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Block diagrams of Quad (QS/SQ) systems with logic

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juanverdaguer

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Mar 21, 2012
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Hello,


I'm doing some research on QS and SQ decoding methods. I'm more or less familiar with the basics of both methods but I'm missing some pieces of the so called "Logic" workaround circuitry. I've done some googling around and found an interesting site (already posted in these forums) with some good diagrams on both methods:

http://www.hi-ho.ne.jp/odaka/quad/QSSQlogic-e.html

The part I'm missing is what the Log and DET blocks mean in the diagrams. Does anybody know what they actually do?

The final outcome of this research will be a software-based decoder for Mac and Win platforms. It's already working with the plain basic decoders but I'd like it to have an optional Logic mode. Let me know if any of you would like to be informed when the software is ready for testing, I'll gladly share a copy with some beta testers.

All the best,


J
 

quadsearcher

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OK, this is a guess. The Log modules could be linear-to-logarithmic converters supplied by the phase shift and summing, they go into comparators and then to positive swing and negative swing detectors DET modules which provide voltage control to VCAs in the final stages.

Disclaimer: I am not an engineer and am only starting to try to learn about phase matrices.

Edit: What are the ABS blocks? Seems to be center steering.
 
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oxforddickie

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I wish you luck in your project, and although i don't wish to get involved, i have a couple of things for you to think about

1, I hope your going to disregard his "adopted" method - it's so wrong

2, there are mistakes all over the place, be very careful
 

juanverdaguer

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Mar 21, 2012
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Thanks for your replies.

@quadsearcher:
It makes sense to think about these blocks as you said. I'm experimenting in the algorithm with this in mind. I'll post my findings in this thread (I'm also wondering about the ABS block...)

@oxforddickie:
Thanks for your suggestions. I find that the methods described in the link (specially the "adopted" ones) have very different coefficients than the ones I'm handling. They seem to come from a mathematical simplification. I'm not sure how well calculated they are. I must say though that this is the first paper in which I see a diagram describing what a 'logic' or 'full-logic' is implemented (although not very clearly).

I guess I should ask you if you could help me find good reliable literature that will allow me to continue the research. I'm mostly based on a number of articles on the AES library (mostly from the 70s, when all this technology was developed) that could serve as reliable sources but maybe I'm missing other important bibliography, specially regarding the 'logic' implementation. Any ideas?
 

oxforddickie

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You appear to be going down the same route as i did, and i don't remember finding anything that described the logic process in real depth, although i'll admit i may have missed something as i was looking for a deeper understanding of how the encoder worked.

From what i found, any (pre-logic) decoding of SQ needs to be based on this encoding equation:

Lt = Lf + (0.707 Lb -j + 0.707 Rb)
Rt = Rf + (-0.707 Lb + 0.707 Rb +j)



During my investigations i found that the original set of SQ test tones were inacurate, so Malcolm revised them, and are available here:

http://hotfile.com/dl/134605830/c673acf/SQTones.rar.html

A special thanks to him for making them available



OD
 

oxforddickie

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One question i forgot to ask, how are you planning to do this? I was going to play around with some basic SQ/QS decoders in audiomulch


OD
 

juanverdaguer

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I completely agree with your formula for SQ decoding. I'm using it certainly.

The test tones are a great share! Thanks so much to you and Malcolm!

A few questions about them:
1. By any chance do you remember the ordering of the signals in this file? I mean, which one is LB, LF, RF and RB.
2. Are there any such test tones for QS?
3. Do you happen to know how were they done? Do they come from an "official" test disc or were they home-made?

I'm developing this on Max6 (Max/MSP). Don't know much about audiomulch but from what I hear the principles of realtime, visual programming environment are the same.

I found some literature that I feel I should consult although these are all rare-to-find books (or I better say, difficult-to-be-delivered-to-Europe, where I'm based); most of the sellers I found online don't deliver internationally, and the ones that do have ridiculous prices.

- Physics of stereo/quad sound by Joseph G Traylor (1977)
- Quad sound by Marvin Tepper (1976)
- Four-channel sound by Leonard Feldman (1973)
- Four Channel Stereo: From Source to Sound by Ken,W. Sessions (1978)

I'd love to get these but I'll appreciate some comments from the quad community before I make any decisions.


J
 

national-kid

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hello It is Odaka.
http://www.hi-ho.ne.jp/odaka/quad/decode.pdf is Circuit.
the Log is Bandpass->Absolute->Logarithmic->amplitude detection
( At the time of a very small input, in order to use stability, the ban on operation is used )
+DET blocks is + Voltage portion
ABS blocks is Absolute

An unclear expression asks you for indication. (I am a Japanese who cannot speak English)
 

national-kid

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http://www.hi-ho.ne.jp/odaka/quad/decode.pdf is circuit diagram.

Log blocks is Bandpass->Logarithmic->Absolute->Amplitude detection
log comparison is set to 0v at the time of a very small input. (For operational stability)

+DET blocks is + Voltage detection.
ABS is Absolute value conversion.

When a sound source is a corner in "corner +-DET", a phase shift is controlled 90 degrees.
A sound source carries out distinction of the front or back by "corner ABS" and "center +-DET", and it controls negative phase addition.

Please point out an unclear expression. (I am a Japanese)
 

oxforddickie

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These tones were created by Malcolm, as i believe were the QS ones, which i have and will make available to you in another post

The order of the signals in the SQ tones (mk2) are:

Front Center, Front Right, Side Right, Back Right, Back Center, Back Left, Side Left, Front Left, Front Center


Not heard of Max6, i'm guessing it's for the Mac?

I have the Leonard Feldman book, which i bought for the DY and EV equations, and i can say you can cross it of the list, as it doesn't really deal with the logic sections of SQ and QS in any depth.


OD
 

national-kid

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http://www.hi-ho.ne.jp/odaka/quad/decode.pdf is circuit diagram.

"Log block" is Bandpass->Logarithmic->Absolute->Amplitude detection
( When processing by DSP, Bandpass->Absolute->Logarithmic->Amplitude detection )
log comparison is set to 0v at the time of a very small input. (For operational stability)

"+DET block" is + Voltage detection.
"ABS block" is Absolute value conversion.

When a sound source is a corner in corner +-DET, a phase shift is controlled 90 degrees.
A sound source carries out distinction of the front or back by the corner ABS and center +-DET, and it controls negative phase addition.

Please point out an unclear expression. (I am a Japanese)
 

Owen Smith

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OD, does your SQ-Final script perform logic decoding or just a basic SQ matrix decode? The threads about the development of the scripts are huge, I won't live long enough to read them all :). Is there a short (ish) description of what it does and how it operates without the history?
 

oxforddickie

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It uses 'phase extraction' to remove the unwanted information. Short enough? :eek:
 

national-kid

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does your SQ-Final script perform logic decoding or just a basic SQ matrix decode?

->Decoder is a logic with.
  Logic is a method (which improve the performance of the W/M logic and F/B logic in general) of the original.

Is there a short (ish) description of what it does and how it operates without the history?
->What will this do?
http://www.hi-ho.ne.jp/odaka/quad/decode2-e.pdf is a brief description. (of circuit diagram)
->history? : "history" mean?
 

oxforddickie

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I'll be honest, no i don't, and i'm afraid i'm just too busy with the blog and tracking down some rare titles to sit and write it all out
 

juanverdaguer

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Mar 21, 2012
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Hi Odaka,

I was examining your QS Logic circuit and I can't figure out what the MIX blocks do. They seem to have no output, where is that signal going? Is it being mixed back to the outputs? And also how do you scale DET to (0 ~ 0.5) in MIX?

A similar question on the SQ Full Logic, how do you scale the output of DET to control the phase shifting (0 ~ 90)? And what does the MIX block do?


Thanks!

J
 
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national-kid

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I can't figure out what the MIX blocks do. where is that signal going? And also how do you scale (0 ~ 0.5) the MIX?

-> Block diagram has been simplified to draw.

A ---+---> AA
|
mix(0-0.5)
|
B ---+---> BB

+---+---+---------------------+
| | 0 | 0.5 (about) |
+---+---+---------------------+
| AA | A | A * 0.65 + B * 0.34 |
+---+---+---------------------+
| BB | B | B * 0.65 + A * 0.34 |
+---+---+---------------------+

http://www.hi-ho.ne.jp/odaka/quad/mix.pdf is actual circuit.
 

oxforddickie

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I've just been looking at the circuit diagram of his QS/SQ decoder, and it's seriously flawed, basically it fails to decode either correctly.


OD
 
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