At Fri, 25 Aug 2006 17:27:12 +0100,
James Courtier-Dutton wrote:
>
> Takashi Iwai wrote:
> > At Thu, 24 Aug 2006 11:16:45 +0200,
> > I wrote:
> >
> >> The difference between us is just how to express and pass the
> >> coefficeints. My suggestion is to pass the values given in the
> >> datasheet as they are, min and max dB.
> >>
> >
> > The below is the latest version I have on my local tree.
> > It's against HG tree.
> >
> >
> > Takashi
> >
> +#ifndef HAVE_SOFT_FLOAT
> + case SND_CTL_TLVT_DB_LINEAR: {
> + int mindb = rec->db_info[2];
> + int maxdb = rec->db_info[3];
> Maybe I am unclear about what rec->min is, but I though that it was the
> lowest value the volume(old % scale) could be.
> So, what exactly is this section trying to do? Just handling error cases?
> + if (volume <= rec->min || rec->max <= rec->min)
> + *db_gain = mindb;
> + else if (volume >= rec->max)
> + *db_gain = maxdb;
> + else {
Yes. The edge condition is also a special case that you can handle
easily.
>
> This makes sense. (part A), when combined with (part B)
> + double val = (double)(volume - rec->min) /
> + (double)(rec->max - rec->min);
>
> This special case is for when mindb = negative infinity.
> + if (mindb <= SND_CTL_TLV_DB_GAIN_MUTE)
> + *db_gain = (long)(100.0 * 20.0 * log10(val)) +
> + maxdb;
> + else {
>
> This makes sense. (Part B) when combined with (Part A)
> It covers a good general case of mapping (linear_min...linear_max) onto
> (dB_min...dB_max)
> + /* FIXME: precalculate and cache these values */
> + double lmin = pow(10.0, mindb/20.0);
> + double lmax = pow(10.0, maxdb/20.0);
> + val = (lmax - lmin) * val + lmin;
> + *db_gain = (long)(100.0 * 20.0 * log10(val));
> + }
> + }
> + return 0;
> + }
> +#endif
>
>
> Summary, I am happy with this now.
Great :)
I'll commit the patch later, then.
Takashi
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