STA326 datasheet(48/64 Pages) STMICROELECTRONICS

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User programmable processing

STA326

48/64

DocID11531 Rev 9

User programmable processing

8.1

EQ - biquad equation

The biquads use the equation that follows. This is depicted in Figure 19 below.

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 28-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

The x represents the channel and the y the biquad number. For example C3H41 is the b0/2

coefficient in the fourth biquad for channel 3

Figure 19. Biquad filter

8.2

Prescale

The prescale block which precedes the first biquad is used for attenuation when filters are

designed that boost frequencies above 0 dBFS. This is a single 24-bit signed fractional

multiplier, with 0x800000 = -1 and 0x7FFFFF = 0.9999998808. By default, all prescale

factors are set to 0x7FFFFF.

8.3

Postscale

The STA326 provides one additional multiplication after the last interpolation stage and

before the distortion compensation on each channel. This is a 24-bit signed fractional

multiplier. The scale factor for this multiplier is loaded into RAM using the same I2C registers

as the biquad coefficients and the mix. All channels can use the same settings as channel 1

by setting the postscale link bit.

Obsolete

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- Obsolete

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