[mythtv-users] 32khz AC3 Streams was: Sound problem with AC3 passthrough

[Nick]

On 15/06/06, Steve Hodge <stevehodge at gmail.com> wrote:
> On 6/15/06, Rob Baumstark <rbaumstark at gmail.com> wrote:
> > I'm convinced that this is either an issue with MythTV's AC3 handling
> > (and there's discussion over in the -dev list about passthrough too,
> > though it doesn't touch this particular issue with it), and/or an
>
> But the same issue occurs with mplayer, right? So it's not MythTV at fault...
>
> > issue with my sound hardware - other cards may be able to pass the
> > 32khz AC3 properly (I base this on the ALSA sound cards page I
> > mentioned earlier in this discussion - I have no proof of any card
> > actually doing this properly though).
>
> Either the hardware or ALSA or the ALSA drivers.

I've just spent a while playing with this to see if I have the same
problem (NF3 board, CN8S/ALC850 audio) and I do.

I did come across the useful iecset tool, and managed to set my SPDIF
to 32000Hz, but it stayed 'rate locked' per the output of iecset and I
still got the accelerated and stuttery AC3 audio. My amp is definitely
detecting Dolby Digital material, but it breaks up every half second
or so.

I'd guess it's the ALSA driver causing the limitation unless it can
query the IEC958 part of the card for its capabilities, but if there
was an easy way to directly query the soundchip for its SPDIF output
rates I'd like to check it out. Another of my SPDIF equipped systems
(using the atiixp driver) does not state that audio is resampled to
48kHz as the ALSA docs do for the intel8x0 driver, so maybe this might
work? I don't get any 32kHz audio at the moment, but it would be nice
to know whether it's supported nonetheless.

Nick
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