIW I don't think the album Quadraphile has a very good SQ Encode. It sounds rather weak for an SQ Encode or so it would seem as I tried both QS and SQ tracks for comparison and found the SQ encode rather poor for demonstration purposes.
I used my Sansui QSD 2 for QS and for SQ my Fosgate 101a .

 

[Sonik Wiz]

That's exactly what I'd do for an objective listening test between SQ vs QS.

Try a few music tracks known for their discreet display in matrix
Encode these 3 HI Rez tracks in QS and SQ for demo purposes.

Tell me how that is an objective listening test? Is it blind A/B or A/B/X? QS encoding is pretty straight forward but SQ... basic, forward oriented, back ward oriented? QS decoded by vintage Sansui, & maybe Fosgate SQ Tate for SQ? Or both decoded by the Surround Master?

I don't think the album Quadraphile has a very good SQ Encode. It sounds rather weak for an SQ Encode or so it would seem as I tried both QS and SQ tracks for comparison and found the SQ encode rather poor for demonstration purposes.

What would make an SQ encoding weak? Weak compared to other SQ encodings or just the QS track of Quadraphile?

I have this record & find the encoding subjectively the same, the big difference being between what is the decoder.

 

[kfbkfb]

Maybe some discrete content that you are very familiar with so subtle changes in imaging can be easily detected, there are some all software SQ and QS encoders available, they could be used so as to provide the best encode.


Kirk Bayne

 

[par4ken]

I'm not sure what the point of such an experiment would be. SQ is at its absolute best when the recording is mixed especially for SQ. The SQ function was added to Involve as an afterthought because many people here requested it. Although it is very good I'm sure that still it could be improved. For one thing using the SM center front to centre back separation should be nearly equal on both but is considerably lower on the SQ decode. My S&IC has about 10 dB better separation (Cf-Cb) than the SM. The Involve decoder was developed based on QS so will naturally function better in that mode. So any such testing would have to favour QS! It would prove only that the SM does a better job on QS, not that QS is inherently better than SQ!

 

[MidiMagic]

What would make an SQ encoding weak? Weak compared to other SQ encodings or just the QS track of Quadraphile?

Saving money on production by making a master for a discrete Q8 and then just running that master through the SQ 4-corners encoder.

Any sound not in the corners or center front will not be encoded optimally.

 

[Sonik Wiz]

Saving money on production by making a master for a discrete Q8 and then just running that master through the SQ 4-corners encoder.

Any sound not in the corners or center front will not be encoded optimally.

The Quadrafile record mentioned by Fizzy had nothing to do with the scenario you described above:
Quadrafile - Wikipedia

To ensure consistency in the mastering process, Thorne took possession of the actual master tapes of the Pink Floyd album Dark Side of the Moon, which caused him considerable paranoia to the extent that he hid the tapes inside his piano, reasoning that it would be unlikely for a burglar to steal such a hefty object or search inside it./QUOTE]