[alsa-devel] Capture from 3+ cards connected to a USB hub - distorted samples
pavel.hofman at ivitera.com
Wed Dec 14 13:19:00 CET 2011
Dne 10.12.2011 00:23, Pavel Hofman napsal(a):
> I have been informed about the following problem which I was able to
> reproduce afterwards:
> * Latest git.alsa-project.org drivers
> * USB 2.0 hub, 3 or more USB soundcards (inexpensive USB sticks, USB
> audio v.1 types, async capture, adaptive playback) hooked to the hub,
> identified A, B, C, D.
> * NONE of these soundcards is playing back
> * Card A begins microphone capturing (mono 48/16), result OK
> * Card B begins capturing (mono 48/16), both results still OK
> * As soon as the third card C begins capturing, the signal captured from
> cards A and B gets distorted. Audacity shows some samples are
> incorrect, distorting the expected sine waveform of the testing signal.
> I can provide screenshots as well as recorded samples, if needed.
> * The signal recorded from card C is OK.
> * If any card hooked to the HUB is playing back (even a fourth one D),
> the distortion does not occur. It happens only when there is no playback
> stream going through the hub. Traffic on another USB port has no effect,
> in fact the test signal for the three cards was provided by a
> multichannel USB card hooked to another USB port.
> It seems to me as if blocks of samples for each card in the USB frame
> sometimes overlap by a few bits, corrupting the neighbouring card
> samples, or are recovered incorrectly.
> I understand I have provided no real data, I am ready to do so plus any
> tests you would consider useful.
> Thanks a lot for suggestions of the next debugging steps I should do.
Hi, please may I ask for help? I think we could fix this likely bug.
Thanks a lot,
More information about the Alsa-devel