sta339bw STMicroelectronics, sta339bw Datasheet - Page 67

• Manufacturer Part Number: sta339bw
• Description: 2.1-channel High-efficiency Digital Audio System
• Manufacturer: STMicroelectronics

STA339BW
6.18.2
Note:
A first-order filter is suggested to guarantee that for every ω
filter obtained as difference (as shown in
filter) frequency response, and the corresponding recombination after the DRC has low
ripple. Second-order filters can be used as well, but in this case the filter shape must be
carefully choosen to provide good low pass response and minimum ripple recombination.
For second-order is not possible to give a closed formula to get the best coefficients, but
empirical adjustment should be done.
DRC settings
The DRC blocks used by B
configure automatically the DRC blocks in anticlipping mode. Attack and release thresholds
can be selected using registers 0x32, 0x33, 0x34, 0x35, while attack and release rates are
configured by registers 0x12 and 0x14.
Band downmixing
The low-frequency band is down-mixed to the left and right channels at the B
Channel volume can be used to weight the bands recombination to fine tune the overall
frequency response.
EQ DRC mode
Setting MDRC = 01, it is possible to add a programmable biquad (the XO biquad at RAM
addresses 0x28 to 0x2C is used for this purpose) to the Limiter/compressor measure path
(side chain). Using EQDRC the peak detector input can be shaped in frequency using the
programmable biquad. For example if a +2 dB bass boost is applied (using a low shelf filter
for example), the effect is that the EQDRC out will limit bass frequencies to -2 dB below the
selected attack treshold.
Generally speaking, if the biquad boosts frequency f with an amount of X dB, the level of a
compressed sinusoid at the output will be TH - X, where TH is the selected attack threshold.
EQDRC works only if the biquad frequency response magnitude is >= 0 dB for every
frequency.
Figure 21. EQDRC scheme
Channel in
Channel in
Channel in
Channel in
BIQUAD
BIQUAD
2
DRC are the same as those described in
Doc ID 15251 Rev 4
Figure
detector
detector
detector
detector
Peak
Peak
Peak
Peak
Standard DRC
Standard DRC
EQDRC
EQDRC
20) will have a symmetric (relative to HP
Attenuation
Attenuation
Attenuation
Attenuation
calculator
calculator
calculator
calculator
0
the corresponding low-pass
Chapter
Register description
2
Atten
Atten
Atten
Atten
6.11. B
DRC output.
2
DRC
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