On 30.03.19 09:28, Fons Adriaensen wrote:
On Fri, Mar 29, 2019 at 08:52:04PM -0700, Paul Davis wrote:
Why can't I tell ALSA to use only the first 2, 4 whatever channels of
the device? I can only open the device if all channels are connected. Is
this always like that or is that a limitation of MOTU's implementation?
ALSA doesn't work that way. You open a device. You tell it how many
channels you want to use.
At least in mmap mode (which is what Jack uses), this doesn't seem
to be so. snd_pcm_hw_params_set_channels () returns an error for
any number of channels not equal to the actual available number.
It makes sense, access is exclusive anyway. The only consequence
is that apps should probably write zeros to any output channels
they don't want to use.
If an app needs only 2 channels and fails to use a card offering
more, that's a bug in the app, not in ALSA.
Makes sense. My thinking was that I could possibly get lower latency and
less overhead if I only acquire two or four channels instead of 24 or 64
from which I leave the majority idle... But I understand its just now
how ALSA was designed.
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