Is Dolby Digital "always" 24-bit /96khz ?

Is Dolby Digital "always" 24-bit /96khz ?

Post by dcaput » Sun, 25 Jan 2004 07:52:47

I purchased a SB MP3+ (USB audio device) for my Notebook PC that
includes an optical port. The packaging does not explicitly state that
I can use it to send 5.1 audio to my AC-3 decoder. Before I bought it,
I called Creative Labs tech. and got "weak reassurance" that it will
work (provided the software supports sending to the s/pdif device).
But before I open the box, I thought I'd check with the experts...

The next model up (Audigy 2nx) is promoted as supporting "24-bit/96khz
Surround Sound" and since the cheaper model doesn't say anything but
"Optical S/PDIF Output" does that necessarily mean it won't work?

(I apologize for the clueless nature of this question - I suppose I
could just spend the extra $50 but that, I'm afraid, is exactly what
they want me to do!)

- Dan C.

Is Dolby Digital "always" 24-bit /96khz ?

Post by +CrimsonLi » Sun, 25 Jan 2004 09:48:51

Your question is a common one, and its down to Creative and most other
soundcard manufacturers being a little coy about thier specifications. As
far as im aware the only consumer PC sound system that encodes standard 5.1
to SPDIF/AC3 is the Nvidia SoundStorm. Many cards offer what they term "Pass
Thru" where a pre-encoded AC3 stream be squirted straight out the SPDIF
connecter correctly, and if you have SPDIF in it'll pass straight through
(propper Pass thru) without being distorted or modified. Some cards (notably
missing on Nvidia's SoundStorm) even have AC3 decode, where they can pull
pre-recorded AC3 streams off DVD's, MP3's or their SPDIF input, and then
output it as 5.1/6.1/7.1 analogue (or their own custom digital signals).

So unless the sound you are sending from your SB MP3+ is a pre-encoded AC3
stream (such as when playing a DVD) all you are going to get from your AC3
decoder is glorious stereo! While various members of the SoundBlaster
family quote 24bit/96kHz; they still cannot manage AC3 encoding, instead
outputting their digital signal via creative's own design of digital

Summary: Simple answer to your question, "will it work?", the answer im
afraid is no!



Is Dolby Digital "always" 24-bit /96khz ?

Post by dcaput » Tue, 27 Jan 2004 02:06:13

I think what you're saying is that it WILL work for DVD playback.

If all I want to do is to play DVD's and WinDVD has an "output to
s/pdif" option, are you saying that the MP3+ will send the raw AC3
output to my external decoder and allow me to enjoy 5.1 surround sound
for a DVD? If so, then what's all this hype about 24-bit/96khz?

Is Dolby Digital "always" 24-bit /96khz ?

Post by +CrimsonLi » Tue, 27 Jan 2004 04:19:05


For the average PC owner 24bit/96kHz is as you rightly suspect, hype. For
the professional user 24/96 does offer increased resolution, and gives you
more slack to play with when mixing or modifying (re-sampling) anything you