[mythtv-users] Audio tuning advice needed

Håkon Alstadheim hakon at alstadheim.priv.no
Tue Jun 10 08:14:53 UTC 2008

Lonnie Borntreger wrote:
> Got a question dealing with the tuning of the capture - as related to 
> the audio part.
> Occasionally, a show will "pump the volume" and it results in "choppy" 
> audio... kind of like something is "clamping" the level.... like a 
> automatic gain control.  Is there something I can change in the stream 
> encoding options in MythTV to eliminate this, or is it completely 
> hardware/driver related?
> Oh, I have all PVR-500s (one Philips, one Samsung) - but they both 
> have this same issue.  Like I said, it doesn't happen often, but it's 
> really annoying when it does.
> Thanks,
> Lonnie Borntreger

In my experience that is most likely a weak/noisy signal resulting in 
rapid switching between mono and stereo. This could also be a driver 
issue, either a bad tuning algorithm or a too trigger-happy switching 
between mono and stereo. I have resorted to forcing mono. For me in 
Norway using the saa7134 driver, the incantation involves putting 
something like:

options saa7134 audio_ddep=4

into /etc/modprobe.conf. The exact value depends on what tv-standard you 
are receiving. Take a peek in the source, or just run through a series 
of edit/modprobe/dmesg -c/rmmod, going throug all the values. The dmesg 
will tell you how the parameter is interpreted, at least if you set 
audio_debug=2  in the options.

Håkon Alstadheim
47 35 39 38

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