Re: [PATCH] Adds dB gain to alsa-driver, alsa-lib.

[James Courtier-Dutton <James@superbug.co.uk>]

Liam Girdwood wrote:
> 
> I'm wondering whether it might be a better idea to use the "db_scale" to
> store the specifics of the gain rather than just a hint.
> 
> IMHO we need to be able to specify:-
> 
>  o number of steps in control
>  o starting dB setting
>  o step size (including negative bit)
> 
> This could either be divided up into the 32 bits of db_scale or by
> adding another member(s) to the struct.
> 
> This would then mean alsa lib doesn't need to know about the dB settings
> for each codec/card (as they are quite different) and the dB information
> would be in the driver where it belongs.
> 
> Liam
> 

We discussed this point some time ago on the list.
the "hint" is better, because it then lets alsa-lib decide which 
conversion function to use.
Problems with your approach were:
1) Control with non-linear dB steps. E.g. attenuation using a different 
scale than gain.
2) Complicates controls where only a lookup table will do.

James



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