Capture from 3+ cards connected to a USB hub - distorted samples

Capture from 3+ cards connected to a USB hub - distorted samples

[Pavel Hofman]

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.

Re: Capture from 3+ cards connected to a USB hub - distorted samples

[Pavel Hofman]

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.

Re: Capture from 3+ cards connected to a USB hub - distorted samples

[Jaroslav Kysela]

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

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Kernel Sound Maintainer
ALSA Project; Red Hat, Inc.

Re: Capture from 3+ cards connected to a USB hub - distorted samples

[Pavel Hofman]

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

Re: Capture from 3+ cards connected to a USB hub - distorted samples

[Pavel Hofman]

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.