From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raymond Yau Subject: Re: Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII Date: Wed, 17 Feb 2010 11:30:52 +0800 Message-ID: <4f3252891002161930i25d411ap6c0b9ad8977f336e@mail.gmail.com> References: <20100215192451.GA17938@tango.0pointer.de> <4B7A5268.5050704@ladisch.de> <20100216142633.GA25489@tango.0pointer.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-px0-f189.google.com (mail-px0-f189.google.com [209.85.216.189]) by alsa0.perex.cz (Postfix) with ESMTP id 7F1DF10384A for ; Wed, 17 Feb 2010 04:30:53 +0100 (CET) Received: by pxi27 with SMTP id 27so1362257pxi.2 for ; Tue, 16 Feb 2010 19:30:52 -0800 (PST) In-Reply-To: <20100216142633.GA25489@tango.0pointer.de> 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: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org 2010/2/16 Lennart Poettering > On Tue, 16.02.10 09:08, Clemens Ladisch (clemens@ladisch.de) wrote: > > > > > Lennart Poettering wrote: > > > Getting back to the invalid dB data from the USB cards: the question > > > is whether the USB descriptor data is badly parsed, and the dB > > > mismatch hence systematic for USB cards, > > > > USB descriptors use units of 1/256th dB, while ALSA uses 1/100th dB. > > When the level is computed from the minimum plus a multiple of the step > > size, rounding errors add up considerately. > > > > ALSA 1.0.21 (kernel 2.6.32) added a different TLV type that reports the > > range with the min/max values to minimize those rounding errors. > > I am really sure that the discrepancy I measure with the Aureon is way > beyond rounding errors. > > Lennart > > if the program use a format FLOAT_LE which is not supported by the hardware and need to use plughw , you have already added error ( resampling and format conversion ) to the result