From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raymond Yau Subject: Re: Mixer volume/decibel mapping Date: Fri, 21 May 2010 08:35:14 +0800 Message-ID: References: <201005191834.57919.vand2@gmx.de> <201005201141.28755.vand2@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pz0-f187.google.com (mail-pz0-f187.google.com [209.85.222.187]) by alsa0.perex.cz (Postfix) with ESMTP id 287721038DD for ; Fri, 21 May 2010 02:35:15 +0200 (CEST) Received: by pzk17 with SMTP id 17so199726pzk.5 for ; Thu, 20 May 2010 17:35:15 -0700 (PDT) In-Reply-To: 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 Development Mailing List List-Id: alsa-devel@alsa-project.org 2010/5/21 James Courtier-Dutton > On 20 May 2010 10:41, Sebastian H. wrote: > > > > That's clear. > > I imagined that maybe the dB scale could be the "real thing" and the > volume > > steps would be a convenient but possibly coarse mapping into a denser > > stepped dB space provided by the hardware/driver. > > This was unlikely but I wanted to ask anyway ;-). > > > > I believe it could be extended to support a continuous range. > For example, some hardware uses a 32bit value to control the gain. > The mix operation is simply "the_sample" * "the_control_value". > So in this case the hardware has a linear control that can be > considered continuous for our purposes. > The conversion from the control value to a usable value would have to > include a user land log operation. > It was never implemented due to lack of demand. > For the cards that do have this 32bit linear value, a simple lookup > table is used in the kernel code to convert it to 256 step values. > If implemented, one could then introduce professional gain controls > that do not produce "clicks" in the output when adjusted. > gain controls with steps in them produce clicks when the gain control > is adjusted. > For example , the 10 band stereo graphic equalizer of au8830 has 32678 steps but the dB range is most likely between -6dB and +6dB I have not measured the dB values but there is no clipping occur at maximum gain just compared with the software equalizer alsaequal where you can hear distortion quite easily snd_vortex_eq_info(struct snd_kcontrol *kcontrol, struct snd_ctl_elem_info *uinfo) { uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER; uinfo->count = 2; uinfo->value.integer.min = 0x0000; uinfo->value.integer.max = 0x7fff; return 0; } How can I implement a dB scale for those 10 EQ gain/atten controls ?