[Alsa-user] snd_via82xx snaps/pops/crackles when recording (only)

[J Y. <yu...@pr...>]

Hi Everyone --

   I have spent several hours trying to get recording to work correctly on 
a hacked Wyse terminal running Slax linux.  Playing works perfectly, but 
recording causes snaps & pops akin to a vinyl record.  I get a light pop 
between every 1/2 second and every 5 seconds (random).

   Any suggestions?  Feel free to RTFM me if there are some tweaks/settings 
I should try.  Thanks!  See below for detail.

-- Justin

###

   Here are the specs:

lspci:
Multimedia audio controller: VIA Technologies, Inc. VT82C686 AC97 Audio 
Controller

uname:
Linux slax 2.6.27.27 #1 SMP Wed Jul 22 07:27:34 AKDT 2009 i686 VIA Samuel 
2 CentaurHauls GNU/Linux

dmesg:
VIA 82xx Audio 0000:00:11.5: setting latency timer to 64

alsa version:
1.0.17

system/motherboard:
Wyse 9450
VT8601 chipset

hardware specs:
VIA Samuel 2 550MHz processor
512MB Disk on Module
512MB SDRAM

programs used:
aplay
arecord
ices (streaming audio)

####

Other info:

- I have tried two Wyse 9450s so far, so it's not a single bad device.

- Recording works without any issues when using Windows XPe on the same 
hardware.

- Playing works without any issues.  Most of the posts I've found via 
google are about crackling noises while playing -- which has never been a 
problem.

- I have never gotten any underruns, overruns, or any other errors in the 
ring buffer (dmesg).

- Load average never exceeds .90 with ices, memory isn't being peaked or 
dropping to swap.

- I primarily used ices to try things, but also used arecord piped to 
aplay with similar results.

####

   I have tried:

- 48000hz vs. 41000hz vs 22050hz vs 1 channel vs 2 channel vs 8-bit vs 
16-bit (mixtures).

- Tweaking the 'periods' and 'buffer_time' settings in ices.  I was able 
to reduce the crackling by going to a period of 2 and a buffer time of 
500ms, but it's still crackling the same as arecord.

- Messing with dxs_support and ac97_quirks settings (no effect).

- Messing with setpci for the latency_timer (no effect).

- Messing with just about every BIOS setting relating to PCI, power 
management, ACPI, PNP, etc.

- Compiling the latest snd-via82xx driver (no effect; I compared the 
source code and the primary changes are related to the 8233 chipsets).

- Using chrt to run ices at REALTIME (made it much worse).

- Using nice to run ices at a higher priority (no effect).

- Killing any extraneous processes.

- Obvious stuff like verifying that the audio source is clean (it is).

- Replacing the power supply.