February 2009

Rev 1

1/6

AN2874

Applications note

BQD filter design equations

1

Introduction

A generalized set of equations is formulated for the design of first-order and second-order

low-pass and high-pass filters. A specialized set of equations is then given for the design of

parametric biquad EQ filters.

The parameters governing the characteristics of the filter are:

!

!

!

Q factor

!

These parameters can be used to determine the coefficients of the filter transfer function.

The transfer function for a first-order filter in the digital z-domain can be written as:

And for a second-order filter as:

This document can be used in conjunction with all the ST digital audio devices having EAQ

filters onboard. These include STA309A, STA320, STA321, STA33xBW and several others.

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