AK4635 datasheet(41/81 Pages) AKM

41 / 81 page

[AK4635]

Rev. 0.6

2007/10

- 41 -

■ Digital Programmable Filter Circuit

The AK4635 has 2 steps of 1st order HPF, 1st order LPF and 5-band Equalizer built-in in a recording path and a playback

path.

(1) High Pass Filter (HPF)

Normally, this HPF is used as a Wind-Noise Reduction Filter. This is composed with 2 steps of 1st order HPF. The

coefficient of both HPF is the same and set by F1A13-0 bits and F1B13-0 bits. HPFAD bit controls ON/OFF of the 1st

step HPF and HPF bit controls ON/OFF of the 2nd step HPF. When the HPF is OFF, the audio data passes this block by

0dB gain. The coefficient should be set when HPFAD = HPF bits = “0” or PMADC = PMPFIL bits = “0”.

fs : Sampling frequency

fc : Cut-off frequency

HPF: F1A[13:0] bits = A, F1B[13:0] bits = B

(MSB = F1A13, F1B13; LSB = F1A0, F1B0)

A =

1 + tan (

πfc/fs)

B =

− tan (πfc/fs)

1 + tan (

πfc/fs)

The cut-off frequency should be set as below.

fc/fs ≥ 0.0001 (fc min = 1.6Hz at 16kHz)

(2) Low Pass Filter(LPF)

This is composed with 1st order LPF. F2A13-0 bits and F2B13-0 bits set the coefficient of LPF. LPF bit controls ON/OFF

of the LPF. When the LPF is OFF, the audio data passes this block by 0dB gain. The coefficient should be set when LPF

bit = “0” or PMPFIL bits = “0”.

fs : Sampling frequency

fc : Cut-off frequency

LPF: F2A[13:0] bits =A, F2B[13:0] bits =B

(MSB=F2A13, F1B13; LSB=F2A0, F2B0)

A =

1 + 1 / tan (

πfc/fs)

B =

− 1 / tan (πfc/fs)

1 + 1 / tan (

πfc/fs)

The cut-off frequency should be set as below.

fc/fs ≥ 0.05 (fc min = 2205Hz at 44.1kHz)

AK4635 Datasheet(PDF) 41 Page - Asahi Kasei Microsystems

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