Kind of shifting the topic back to some older comments a bit....
In the discussion in this and other threads, about getting audio from the
AC3 on
PBS and other channels, there have been some comments about the possibility of losing dialog, if you just take the R/L channels, since apparently from some sources, dialog comes mainly out of the center channels.
I've seen this happen a couple times in the past (not from PBS), but have always had pretty good luck using either the Soundblaster Extigy or the Sonic Voom headphone decoder.
However I've run into a satellite example that does seem to have the dialog coming out of the center channel. On another forum, I've been involved in a discussion about the audio that accompanies the CBS NFL games, either OTA, via NFL Sunday Ticket, Dishnet/DTV local channels, or raw satellite feeds. One person on this other forum doesn't like to listen to the dumb network sportscasters, but prefers to just hear the crowd noise. So what he does, is feeds the audio into a surround sound home theater system, but he unplugs the center speakers. He says that by doing this, he gets just the crowd noise, and very little dialog from the commentators.
I was curious about whether this was true from the raw sat feeds, so yesterday I was experimenting a bit with the AC3 audio from an NFL sat feed. Sure enough, on the NFL games, the majority of the dialog is coming over the center speaker. If I disconnected the center speaker, then I still got a little dialog coming through the R/L speakers, maybe 15-20% of the volume in the center speaker. However in the surround speakers, the dialog was almost completely missing. It was primarily crowd/stadium audio. However there seemed to be two big problems, with respect to using this as hoped.... when ever there WAS audio coming out of the other speakers, the volume level in the surround speakers seemed to go down significantly. This was kind of annoying. Also, when the commercials came on, it came BOOMING out of the surround speakers, which was REALLY annoying.
Anyway, I had hopes that separating out the surround speakers might filter out the commentator's dialog, but it doesn't really work very well. But this does show, that just extracting the R/L channels isn't always going to be a good solution for listening to AC3 audio, if the source is one like this where the dialog is found on the center channel.
I've never noticed a problem with the PBS channels, however, although I'm not sure if it's because the Soundblaster Extigy might mix the center/surround channels into the stereo output, when not using a surround system. I'm pretty sure that the sonic voom decoder doesn't do any mixing, so I guess that I just haven't run into any AC3 that has dialog on center speaker.