On Thu, 10 Apr 2008, Lennart Poettering wrote: > On Thu, 10.04.08 10:16, Jaroslav Kysela (perex@xxxxxxxx) wrote: > > > Mixer > > ===== > > > > Please explain this question (why you need the dB <-> value conversion, > > we assumed that application works in dB or integer range not both): > > > > 'It is possible to query the dB range of a smixer element. And it is > > possible to query and set the current dB level. However, it is not > > possible to have a dB value converted to an integer level or vice versa, > > without touching the actual setting. i.e. a question like "What is the > > integer level 0 dB corresponds to?" can not be answered by ALSA. Which > > happens to be a serious limitation.' > > I can think of many reasons, they all have to do with the fact that > the dB scale is not integral, i.e. in contrast for the normal integer > scale you won't always get what you are asking for, because the > hardware only supports a value below or above what you asked for: a) a > volume control tool might want to show a slider that is linear to the > dB scale, but also shows which dB values are actually selectable from > it via small black lines on the side (or suchlike) b) PA doesn't make > use of positive dB values -- it limits itself to attenuation via the > mixer. However, right now there is no way to find out which actually > supported dB value is the nearest one to 0dB. c) Several different dB > values may refer to the same actual hw setting. It would be good if a > specific dB value actually maps to the same integer hw setting as some > other value, to surpress redundant "volume change" events. OK. I see your points. I've added these functions to alsa-lib's API: snd_mixer_selem_ask_playback_vol_dB snd_mixer_selem_ask_capture_vol_dB snd_mixer_selem_ask_playback_dB_vol snd_mixer_selem_ask_capture_dB_vol Jaroslav ----- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
