[alsa-devel] Mixer volume/decibel mapping
clemens at ladisch.de
Fri May 21 08:35:31 CEST 2010
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 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.
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