[alsa-devel] Mixer volume/decibel mapping

[Clemens Ladisch]

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/
sound/i2c/other/ak4xxx-adda.c
sound/pci/oxygen/hifier.c
sound/pci/oxygen/oxygen.c
sound/pci/ymfpci/ymfpci_main.c
sound/soc/codecs/stac9766.c
sound/soc/codecs/wm8350.c
sound/soc/codecs/wm8400.c
sound/soc/codecs/wm8990.c

> 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.

It is implemented.

> 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.

Which driver is this?  It should be changed to use the full range.


Regards,
Clemens