sta335bw STMicroelectronics, sta335bw Datasheet - Page 47

• Manufacturer Part Number: sta335bw
• Description: 2.1 Channels High Efficiency Digital Audio System
• Manufacturer: STMicroelectronics

STA335BW
5.12.18
5.12.19
5.12.20
User-defined EQ
The STA335BW provides the ability to specify four EQ filters (biquads) per each of the two
input channels. The biquads use the following equation:
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 STA335BW allows specification of 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 noted 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 STA335BW 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 STA335BW 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 7FFFFFh. When Line output is being utilized,
channel 3 post-scale will affect both channels 3 and 4.
Y[n] = 2(b
= 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
Table
0
1
2
0
/2)X[n] + 2(b
1
2
/2
/2
1
/2
X[n-1] + b
29.
2
1
X[n-2] – a
/2)X[n-1] + b
1
Y[n-1] – a
2
X[n-2] – 2(a
2
Y[n-2]
2
C registers as the biquad coefficients
1
/2)Y[n-1] – a
2
C registers as the biquad
2
Y[n-2]
Register description
47/54
2