2010/5/21 James Courtier-Dutton <james.dutton@xxxxxxxxx> > On 20 May 2010 10:41, Sebastian H. <vand2@xxxxxx> 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. > I thinks Sebastian's question is whether he can use snd_mixer_selem_set_playback_ dB() set any values in between the volume steps e.g. Master volume control of ac97 is 1.5 dB per step, when using snd_mixer_selem_set_playback_dB() to set -0.9dB , how can the mixer application know what dB value has been set since the value is in between -1.5dB and 0dB without snd_mixer_selem_get_playbackdB() _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
