[mythtv-users] Intermittent audio issues - snd-via82xx

Michael T. Dean mtdean at thirdcontact.com
Tue Jun 27 17:10:23 UTC 2006


On 06/26/2006 06:34 PM, Ben Lancaster wrote:
> On 26 Jun 2006, at 23:02, Ben Lancaster wrote:
>
>   
>> I have two devices: /dev/dsp and /dev/adsp
>>
>> First question (probably a stupid one): what's the difference  
>> between the two?
>>     
>
> Ah hah, to answer my own question, /dev/dsp is the OSS (emulated)  
> device, and /dev/adsp is ALSA one

Not really.  Both /dev/dsp and /dev/adsp are OSS-compatible devices 
created in response to loading the ALSA OSS emulation modules, so they 
both require the use of OSS emulation.  However, traditionally, OSS used 
/dev/dsp0 for the 0th sound card's 0th device and /dev/dsp1 for the 0th 
sound card's 1st device.  ALSA emu requires sound card 0's to use 
/dev/dsp0 (and sound car 1 to use /dev/dsp1), so ALSA invented the 
"adsp" name for "additional" devices on the sound card (see 
http://alsa.opensrc.org/OSS+device).  (The OSS device names without 
trailing number--i.e. "/dev/dsp"--are typically links to those with a 
trailing "0", but you can specify that the device names be created 
without the number.)

Normally, in ALSA OSS emu, /dev/dsp0 is mapped to ALSA's hw:0,0 (0th 
sound card, 0th device) and /dev/adsp0 is mapped to ALSA's hw:0,1 (0th 
sound card, 1st device).  However, you can change these mappings with 
the module's {,a}dsp_map options.  See 
http://www.alsa-project.org/~iwai/OSS-Emulation.html.

ALSA devices are /dev/snd/* .

Mike


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