[pulseaudio-tickets] [PulseAudio] #873: static made of 2-sec-delayed bursts of the input sound

[PulseAudio]

#873: static made of 2-sec-delayed bursts of the input sound
--------------------------+-------------------------------------------------
 Reporter:  bit4          |       Owner:  lennart
     Type:  defect        |      Status:  new    
Milestone:                |   Component:  daemon 
 Keywords:  noise static  |  
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 When recording through PulseAudio I get periodic noise with very precise
 characteristics:

 The noise is made of short bursts, each being 1-6 samples long (at 44100
 samples per sec). The bursts occur at regular intervals of 20-24
 milliseconds and are taken from the sound that was recorded exactly (as
 far as I can tell) 2 seconds earlier.

 When I record directly through Alsa, the sound is clean.

 When I unmute the sound source (Mic or Line-In), the sound that I hear is
 clean.

 I tried the following, none of which had any effect on the noise (except
 when noted):[[BR]]
 - Use a different microphone.[[BR]]
 - Capture sound that comes in through Line-In instead of Mic.[[BR]]
 - Use different recording software (the noise appears in audacity, arecord
 and skype).[[BR]]
 - Turn down the volume.[[BR]]
 - Mute and set the volume of all other input/output controls in the mixer
 to zero.[[BR]]
 - Change all possible parameters of the sound card driver and reboot after
 each change.[[BR]]
 - Use a different sound card that uses a different driver (this time the
 noise appeared after a 0.5 sec delay instead of 2 sec).[[BR]]
 - Add '''tsched=0''' to the '''load-module module-udev-detect''' line in
 /etc/pulse/default.pa[[BR]]
 - Change /etc/pulse/daemon.conf to have '''default-fragment-size-msec =
 5''' (instead of 10) and then restart the pulsaudio daemon.[[BR]]
 - Change /etc/pulse/daemon.conf to have '''default-fragment-size-msec =
 25''' and then restart the pulsaudio daemon.[[BR]]
 - Change /etc/pulse/daemon.conf to have '''default-fragment-size-msec =
 85''' and then restart the pulsaudio daemon.[[BR]]
 - Change /etc/pulse/daemon.conf to have '''default-fragments = 16'''
 (instead of 8) and then restart the pulsaudio daemon.[[BR]]
 - Delete all contents of ~/.pulse and restart pulseaudio, then verify that
 it created new files in ~/.pulse[[BR]]
 - Completely remove pulseaudio (including config files) and re-install
 it.[[BR]]

 All of this suggests that:

 1 - The problem is in PulseAudio or in Alsa and not in the sound card
 driver or hardware.

 2 - There is a buffer somewhere, 2 seconds long, that is reused for new
 sound data without being filled completely. It seems to be filled with
 incomplete sound fragments ~20 millisec long, but 1-6 audio samples too
 short, so that the previous contents of the buffer show through.

 See the attached image for a thousand words worth of the problem
 description.

 Hardware:[[BR]]
 - Gigabyte GA-X48-DQ6 motherboard[[BR]]
 - Integrated Intel HDA sound card (ALC889A)[[BR]]
 - A second PCI sound card: Trident 4DWave NX.

 Software:[[BR]]
 - Kubuntu Maverick 10.10, fully patched[[BR]]
 - Pulseaudio 0.9.21-63-gd3efa-dirty[[BR]]

 Attached the output of:[[BR]]
 $ cat /proc/asound/cards[[BR]]
 $ pactl stat[[BR]]
 $ pactl list[[BR]]
 $ lsmod[[BR]]
 $ lspci[[BR]]

 Please contact me at bit4pa at gogito dot homeip dot net if you need more
 info.

-- 
Ticket URL: <http://pulseaudio.org/ticket/873>
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