STA335BWSQS datasheet(57/70 Pages) STMICROELECTRONICS

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STA335BWSQS

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STA335BWSQS generates the RAM addresses as offsets from this base value to write the

complete set of coefficient data.

6.12.18

User-defined EQ

The STA335BWSQS 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 as follows:

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 STA335BWSQS 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 68.

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)

6.12.19

Pre-scale

The STA335BWSQS 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.

6.12.20

Post-scale

The STA335BWSQS 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 0x7FFFFF. When line output is

being used, channel 3 post-scale affects both channels 3 and 4.

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