Cannot set channels number for the output of a USB audio 2.0 class compliant device
Cannot set channels number for the output of a USB audio 2.0 class compliant device
- Subject: Cannot set channels number for the output of a USB audio 2.0 class compliant device
- From: Philippe Wicker <email@hidden>
- Date: Wed, 30 Mar 2016 15:02:06 +0200
Hello all,
Don’t know if I should have posted this to the USB list but as it
concerns the firmware of an audio 2.0 device I thought that there could
be people here able to give me some hints about my problems.
I’m working on the firmware of a device which is a USB audio 2.0 class
compliant device. This device supports sample rate from 44.1 to 192KHz
(discrete values 44.1, 48, 88.2, 96, 176.4 and 192). And we want it to
support for both Input and Output 8 channels (6 analog + 2 ADAT) at 192
and 176.4, 10 channels (6 analog + 4 ADAT) at 88.2 and 96, and 14
channels (6 analog + 8 ADAT) at 44.1 and 48. All the channels support a
unique 24 bits resolution.
For now I’m trying to do that using alternate settings and I check it
using the “Audio Devices” window of Audio MIDI Setup. Apart the AS
Interface for the zero bandwidth I have 2 sets of 3 alternate interfaces
(1 set for the input and the 2nd set for the output). The channels
number is specified within the Class Specific AS Interface descriptors,
and the resolution is specified within Type 1 Format descriptors.
Looking at the Audio Devices window, it works for the “Input” tab, but
not for the “Output” tab.
The “Input" tab displays 1 popup where I can choose the sample rate, and
a 2nd one where I can choose the number of channels.
On the other hand the “Output” tab correctly displays the sample rate
popup, but gives me only the “14ch - 24bit integer” choice. If I set the
“output” descriptors so that the alternate settings provides different
resolutions (instead of channels numbers) then the right popup is
correctly populated with the 3 resolutions.
So I cannot get a "8 in / 8 out” configuration which what I want to
achieve. I have at best an "8 in / 14 out” config which is too much (not
enough bandwidth at high sample rates).
Is this non-symetic behaviour the expected one? Any idea?
More generally, is there a better way to manage this kind of
multw-configurations where the number of channels is correlated with the
actual sample rate?
Thanks,
Philippe
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden