Mixer volume dB settings.

Mixer volume dB settings.

[James Courtier-Dutton]

Hi,

I am thinking of a method to provide dB volume setting with alsamixer.
My suggestion is to add another variable to the mixer control structure. 
This variable will be an integer identifying the conversion function.
If set to 0, no conversion function has been defined. If set to 1 or 
above, use a lookup table in alsa-lib to select the conversion function.
The user land api would then be:
snd_mixer_convert_hardware_to_db( hardware_value, conversion_function, 
&db_value);
snd_mixer_convert_db_to_hardware( db_value, conversion_function, 
hardware_value )

The reason for this, is that it seems to me that only the hardware 
driver will have full knowledge of what the conversion function should 
be, and setting a simple integer for conversion_function_type would seem 
the simplest solution.

The global conversion functions could then be defined in an alsa-lib 
config file.

This would also allow the application to increase/decrease the hardware 
value, but display to the user the dB value.

Any comments?

If this seems ok, I will start implementing it.

James


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Re: Mixer volume dB settings.

[Jaroslav Kysela]

On Sun, 31 Jul 2005, James Courtier-Dutton wrote:

> Hi,
> 
> I am thinking of a method to provide dB volume setting with alsamixer. 
> My suggestion is to add another variable to the mixer control structure. 
> This variable will be an integer identifying the conversion function. If 
> set to 0, no conversion function has been defined. If set to 1 or above, 
> use a lookup table in alsa-lib to select the conversion function. The 
> user land api would then be: snd_mixer_convert_hardware_to_db( 
> hardware_value, conversion_function, &db_value); 
> snd_mixer_convert_db_to_hardware( db_value, conversion_function, 
> hardware_value )
> 
> The reason for this, is that it seems to me that only the hardware 
> driver will have full knowledge of what the conversion function should 
> be, and setting a simple integer for conversion_function_type would seem 
> the simplest solution.
> 
> The global conversion functions could then be defined in an alsa-lib 
> config file.
> 
> This would also allow the application to increase/decrease the hardware 
> value, but display to the user the dB value.
> 
> Any comments?

I already defined the interface in alsa-lib/include/mixer.h. Look for dB 
functions there.

Also, the skeleton of the new mixer with abstraction layer is quite 
finished. I need only implement a first real code for one driver as 
example and we can start adding the abstraction code for all cards.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SUSE Labs


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Re: Mixer volume dB settings.

[James Courtier-Dutton]

Jaroslav Kysela wrote:
> On Sun, 31 Jul 2005, James Courtier-Dutton wrote:
> 
> 
>>Hi,
>>
>>I am thinking of a method to provide dB volume setting with alsamixer. 
>>My suggestion is to add another variable to the mixer control structure. 
>>This variable will be an integer identifying the conversion function. If 
>>set to 0, no conversion function has been defined. If set to 1 or above, 
>>use a lookup table in alsa-lib to select the conversion function. The 
>>user land api would then be: snd_mixer_convert_hardware_to_db( 
>>hardware_value, conversion_function, &db_value); 
>>snd_mixer_convert_db_to_hardware( db_value, conversion_function, 
>>hardware_value )
>>
>>The reason for this, is that it seems to me that only the hardware 
>>driver will have full knowledge of what the conversion function should 
>>be, and setting a simple integer for conversion_function_type would seem 
>>the simplest solution.
>>
>>The global conversion functions could then be defined in an alsa-lib 
>>config file.
>>
>>This would also allow the application to increase/decrease the hardware 
>>value, but display to the user the dB value.
>>
>>Any comments?
> 
> 
> I already defined the interface in alsa-lib/include/mixer.h. Look for dB 
> functions there.
> 
> Also, the skeleton of the new mixer with abstraction layer is quite 
> finished. I need only implement a first real code for one driver as 
> example and we can start adding the abstraction code for all cards.
> 
> 						Jaroslav
> 

Shall we pick a card we both have. I have a intel8x0 motherboard, and 
most creative cards. Do you have either of those?



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Re: Mixer volume dB settings.

[James Courtier-Dutton]

Jaroslav Kysela wrote:
> On Sun, 31 Jul 2005, James Courtier-Dutton wrote:
> 
> 
>>Hi,
>>
>>I am thinking of a method to provide dB volume setting with alsamixer. 
>>My suggestion is to add another variable to the mixer control structure. 
>>This variable will be an integer identifying the conversion function. If 
>>set to 0, no conversion function has been defined. If set to 1 or above, 
>>use a lookup table in alsa-lib to select the conversion function. The 
>>user land api would then be: snd_mixer_convert_hardware_to_db( 
>>hardware_value, conversion_function, &db_value); 
>>snd_mixer_convert_db_to_hardware( db_value, conversion_function, 
>>hardware_value )
>>
>>The reason for this, is that it seems to me that only the hardware 
>>driver will have full knowledge of what the conversion function should 
>>be, and setting a simple integer for conversion_function_type would seem 
>>the simplest solution.
>>
>>The global conversion functions could then be defined in an alsa-lib 
>>config file.
>>
>>This would also allow the application to increase/decrease the hardware 
>>value, but display to the user the dB value.
>>
>>Any comments?
> 
> 
> I already defined the interface in alsa-lib/include/mixer.h. Look for dB 
> functions there.
> 
> Also, the skeleton of the new mixer with abstraction layer is quite 
> finished. I need only implement a first real code for one driver as 
> example and we can start adding the abstraction code for all cards.
> 
> 						Jaroslav
> 

Can you point me in the direction of the new mixer abstraction layer.
It is unclear to me which alsa-lib files are associated with the 
abstraction layer.

I am thinking that the alsa-driver module for the sound card will have 
to attach an index value identifying the vol % -> dB conversion routine 
to use with the mixer element. Then alsa-lib could then simply do a 
lookup for the index and then process the associated conversion routine.

The reason for this is that I think that the same sound card controller 
chip might have different other sound chips associated with it, but the 
mixer elem name might be the same for both. I suppose we could then give 
a different name in the driver, and then rename it at the abstraction layer.

Any pointers you can give would be helpful.

James


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