[mythtv-users] Yet another sound problem

[Kevin Kuphal]

David Wadler wrote:

> A few months ago, I set up Myth on my machine (2.4.x kernel on 
> Gentoo) and had lots of issues with sound.  Ultimately, I fixed it by 
> loading the tvmixer module.  I don't know why that fixed it, but as 
> soon as I loaded the module and restarted mythfrontend, everything 
> sounded good.
>  
> I had to wipe my drive (don't ask) and am now running a 2.6.6 kernel.  
> The new kernel made it very easy to get ALSA up-and-running and I'm 
> using it in Xine, mplayer, XMMS, and other apps.  However, when I set 
> Myth to use ALSA:default, I got choppy video (lots of prebuffering 
> messages) and audio that wasn't quite right.  It sounds clipped.  I 
> played with the mixer levels, and no matter how low I go, there 
> remains distortion.  I switched to /dev/dsp and /dev/adsp, both of 
> which work, but both of which have the same audio distortion.  In 
> addition to adjusting the levels with my soundcard, I also tried to 
> adjust the TV-Card's mixer, by doing alsamixer -c 1.  I can only 
> adjust the level attached to "Capture" and changing it doesn't have 
> any effect.
>  
> ALSA gives me great sound in my other apps and I'm fairly confident 
> that I have it set up correctly.  I don't know what I'm missing in 
> Myth.  I'd be okay with using OSS with Myth, provided I can get clean 
> sound.  Any ideas?
>  
> Loaded modules:
>  
> Module                  Size  Used by
> snd_pcm_oss            48932  2
> snd_mixer_oss          17344  1 snd_pcm_oss
> tvmixer                 4720  1
> snd_bt87x              11204  0
> tuner                  17356  0
> tvaudio                20428  0
> tda7432                 6924  0
> bttv                  143980  2
> video_buf              16516  1 bttv
> i2c_algo_bit            8904  1 bttv
> btcx_risc               3848  1 bttv
> i2c_core               18756  6 
> tvmixer,tuner,tvaudio,tda7432,bttv,i2c_algo_bit
> snd_via82xx            22208  2
> snd_pcm                84580  3 snd_pcm_oss,snd_bt87x,snd_via82xx
> snd_timer              20996  1 snd_pcm
> snd_ac97_codec         61444  1 snd_via82xx
> snd_page_alloc          8964  3 snd_bt87x,snd_via82xx,snd_pcm
> snd_mpu401_uart         6144  1 snd_via82xx
> snd_rawmidi            20128  1 snd_mpu401_uart
> snd_seq_device          6536  1 snd_rawmidi
> snd                    46564  10 
> snd_pcm_oss,snd_mixer_oss,snd_bt87x,snd_via82xx,snd_pcm,snd_timer,snd_ac97_codec,snd_mpu401_uart,snd_rawmidi,snd_seq_device
>  
> Thanks,
> David

What kind of audio hardware are you running and what kind of capture 
card?  Are you using a soundcard with the audio from your capture card 
going to the line-in on your soundcard?  Judging from the tvaudio being 
loaded I guess you are pulling the sound directly from your capture 
card.  I recently had a problem with btaudio and solved it (crossing 
fingers) by using the ALSA bt87x driver instead of btaudio.  Perhaps if 
you loaded that to pull sound from your card you might have better luck.

BTW, the native ALSA support in Myth is not ready for primetime so for 
sure you should use OSS emulation on /dev/adsp.  I've tried to put 
together some patches to improve the ALSA support but they're a work in 
progress still and not in CVS yet.

Kevin