STA333BW
5 Processing data paths
Processing data paths
Figure 7 and
Figure 8
below show the data processing paths inside STA333BW. The whole processing chain is composed of two consecutive sections. In the first one, dual-channel processing is implemented and in the second section each channel is fed into the post mixing block either to generate a third channel (typically used in 2.1 output configuration and with crossover filters enabled) or to have the channels processed by the DRC block (2.0 output configuration with crossover filters used to define the cut-off frequency of the two bands).
The first section, Figure 7
, begins with a 2x oversampling FIR filter providing 2 * f
S
audio processing. Then a selectable high-pass filter removes the DC level (enabled if HPB = 0).
The left and right channel processing paths can include up to 8 filters, depending on the selected configuration (bits BQL, BQ5, BQ6, BQ7 and XO[3:0]). By default, four user programmable, independent filters per channel are enabled, plus the preconfigured de-emphasis, bass and treble controls (BQL = 0, BQ5 = 0, BQ6 = 0, BQ7 = 0).
If the coefficient sets for the two channels are linked (BQL = 1) it is possible to use the de-emphasis, bass and treble filters in a user defined configuration (provided the relevant
BQx bits are set). In this case both channels use the same processing coefficients and can have up to seven filters each. If BQL = 0 the BQx bits are ignored and the fifth, sixth and seventh filters are configured as de-emphasis, bass and treble controls, respectively.
Figure 7. Left and right processing, section 1 x2
FIR
I2S input interface
FIR
FIR sampling
Hi-Pass
Filter
Biquad
#1
Biquad
#2
Biquad
#3
Biquad
#4
Moreover, the common 8th filter can be available on both channels provided the predefined crossover frequencies are not used, XO[3:0] = 0, and the DRC is not used.
In the second section,
Figure 8 , mixing and crossover filters are available. If DRC is not
enabled they are fully user-programmable and allow the generation of a third channel
(2.1 outputs). Alternatively, in mode DRC, these blocks are used to split the sub-band and define the cut-off frequencies of the two bands. A prescaler and a final postscaler allow full control over the signal dynamics before and after the filtering stages. A mixer function is also available.
DocID13773 Rev 5 17/68
68
Processing data paths
Figure 8. Left and right processing, section 2
STA333BW
18/68 DocID13773 Rev 5
