[mythtv-users] "Squeaky" audio when using Plextor M402U

Rod Smith mythtv at rodsbooks.com
Mon Apr 2 02:39:53 UTC 2007


On Sunday 01 April 2007 20:08, Chris DiLorenzo wrote:
> I'm using a Plextor M402U to capture from DirecTV.  I am running Gentoo
> with the 2.6.18 kernel.  I patched the Go7007 drivers and was able to build
> them with no problems.  When I use the gorecord application, I am able to
> capture video with no problems.
>
> However, when I use MythTV (ver 0.20) I can capture shows, but the sound is
> horrible.  There is this annoying high pitched hum or squeak and the voices
> are distorted.  It is not my frontend  system since the distortion occurs
> when I play the files with mplayer directly on the bcakend.
...
> If you want to hear an example, you can download a nuv from
> http://home.comcast.net/~dilorc/Bad_MP3.nuv

That sounds very similar to the problem I had with an AVerMedia AVerTV M150-D, 
which is a PCI MPEG-2 capture card. I eventually found a solution, as 
detailed on the MythTV wiki entry for that card and on the MythTV wiki sound 
troubleshooting page:

http://www.mythtv.org/wiki/index.php/AVerMedia_M150-D
http://www.mythtv.org/wiki/index.php/Sound_Troubleshooting

In brief, the solution was to use an external channel-change command that uses 
v4lctl to do the job. I hypothesize that the stream provided by the card 
becomes unstable when the channel changes and that MythTV tries to access the 
data stream too soon, causing it to corrupt the audio for the rest of the 
recording. Using an external tuning command introduces enough delay to 
correct the problem. This is, however, just speculation on my part, and I 
can't be sure that you're seeing the same problem. If my fix does the job for 
you, though, I encourage you to edit the sound troubleshooting wiki entry 
appropriately and add a note about this to the M402U entry (there are two, 
actually; one is titled for the Plextor ConvertX).

-- 
Rod Smith
http://www.rodsbooks.com


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