sta381bw STMicroelectronics, sta381bw Datasheet - Page 142

• Manufacturer Part Number: sta381bw
• Description: Sound Terminal 2.1-channel High-efficiency Digital Audio System
• Manufacturer: STMicroelectronics

Register description: Sound Terminal compatibility
7.16.2
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Sub-band decomposition
The sub-band decomposition for B
The cutoff frequency can be programmed in two ways, using the XO bits in register 0x0C, or
using the “user programmable” mode (coefficients stored in RAM addresses 0x28 to 0x31).
For the user-programmable mode, use the formulas below to compute the high-pass filters:
where alpha = (1-sin(ω
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 chosen to provide good low-pass response and minimum ripple recombination. For
second-order filters, it 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.
Extended post-scale range
Table 154. Extended post-scale range
Post-scale is an attenuation by default. When PS48DB is set to 1, a 48-dB offset is applied
to the coefficient RAM value, so post-scale can act as a gain too.
b0 = (1 + alpha) / 2
b1 = -(1 + alpha) / 2
b2 = 0
PS48DB
0
1
0
))/cos(ω
Post-scale value is applied as defined in coefficient RAM
Post-scale value is applied with +48 dB offset with respect to the
coefficient RAM value
2
DRC are the same as those described in
Doc ID 018835 Rev 2
0
), and ω
2
DRC can be configured specifying the cutoff frequency.
Figure
0
a0 = 1
a1 = -alpha
a2 = 0
is the cutoff frequency.
24) will have a symmetric (relative to the HP
Mode
0
the corresponding low-pass
Chapter
2
7.11. B
DRC output.
STA381BW
2
DRC