max9856 Maxim Integrated Products, Inc., max9856 Datasheet - Page 27

• Manufacturer Part Number: max9856
• Description: Max9856 Low-power Audio Codec With Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9856 digital audio interface includes digital
first-order highpass filters (Table 8) for both the DAC
input and the ADC output. The corner frequency for
each filter is selectable from 5Hz to 4kHz. The DAC fil-
ter (DACHP) can be used to reduce the low-frequency
ADC Interface Register Bit Description (continued)
Table 8. Digital Highpass Filters
0x0B
REG
REGISTER
ANTH
______________________________________________________________________________________
B7
0
ADC Noise Gate Threshold. The MAX9856 features a noise gate that reduces the audible noise at
low signal levels. The noise gate attenuates the output at a rate of 1dB for each 2dB the signal is
below the threshold. ANTH specifies the noise gate threshold level relative to the final ADC output
signal level.
The noise gate can be used in conjunction with AGC or on its own. When AGC is enabled, the noise
gate reduces the output level only when the AGC has set the gain to the maximum setting. Choose a
threshold between -28dB and -48dB when used in conjunction with the AGC. When the AGC is
enabled, the effective noise gate thresholds are increased by 20dB due to the microphone PGA
being set to maximum gain by the AGC.
DirectDrive Headphone Amplifiers
B6
Digital Filters
Low-Power Audio CODEC with
ADCHP
0x0 to 0x5
B5
VALUE
0xA
0xB
0xC
0xD
0x6
0x7
0x8
0x9
0xE
0xF
ADC NOISE GATE THRESHOLD LEVELS
B4
energy sent to speakers incapable of reproducing low
frequencies. The ADC filter (ADCHP) can reduce low-
frequency noise such as wind noise from being con-
verted. The cutoff frequency depends on sample rate
and is shown in Table 9.
FUNCTION
B3
0
B2
THRESHOLD (dB)
Disabled
-64
-60
-56
-52
-48
-44
-40
-36
-32
-28
DACHP
B1
B0
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