STA335BW datasheet(47/54 Pages) STMICROELECTRONICS

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STA335BW

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5.12.18

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:

Y[n] = 2(b0/2)X[n] + 2(b1/2)X[n-1] + b2X[n-2] – 2(a1/2)Y[n-1] – a2Y[n-2]

= b0X[n] + b1X[n-1] + b2X[n-2] – a1Y[n-1] – a2Y[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 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 Table 29.

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)

5.12.19

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 I2C registers as the biquad coefficients

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.

5.12.20

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 I2C registers as the biquad

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.

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