Register description: New Map
STA380BW
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with the original signal. Limiter 1 (DRC1) is then used to control the amplitude of the left/right
high-frequency components, while limiter 2 (DRC2) is used to control the low-frequency
components (see
Section 6.22: Dynamic control registers (addr 0x23 - 0x26 / addr 0x43 -
The cutoff frequency of the high-pass filters can be user-defined, XO[3:0] = 0, or selected
from the pre-defined values.
DRC1 and DRC2 are then used to independently limit L/R high frequencies and LFE
channel amplitude (see
Section 6.22: Dynamic control registers (addr 0x23 - 0x26 / addr
) as well as their volume control. To be noted that, in this configuration, the
dedicated channel 3 volume control can actually act as a bass boost enhancer as well (0.5
dB/step resolution).
The processed LFE channel is then recombined with the L and R channels in order to
reconstruct the 2.0 output signal.
Sub-band decomposition
The sub-band decomposition for B
2
DRC can be configured specifying the cutoff frequency.
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(
0
))/cos(
0
), and
0
is the cutoff frequency.
A first-order filter is recommended to guarantee that for every
0
the corresponding
low-pass filter obtained as difference (as shown in
) will have a symmetric (relative
to the HP 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
2
DRC are the same as those described in
control registers (addr 0x23 - 0x26 / addr 0x43 - 0x46)
2
DRC 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
2
DRC output.
Channel volume can be used to weight the bands recombination to fine-tune the overall
frequency response.
b0 = (1 + alpha) / 2
a0 = 1
b1 = -(1 + alpha) / 2
a1 = -alpha
b2 = 0
a2 = 0
Obsolete Product(s) - Obsolete Product(s)