From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eliot Blennerhassett Subject: Re: Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII Date: Wed, 17 Feb 2010 13:52:11 +1300 Message-ID: <4B7B3DBB.30703@audioscience.com> References: <4B7A5268.5050704@ladisch.de> <20100216143200.GB25489@tango.0pointer.de> <20100216144047.GB10586@sirena.org.uk> <20100216154015.GA612@tango.0pointer.de> <20100216210703.GA18109@tango.0pointer.de> <20100216223938.GA23623@sirena.org.uk> <20100216224212.GA1486@tango.0pointer.de> <4B7B2E9F.3080809@audioscience.com> <20100217001047.GB6766@tango.0pointer.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp3.clear.net.nz (smtp3.clear.net.nz [203.97.33.64]) by alsa0.perex.cz (Postfix) with ESMTP id ABD3324389 for ; Wed, 17 Feb 2010 01:53:03 +0100 (CET) Received: from [192.168.1.6] (121-72-250-62.cable.telstraclear.net [121.72.250.62]) by smtp3.clear.net.nz (CLEAR Net Mail) with ESMTP id <0KXY0077MNSAM560@smtp3.clear.net.nz> for alsa-devel@alsa-project.org; Wed, 17 Feb 2010 13:53:00 +1300 (NZDT) In-reply-to: <20100217001047.GB6766@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 Lennart Poettering wrote: > On Wed, 17.02.10 12:47, Eliot Blennerhassett (linux@audioscience.com) wrote: > >> For our cards this is adjustable, but lets say for consumer cards it is >> fixed. This information is not currently available via the ALSA >> API. > > I wonder how realistic it would even be to add an API for > this. i.e. can we even know the refernce level? On many cards most > likely not. For example, for my integrated USB speakers speaking of a > reference voltage would already be misleading... Certainly. Same for laptop speakers. Perhaps could define 0dB as the highest valid volume setting that doesn't cause distortion in the audio when playing a full scale digital signal. Otherwise the absolute reference might be dBSPL at X metres from the speaker ;) (before anyone answers - in this context I'm joking.) > Yepp, that's the exactly what I was asking, Jaroslav's measurements > suggested to shift one of the mixer controls from 0..x dB to -x..0 dB > and I was just wondering why, since we don't define the ref level in > ALSA, hence the shift is kinda arbitrary... > > Anyway, I am not pushing for adding an API for reference levels to > ALSA. We define controls with names like "LineIn0 Level","LineOut1 Level" which we document as having units of dBu. Given that no other driver has this, its the de-facto standard ;) > As mentioned for the PA case I decided to shift 0dB to max > amplification in any case, which I think is a workable way to avoid > this problem. Sure.