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

[Liam Girdwood <liam.girdwood@wolfsonmicro.com>]

On Thu, 2005-12-15 at 18:34 +0000, James Courtier-Dutton wrote:

> 
> The only piece of information reported by the kernel sound driver is a 
> db_scale value.  It is a unsigned int at application layer, but the 
> current IOCTL TLV truncates this to 32bit unsigned int. alsa-lib then 
> uses this value to decide which translation function to apply to the 
> currently available "volume" value.
> I view this "db_scale" value as simply a hint from the low level driver 
> at which conversion function should be used.
> The conversion function in alsa-lib can then be as simple or as 
> complicated as required.
> 

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

 



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