A Philosophical Issue (matrix synthesizing surround sound)

[LB-V]

Maybe a drawing (hand/computer) with the mapping of sound locations in stereo to the sound locations in created surround sound (matrix decoding with and without preprocessing [CBS et al.]) would be helpful in explaining what the various matrix decoding systems do to create surround sound.


Kirk Bayne

I'm thinking maybe a Worleyscope might do the trick.....joking aside, I bet I will be able to literally see the difference.

 

[kfbkfb]

https://www.discogs.com/release/5794742-No-Artist-Denon-Audio-Technical-CD
(tests 69 and 70 could be useful for determining where sounds are placed by various matrix decoders)


Kirk Bayne

 

[zeerround]

You can get DAW plugins that can do a constant phase shift ("at all frequencies" but the mileage varies with the technical implementation).

There were free ones, back in the day, but now none that are 64bit, AFAIK. For paid, I don't care for voxengo plugins but one such is pha-979. I have Flux SE EVO Channel.

For +/- 90 degrees Plogue Bidule has a built it FIR, and I recently tried both that and the EVO channel to resurrect some old Plogue Bidule quad encode and decode layouts. The one layout I found in my archive (would have thought there were more but...) has parts labeled SQ standard encoder, SQ Forward Oriented Encoder, and Shadow Vector SQ Decoder.

Hmm, maybe I should search for "QS" and "SQ" instead of quad.

FYI Plogue Bidule is great for this kind of stuff, vs. a more traditional DAW.

 

[zeerround]

Searching for "QS" Bidule layouts I have "QS Decoder with Pre Synth" by EOH (Aart), and some variants.

Other "QS" layouts have groups labeled "Sansui QS Decoder w Pre Synth mode", but it looks to be the same/similar as the above.

 

[kfbkfb]

https://www.quadraphonicquad.com/forums/threads/1974-12-sq-stereo-enhancement-cbs-labs.29763/
IMHO, an all-software implementation of the CBS SQ stereo enhancement would be useful, stereo LPs, cassette tapes and other stereo sources could be digitized, processed thru the SQ enhancement algorithm and output as a stereo data file ready to be played into the SM (set to SQ mode).

I don't have DAW software on my PC, how "standalone" can the SQ forward oriented encoder be?


Kirk Bayne

 

[zeerround]

For the Plogue Bidule approach, it looks like I can do the SQ forward oriented encoder with Plogue Bidule and nothing else. We can test first if you want to PM me.

If we are also talking the crosstalk cancellation piece, that has a VST plugin in it that is only available in 32 bits (modern VST hosts are 64bits) and using a "bridge" with the latest version of the VST says the settings in the crosstalk layout are invalid. I can "read until your eyes bleed" to see how to implement the cross talk approach in modern software if needed. The function of the VST is carve out certain portions of the audio spectrum so some kind of filter could probably be used instead.​

FYI Plogue Bidule is $95US and there is a demo version that lasts for 3 months, assuming you catch it when it is first released. The current demo expires 11 days.

https://plogue.com/products/bidule.html​

I haven't tried it yet but PB (the VST version) should be able to be used inside the Reaper Batch File Processor, such that the whole thing could be made drag and drop, as people are doing with Penteo upmixer, etc. Reaper is NOT free, but works on the honor system.

Without Reaper you would do it one song (or single file album) at a time, loading the audio file into Plogue Bidule, choosing an output file, pressing play... (it can work faster than realtime).

 

[zeerround]

It would be helpful if one of you could express what you want in as simple terms as possible. "Reading till my eyes/ears blead" it is hard to keep track.

These two encoder types are easy to do in Plogue Bidule (from Wikipedia on SQ encoding):

Basic SQ Encoding Matrix[7]	Left Front	Right Front	Left Back	Right Back
Left Total	1.0	0.0	-j0.7	0.7
Right Total	0.0	1.0	-0.7	j0.7

j = + 90° phase-shifthttps://en.wikipedia.org/wiki/Stereo_Quadraphonic#endnote_Hilbert_transform

To provide mono-compatibility a variation on this matrix was proposed:

Modified SQ Encoding Matrix[7]	Left Front	Right Front	Left Back	Right Back
Left Total	1.0	0.0	0.7	-j0.7
Right Total	0.0	1.0	-j0.7	0.7

j = + 90° phase-shifthttps://en.wikipedia.org/wiki/Stereo_Quadraphonic#endnote_Hilbert_transform

The "SQ Forward Oriented Encoder" I have matches the "Modified SQ Encoding Matrix" above in that it uses two -90 degree phase shifts (LB and RB).


A simple diagram or table of the final desired solution please.

Note that phase shifts of 0, 180, and +/- 90 are easily doable in Plogue Bidule without any other software. Other Phase shifts, that can't be constructed from the above, would require another (paid) VST to be included.

 

[par4ken]

For the Plogue Bidule approach, it looks like I can do the SQ forward oriented encoder with Plogue Bidule and nothing else. We can test first if you want to PM me.

If we are also talking the crosstalk cancellation piece, that has a VST plugin in it that is only available in 32 bits (modern VST hosts are 64bits) and using a "bridge" with the latest version of the VST says the settings in the crosstalk layout are invalid. I can "read until your eyes bleed" to see how to implement the cross talk approach in modern software if needed. The function of the VST is carve out certain portions of the audio spectrum so some kind of filter could probably be used instead.​

FYI Plogue Bidule is $95US and there is a demo version that lasts for 3 months, assuming you catch it when it is first released. The current demo expires 11 days.

https://plogue.com/products/bidule.html​

I haven't tried it yet but PB (the VST version) should be able to be used inside the Reaper Batch File Processor, such that the whole thing could be made drag and drop, as people are doing with Penteo upmixer, etc. Reaper is NOT free, but works on the honor system.

Without Reaper you would do it one song (or single file album) at a time, loading the audio file into Plogue Bidule, choosing an output file, pressing play... (it can work faster than realtime).

The Forward Oriented Encoder is how to do SQ stereo enhancement. The stereo signal goes to the back encoder inputs. You will get out a 270° SQ enhanced signal. Left encoded to Lb and R encoded to Rb center stays up front.

 

[zeerround]

Check this:

h**ps://drive.google.com/drive/folders/1-6hyRdwdRPy0_j4dCcQ7FTocj4u2Febr?usp=sharing​

Correlated noise Left to Right pan sweep test signal and SQ enhanced version. Also screen shots of the "layout" in Plogue Bidule. And lastly, a "Shadow Vector SQ Decode" (5.0) of the enhanced signal.

Input test signal:

SQ Enhanced Output:

Shadow Vector SQ Decode of enhanced signal (5.0):

 

[zeerround]

Seems like it's flipping L for R.

Was I supposed to flip L for R on the LB RB inputs?

 

[par4ken]

Seems like it's flipping L for R.

Was I supposed to flip L for R on the LB RB inputs?

Yes, I was thinking that would have been done by the software. So try with the inputs reversed!

 

[zeerround]

5.0 (Quad SQ Shadow Vector decode)

Files added to google folder.