sta339bw STMicroelectronics, sta339bw Datasheet - Page 61

• Manufacturer Part Number: sta339bw
• Description: 2.1-channel High-efficiency Digital Audio System
• Manufacturer: STMicroelectronics

STA339BW
6.12.18
6.12.19
6.12.20
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 * (b
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:
where x represents the channel and the y the biquad number. For example, C2H41 is the b
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 lo-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
By default, all user-defined filters are pass-through where all coefficients are set to 0, except
the b
Pre-scale
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 multiply is loaded into RAM using the same I
and the bass-management. All channels can use the channel-1 pre-scale factor by setting
the Biquad link bit. By default, all pre-scale factors are set to 0x7FFFFF.
Post-scale
The STA339BW provides one additional multiplication after the last interpolation stage and
the distortion compensation on each channel. This post-scaling 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 I
coefficients and the bass-management. This post-scale factor can be used in conjunction
with an ADC equipped micro-controller to perform power-supply error correction. All
channels can use the channel-1 post-scale factor by setting the post-scale link bit. By
default, all post-scale factors are set to 0x7FFFFF. When line output is being used,
channel-3 post-scale will affect both channels 3 and 4.
= b
CxHy0 = b
CxHy1 = b
CxHy2 = -a
CxHy3 = -a
CxHy4 = b
0
/2 coefficient which is set to 0x400000 (representing 0.5)
0
* X[n] + b
0
/ 2) * X[n] + 2 * (b
1
2
0
1
2
/ 2
/ 2
/ 2
1
* X[n-1] + b
Doc ID 15251 Rev 4
1
2
/ 2) * X[n-1] + b
Table
* X[n-2] - a
72.
1
* Y[n-1] - a
2
* X[n-2] - 2 * (a
2
C registers as the biquad coefficients
2
* Y[n-2]
2
1
C registers as the biquad
/ 2) * Y[n-1] - a
Register description
2
* Y[n-2]
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2