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Signal processing library functions

PM0014

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Signal processing library functions

6.1

Overview

In this part, a set of signal processing functions for C programmers on ST10 are presented.

6.2

Data type

LibST10.h (C compiler package) defines the data types used for ST10 programming.

The following types are used in the library:

●

Filter: structure containing all the elements needed for filtering.

Filt.NumberCoeffs : number of filter coefficients.

Filt.NumberOutputSamples : number of output samples.

Filt.CoeffPtr : pointer on filter coefficients.

Filt.InputPtr : pointer on input samples.

Filt.OutputPtr : pointer on output samples.

Filt.DelayLinePtr : pointer on delay line.

Library’s users have to fill the different fields of this structure before calling any filtering

function.

According to the filter type, the number of coefficients definition changes.

Examples:

.FIR:

y(n)=a0*x(n)+a1*x(n-1)+...+a15*x(n-15)

Store NumberCoeffs=16

.IIR direct form

y(n)=b0*x(n)+b1*x(n-1)+...+b15*x(n-15)+a1*y(n-1)+...+a15*y(n-15)

Store NumberCoeffs=32

(a0=0 is stored in memory)

.IIR cascaded biquad form

y(n)=b00*x(n)+...+a02*y(n-2)+.....+a92*y(n-2)

Be careful: store NumberCoeffs = NumberCells = 10 !

The delay line is a buffer in memory used by filtering functions to store previous samples

needed to perform calculation of the next output sample. The delay line size depends on the

number of coefficients.

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