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 {
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.
James
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