An introduction to computer audio
In Sound > Preferences you can choose the devices.
My DAC presents itself as a Texas Instruments Benchmark 1.0 USB Audio.
It is available as a ALSA and a OSS device.
When choosing test OSS works, ALSA gives an error
After endless Googling, waddling forums, changing permissions, looking in conf files, finally I found the answer:
sudo killall -9 pulseaudio
Later I found that there is a nice GUI to end processes too!
Choose Pulseaudio as the sound device.
Pulseaudio as delivered with Ubuntu is a zero configuration version. Indeed you can't configure anything.
After installing some additional software all output devices are nicely shown.
Tried a lot of parameters, spend hours on forums but no sound from the USB.
Looks like Pulseaudio and ALSA don't work together in this case.
Opened the Synaptic Package Manager and removed Pulseaudio completely and now the DAC is playing both OSS and ALSA
One advantage of spending hours on all kind of forums.
If Amarok wants a parameter (they don't like list boxes in the Linux world), I know that plughw:1 is my USB DAC.
If you want bit perfect output, specify hw: instead of plughw:
ALSA will talk straight to the sound card without mixing, sample rate conversion, etc.
As a consequence, what the media player is sending to the sound card should match its properties like bit depth, sample rate and number of channels exactly.
If anyone is using mpd on Linux with a 24-bit USB DAC (such as the Wavelength Proton), mpd recently incorporated S24_3LE support into the latest version in git. This means mpd can send audio straight to the DAC instead of processing in alsa first. This means no 32-bit conversion in mpd before being converted to S24_3LE in alsa. mpd converts straight to S24_3LE and outputs to the DAC if you specify hw:0,0. I'm noticing a definite improvement on my Audioengine 2A's. Once this change makes it's way to an mpd release instead of only being in the git repository, I bet audiophile mpd users take immediate notice of the change.