Peter Ujfalusi wrote: > On Friday 21 May 2010 09:35:31 ext Clemens Ladisch wrote: > > James Courtier-Dutton wrote: > > > 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. > > > > Such controls already exist: > > > > $ grep -rl DB_LINEAR sound/ > > ... > > The DB_SCALE also provides linear mapping: > For example, if the HW volume control has a range 0 .. 100 > In HW these means: > 0 == -10dB, 1 == -9.8dB, 2 == -9.6dB .. 99 = 9.8dB, 100 = 10dB > So it is linear. This is not what is meant by "linear", because dB values are not linear. DB_LINEAR means that the mixer control value is a multiplier for the PCM sample value, as James wrote. A DB_LINEAR mapping has 0 == -infinity dB, full scale == 0 dB, and the mapping between mixer control values and corresponding dB values it _not_ linear. TLV_DB_LINEAR_ITEM is a quite misleading name, but it actually means "dB mapping for a mixer control whose value has a linear effect on the sound output", _not_ a linear value <-> dB mapping. Regards, Clemens _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
