ADAU1373 Datasheet, PDF (65/296 Pages) Analog Devices – Low Power Codec with Speaker and Headphone Amplifier

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:
(6)
k = 10 ²⁰ = 1.995262314968880
α
(1 − sin( ⁶⁰⁰⁰ × 2π ))
=
48000
= 0.414213562373095
cos( ⁶⁰⁰⁰ × 2π )
48000
p0 = ^{(1 + k) − (1 − k) × α = 1.703756731973916}
2
p1 = ^{(1 − k) − (1 + k) × α = −1.117970294347011}
2
p2 = 0
d1 = α = 0.414213562373095
d2 = 0
1. 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
2. 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
3. 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
Register 0x7F can be used to set the parameters of the block
(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
ADAU1373
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. 7 6 5
43 21
0
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
5
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
Rev. 0 | Page 65 of 296