From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jaroslav Kysela Subject: Re: Capture from 3+ cards connected to a USB hub - distorted samples Date: Wed, 14 Dec 2011 13:30:42 +0100 Message-ID: <4EE896F2.9090806@perex.cz> References: <4EE29877.2050804@ivitera.com> <4EE89434.9040609@ivitera.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail1.perex.cz (unknown [77.48.224.245]) by alsa0.perex.cz (Postfix) with ESMTP id D5397103822 for ; Wed, 14 Dec 2011 13:31:29 +0100 (CET) In-Reply-To: <4EE89434.9040609@ivitera.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Pavel Hofman Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org 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 Linux Kernel Sound Maintainer ALSA Project; Red Hat, Inc.