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Old 20th August 2009, 10:01 PM   #1
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Default Creating 5.1 Multi Channel sound from 2 channel

I have no idea where to post this, I have turned my stereo into 5.1 multi channel system. The source is a CD/SACD/DVD player. The front left and right go to aux inputs on my stereo pre-amp; the other outputs (left rear, right rear, center channel and subwoofer go directly to amplifier inputs. The DVD/SACD/CD player has a 'surround' mode which makes stereo CD's sound quite pleasing. I have decided that I would like to build a 5.1 channel preamp. I would like to include a processor that would turn 2 channel into a simulated 5.1 like my disc player does so I could have 5.1 sound from my turntable and FM. Does any body know of a circut that does this? Perchance there already exists a thread on this subject? I have looked but couldn't find any information.
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Old 20th August 2009, 11:57 PM   #2
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"Dolby Surround" from stereo is quite easy to do. But that is only extracting an ambience surround channel (a delayed stereo difference signal L-R).
The 0.1 part can be closely approximated by low-pass filtering a mono mix.

Getting 5 channels out of two requires digital signal processing. Not impossible, but not at all simple - hencce the paucity of DIY designs.
A lot easier to buy an outboard sound field processor.
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Old 21st August 2009, 01:44 AM   #3
andy_c is offline andy_c  United States
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Quote:
Originally Posted by jenkrich View Post
I have decided that I would like to build a 5.1 channel preamp. I would like to include a processor that would turn 2 channel into a simulated 5.1 like my disc player does so I could have 5.1 sound from my turntable and FM. Does any body know of a circut that does this? Perchance there already exists a thread on this subject? I have looked but couldn't find any information.
Hi Richard,

I don't know of any DIYAudio threads on the subject, but this PDF file from Dolby talks about the Dolby Prologic II decoder, which takes 2-channel stereo and generates 5.1 from it. There's also a decoder called "DTS Neo 6 music" that does a similar thing, and seems to be more well-liked than the Dolby method. There's a short thread here that discusses this. I may be able to dig out that AES paper they reference if you need it.

Last edited by andy_c; 21st August 2009 at 01:49 AM.
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Old 27th August 2009, 09:36 PM   #4
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Default Thanks Andy and Steerpike but here's my feeble idea.

I was thinking you might not have to do it digitally although digital would probably be superior. I am an old guy and you may not remember quadrophonic records but I do. What always struck me was how well 2 channel sounded when played through an SQ decoder. I found myself never turning off the SQ decoder when playing 2 channel athough it was simple to do. But the introduction of the center channel is a marked improvement over the older 4 channel with no center channel. Some of the older preamps had a center channel out. So my addled brain thinks why not do the same for the center channel and send the left and right signals to an SQ type decoder to generate Left Front, Right Front and Left Rear, Right Rear signals. Would this result in a reasonable 5 channel representation of the 2 channel? If I can track down an old SQ decoder or the circuit, I will be reporting back on this approach. If this is a really dumb idea, I'd appreciate someone telling me why before I get to deep into this project.-
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Old 28th August 2009, 02:07 AM   #5
star882 is offline star882  United States
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There are circuits that generate the extra channels for 5.1. They do not work as well as true 5.1.
http://sound.westhost.com/project18.htm
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Old 1st September 2009, 07:29 AM   #6
dangus is offline dangus  Canada
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It makes more sense to just get a surround receiver. Digital surround (pre HDMI) receivers are basically obsolete, and pre-digital (DD, DTS) more so. Either of those would do the job. Outboard surround decoders would work too, but those are less common. The trick is to find a seller that recognizes that this gear is obsolete and will sell it for a reasonable price.

Another option... use an obsolete(ish) PC with a 5.1 channel sound card like the SB Live. The Live has a header that can be used for an external volume up/down switch, so you wouldn't even need a keyboard/mouse to control it.
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