Adding ambient rears ~ from stereo material

[rick57]

Not sure what is the right forum for this (now stated more clearly):

I believe that early “Dolby surround” decoders worked by: the signal difference between left and right channels (L-R) is taken, delayed electrically 15 to 30 ms, then sent to two rear speakers.

For synthesising rear ambient channels from stereo material, is it better to use Pro Logic or Pro Logic II, or not much difference? (I know there are more sophisticated decoding algorithms, but a low cost option will suffice to start with).

Does anyone use this for ambience “recovery” (synthesis) – is it useful?
Which types of music does it work well on?

Any advice appreciated

Richard

[Dick West]

You need to supply more info. Do you want to add active circuitry, spend more money, or are you looking just to get a cheap (passive) way to add ambience?

You are familiar with the early Hafler ambience circuit (Dynaquad)? It used the L&R amp to also drive a pair of ambience (L-R) speakers. This was a mono signal and the rear speakers were connected out of phase with each other. Many people felt this was good enough for some added ambience, depending on the music source's stereo mix.

Years ago I did just that, added the Hafler ambience hookup to a stereo amp. My rear speakers were placed in the rear corners of the room and laid on their backs so their sound had a little added delay from the ceiling bounce. Then, I used a pair of cheap graphics equalizers as buffers to derive a L+R signal that was fed to a second equalizer to derive a center channel feed and a low passed sub woofer feed. All my 5 speakers were identical and all their crossovers were identical (phase is very important) and they produced a nice open spacious sound -- especially with some older movies that had Dolby Stereo sound tracks. And, only two stereo amps were required!

If you want to experiment with other ambience effects, get a receiver and try out the wide variety of choices such as Dolby Pro Logic, PLII (the digital improved DLP sound), or try the Cirrus Surround Sound, etc., etc.

There is a wide variety of surround sound processing algorythms available. You and your room and your speakers may prefer one over the other.

But, the question remains. Do you want cheap (passive) ambience retrieval or do you want to add active circuitry. Building your own DPL or other surround sound "black box" is not recommended as the main chips are not readily available and not cost effective to build.

[rick57]

Hi Dick

I’m after a “use sometimes” two extra channels for music. It would be way too expensive for me to match the sound quality of the front speakers and amps, in the rears.

I might start with the L&R amp to drive a pair of ambience (L-R) speakers, but given the price of old processors & receivers . .

I originally intended to just get a processor; but if I get a receiver - can many of them be hooked up to preamp-out, then bypass all receiver circuits for the front two (very high resolution) speakers, and synthesise & amplify the rear two?

I think I recall (from 10-15 years ago) some brands had a front bypass option. Does anyone know which companies or products did this?

Thanks

[rabbitz]

If you need a simple solution and can live with Pro Logic, one of the best would be the Yamaha DSP-E492 as it's only a processor with centre and rear amplification. The discrete amplifiers are of good quality, well made and better than most of the receivers, plus can handle low impedances.

There's minimal effects available which is no loss and you can adjust the delay in the rears.

You can pick these up off eBay very cheaply and sorry I sold mine years ago as was a great product.

http://www2.yamaha.co.jp/manual/pdf/...m/DSP-E492.pdf

[rick57]

Thanks rabbitz


that’s the best solution I’ve seen yet!

How well matched were your ambient rears to your front two?

What sorts of music did it work best on?

Cheers

[rick57]

That Yamaha looks a neat solution.

Anyone know if there were later similar units of any brand, using (adjustable parameters) DPL 2?

Cheers

[rabbitz]

I didn't use it on music except for the odd concert CD. It was just a solid well thought out device that was so flexible.

[rick57]

I could imagine it could be good for live CDs.

But I’m puzzled, if it was so flexible, and you rarely used it on music, what was it’s primary use?

Cheers

[audiobomber]

Originally posted by rick57
I believe that early “Dolby surround” decoders worked by: the signal difference between left and right channels (L-R) is taken, delayed electrically 15 to 30 ms, then sent to two rear speakers.

As far as I'm concerned, Dolby Pro-Logic is a disaster with music. It always sounds phasey and mushy. The best processing for music is the passive Hafler circuit. No extra amps needed either, all you do is connect a speaker or two across your main amp terminals in L-R configuration. There's a lot of info on the net, just Google it. e.g. http://sound.westhost.com/project18.htm.

I used a Hafler circuit, then I bought a Dolby PL receiver, which I quickly returned because my hafler setup was better. Eventually I bought a good 5-channel discrete system, which I've also dumped recently. I prefer stereo to m-c music, and I found too much rear info pulled my attention out of a movie.

I'm tempted to set up a Hafler system again. It provides a very nice sense of envelopment on movies (as opposed to discrete m-c where the rears don't necessarily have anything to do with the fronts). It's nice for some music, ie electronica, but I prefer stereo for most types of music.

[rick57]

So the Hafler is *better than Dolby PL? I thought they might be on a par. That’s the nail in that coffin – and I was about to get a Dolby PL processor on eBay.

Thanks for all the advice.

Cheers