Re: [Alsa-user] Musical Fidelity V-DAC, usb sound

[Niels <zor...@ho...>]

On Thursday 07 May 2009 15:43, Clemens Ladisch wrote:

> Niels wrote:
>> - This is with Kubuntu 9.04. For some reason it ships with ALSA
>> 1.0.18rc3. Is it worth upgrading,
> 
> Probably not, AFAIK there haven't have any relevant changes.
> 
>> and how would I do that, other that wait for an automatic update?
> 
> Download, compile and install the 1.0.20 alsa-driver package.
> 

I did that, no problems.

>> - speaker-test says it outputs to "Front left", but it actually outputs
>> to both left and right.
> 
> Doesn't it ever output to "front right"?  This looks like a mono mode.
> 
> What device name and number of channels did you tell speaker-test to use?
> 

I disabled the internal sound card, so that the usb-audio is now the only
sound card:

$aplay -l
**** List of PLAYBACK Hardware Devices ****
card 1: default [USB Audio DAC   ], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


But now speaker-test fails:

$ speaker-test

speaker-test 1.0.20

Playback device is default
Stream parameters are 48000Hz, S16_LE, 1 channels
Using 16 octaves of pink noise
ALSA lib confmisc.c:768:(parse_card) cannot find card '0'
ALSA lib conf.c:3513:(_snd_config_evaluate) function snd_func_card_driver
returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:3513:(_snd_config_evaluate) function snd_func_concat
returned error: No such file or directory
ALSA lib confmisc.c:1251:(snd_func_refer) error evaluating name
ALSA lib conf.c:3513:(_snd_config_evaluate) function snd_func_refer returned
error: No such file or directory
ALSA lib conf.c:3985:(snd_config_expand) Evaluate error: No such file or
directory
ALSA lib pcm.c:2211:(snd_pcm_open_noupdate) Unknown PCM default
Playback open error: -2,No such file or directory


There seems to be a problem with card0 vs. card1.


>> - How do I disable dmix and other possible sources of signal degradation
>> completely?
> 
> Dmix does not degrade the signal because its design requires it to run
> with a sample rate and a sample format directly supported by the device.
> 
Ah, that's good then.


> You can disable dmix by telling your application(s) to use another
> device name instead of "default".
> 
>> - How do I make sure ALSA doesn't resample or normalize the signal along
>> the way?
> 
> Use a device name like "dmix" or "hw".
> "default" and "plughw" include resampling, if needed.
> 
> In no case is there any normalization.
> 

Judging from /usr/share/alsa/cards/USB-Audio.conf I have a number of devices
available, such as 
USB-Audio.pcm.front.0
USB-Audio.pcm.default
USB-Audio.pcm.default_playback_dmix_yes
USB-Audio.pcm.default_playback_dmix_no

however they don't all show up in "aplay -L". There's no way to select a
specific device in KDE's sound system, so I'd have to configure ALSA to use
a certain device as default. How would I do that?


>> - How do I test various sample rates and bit depths?
> 
> Play a file with the desired properties to the "hw" device.
> 

Clever, I'll try that!


>> How do I get ALSA to tell me what the device supports?
> 
> Have a look into /proc/asound/card???/stream0.
> 
Apparently it only supports 16 bit, 32000, 44100, 48000 Hz. The card
does "24 bit 192kHz upsampling", so I'd hoped to have something like that
available for playing samples. Ho-hum, I guess not.


Thanks!
Niels