AK4636 Datasheet, PDF (55/105 Pages) Asahi Kasei Microsystems – 16-Bit Mono CODEC with ALC & MIC/SPK/Video-AMP

[AK4636]
6. Noise Suppression
The Noise Suppression is enabled when NSCE bit (Noise suppression enable bit) = “1” during ALC operation (ALC1 bit
= “1”). This function attenuates output signal level automatically when minute amount of the signal is input.
NSCE bit: Noise Suppression Enable
0: Disable (default)
1: Enable
(1) Noise Level Suppressing Operation
The output signal (Note 34) is suppressed when the input peak level is lower than “Noise Suppression Threshold Low
Level” set by NSTHL3-0 bits (Table 38) during the waiting time set by WTM2-0 bits (Table 30).
VOL value is changed by this noise suppressing operation only at the individual zero crossing points of Lch and Rch or at
the zero crossing timeout. Noise level suppressing operation has common zero cross timeout period to ALC recovery
operation which is set by ZTM1-0 bits. (Table 29)
This operation sets the volume automatically to the reference level (Table 42) with zero cross detection in the period
which is set by ZTM1-0 bits (Table 29). It is executed in the cycle of WTM2-0 bits settings.
Note 34. When the input signal volume is smaller than the value set by NSREF7-0 bits, normal ALC recovery operation
is executed.
NSTHL3
0
0
0
0
0
0
0
0
1
1
1
NSTHL2
NSTHL1
NSTHL0
Noise Suppression
Threshold Low Level
Step
0
0
0
−81dB
(default)
0
0
1
−78dB
0
1
0
−75dB
0
1
1
−72dB
1
0
0
−69dB
1
0
1
−66dB
3dB
1
1
0
−63dB
1
1
1
−60dB
0
0
0
−57dB
0
0
1
−54dB
0
1
0
−51dB
Table 38. Noise Suppression Threshold Low Level
NATT1 bit NATT0 bit ATT STEP
0
0
1/4 (Note 35)
0
1
1/2 (Note 36)
1
0
1
1
1
2
Table 39. Noise ATT Settings
(default)
Note 35. 1step attenuated in 4 x “WTM cycles”.
Note 36. 1step attenuated in 2 x “WTM cycles”.
MS1012-E-01
- 55 -
2010/08