From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Hofman Subject: Re: USB Audio questions Date: Wed, 17 Aug 2011 00:11:55 +0200 Message-ID: <4E4AEB2B.4030700@ivitera.com> References: <1313432124-22591-1-git-send-email-lars@metafoo.de> <1313432124-22591-2-git-send-email-lars@metafoo.de> <000001cc5b8a$4a6577c0$df306740$@bossart@linux.intel.com> <4E4A100D.9020302@ladisch.de> <000601cc5c2a$87a26350$96e729f0$@bossart@linux.intel.com> <131d4536813.-8375004616171444232.4180326891785246293@zoho.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.pilsfree.net (mail.pilsfree.net [81.201.60.141]) by alsa0.perex.cz (Postfix) with ESMTP id 10ED810383B for ; Wed, 17 Aug 2011 00:12:04 +0200 (CEST) In-Reply-To: <131d4536813.-8375004616171444232.4180326891785246293@zoho.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: Torsten Schenk Cc: 'ALSA Development Mailing List' , Pierre-Louis Bossart List-Id: alsa-devel@alsa-project.org Dne 16.8.2011 22:41, Torsten Schenk napsal(a): > Hi Pierre, > > - The device/driver sends per urb a constant number of packets (as > you already also discovered). The number of samples per packet differ > however (+- 1 sample per packet). I accuse the asynchronousity > between the urb interval and the sound card's internal clock for this > fact. The device expects the driver to send back an urb with exactly > the same structure. The device produced crackling noise if the > samples per packet were not equal. I cannot say to what extend this > is true (i.e. if you could wait some packets until catching up the > difference without producing crackles) Could we attribute this to the adaptive mode and PLL striving to produce steady stream of well-timed samples to the DAC? IMHO the lower variation in samples per packet, the lower jitter of the PLL-recovered clock. Pavel.