[alsa-devel] Noisy USB audio stream using MPlayer

[Takashi Iwai]

At Mon, 22 Jun 2009 01:17:25 -0700 (PDT),
Eran Ben-Avi wrote:
> 
> 
> Hi,
> 
> I encountered some issue with my USB audio device and couldn't find any similar issue in previous mailing lists, any help will be appreciated.
> When playing an audio stream using MPlayer Ver1.0rc2-4.1.2 (tried different sample rates 44K, 48K and different files WAV , MP3) using my Creative SB0271 USB device on ARM based system(Marvell Kirkwood SoC) and kernel 2.6.22.18, I hear an interfering constant noise additionally to the original audio stream.
> At the beginning I heard this noise also when I used aplay(for WAV) but after I reinstalled the ALSA-LIB and ALSA-UTILS(version 1.0.14rc4), the aplay suddenly started to work smooth.
> I tested different USB audio device(AKM) but got same noisy results.
> Another piece of information I can provide is that increasing the CPU utilization eliminates the noise completely - maybe a timing issue ???

Could it be the cache coherency?
The usb-audio driver uses vmalloc'ed buffers as intermediate buffers,
and they can be  exposed to user-space via mmap.

Does the problem disappears when you disable mmap support by
commenting out SNDRV_PCM_INFO_MMAP* in snd_usb_hardware info field?


Takashi