On Wednesday 10 May 2006 22:10, Perry Gilfillan wrote:
> I'm trying to understand the physical paths of the audio RCA
> connectors for tv-out on the PVR-350.
>
> My expectation was that the decoded MPEG stream audio from the
> cx2341x decoder is routed to the msp44xx sound processor. If this is
> the case then snd-tvmixer [ http://www.gilfillan.org/v3tv/ALSA/ ]
> might be able to control the volume. No joy yet.
No, the output goes straight from the MPEG decoder to the audio-out
cable. The mspx4xx controls the recording level for the MPEG encoder
(the audio input side).
>
> I did finally do the obvious 'Watch TV' test and find that
> snd-tvmixer DOES control the PVR-350's encoder audio. Changes to the
> volume in alsamixer are delayed by the latency introduced by
> buffering.
>
> I've found reference to using ivtvctl to control volume on the
> tv-out, but that only affects the encoding stream, not the tv-out.
>
> TV-out with X is working well. I'm not using the ivtvdev xdriver
> yet. There is no sound card, so patching the audio through another
> mixer device does not enter into the discussion.
>
> The system in question is running Gentoo. I've been running with
> kernel 2.6.14-gentoo-r4 and ivtv-0.4.0-r3. I've just installed
> gentoo-sources-2.6.16-r7 and ivtv 0.6.2 from svn. The newer versions
> have the same result that ivtvctl and snd-tvmixer are unable to
> affect the volume at the tv-out connectors.
>
>
> The question remains, does the audio from the MPEG decoder go through
> any device on the PVR-350 that would provide volume control before
> reaching the RCA sockets?
>
> I saw nothing in fw-decoder-api.txt about volume. Does the cx23415
> MPEG audio decode stage provide any DSP functions?
No.
Well, that should clear up things :-)
Regards,
Hans
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