STA321 datasheet(39/157 Pages) STMICROELECTRONICS

Part #	STA321

Description	4-channel digital audio system with FFX??driver

PDF	157 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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39 / 157 page

STA321

Digital processing stage

Doc ID 15351 Rev 3

39/157

6.6

Biquads

The biquads are based on the following equation and is shown diagramatically in Figure 20.

Y[n] = b0 * X[n] + b1 * X[n-1] + b2 * X[n-2] - a1 * Y[n-1] - a2 * Y[n-2]

where Y[n] represents the output and X[n] represents the input. Fractional multipliers

are 24-bit signed with coefficient values in the range -1 (0xFFFFFF) to +1 (0x7FFFFF).

Figure 20.

Biquad filter

6.6.1

Presets

By default all the biquads values in RAM are set to give a bypass function; in actual fact, the

signal passes through unchanged. The coefficients for this are:

a1 / 2 = 0, a2 / 2 = 0, b0 / 2 = 0.5 (0x400000), b1 / 2 = 0, b2 / 2 = 0.

6.7

High-pass filter

The standard high-pass filter is provided by the STA321

Figure 21.

High-pass filter frequency response

b0/2

b1/2

Z -1

-a1/2

-a2

Z -1

−30

−25

−20

−15

−10

−5

Freq. [Hz]

High Pass Filter

STA321 Datasheet(PDF) 39 Page - STMicroelectronics