Hi folks.

I'm just curious...I have an old JVC amp in my basement, which has speaker connections for surround sound (front pair, rear pair, and center). This amp was built in the 90s sometime, and has nothing but 2 channel analog inputs for the various sources.

My question is...what was the point of surround sound (and/or Dolby) if there were only 2 audio channels? What, exactly, got fed to the rear speakers and the center speaker? How did it differ from the 2 primary channels?

I mean, today, if you listen to something today w/ 5.1 audio, there are several (4/5/6?) different audio streams, right?

Thanks!

Your receiver was designed to handle Dolby Surround, an analog, 2-channel matrixed surround system. The center and surround channels were matrixed into the 2 channel signal and extracted by the Dolby Surround processing. By the 90s it was probably Dolby Pro logic that did the processing.

Do a search on "Dolby Surround Sound."

Your JVC has a Pro Logic decoder. Here's an article (http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/208_Dolby_Surround_Pro_Logic_Decoder.pdf)I wrote about Pro Logic in 1988. It has more details on page 1-2 explaining how the sound was encoded into a 2-channel signal.

My question is...what was the point of surround sound (and/or Dolby) if there were only 2 audio channels? What, exactly, got fed to the rear speakers and the center speaker? How did it differ from the 2 primary channels?There's more than one way to deliver multi-channel sound. Consumers here in America were introduced to surround sound via quadraphonic tapes and vinyl records in September of 1970. That's almost a quarter century before consumers would get discrete multi-channel on laserdisc. By the mid-to-late 1980s, Fosgate and Lexicon were selling 7.1-channel pre-pros. Keep in mind that DD and DTS 5.1 soundtracks were still 8 years away. So what were people doing with surround set-ups when the delivery media of the time could only handle 2 discrete (and I use that term lightly) channels? Well, they were listening to a couple of things.

Turns out that multi-channel sources could be matrixed into stereo for delivery and backwards compatibility. You essentially fold the original 4 or 5 channels down to 2, using specific encoding techniques. Upon playback, apply the proper decoder (or something close enough) and you recover the original multi-channel mix (or something close enough). Your JVC probably had a Dolby Pro Logic decoder built in, for use with Dolby Surround encoded movies.

The other thing folks were listening to in surround was 2-channel music. Remember, it's music (not movies) that introduced consumers to surround sound back in the '70s. Quad was an encode/decode process. But later surround processing (from companies like Fosgate, Lexicon and Meridian) was designed for un-encoded stereo material.

The recipes vary, but there's a common method when it comes to surround processes. If you listen using only 2 speakers, you'll notice that lots of sounds tend to phantom image in the centre of the soundstage. With surround sound, a circuit looks for those correlated (in-phase) mono sounds and steers them to centre speaker. That's where you'd hear those sounds from anyway. When listening with 2 speakers, you'll also notice that some sounds tend to image outside the front soundstage. On a surround set-up, the processing looks for those decorrelated (out of phase) sounds and steers them to the surround speakers. The surround decoding in your old JVC works similarly.

So, there's enough information in 2 channels of sound to support more (way more) than 2 speakers. The more speakers you map that content to, the less you rely on phantom imaging. The less you rely on phantom imaging, the more stable your soundfield. And that's "the point" of listening to 2-channel material in surround (to answer your original question).

Thanks for the replies everybody.

So, to paraphrase, there actually were more than 2 channels in the audio, but they were encoded into 2 streams, correct? And they did this with analog signaling?

That's really funky. I'm a software developer and deal w/ digital audio data, so the idea of encoding analog audio like that seems foreign to me.

Would such an amp be useful today? Do today's devices (ie. a DVD player) encode their analog outputs for Dolby (pro logic) surround, assuming the source material is 5.1?

So, to paraphrase, there actually were more than 2 channels in the audio, but they were encoded into 2 streams, correct?The multiple channels were matrix encoded to 2 channels (not 2 streams). And they did this with analog signaling?Yes, all analogue at first. But, by the mid 1980s, 2-channel (CD quality) digital audio was becoming available on laserdiscs. Studios also started converting their mixing facilities from analogue to digital production. That's really funky. I'm a software developer and deal w/ digital audio data, so the idea of encoding analog audio like that seems foreign to me.Most people were introduced to surround sound during the discrete multi-channel era (mid-to-late '90s onward) and have no idea that it goes back 40 years. Would such an amp be useful today? Do today's devices (ie. a DVD player) encode their analog outputs for Dolby (pro logic) surround, assuming the source material is 5.1?Doubt such a decoder would be useful these days. DVD players can output any soundtrack as 2-channel analogue audio; some players even give you the downmix options (Dolby Surround encoded or plain stereo). But why would you want to listen to a 2-channel downmix when the original multi-channel mix is available?

Most people were introduced to surround sound during the discrete multi-channel era (mid-to-late '90s onward) and have no idea that it goes back 40 years.

My first multichannel system was a Lafayette Radio Electronics 4-channel surrond system that decoded CBS SQ and Sansui SQ matrix vinyl records. No logic steering, just the modified Hafler decoding. Sounded pretty awsome back in the 70's.

I later experimented with adding a standalone Dolby Pro Logic Decoder to my Carver Sonic Holography system. Talk about a far out experience! Jimi hendrix was all over my room and I didn't need drugs or anything. :cool:

Its been all downhill since into the depths of Dolby True HD and DTS HD-MA. :D

upgrade

I later experimented with adding a standalone Dolby Pro Logic Decoder to my Carver Sonic Holography system.Wow, combining interaural crosstalk cancellation with matrix decoding, the soundstage must have wrapped around the room. I likewise experimented with different surround processing for music (movies remain a distant second priority). Tried Yamaha, Fosgate, Meridian, before settling on Lexicon (good processing + lots of customizable parameters).

Having lived with surround sound well before discete multi-channel, it's interesting to read some of the comments from recent converts. Most don't realize that consumer surround sound is almost 40 years old, or that 7.1 isn't anything new (introduced 23 years ago). Folks think "stereo" means 2 channels (was originally 3 channels when Bell Labs was developing it in the early 1930s) and that the centre channel was meant for dialogue (first used on Disney's 'Fantasia', hardly a dialogue driven film). Its been all downhill since into the depths of Dolby True HD and DTS HD-MA.LOL. You know how vinyl playback made huge improvements after CDs came out? Same with surround processing; some of the biggest improvements happened after (because) discrete multi-channel came out. Add to that the ability to have bit-for-bit copies of studio masters on Blu-ray, and I think we're in a golden age for home audio. It's really never been better.

Wow, combining interaural crosstalk cancellation with matrix decoding, the soundstage must have wrapped around the room. I likewise experimented with different surround processing for music (movies remain a distant second priority). Tried Yamaha, Fosgate, Meridian, before settling on Lexicon (good processing + lots of customizable parameters).

Having lived with surround sound well before discete multi-channel, it's interesting to read some of the comments from recent converts. Most don't realize that consumer surround sound is almost 40 years old, or that 7.1 isn't anything new (introduced 23 years ago). Folks think "stereo" means 2 channels (was originally 3 channels when Bell Labs was developing it in the early 1930s) and that the centre channel was meant for dialogue (first used on Disney's 'Fantasia', hardly a dialogue driven film). LOL. You know how vinyl playback made huge improvements after CDs came out? Same with surround processing; some of the biggest improvements happened after (because) discrete multi-channel came out. Add to that the ability to have bit-for-bit copies of studio masters on Blu-ray, and I think we're in a golden age for home audio. It's really never been better.

Nonsense. I'd rather have 4 synchronized records to be the 7.1 soundtrack for bluray. THAT would be a leap forward! :p:eek::D

I think I watched more movies way "back in the 90s" in PL than I have ever watched in DD5.1.

I was in Jim Fosgate's Utah theater last week. The entire signal path from the phono preamp thru the Pro Logic II to the crossovers and power amps is entirely tubes. He played Take 5 from a remastered vinyl pressing and the drum kit's dynamics and sense of palpable shimmer on the cymbals floored me. It sounded like they were sitting there playing.

Nary a single DSP in the pipe. Amazing, that old time technology!

Wow, combining interaural crosstalk cancellation with matrix decoding, the soundstage must have wrapped around the room.

Yes, but only if you locked your head in a vise. :eek:

I think I watched more movies way "back in the 90s" in PL than I have ever watched in DD5.1.

Ditto....I watched a TON of VHS "surround sound" movies back in the day...good times...:)

My first multichannel system was a Lafayette Radio Electronics 4-channel surrond system that decoded CBS SQ and Sansui SQ matrix vinyl records. No logic steering, just the modified Hafler decoding. Sounded pretty awsome back in the 70's.

I later experimented with adding a standalone Dolby Pro Logic Decoder to my Carver Sonic Holography system. Talk about a far out experience! Jimi hendrix was all over my room and I didn't need drugs or anything. :cool:

Its been all downhill since into the depths of Dolby True HD and DTS HD-MA. :D

I sold quad systems at Radio Shack back in the 70's. I still have a set of Nova 7 and 8's from my old quad system.

http://www.radioshackcatalogs.com/catalogs/1973/

I sold quad systems at Radio Shack back in the 70's. I still have a set of Nova 7 and 8's from my old quad system.

http://www.radioshackcatalogs.com/catalogs/1973/

Cool site!

I had the Color Organ, page 16. I used four Solo-1s, page 35 for the reverb speakers with my Carver system. Nova-20 headsets, page 40.

http://www.radioshackcatalogs.com/catalogs/1973/Talk about audioporn! Nice site: good interface and nostalgic images. Thanx, worth bookmarking.