[alsa-devel] Capture from 3+ cards connected to a USB hub - distorted samples
Hi,
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
Now:
* 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.
BUT
* 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.
Regards,
Pavel.
Dne 10.12.2011 00:23, Pavel Hofman napsal(a):
Hi,
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
Now:
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.
BUT
- 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,
Pavel.
Date 14.12.2011 13:19, Pavel Hofman wrote:
Dne 10.12.2011 00:23, Pavel Hofman napsal(a):
Hi,
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
Now:
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.
BUT
- 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.
This looks like a USB core issue (lost / unsynced URBs from isochronous transfers). I would try recent linux kernels and/or ask on the USB development list for a help.
Jaroslav
Dne 14.12.2011 13:30, Jaroslav Kysela napsal(a):
Date 14.12.2011 13:19, Pavel Hofman wrote:
Dne 10.12.2011 00:23, Pavel Hofman napsal(a):
Hi,
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
Now:
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.
BUT
- 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.
This looks like a USB core issue (lost / unsynced URBs from isochronous transfers). I would try recent linux kernels and/or ask on the USB development list for a help.
Hi Jaroslav,
Thanks a lot for your suggestion. I tested latest stable kernel 3.1.5. The behaviour has somewhat improved (3 cards OK), but still IMO incorrect (the fourth card D distorts captured streams from C and D). I will ask at the usb development list.
Regards,
Pavel
Dne 18.12.2011 21:17, Pavel Hofman napsal(a):
Dne 14.12.2011 13:30, Jaroslav Kysela napsal(a):
Date 14.12.2011 13:19, Pavel Hofman wrote:
Dne 10.12.2011 00:23, Pavel Hofman napsal(a):
Hi,
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
Now:
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.
BUT
- 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.
This looks like a USB core issue (lost / unsynced URBs from isochronous transfers). I would try recent linux kernels and/or ask on the USB development list for a help.
Hi Jaroslav,
Thanks a lot for your suggestion. I tested latest stable kernel 3.1.5. The behaviour has somewhat improved (3 cards OK), but still IMO incorrect (the fourth card D distorts captured streams from C and D). I will ask at the usb development list.
I checked USB communication with wireshark and the reduced data payload in URBs for card C and D suggest I am already hitting ceiling of the hub throughput. I think the hub support is already correct in the latest kernel.
Best regards,
Pavel.
participants (2)
-
Jaroslav Kysela -
Pavel Hofman