[alsa-devel] Mixer volume/decibel mapping
superquad.vortex2 at gmail.com
Fri May 28 15:04:34 CEST 2010
2010/5/25 Clemens Ladisch <clemens at ladisch.de>
> Raymond Yau wrote:
> > I have doubt about DECLARE_TLV_DB_LINEAR(ak4396_db_scale,
> TLV_DB_GAIN_MUTE, 0);
> > since the datasheet mention that dB range is only -48dB to 0dB
> > ATT = 20 log10 (ATT_DATA / 255) [dB]
> > How can AK4396 has scale of -inf DB to 0dB in the driver code ?
> When ATT_DATA = 0, there is no output, which is an attenuation of -inf.
> The next value, ATT_DATA = 1, results in ATT = -48 dB.
refer to ice1712/prodigy_hifi.c , why the comment is -64dB to 0dB ?
* ak4396 mixers
* DAC volume attenuation mixer control (-64dB to 0dB)
static int ak4396_dac_vol_info(struct snd_kcontrol *kcontrol, struct
uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
uinfo->count = 2;
uinfo->value.integer.min = 0; /* mute */
uinfo->value.integer.max = 0xFF; /* linear */
This is true regardless of the precision of the multiplier. Even a one-
> bit factor behaves like this; in fact, this would describe a mute switch.
This mean that the dB range should be calculated from the next step above
the min_dB and max_dB when min_dB regarded as a mute switch
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