STA339BW
5
Processing data paths
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
Sampling
Sampling
If BQ5=1 If BQ6=1 IF BQ7=1
frequency = fs
frequency = 2 * fs
and BQL=1 and BQL=1 and BQL=1
Biquad
Biquad Biquad
#5
#6
#7
x2
FxI2R
PPrre-Sscale Hi-Ppass
oFvIRer
fFilitleterr
Biquad
#1
Biquad
#2
Biquad
#3
Biquad
#4
De-Emph.
Bass
Treble
L
L
saomvpelring
From
I2S input
interface
If HPB=0
User-defined filters
If DEMP=0
If C1TCB=0
BTC: bass boost/cut
TTC: treble boost/cut
If DSPB=0 and C1EQBP=0
If BQ5=1 If BQ6=1 IF BQ7=1
and BQL=1 and BQL=1 and BQL=1
Biquad
Biquad Biquad
#5
#6
#7
x2
FxI2R
PPrre-Sscale Hi-Ppaassss
oFvIRer
Ffiilltteerr
Biquad
#1
Biquad
#2
Biquad
#3
Biquad
#4
De-Emph.
Bass
Treble
LR
saomvpelring
If HPB=0
User-defined filters
If DSPB=0 and C2EQBP=0
If DEMP=0
If C2TCB=0
BTC: bass boost/cut
TTC: treble boost/cut
DocID15251 Rev 7
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