On Wednesday 16 November 2011 18:28, Al Thompson wrote: The kind of Dolby surround encoding where you just hear a stereo mix if you don't have an encoder (as opposed to a blast of noise) isn't 5.1; it's more like "3.0", or maybe quad as discussed below. The surround channel is encoded by shifting its phase and adding it to the other channels. I've had albums that weren't recorded in surround but sounded that way with surround equipment because of various effects the producer used, such as Amarok by Mike Oldfield. I think you could encode a center channel too. When I was hanging out with a friend who works at a TV station when they first started broadcasting in surround, during the test pattern before a show with surround, a narrator would say "This is the left channel. This is the right channel. Center, and surround," with his voice coming out of each speaker appropriately if you had a surround system. (When we watched Star Trek on the sat feed, it was Michael Dorn doing the narration, which is why I still remember.) Rob

On Thursday 17 November 2011 17:28, Julien Claassen wrote: My memory was that the surround channel was added to one channel normally and to the other channel inverted, but the Wikipedia article on Dolby surround says it's phase-shifted 90 degrees in one and -90 in the other (and, apparently, multiplied by sqrt(2)/2). That's why I didn't mention specifics in my first post. But if you wrote a Csound orchestra to decode DTS noise into stereo, you certainly should be able to do it for plain old Dolby surround! Start messing with phase and adding channels together, and you ought to get something useful out of it. Rob

On Sat, Nov 19, 2011 at 04:11:42PM +0100, Julien Claassen wrote: No surprise. You can't mix 3 (or more) signals into 2 and recover them independently. To decoded your CD to surround you need a Dolby Prologic II decoder which consists of two parts: * A matrix recovering the missing channels (with lots of crosstalk from the others, but things are done in a way as to make this acceptable), * 'Logic' which detects the dominant sound directions and modifies the matrix to optimise for that. So in a movie you could e.g. have a gunshot or explosion coming only from the left surround speaker (most other sound would be pulled to that direction as well). This part is pretty useless for music. Jconvolver could easily do the matrix part. How the logic part is supposed to work exactly isn't described in any open documents AFAIK. For a music CD the surround channels would probably contain just room ambience and reverb. These are present in the stereo signals as well, at a lower level (as required for stereo) and mostly out of phase. The center channel is panned halfway between L and R by the encoding, there is no need to decode it except for film dialogue. So you can just listen to this in stereo and not miss anything. -- FA Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl.