(1970s) Hardware (SQ and QS) Encoder Phase Shifters

[kfbkfb]

IIRC, there were only a few hardware SQ and QS encoders (from CBS, Sony, Sansui)
built/used for all of the 1970s matrix encoded content.

I haven't looked at the circuit diagrams of these encoders, but there were obviously
limitations on how accurate the (hardware) 90 degree phase shifters were.

This might be getting way past the point of diminishing returns, but I was wondering
if there could be a (probably software) correction algorithm that reduces the phase
shift error caused by the hardware encoders, this corrected matrix encoded content
could then be processed by the Surround Master.


Kirk Bayne

 

[proufo]

IIRC, there were only a few hardware SQ and QS encoders (from CBS, Sony, Sansui)
built/used for all of the 1970s matrix encoded content.

I haven't looked at the circuit diagrams of these encoders, but there were obviously
limitations on how accurate the (hardware) 90 degree phase shifters were.

This might be getting way past the point of diminishing returns, but I was wondering
if there could be a (probably software) correction algorithm that reduces the phase
shift error caused by the hardware encoders, this corrected matrix encoded content
could then be processed by the Surround Master.


Kirk Bayne

You would be digitizing the content twice, inelegant IMHO. Maybe the shifters in the SM are good.

Better, let's ask the guys to include an SPDIF input in the next-Gen SM. Just for kicks (and to play the odd SQ encoded CD).

 

[par4ken]

When they came out with the SQ version of the Surround Master it was decode by the book. Latter they came out with the vinyl version which I'm assuming altered the decode to better match the imperfect original encode? It's seems an odd situation when the decoder is more accurate than the encoder. The way QS works I don't think the slightly imperfect phase shift would make much of difference, unless your concern is absolute phase of all output signals.

 

[Sonik Wiz]

This might be getting way past the point of diminishing returns,

Ha well I remember a phrase/concept from an audio magazine about the increasing importance of the diminishing returns....

Anyway the concept of correcting for phase shift anomalies in an encoder is pretty intriguing. To do that you would need to know where & how much error there was in the original phase shift. I have no information on SQ encoding accuracy but in Sansui patent 3,787,622 it described the preferred embodiment of an encoder using only 4 pole phase shift. I had at one time a Sansui QSE-5B encoder & IIRC each phase shift circuit did only use 4 transistors. However it also shows the phase shift ripple being very small:

So maybe the error doesn't contribute enough to be concerned about? And in practice I bet phase discrepancies even varied unit to unit in production.

 

[Sonik Wiz]

When they came out with the SQ version of the Surround Master it was decode by the book. Latter they came out with the vinyl version which I'm assuming altered the decode to better match the imperfect original encode? It's seems an odd situation when the decoder is more accurate than the encoder. The way QS works I don't think the slightly imperfect phase shift would make much of difference, unless your concern is absolute phase of all output signals.

Well when you think ~1974 tech everyone used 5% resistors and a good (non-electro) cap was 10%. Unless they did a lot of hand matching I can certainly see why todays endocer/decoder is easily built to much higher quality components. And SQ/UHJ were so dependent on phase shift I bet things were fortunate enough just to work out as well as they did.'
'
RE: absolute output phase
That's another thing I liked about the QS way of doing things; all decoding could be done with simple level & polarity shifts. No phase shift correction was needed until the final output to straighten out the 90 deg encode matrix. And in Sansui patents they considered that optional. Certainly it wouldn't help & maybe even hurt a bit when playing back stereo.

 

[kfbkfb]

I guess I'm spoiled by digital audio, I specifically bought a CD player
(Magnavox (Philips)) with 2 DACs so there would be no phase shift
between the channels.

The hardware encoder phase errors were probably swamped by the
phase anomalies in the Vinyl Record System and the
Analog Magnetic Tape Systems (IIRC, CBS/Columbia didn't want
to release SQ encoded Compact Cassettes due to the phase issue).


Kirk Bayne