[alsa-devel] Noisy USB audio stream using MPlayer

[Takashi Iwai]

At Tue, 23 Jun 2009 03:03:43 -0700 (PDT),
Eran Ben-Avi wrote:
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> ----- 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 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?
> 
> 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.

Because dmix requires the mmap explicitly by its nature.

Pass mplayer an appropriate option to use directly "hw" PCM device.
(plughw might work with alsa-lib 1.0.20, too)


Takashi