STA308

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Y[n] represents the output and X[n] represents the input. Coefficients are defined in the following manner:

CxHx0 = b2

CxHx1 = b0/2

CxHx2 = -a2

CxHx3 = -a1/2

CxHx4 = b1/2

The first x represents the channel and the second the biquad number. For example C3H41 is the b0/2 coeffi-

cient in the fourth series biquad in channel 3. The biquad link bit allows all channels to use the coefficients of

channel 1.

Bass Management

Channel 6 provides the ability to scale and mix all channels before the biquad block. This allows for information

from any channel to be redirected to this channel and then filtered appropriately for a subwoofer application.

When the BME bit is set (bit D5 of Configuration Register A, at address 00h) the input to the biquad section is

routed from the scale and mix block instead of the normal channel 6 1st stage interpolation output. Eight scaling

coefficients are provided to perform this function. They are labeled CxBMS with x representing the channel that

is being scaled. Each input channel is multiplied by its corresponding scale factor and summed. The output of

the summation is the output of the scale and mix block.

Post-Scale

The STA308 provides one additional multiplication after the last interpolation stage and before the distortion

compensation on each channel. This is a 24-bit signed fractional multiply. The scale factor for this multiply is

loaded into RAM using the same I2C registers as the biquad coefficients and the bass-management. All chan-

nels can use the channel 1 by setting the post-scale link bit.

RAM Block for Biquads and Bass Management:

Index

(Decimal)

Index

(Hex)

Coefficient

Default

0

00h

Channel 1 - Biquad 1

000000h

1

01h

C1H11(b0/2)

3FFFFFh

2

02h

C1H12(a2)

000000h

3

03h

C1H13(a1/2)

000000h

4

04h

C1H14(b1/2)

000000h

5

05h

Channel 1 - Biquad 2

C1H20

000000h

……

…

…

…

24

18h

Channel 1 - Biquad 5

C1H54

000000h

25

19h

Channel 2 - Biquad 1

C2H10

000000h

26

1Ah

C2H11

3FFFFFh

……

…

…

…