It has become clear that my 5.1 channel to 7.1 channel expansion system based on an early surround processor is not working as I expected. When either left or right surround is playing by itself, BOTH back surrounds play at a somewhat reduced level. So the back surrounds are no longer stereo, as I intended.
I tried every control on my SSI System 1000 II processor, and nothing could change this.
I'm not actually sure I ever tested discrete 5.1 signals this way. I simply plopped in a 5.1 disc, and played it through the processor, not at all, or unprocessed, and decided it sounded "better" overall through the processor in a quick subjective test.
What may be happening is one of two things. Either the processor, now 35 years old, isn't working correctly. OR this is correct operation, and what I'm seeing is actually the result of "steering", the function that keeps a sound localized to a single speaker if it seems to be coming from one.
Steering is very appropriate if you're deriving side surrounds from a 2 channel signal, encoded or not. But I don't think it is really appropriate to deriving back surrounds from side surrounds. The backs should be pretty close to the same signal, only with a tad of blending...less separation than the sides, but not mono either. And possibly with a bit more delay. That's what I had hoped to get.
What I really need is some more interesting test material, that moves a virtual source from right side surround to left side surround, and then see what happens in the backs with some surround deriving process.
For now, but this doesn't seem quite right either, I'm duplicating the sides in the back for 5.1 material. I tried duplicating and not playing the backs at all, and decided I liked it with the backs if I set the backs to a much reduced level compared with the sides. This only seems to widen and pull the sides slightly to the rear from their roughly 90 degree position appropriate to a 7.1 system--the inherent incompatibility between 5.1 and 7.1 I discussed a few months ago thereby being somewhat fixed.
However, I'm using my SSI 1000 to adjust the level, from stereo inputs to front outputs. This is unavoidably removing the center information from the backs...which I'm not sure is a good idea either. A simple buffer with volume control might be better.
I tried every control on my SSI System 1000 II processor, and nothing could change this.
I'm not actually sure I ever tested discrete 5.1 signals this way. I simply plopped in a 5.1 disc, and played it through the processor, not at all, or unprocessed, and decided it sounded "better" overall through the processor in a quick subjective test.
What may be happening is one of two things. Either the processor, now 35 years old, isn't working correctly. OR this is correct operation, and what I'm seeing is actually the result of "steering", the function that keeps a sound localized to a single speaker if it seems to be coming from one.
Steering is very appropriate if you're deriving side surrounds from a 2 channel signal, encoded or not. But I don't think it is really appropriate to deriving back surrounds from side surrounds. The backs should be pretty close to the same signal, only with a tad of blending...less separation than the sides, but not mono either. And possibly with a bit more delay. That's what I had hoped to get.
What I really need is some more interesting test material, that moves a virtual source from right side surround to left side surround, and then see what happens in the backs with some surround deriving process.
For now, but this doesn't seem quite right either, I'm duplicating the sides in the back for 5.1 material. I tried duplicating and not playing the backs at all, and decided I liked it with the backs if I set the backs to a much reduced level compared with the sides. This only seems to widen and pull the sides slightly to the rear from their roughly 90 degree position appropriate to a 7.1 system--the inherent incompatibility between 5.1 and 7.1 I discussed a few months ago thereby being somewhat fixed.
However, I'm using my SSI 1000 to adjust the level, from stereo inputs to front outputs. This is unavoidably removing the center information from the backs...which I'm not sure is a good idea either. A simple buffer with volume control might be better.
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