STA320 datasheet(30/37 Pages) STMICROELECTRONICS

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■ write bottom 8-bits of coefficient b2 in I

2C address 1Ah

■ write top 8-bits of coefficient a1 in I

2C address 1Bh

■ write middle 8-bits of coefficient a1 in I

2C address 1Ch

■ write bottom 8-bits of coefficient a1 in I

2C address 1Dh

■ write top 8-bits of coefficient a2 in I

2C address 1Eh

■ write middle 8-bits of coefficient a2 in I

2C address 1Fh

■ write bottom 8-bits of coefficient a2 in I

2C address 20h

■ write top 8-bits of coefficient b0 in I

2C address 21h

■ write middle 8-bits of coefficient b0 in I

2C address 22h

■ write bottom 8-bits of coefficient b0 in I

2C address 23h

■ write 1 to WA bit in I

2C address 24h

The mechanism for writing a set of coefficients to RAM provides a method of updating the five coefficients cor-

responding to a given biquad (filter) simultaneously to avoid possible unpleasant acoustic side-effects. When

using this technique, the 6-bit address would specify the address of the biquad b1 coefficient (e.g. 0, 5, 10, …,

20, … 35 decimal), and the STA320 will generate the RAM addresses as offsets from this base value to write

the complete set of coefficient data.

5.14.22User-Defined EQ

The STA320 provides the ability to specify four EQ filters (biquads) per each of the two input channels. The bi-

quads 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 multipli-

ers, with coefficient values in the range of 800000h (-1) to 7FFFFFh (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 STA320 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 2nd order filters

that use the biquad equation noted above. They are loaded into the C12H0-4 and C3Hy0-4 areas of RAM noted

in the table below.

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