[alsa-devel] Mixer volume/decibel mapping

[James Courtier-Dutton]

On 25 May 2010 09:38, Clemens Ladisch <clemens at ladisch.de> wrote:
> Raymond Yau wrote:
>> 2010/5/21 Clemens Ladisch <clemens at ladisch.de>
>> > Peter Ujfalusi wrote:
>> > > The DB_SCALE also provides linear mapping:
>> > > For example, if the HW volume control has a range 0 .. 100
>> > > In HW these means:
>> > > 0 == -10dB, 1 == -9.8dB, 2 == -9.6dB .. 99 = 9.8dB, 100 = 10dB
>> > > So it is linear.
>> >
>> > This is not what is meant by "linear", because dB values are not linear.
>> >
>> > DB_LINEAR means that the mixer control value is a multiplier for the
>> > PCM sample value, as James wrote.  A DB_LINEAR mapping has
>
> ... in practice ...
>
>> > 0 == -infinity dB, full scale == 0 dB, and the mapping between mixer
>> > control values and corresponding dB values it _not_ linear.
>> >
>> > TLV_DB_LINEAR_ITEM is a quite misleading name, but it actually means
>> > "dB mapping for a mixer control whose value has a linear effect on the
>> > sound output", _not_ a linear value <-> dB mapping.
>>
>> seem max(full scale) is more then 0dB for some codecs , only three drivers
>> have 0dB as max and TLV_DB_GAIN_MUTE  (-99999.99dB) as min
>
> And these three are for hardware that use it as a plain multiplier.
>
> All the others seem to be mistakes:
>
>> soc/codecs/stac9766.c:static const DECLARE_TLV_DB_LINEAR(master_tlv, -4600, 0);
>> soc/codecs/stac9766.c:static const DECLARE_TLV_DB_LINEAR(record_tlv, 0, 2250);
>> soc/codecs/stac9766.c:static const DECLARE_TLV_DB_LINEAR(beep_tlv, -4500, 0);
>> soc/codecs/stac9766.c:static const DECLARE_TLV_DB_LINEAR(mix_tlv, -3450, 1200);
>
> These are wrong, both the AC'97 spec and the STAC9766 datasheet say
> that there is a linear register value/dB mapping; these should all use
> DECLARE_TLV_DB_SCALE.
>
>> soc/codecs/wm8350.c:static DECLARE_TLV_DB_LINEAR(pre_amp_tlv, -1200, 3525);
>> soc/codecs/wm8350.c:static DECLARE_TLV_DB_LINEAR(out_pga_tlv, -5700, 600);
>
> According to the datasheet, these should use DECLARE_TLV_DB_SCALE (like
> all the others in this file).
>
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(rec_mix_tlv, -1500, 600);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(in_pga_tlv, -1650, 3000);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(out_mix_tlv, -2100, 0);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(out_pga_tlv, -7300, 600);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(out_omix_tlv, -600, 0);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(out_dac_tlv, -7163, 0);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(in_adc_tlv, -7163, 1763);
>> soc/codecs/wm8400.c:static const DECLARE_TLV_DB_LINEAR(out_sidetone_tlv, -3600, 0);
>> soc/codecs/wm8400.c:    0,7, TLV_DB_LINEAR_ITEM(-1200, 600),
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(rec_mix_tlv, -1500, 600);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(in_pga_tlv, -1650, 3000);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(out_mix_tlv, 0, -2100);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(out_pga_tlv, -7300, 600);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(out_omix_tlv, -600, 0);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(out_dac_tlv, -7163, 0);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(in_adc_tlv, -7163, 1763);
>> soc/codecs/wm8990.c:static const DECLARE_TLV_DB_LINEAR(out_sidetone_tlv, -3600, 0);
>> soc/codecs/wm8990.c:    0, 7, TLV_DB_LINEAR_ITEM(-1200, 600),
>

Could this maybe explain why pulseaudio was having such problems with
alsa with regards to gain controls????