[mythtv-users] the dreaded audio pop

[bstoneaz]

I'm getting random and sometimes frequent/sometimes infrequent cases where myth is recording audio pops.  These occur with my recording with the backend and the frontend idle.  What has stumped me is that I have many recordings now that are perfect, and some where there is much popping present, and this is after I have been investigating and tweaking based on recommendations from the archives.  The last two recordings I tried had one almost perfect, and the other with so many pops in a 30min period I would have called it a static; I was using RTJPEG at 480x480 and the top shows <30% system load and I don't see any load spikes. Based on this I don't think its an issue of my cpu horsepower so I've been trying a lot of things to fix it.  When I listen to the line in from the tuner the audio sounds perfect.  Also these cases are with channels with a good incoming video quality.  
 
So I'm stumped and need some advice.

Here's the setup and some options I've tried:
1.8GHz pentium4, 1/2 gig ram, SoundBlaster Live! (not 5.1), AverTV stereo with audio pass through to Live line in, Redhat 9, ALSA .95 (also tried .94), mythtv 0.10, running both backend and frontend on the same system.
yes DMA is on.  and this is with a single 120G drive with an 8MB buffer.
the vid card is a GF2MX running the nvidia driver and it's working aok.  the card output is at 800x600
I've reniced the frontend -10 and backend -15
I've killed or removed all non-essential services.
I've been using KDE, but I've tried TVWM and Gnome with the same jitter, jerky, pop occurring randomly.
I've optimized the redhat kernel for the p4
I added noatime to my /etc/fstab for the two hard drive partions
I forced the SBLive IRQ to be on 7 and it's not a shared IRQ
I've tried a few optimizations with myth so far, including some where I've added extra statements in for the libs to include -march=pentium4 (and tried w/ and w/out sse flags)

As far a settings, I'm using
mp3 recording, 44.1kHz. no change with uncompressed
and 480x480 mpeg4 and rtjpeg.
on average with mpeg4 recording the load average is about 0.8-1 and it's pushing the cpu. I see video jerks some times, but most audio pops aren't associated with video jerkiness. 
on average with rtjpeg is well under half load and I don't see any load spikes (noted really good/bad cases above).  

If I had to guess, this looks like a lack of audio buffering in myth, but since I haven't seen anything in the archive, and no myth errors I've been trying different options.
rgds
Brent
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