Raymond Yau wrote:
2010/5/25 Clemens Ladisch clemens@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 ?
/*
- DAC volume attenuation mixer control (-64dB to 0dB)
*/
Apparently just copied from pontis.c.
static int ak4396_dac_vol_info(struct snd_kcontrol *kcontrol, struct snd_ctl_elem_info *uinfo) { uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER; uinfo->count = 2; uinfo->value.integer.min = 0; /* mute */ uinfo->value.integer.max = 0xFF; /* linear */ return 0; } ... static const DECLARE_TLV_DB_SCALE(db_scale_wm_dac, -12700, 100, 1);
And this defines a dB scale from -127 dB to +128 dB, which will break PulseAudio's volume calculations.
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
No; the AK4396 datasheet mentions -48 dB only because this is the minimum attenuation that isn't completely mute. The minimum of the ATT_DATA registers _is_ zero, i.e. -inf dB, and therefore TLV_DB_GAIN_MUTE is the correct minimum for the dB range.
Regards, Clemens