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A Heads Up…..

30 Oct

This is just a mention (for those that don’t keep a weather eye on the blogs) that a planned series of Quadraphonic live recordings have started to be made available over on the SACD-to-DVDA resurected blog.

 

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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.

 

The Importance Of Accurate Decoding: QS

26 Jul

As a further extension of my look into the matrix systems, i thought it might be helpful, for those not aware of their inner workings, to show the importance of accurately decoding these AM sources, and what happens when it’s not done correctly.

To reduce the mathematical load on you all,  i’ll not go too deeply into those inner workings, but i must state that i will be using the terms Fc (Front Centre) and Rc (Rear Centre) which are not part of any quadraphonic system but will be used to (hopefully) help show how this area is affected in the encode/decode process.

QS

The most popular, and successful, of the three Japanese matrix systems that were based on the RM standard, is one of the simpler PAM systems: (j = +-90 degrees)

Lt = (0.924 Lf + 0.383 Rf) + (0.924 Lb j + 0.383 Rb j)

Rt = (0.383 Lf + 0.924 Rf) + (0.383 Lb -j + 0.924 Rb -j)

Above is the QS encode equation, from which the encoder used to create the stereo compatible signal is based on. The way this system works means that each of the stereo channels contains an amount of all four channels.

The Front Channels do not have any adjustment to their phase, only having the Left and Right ‘blended’ to a predetermined amount (which is actually THE MATRIX). The effect on the Fc is that it remains in phase with the front left and right channels.

The Rear channels are similarly blended, but only after having ther phase shifted by +-90 degrees. It is this phase shifting that finally allowed four channels to be encoded and decoded without the severe limitations that crippled the  previous two AM systems. The effect on the Rc is that, because rear left is shifted 90 degrees and rear right is shifted -90 degrees, the “imaginary” point Rc is actually 180 degrees out of phase with Fc.

The “blending” is not just figures plucked out of thin air, but are the result of a great deal of work by the systems designers and is the heart of the whole matrix. The phase shifting is purely a means to an end, nothing more.

There’s one small point that needs to be mentioned here, and that is mono compatibility. I’ve read a few times now that SQ isn’t mono compatible but QS is. That is pure poppycock!

Any matrix system that uses +-90 on the rears, as both QS and SQ do, can never be mono compatible. Why? Quite simply, when the two channels are summed together to create a mono signal, any information that has been panned to be in, or around, the Rc area is cancelled out. It’s basic maths and 100% pure fact.

So, hopefully that gives something of a slight overview of what is actually on each of the channels when playing a QS record, but what about decoding?

This is where it can get very mathy, i’m afraid, so what we’ll look at is what we get out of a basic decode and a none accurate decode. The non-accurate version is just an idea because there are so many ways to do it wrong, but only one way to do it right.

So, if a particular decoder is fitted with some form of Separation Enhancement circuitry then it needs to be fed with four accurately decoded signals. What is to be expected from an accurate QS decoder is:

Front Left’ = Front L + j Rear L + j Rear R

Front Right’ = Front R = -j Rear R + -j Rear L

Rear Left’ = Rear L + -j Front L + -j Front R

Rear Right’ = Rear R + j Front R + j Front L

OK, how many thought that all you got was the main (wanted) channel? Afraid not. This is what you get when the decoder is mathematically correct, which is rather like the dodo, not seen in these times.

So, lets look at a perfectly normal output from a decoder that doesn’t follow the QS rulebook:

Front Left’ = Front L + <>Front R + j <>Rear Left + j <>Rear R

Front Right’ = Front R + <>Front L + -j <>Rear R + -j <>Rear L

Rear Left’ = Rear L + <>Rear R + -j <>Front L + -j <>Front R

Rear Right’ = Rear R + <>Rear L + j <>Front R + j <>Front L

The above assumes the correct usage of +-90 phase shifting. If that is not correct then the picture gets very messy. The use of <> indicates a variable level, which is hard to work out due to the non-correct method of decoding. Also not shown is the effect (even on the Front channels) of phase shifting caused by the mutual and un-mutual phase addition/cancellation.

Feed the above into some form of Separation Expansion circuitry and you get poorly focused imagery that wanders with movement of the head, amongst other things. Unfortunately, this is quite common.

I understand that most would just shrug their shoulders and say that it doesn’t mean anything to them, so you will be able to actually hear the difference later.

Just what is RM?

13 Jul

One of the more confusing things about the Quadraphonic period in Japan is what is RM and what relationship do the three matrix systems QM, QS and QX have with it.

I’ve searched for as much information regarding this subject as is possible, and all i have come up with is that much information is missing, probably locked away in various vaults that will most likely never see the light of day.

What i have pieced together is:

The format we call RM is in fact a set of specifications laid down by the Japanese authorities as a guide line for any company wishing to produce their own matrix system. In the end three companies took on the work, Toshiba (QM), Sansui (QS) and Nippon-Columbia (QX), all being ‘based’ on the RM standard, but all three different, and therefore incompatible, if the idea of an accurate decode is wanted.

Different labels chose to go with their choice of system and albums were initially released in all three formats. There was also equipment for all three systems available in the market place, but quite quickly Sansui’s QS system won the day and became ‘the’ Japanese home grown matrix system.

What what of RM? There were releases on a few labels that actually state that the RM matrix system was used. Did the Japanese actually create RM encoders before QM, QS or QX came about? That would make sense because to demonstrate the idea of the matrix system that  had been decided upon as the basis of any future quad matrix system, there would need to be demonstration material.

It could be that some labels, eager to get in early, used the RM system for some early releases, before the format war began.

Fast forwarding to today, all of that leaves us in a little quandry, how to get the best out of the Four different matrices used in the early 1970’s. Unfortunately it has been almost impossible to find out exactly how QM, QX and RM worked, so we are left having to decode these albums using QS, which isn’t optimal or ideal if your after as accurate decode as possible.

But, until the day some information becomes available, it’s the bet we can do.

The reason i’m writing this is because of the next release, which i’ve finally given in after a few years holding back, has been decoded using QS. There are a number of Japanese releases that mention that it’s a 4-Channel LP, but say absolutely nothing else, which i’m suspecting could possibly be RM encoded. It’s interesting to note those albums were single inventory and any mention of them being quad was quickly dropped.

Seeing as the label who released this particular album was A&M, who went on to start using QS, you’d have thought that if RM and QS were compatible they’d have made a point by continuing labelling them, instead of removing any mention of them being quad.

I realise this is just my view on a rather complex issue, and there are other views, but all we are left with is an issue with very little to go on.

Ralf Nowy – Lucifer’s Dream – Updated

11 Jun

Have just made available a corrected version of the “Ralf Nowy – Lucifer’s Dream” release, which corrects an issue with the stereo track.

Web Radio Programme Broadcasting Quadraphonic Material

13 Aug

This may be old news to some of you, but there is an interesting radio broadcast on the internet that broadcasts quadraphonic material. The station broadcasts in mp3, so i’m not sure how well it decodes, i’m recording it as i type as a test, but it may be an interesting project for those so equipped

The radio station is here: http://radiomaxmusic.com

The program is broadcast twice on Sundays, at 9am and 9pm USA ET and is called “VINYL RESTING PLACE WITH WILLIE B

He broadcasts mainly in QS, which allows him to use 4-channel tapes he has, just listened to some unreleased quad mixes of ‘Paul Revere and The Raiders”

Hopefully you’ll be able to catch the repeat at 9pm USA ET.

Would be nice to hear of your views etc  🙂

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 PAM  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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