AN3984 Datasheet, PDF (1/46 Pages) STMicroelectronics – The purpose of this document is to provide a tool to calculate

AN3984
Application note
IIR filter design equations for Sound Terminal^® devices
Introduction
The purpose of this document is to provide a tool to calculate the IIR filter coefficients to
program the Sound Terminal^® devices from STMicroelectronics.
For each filter the procedure and the formulas to calculate the coefficient will be described;
the Matlab code is given in Appendix A: Matlab code (functions) on page 24.
A generalized set of equations can be formulated for the design of first-order low-pass and
high-pass filters and of second-order filters.
A specialized set of equations is devised for designing parametric biquad EQ filters. As with
any other filter design procedure, the desired characteristics of the filter are to be made
available.
The parameters governing the characteristics of each filter are:
■ fc: filter cutoff frequency which is the -3dB corner frequency or the midpoint frequency in
a peak or notch filter
■ fs: sampling frequency
■ Q: quality factor (not applicable for low and high-shelf filters)
■ Slope: applicable only for low and high-shelf filters
■ Gain: the boost or the attenuation at f = fc
These parameters can be used to determine the coefficients of the digital filter transfer
function.
September 2011
Doc ID 022240 Rev 1
1/46
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