[linux-audio-user] spdif output clicking noises

[Joshua Boyd]

On Mon, Aug 28, 2006 at 07:51:14PM +0100, Andrew Lyon wrote:

> When playing media using mplayer or xine,  and outputting using
> ac3/dts passthru spdif, if I pause and resume playback, or seek, there
> are brief, horrible clicking noises when playback resumes,  I assume
> this is because the stream is interrupted and resumes wherever it left
> off, so it outputs some garbage data that causes the noises.
> 
> Is there any way to prevent this? Perhaps it is possible to make alsa
> dump the first 1/2 or even 1/4 second of audio that is played? That
> would avoid the noises and I  could live with a slight delay when
> playback  starts.

It is in part a problem with your AC3/DTS decoder.  I have a creative
labs decoder (surround sound speaker set of some sort of built in
AC3/DTS decoder), and it has terrible clicking/cracking/popping sounds.
OTOH, the Dolby Digital decoder (Dolby DP564, a 2U reference decoder),
generally does not have such trouble.

You may be right about it being caused by garbage in the signal upon
restart.  At least, such garbage would cause such trouble.  If so, just
dumping the first 1/4 second or whatever won't automatically fix it,
since that could be throwing away the garbage, then likely the start of
the next AC3 or DTS packet as well.  A better solution would be to
intelligently not transmit incomplete AC3 packets, which means it isn't
quite a true pass through anymore.

I suggest you take this to the mplayer or xine mailing lists.

-- 
Joshua D. Boyd
jdboyd at jdboyd.net
http://www.jdboyd.net/
http://www.joshuaboyd.org/