sta339bw STMicroelectronics, sta339bw Datasheet - Page 66

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

Register description
6.18.1
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Dual-band DRC
The STA339BW provides a dual-band DRC (B
path, as depicted in
Figure 20. B
The low-frequency information (LFE) is extracted from the left and right channels by
removing the high frequencies with a programmable Biquad filter, so that, using the original
signal, the difference signal can be computed. Limiter 1 (DRC1) is then used to control the
left and right high-frequency component amplitudes while limiter 2 (DRC2) is used to control
the low-frequency components (see
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 the left- and right-channel high
frequencies and the LFE-channel amplitude (see
control. Note that, in this configuration, the dedicated channel-3 volume control can actually
be used 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
The cut off frequency can be programmed in two ways, using XO bits in register 0x0C, or
using “user programmable” mode (coefficients stored in RAM adresses 0x28 to 0x31).
For the user programmable mode, use the formulae below to compute the high pass filters:
where alpha = (1-sin(ω
R
R
R
R
L
L
L
L
b0 = (1 + alpha) / 2
b1 = -(1 + alpha) / 2
b2 = 0
2
DRC scheme
Figure
0
))/cos(ω
20. Dual-band DRC is activated by setting MDRC[1:0] = 1x.
Doc ID 15251 Rev 4
Hi-pass
Hi-pass
Hi-pass
Hi-pass
Pass
Pass
B
B
Pass
Pass
B
B
0
Filter
Filter
Filter
Filter
2
2
filter
filter
2
2
filter
filter
DRC
DRC
DRC
DRC
), and ω
2
XO
XO
XO
XO
DRC can be configured specifying the cutoff frequency.
Chapter
0
a0 = 1
a1 = -alpha
a2 = 0
is the cutoff frequency.
-
-
-
-
6.11).
2
DRC) on the left- and right-channel data
Chapter
Volume
Volume
Volume
Volume
Volume
Volume
Volume
Volume
Ch1
Ch1
Ch3
Ch3
Ch3
Ch3
Ch2
Ch2
6.11) as well as their volume
DRC1
DRC1
DRC2
DRC2
DRC2
DRC2
DRC1
DRC1
Limiter
Limiter
Limiter
Limiter
Limiter
Limiter
And
And
And
And
And
And
Vol
Vol
Vol
Vol
Vol
Vol
+
+
+
+
STA339BW