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Old 21st Sep 2020, 12:30 pm   #1
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Default Surround Sound Experiments?


Whilst listening to "Pick Of The Pops" from September 1973 this morning I was looking through the magazines that were on the newsagents' stall that date, and in "Practical Electronics", the P.E. "Rondo" Surround Sound System was introduced.

I've only just downloaded the construction plans now, but is it feasible to take a standard stereo signal input from a phone, PC, tuner, and "encode" it into a "pseudo–surround" system, or does the original material have to be "SQ" or "4Q" encoded from the start?

Anybody got some links to circuit ideas, projects, etc?

Chris Williams
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!
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Old 21st Sep 2020, 2:38 pm   #2
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Default Re: Surround Sound Experiments?

The SQ and QS systems are described as ambisonics. You do need encoded material to
obtain the optimum effect although signals can be derived from a stereo source.

I built a 4 channel amp in 1977 and I used the basic matrix circuit (MC1312 IC) although
more elaborate logic switching circuits existed. The only SQ disc I had was "Dark Side of
the Moon" which did sound different to the standard stereo version.
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Old 21st Sep 2020, 4:07 pm   #3
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Default Re: Surround Sound Experiments?

Originally Posted by Chris55000 View Post
...Anybody got some links to circuit ideas, projects, etc?...
Hi, if you want to experiment with pseudo surround/4 channel the Hafler circuit is very simple and can give some interesting results when listening to synthesizer music ("Only You" by Yazoo or some early Depeche Mode tracks are worth trying)

The Hafler circuit is nothing more than a second set of speakers, placed at the opposite end of the room to the main ones, with the negative terminals connected together, the positive terminals then being connected to the corresponding left and right stereo channels - this provides out of phase information to the rear speakers.

I believe that some BRC music centres used a similar circuit with additional switching to allow the second speakers to be used as second room speakers if required instead of rear "surround" speakers. I think a couple of limiting resistors may have been included in the left and right channel positive connections when the circuit was switched to surround.

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Old 21st Sep 2020, 8:22 pm   #4
dave walsh
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Default Re: Surround Sound Experiments?

That's interesting Andrew. I found out about the Hafler system in the seventies when Sony was failing with their "4 Channel" surround sound product. New equipment and compatible new records required I could never see the attraction. Lots of people seemed to be trying to create their own solid state equivalent for "ordinary vinyl" but the theory baffled me, never mind the construction!

The basic Hafler [I think I saw it in Wireless World] was so simple by comparison and 'cheep', as you were mainly recovering out of phase mid range frequencies, so Hi Fi Speakers were not required. My Heath Robinson stereo was a Garrard SP25 Deck, one channel through the Tape Recorder Audio section [it had a PA input] and the other via one of Mr Sinclair's IC boards into home made boxes containing surviving speakers from a burnt out stack. For surround sound, I re-cycled two car Spkrs [the ones encased in a plastic moulding]-not even proper cabinets. They were easily concealed behind the sofa and single wired [in series] from the L+ to R+ terminals. Apparently you could insert a pot as a balance control but I didn't bother with that.

It seemed to work very well but was somewhat random as it depended entirely on the Studio Microphone layout and the amount of 180 degree info they'd picked picked up on the day! My best result was with the Beach Boys LP "Surf's Up" which was a very early warning about the environment. You could hear water lapping behind the sofa at the back of the room. I was told that the Beatles Abbey Road album was very effective as well but I didn't have that on vinyl-only R to R.
I say this because I understood that the system only worked with vinyl records but maybe that's not true? I notice that a vinyl source is the only one that Chris didn't mention but that's probably a coincidence. Vinyl or not, it's so very easy to experiment with this simple but rewarding circuit. I plan to go back to it soon.

Dave W

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Old 21st Sep 2020, 8:41 pm   #5
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Default Re: Surround Sound Experiments?

I seem to recall most of the German setmakers did something here.
NordMende had their "Quadronado" as I recall. Korting had a model 7404 which I am fairly sure was Quado. One model down was the 7402 (I bought one new, still have it) and that had a (volume controllable) Haffler output.
Never had and Quado stuff or material, so can't offer more than that.
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Old 21st Sep 2020, 10:24 pm   #6
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Default Re: Surround Sound Experiments?

Originally Posted by dave walsh View Post
I was told that the Beatles Abbey Road album was very effective as well but I didn't have that on vinyl-only R to R.
I say this because I understood that the system only worked with vinyl records but maybe that's not true?
The Hafler system works with any stereo source. As a youngster I remember creating a recording system where we tried to use a microphone as a rear channel microphone by connecting it across the positive inputs of the main stereo microphones (everything was unbalanced). It worked amazingly well when played back through a Hafler system.
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Old 21st Sep 2020, 10:29 pm   #7
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Look up the Roland Spatial processing system; phenominally expensive, but oh so good.

The demo I heard was a fly buzzing around the room, which then flew into you.
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Old 22nd Sep 2020, 1:39 am   #8
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Default Re: Surround Sound Experiments?

The Oxygene by Jean-Michel Jarre LP was another good one for quad systems.

Although not recorded in any of the 4 channel formats, some of the sounds and instruments rotate around the sound stage at various points during playback.
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Old 22nd Sep 2020, 7:44 am   #9
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Default Re: Surround Sound Experiments?

I once played around with surround sound, I built a sound "processor", It took the low level preamp out signals.
Basically left and right channels were not modified and just amplified, that was front right and left. The front centre channel was left plus right.
The rear channel was Left minus Right but I used a bucket brigade delay line to move the rear sound back and give the apperance of distance.

It sounded pretty good.

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Old 22nd Sep 2020, 8:21 am   #10
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Default Re: Surround Sound Experiments?

SQ quadraphonic has been a lockdown project of mine. It kicked off when I found that one of my classical LPs was actually SQ compatible. Initially I used software to decode a stereo .wav into a Dolby digital .ac3 to play through my AV system. I then obtained a Sony decoder which gives even better results and my SQ LP collection has steadily grown.

It's actually rather better than its reputation and it's a pity that they couldn't have all agreed on a single system.

As regards pseudo quad I prefer to leave the Sony set to SQ mode rather than its dedicated 2>4 setting. But as others have said it's rather recording dependent and straight stereo is often preferable.

The PE Rondo uses basic decoding without logic so front / rear separation is poor, but the article does explain how this can be improved with logic etc in commercial designs.

See here for a modern decoder/synthesiser:

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Old 22nd Sep 2020, 9:03 am   #11
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Default Re: Surround Sound Experiments?

The Hafler arrangement was a pair of rear speakers connected differentially across the hot side connections to the front speakers, but it was usual to add a meaty wirewound variable resistor from the junction of the rear speakers to ground.

With this set to zero Ohms, the rear speakers became duplicates of the signals from the front pair. As the variable resistor was brought up, the rear signals became more and more the differential signal and they also usually became quieter. So the variable resistor acted as a level control for the rear speakers, you got more volume out of them, but at the expense of less 'separation' So you set it to suit your own preference.

David Hafler, by the way was also the designer of the ST70 amplifier which seems to have legendary status, as well as the DH200 Mosfet job which was the step above the endless clones of the Hitachi applications note clones.

Back in the day there were three 'quadraphonic' or 'surround-sound' systems being marketed.

CD-4 was by RCA and it really worked! Essentially it used a multiplex technique like stereo FM radio to carry two separate signals on each stareo channel of a stereo-cut record. Because the zenith pilot-tone system essentially stacks a difference signal in a band of frequencies higher than the normal audio, CD-4 records had to be cut at low speed, and than they required something really, really special in the line of pickup cartridges and styli. The records wore out. Even with the special stylus/cartridge, the high frequency content of the groove got steam-rollered and worn off. So the records eventually degraded to stereo, by losing the front-rear difference signal.

SQ and QS were rival 'matrix' systems. Compared to CD-4, they didn't really work. They produced a bit more effect than the Hafler circuit, but there was no way you could record an orchestra and reliably hear where all the things were around you. Occasionally, some recordings produced some dramatic results. As said, synthesiser tracks could be interesting. What these systems did do is to thicken the sound out somewhat, making it not sound like coming from somewhere on a thin line between your front speakers. I still have my SQ copies of Dark Side of the Moon and Atom Heart Mother. They were different mix downs, so even on plain stereo gear they sound different to the originals.

SQ was Sony/CBS in cahoots. Sanyo was in the QS camp.

The choice was between two systems that didn't actually work and one much more expensive system that worked for a small number of playings until your record wore out.

Joe public voted with his feet, and picked stereo. Two channels, no monkey business.

Meanwhile other people mucked around with logic trying to get clues from the recorded music and to then try to direct the sound to come from the direction it thought it must have come from. It produced better results than the plain matrix SQ and QS varints on some tests, but then that was the criterion the logic enhanced matrix systems had been designed for.... quelle surprise! On other stuff, it was sometimes OK, but often no better. Joe public stuck to stereo. Joe had it right.

Calrec did their soundfield microphone and it really could detect differences in angle of arrival. Mikeing-up multidimensional sounds and also sticking speakers in appropriate places were not the problem. The whole business die because of the issue of trying to squeeze three or more channels of information into what used to carry two without any loss of quality.

Long before the VHS-Beta wars, the home entertainment industry gave itself a lesson it clearly forgot.

I tried the Hafler circuit, and an SQ matrix chip as well a smaking my own matrix circuit. I bought a few SQ discs. CD-4 was out of my financial reach. I built a 4 channel amplifier...

Then I went back to plain old stereo.

Hifi News did publish a rather good review of Ummagumma, especially about "Several species of small furry animals gathered together in a cave and grooving with a pict" If any track ever said that a record producer was having a hard time scraping up enough material to fill a double album, this has to be it! I certainly dare not play it here in Scotland for fear of it being overheard and misinterpreted. This is no hardship, hearing it once in a lifetime is enough.


* It is, after all, the Llanfairpwll.......... of record track titles.
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
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Old 22nd Sep 2020, 4:04 pm   #12
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Default Re: Surround Sound Experiments?

I must apologise to the late David Hafler because I used his technique in my 1971 Vauxhall Viva Estate, but didn't know about him until now.

I knew the technique as "Ambience Recovery".
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Old 23rd Sep 2020, 6:24 pm   #13
Sean Johnston
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Default Re: Surround Sound Experiments?

I first tried the Hafler circuit as a kid nearly 50 years ago with my first stereo cassette/tuner/turntable, and have used it again consistently for the past couple of years with digital sources. To my ears, it generally improves the average recording - sometimes remarkably so - but with variable effects.
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