STA3398 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
STA3398
STMicroelectronics
'STA3398' PDF : 78 Pages View PDF
Register description
STA339BW
7.12.18
User-defined EQ
The STA339BW can be programmed for four EQ filters (biquads) per each of the two input
channels. The biquads use the following equation:
Y[n] = 2 * (b0 / 2) * X[n] + 2 * (b1 / 2) * X[n-1] + b2 * X[n-2] - 2 * (a1 / 2) * Y[n-1] - a2 * Y[n-2]
= b0 * X[n] + b1 * X[n-1] + b2 * X[n-2] - a1 * Y[n-1] - a2 * Y[n-2]
where Y[n] represents the output and X[n] represents the input. Multipliers are 24-bit signed
fractional multipliers, with coefficient values in the range of 0x800000 (-1) to 0x7FFFFF
(0.9999998808).
Coefficients stored in the user defined coefficient RAM are referenced in the following
manner:
CxHy0 = b1 / 2
CxHy1 = b2
CxHy2 = -a1 / 2
CxHy3 = -a2
CxHy4 = b0 / 2
where x represents the channel and the y the biquad number. For example, C2H41 is the b2
coefficient in the fourth biquad for channel 2.
Additionally, the STA339BW can be programmed for a high-pass filter (processing
channels 1 and 2) and a low-pass filter (processing channel 3) to be used for
bass-management crossover when the XO setting is 000 (user-defined). Both of these filters
when defined by the user (rather than using the preset crossover filters) are second order
filters that use the biquad equation given above. They are loaded into the C12H0-4 and
C3Hy0-4 areas of RAM noted in Table 73.
By default, all user-defined filters are pass-through where all coefficients are set to 0, except
the b0/2 coefficient which is set to 0x400000 (representing 0.5)
7.12.19
Prescale
The STA339BW provides a multiplication for each input channel for the purpose of scaling
the input prior to EQ. This pre-EQ scaling is accomplished by using a 24-bit signed
fractional multiplier, with 0x800000 = -1 and 0x7FFFFF = 0.9999998808. The scale factor
for this multiplication is loaded into RAM using the same I2C registers as the biquad
coefficients and the bass management. All channels can use the channel-1 prescale factor
by setting the Biquad link bit. By default, all prescale factors are set to 0x7FFFFF.
7.12.20
Postscale
The STA339BW provides one additional multiplication after the last interpolation stage and
the distortion compensation on each channel. This postscaling is accomplished by using a
24-bit signed fractional multiplier, with 0x800000 = -1 and 0x7FFFFF = 0.9999998808. The
scale factor for this multiply is loaded into RAM using the same I2C registers as the biquad
coefficients and the bass management. This postscale factor can be used in conjunction
with an ADC equipped microcontroller to perform power-supply error correction. All
channels can use the channel-1 postscale factor by setting the postscale link bit. By default,
all postscale factors are set to 0x7FFFFF. When line output is being used, channel-3
postscale will affect both channels 3 and 4.
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DocID15251 Rev 7
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