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The Rolling Stones – Brussels 17th October 1973

11 Aug

Gathering Moss

The original master for this recording no longer exists, so like many of these live recordings from the past, the quality may not be up to what would be expected in an official release.

This concert has had a minor amount of correction/repair performed on the source that had no negative effect on the encoded information. This has been decoded using the SQd process.

This release is intended as a replacement for the poor quality version that is doing the rounds on various sites, and is released for FREE distribution only.

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The Importance Of Accurate Decoding: SQ

26 Jul

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

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

It looks so simple, doesn’t it, and yet this frightenly complex little (encode) equation can cause nightmares when it comes to decoding it…, and i speak as one of those who have been affected!

SQ was but just one of Benjamin Bauer’s inventions, and it’s fair to say that it was the more popular of the two competing PAM systems during the 1970’s. But it’s not perfect by any means.

Unfortunately the one point that CBS used in early advertising against the Sansui QS system was also it’s (never mentioned) Achilles Heal, and it wasn’t until a couple of years ago it was finally dealt a blow in the name of depth, separation and imagery.

So, let’s look at what a correctly decoded SQ signal looks like:

Front Left’ = Front Left + 0.707 -j Rear Left + 0.707 Rear Right

Front Right’ = Front Right + -0.707 Rear Left + 0.707 j Rear Right

Rear Left’ = Rear Left* + j Front Left

Rear Right’ = Rear Right* + -j Front Right

* = as part of the decoding process the levels of the rear channels are automatically returned to their ‘pre-encoded’ level

And this is what you get when it’s not decoded correctly: (Assuming correct usage of +-90 degree phase shifting)

Front Left’ = Front Left + 0.707 -j Rear Left + 0.707 Rear Right

Front Right’ = Front Right + -0.707 Rear Left + 0.707 j Rear Right

Rear Left’ = j Front Left + 0.707 Rear Left + 0.707 j Rear Right

Rear Right’ = -j Front Right + j-0.707 Rear Left + 0.707 Rear Right

This is just one of many variations of what has been done, sometimes there’s only one of the phase shifts used, and there’s even been times when there’s been no phase shifting done at all!

The situation above is that the rear channel information is being output from both the fronts and rears, and at the same levels. This causes a somewhat foggy phase mess where sounds may come from the approximate direction it is supposed to come from, but can move from the rears to the fronts, or visa-versa, with the movement of the head of just leaning to the front or back.

I’m sure, buy now, you’ve noticed the elephant in the room. The major drawback to SQ is that the front channels receive no processing at all, so what you hear is the entire four channel encoded stereo information. And it’s this that limits SQ’s ability to produce a clean image with good levels of low level detail and separation.

Every single decoder from the basic 10/40 type to the king of SQ decoders, The Tate, suffer in this respect. There was nothing that could be done about it, so it was NEVER discussed. Even in our technically enlightened times there’s no way of dealing with the problem using hardware.

But, as previously mentioned, a few years ago i stumbled upon a way of dealing with this issue, and although the process is only working at 50% of its capacity, the difference it makes is quite remarkable, allowing SQ decodes to be heard without the limitations that have been accepted as the norm since it was released 47 years ago.

Oh, and the process is called “Phoenix”, and has come into use with all of the other matrix decoding process’s, with differing levels of improvement, to boot.

 

John Keating – Space Experience

16 Jul

Whilst wandering around the Hi-Fi shops in London during the early to mid 1970’s, you’d either hear this being played or see it on a turntable ready for the next inquirer looking at what quad could offer him/her. It’s easily the most consistent quad demonstration album and deserves to be in everyone’s collection.

 

 

This Is EMI Quadraphonic Sound

14 Jul

SQ

Deodato + Airto – In Concert

10 Jul

No Stereo Track

 

SONY SQ Sampler QSP 13018

9 Jul

SONY SQ Sampler

 

The Art Of The Decoder, Pt1

24 Jun

For quite some time now i’ve meant to do a basic introduction to Matrix Decoding. This isn’t going into any mathematics, or how to do, or not to do, and why (not). The main idea is to get you, the reader, up to scratch with what the decoder is, what it’s supposed to do, and anything else that pops up.

So, to start, let’s take a visit to dictionary corner:

ENCODER

An encoder is a device, circuit, transducers, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed or compressions.

DECODER

A decoder is either a hardware device or piece of software that converts coded data back into its original form

So, from the above we can see that a decoder is principly a device to return a previously mathematical encoded message/signal back to its original form.

In the beginning there was…..

So, in an attempt to convince the general public the need for quadraphonic reproduction in their homes, it was decided that such signals needed to be available for playback via the recently introduced Stereophonic Long Playing record. (remember this for later!)

A brief attempt at just using Amplitude matrix encoding, where it was impossible to decoded the four channels back in the same format as they were encoded, showed that there was interest in the general public, but another method was needed to be able to return the four channels back as they were encoded.

When the PAM (Phase Amplitude Matrix) method of encoding/matrixing four audio channel audio into two, using 90 degree phase shifting, was developed by Peter Scheiber, things moved on at quite a pace. There were a number of competing PAMĀ  systems available, but after a short while there were only two systems still being used, these being Sansui’s QS and Columbia’s SQ systems.

They were quite different in their method of encoding, to the point that they were completely incompatible with each other. But one problem they did share was poor separation between the Front and Rear channels

SANSUI QS

Also know as RM, this system utilised all four audio channels to encode them into a compatible stereo signal. This is certainly the easiest of the two systems to decode, mainly because it used all four channels in the encoding process.

COLUMBIA SQ

Invented by Ben Briar whilst working for Columbia, this system took a completely different route by only utilising the two Rear channels in the encoding process. But by doing this caused some problems, most of which were never discussed outside of the companies laboratory. Also to correctly decode the rear channels it had to be done the correct way, there was no other way of doing it,

When is a Decoder not just a Decoder?

The word Decoder has become to mean more that it was originally meant to be. At first the competing companies sold what we would now call ‘Basic Decoders’, but their performance wasn’t that good, for any of the systems. The problem was due to the low level of seperation these matrix systems gave, bepending on system and circumstances, it was between 3db and 7db. Not much, so the companies developed various methods of improving their performance, which we shall just call Logic systems.

Basically these additions to the decoder circuitry varied the four levels from the decoder at such a rate/level, to give the impression that there was a greater level of seperation than there actually was by using the information in the audio itself. Unfortunately, such systems gave variable audible performance and one annoying side-effect….’Pumping’.

Now, as we can see from the above, including the logic circuitry in with the decoder, it became more than the name suggested. I make this point for one very good reason, which is that people seem to have forgotten that any decoder for either system must include both parts, the system decoder and the logic cicuitry designed to work with the information from the decoder.

I’ll leave it there for now so you can chew over what has been put forward in this basic introduction to the world of PAM.

 

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