ADAU1373BCBZ-R7 datasheet(65/296 Pages) AD

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ADAU1373

Rev. 0 | Page 65 of 296

High-Pass Shelving Filter

If Band 7 is intended to operate as a high-pass shelving filter

and the cutoff frequency of the filter is 6 kHz, peak gain is 6 dB,

and the input signal sampling frequency is 48 kHz, the coeffi-

cients are as follows:

)

(

= 1.995262314968880

)

48000

6000

cos(

))

48000

6000

sin(

(

−

= 0.414213562373095

)

(

)

(

−

= 1.703756731973916

)

(

)

(

−

= −1.117970294347011

p2 = 0

d1 = α = 0.414213562373095

d2 = 0

Transfer the coefficients to integer numbers:

p0 = round(1.703756731973916 × 8192) = 13957

p1 = round(−1.117970294347011 × 8192) = −9158

p2 = 0

d1 = round(0.414213562373095 × 8192) = 3393

d2 = 0

Represent the integer coefficients using 16-bit, twos

complement hexadecimal values:

p0 = 16-bit 0x3685

p1 = 16-bit 0xDC3A

p2 = 16-bit 0x0000

d1 = 16-bit 0x0D41

d2 = 16-bit 0x0000

Therefore, the registers representing the EQ7 coefficients

should be set as follows:

EQ7 COEF0M = 8’0x36, EQ7 COEF0L = 8’0x85;

EQ7 COEF1M = 8’0xDC, EQ7 COEF1L =8’0x3A;

EQ7 COEF2M = 8’0x0D, EQ7 COEF2L = 8’0x41

BASS ENHANCEMENT

The bass enhancement block can be used to increase the low

frequency content of the stereo signal. Register 0x7E and

(see Table 27 and Table 28).

The left and right channels sum together to perform the bass

enhancement algorithm. If only the left channel is selected, the

left channel performs the desired flow alone. The input selection

for the block is available via the BASS_SEL bits (Register 0x7F,

Bits[1:0]). The input to the block is low-pass filtered. The cutoff

frequency for the low-pass filter (LPF) can be set using the

BASS_LPF bit (Register 0x7E, Bit 5). The signal is passed through

the clipper, which generates the harmonics of the input signal.

The clipper threshold can be set using the BASS_CUT bits

(Register 0x7E, Bits[4:2]). The input signal that exceeds the clip

threshold is clipped. The clipped signal is then passed through

the band-pass filter, which removes the low and high frequency

content. This bass-rich signal is then mixed with the high-pass

filtered version of the input signal to form the final processed

signal. The BASS_SPK bits (Register 0x7E, Bits[1:0]) can be

used to set the low cutoff frequency of the speaker in the system

to prevent overloading of the speaker. The gain can be set using

the BASS_GAIN bits (Register 0x7F, Bits[4:2]).

Table 27. Bit Map of Register 0x7E and Register 0x7F

Reg.

Addr.

0x7E

BASS_LPF

BASS_CUT[2:0]

BASS_SPK[1:0]

0x7F

BASS_GAIN[2:0]

BASS_SEL[1:0]

Table 28. Register 0x7E and Register 0x7F Bit Descriptions

Reg.

Addr.

Bits

Bit Name

Description

0x7E

[7:6]

RESERVED

Reserved

BASS_LPF

Bass output frequency range

0: 801 Hz

1: 1001 Hz

[4:2]

BASS_CUT

Bass signal extend density (clip

level)

000: Reserved

001: 0.125

…: Step size of 0.125

111: 0.875

[1:0]

BASS_SPK

Cutoff frequency setting

00: 158 Hz

01: 232 Hz

10: 347 Hz

11: 520 Hz

0x7F

[7:5]

RESERVED

Reserved

[4:2]

BASS_GAIN

Bass enhancement gain

000: Reserved; not open to user

001: 0 dB

010: 6 dB

011: 9.5 dB

100: 12 dB

101: 14 dB

110: 15.5 dB

111: 17 dB

[1:0]

BASS_SEL

Left/right channel selection

00: both channels off

01: left channel on

10: right channel on

11: both channels on

ADAU1373BCBZ-R7 Datasheet(PDF) 65 Page - Analog Devices

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