Re: [RFC] TLV entry for linear volume

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

Takashi Iwai wrote:
> Hi,
>
> some codecs and dsp chips use linear volumes instead of logarithmic
> one.  The patch below adds a new TLV type for such a volume type.
> In alsa-lib, it's converted to dB on the fly.
>
> If no one has objection, I'll push it together with AC97-TLV and
> other similar patches after 1.0.12 release.
>
>
> Takashi
>   
I have not had time to look at the AC97-TLV, but if it works, I can't 
see why I would object.

I have never come across a sound card with linear volumes.
Could you identify a few of them, and also better explain the formula 
you are using for the conversion to dB gain.
*db_gain = (long)(100.0 * 20.0 *
                      log10((double)(volume - rec->min) /
                        (double)(max - min)));

So, 0 dB is when (volume - rec->min) / (max - min) == 1
So, for +6 dB gain, the volume will need to be higher than max?
Does this sound right? In that case, maybe "max" is not a good name for 
it because volume can be greater than max.

James




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