Re: [Alsa-user] Re: Still no sound with raw AC3 and intel8x0

[Dominique D. <dom...@fr...>]

Clemens Ladisch <cl...@la...> writes:

>> > Does it work if you play a stereo PCM stream to hw:0,2?
>>
>> Yes.
>>
>> A DTS stream also works (although my amplifier recognizes it as a DTS
>> stream from a CD audio, not from a DVD).
>
> That's strange, there should be no difference between DTS and AC3 as
> far as the sound card is concerned.

Yes. Moreover, the DTS stream is detected as coming from a CD (albeit
at 48Khz, go figure).

That makes me wonder how a yamaha amplifier (DSP A1) is able to
detect whether a DTS stream is coming from a CD or a DVD.

I guess that some flag is present is the DTS from DVD stream that is
missing (unset) in the DTS from CD stream. 

I (also) guess that this flag is mandatory for AC3 stream that can
only come from DVD (well, that's the point of view of my amplifier).

I guess (again) that the stream from my nforce board does not set this
mysterious flag. So only PCM and DTS (seen as coming from a CD) is
working. AC3 without this flag is rejected by my amplifier (this would
explain why I sometimes hear a very short scratchy (may be a short
lived white noise) when I start to play the AC3 stream from ac3dec.

That's a lot of guesswork.... I'll try to find some data regarding DTS
in SPDIF encapsulation. 

AFAIR, the DTS on CD is a hack and a CD player is tricked into
believing that DTS is regular audio. The DVD forum did not accept this
hack and required a specific flag that was later introduced in DVD
player. That's why early DVD player are not DTS compatible.

HTH