[Arny Krueger]

"ChrisCoaster" wrote in message


Just wanted to clear up a few facets on how the most
widely used digital discrete-5-channel surround sound
format works.

First, is the maximum bit-rate around 196kbps per
channel, or is that the summed bitrate of all channels
combined?

Do the math. Dolby digital runs over the same kind of digital channel as 48
KHz 2-channel PCM.

I have an audio DAC that will lock up on a DD digital stream. It reports
that it is 48 KHz 2-channel PCM. It puts out some pretty good white noise.

Total bitrate = 2 * 16 * 48 KHz = 1536 kbps.

However, while there are 6 discrete channels, one of them has a very low
data rate, because it is sharply low pass filtered.

1536 kbps / 5.1 = 301. kbps

1536 kbps / 5 = 307.2 kbps

Next, if I understand correctly, Dolby Digital does not
run all 5 main channels at the maximum bitrate at all
times. Does this mean it "pools" the maximum bitrate for
the *busiest* channel(s) at any given point in the
soundtrack?

What you are asking is whether DD is VBR.

DD can be VBR. Standard decoders can handle the feature if it appears in the
bitstream.

And what is the lowest bitrate a "quiet"
channel allowed to run at?

It's not about quiet, its about complexity. But of course a totally dead
channel has zero complexity = essentially zero data rate.

Finally, is the LFE(sub) channel running at a fixed
bitrate that doesn't vary like the 5 mains?

AFAIK, the LFE can be VBR as well.