STA339BWS datasheet(18/79 Pages) STMICROELECTRONICS

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Processing data paths

STA339BWS

18/79

DocID015276 Rev 8

Processing data paths

Figure 7 and Figure 8 below show the data processing paths inside STA339BWS. 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

dual-band 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 * fS 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

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 dual-band DRC is not used.

In the second section, Figure 8, mixing and crossover filters are available. If B2DRC is not

enabled they are fully user-programmable and allow the generation of a third channel

(2.1 outputs). Alternatively, in mode B2DRC, 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.

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