STA339BW datasheet(21/78 Pages) STMICROELECTRONICS

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STA339BW

Processing data paths

The whole processing chain is composed of two consecutive sections. In the first one

dual-channel processing is implemented, as described below. Then each channel is fed into

the post-mixing block where there is a choice of processing, either the dual-band DRC is

disabled or it is enabled. When B2DRC is disabled a third channel, typically used in 2.1

output configuration and with cross-over filters enabled, is used. When B2DRC is enabled

the 2.0 output configuration with cross-over filters for defining the cutoff frequency of the two

bands is used.

The first section, Figure 8, begins with a 2x oversampling FIR filter allowing a 2 * fs audio

processing. Then a selectable high-pass filter removes the DC level (enabled if HFB = 0).

The channel 1 and 2 processing chain can include up to 8 filters, depending on the selected

configuration (bits BQL, BQ5, BQ6, BQ7 and XO[3:0]).

By default, four 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 are linked (BQL = 1) then it is possible to use the de-emphasis, bass

and treble filter in a user defined configuration (provided the relevant BQx bits are set to 1).

In other words both channels use the same processing coefficients and can have up to 7

filters each. Note that if BQL = 0 the BQx bits are ignored and the 5th, 6th and 7th filters are

configured as de-emphasis, bass and treble controls, respectively.

Moreover the common 8th filter, from the subsequent processing section, can be available

on both channels (provided the pre-defined cross-over frequencies are not used,

XO[3:0] = 0, and the dual-band DRC is not used).

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

(lower schematic in Figure 9) they are fully user-programmable and allow a third channel

(2.1 outputs) to be generated. Alternatively, in B2DRC mode (upper schematic in Figure 9),

those blocks will be used to split the sub-band and define the cutoff frequencies of the two

bands. A prescaler and a final post scaler allow full control over the signal dynamics before

and after, respectively, the filtering stages. A mixer function is also available.

Figure 8. Left and right processing part 1

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