[mythtv-users] Occasional metallic sound when recording

[Joseph A. Caputo]

On Wednesday 22 October 2003 20:14, Eloy A. Paris wrote:
> Hi,
>
> I sent the message below to the alsa-devel mailing list. One of the
> responses (see below) suggests it might be a problem in MythTV. I
> doubt it but I just wanted to post here to see if anyone has
> experienced something similar. I searched the archives and didn't
> find anyone reporting a similar problem. This is very annoying, and I
> would really like to solve it because I've recorded several programs
> that are hard to understand because of the metallic noise.
>
> Thanks for any pointers.
>
> Eloy.-
>
> ========= Original message =========
>
> Date: Wed, 22 Oct 2003 12:22:19 -0400
> To: alsa-devel at lists.sourceforge.net
> Subject: Occasional metallic sound when recording (cs46xx)
>
> Hello,
>
> I am trying to troubleshoot a very annoying problem I have with a
> Santa Cruz Turtle Beach (cs46xx). Sometimes, when recording, the
> recorded sound is very metallic. If when I get the metallic sound I
> run alsamixer and toggle the capture facility of the ADC on and off,
> sound is fixed and back to normal.
>
> This problem happens randomly but is very annoying, specially if I
> program my PVR (MythTV) to automatically record a show - the show can
> get recorded with metallic sound, which makes it very hard to
> understand during playback.
>
> This is not MythTV-specific since I have been able to reproduce the
> problem using other applications, like the Gnome sound recorder. It
> is unrelated to full-duplex operation since when recording a show
> MythTV doesn't open /dev/dsp for writing.
>
> I really have no idea about how to troubleshoot this. I don't think
> the problem is hardware, but is driver-related instead.
>
> Any suggestions? Are there any debug switches I can enable to get
> more information about the problem? I can recompile the drivers and
> try anything. I really want to see this fixed, so if anyone has any
> ideas to try just let me know.
>
> ========= One reply =========
>
> its almost certainly a software problem in mythTV and gnome sound
> recorder. i've written code that does this several times - every time
> it takes me ages to figure out why, and then i can never remember
> when i do it the next time. its related to off-by-1 errors in
> processing incoming audio.
>
> not necessarily, of course, just a point of view.



I also have a CS46xx-based sound card with ALSA drivers, and have 
experienced something similar regarding the 'tinny' sound.  Mostly I've 
noticed that if another process has the sound card open when I fire up 
either the frontend or the backend, then I get the metallic sound on 
either playback or record, respectively.  To correct the situation I 
have to restart the Myth process after closing the 3rd program.  Note 
that my soundcard (and probably yours, too) supports multiple 
simultaneous opens, so if another process has the sound card open it 
doesn't necessarily hang Myth as happens with other sound cards when 
people, for instance, forget to disable aRTs.  I don't know if it's a 
driver issue or a hardware issue, but I'll bet if you make sure nothing 
else is accessing your dsp device when you start Myth (or probably more 
accurately, before Myth does an 'open' on the device (like when 
starting a recording, playback or MythMusic session)), you'll probably 
see this problem disappear.

-JAC