[alsa-devel] Noisy USB audio stream using MPlayer

Eran Ben-Avi eranpublic at yahoo.com
Tue Jun 23 12:03:43 CEST 2009

----- Original Message ----
> From: Takashi Iwai <tiwai at suse.de>
> To: Eran Ben-Avi <eranpublic at yahoo.com>
> Cc: alsa-devel at alsa-project.org
> Sent: Monday, June 22, 2009 7:41:19 PM
> Subject: Re: [alsa-devel] Noisy USB audio stream using MPlayer
> 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, 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?

When I disabled the mmap support I got the following messages while running the mplayer:

[AO_ALSA] alsa-lib: pcm_direct.c:874:(snd_pcm_direct_initialize_slave) slave plugin does not support mmap interleaved or mmap
 noninterleaved access
[AO_ALSA] alsa-lib: pcm_dmix.c:876:(snd_pcm_dmix_open) unable to initialize slave
[AO_ALSA] Playback open error: Invalid argument
Opening /dev/dvb/adapter0/audio0
DVB AUDIO DEVICE: No such file or directory

seems like ALSA-LIB doesn't really like it.

> Takashi
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