NAME¶

math::filters - Digital filters

SYNOPSIS¶

package require Tcl 8.6

package require TclOO

package require math::filters ?0.1?

::math::filters::filterButterworth lowpass order samplefreq cutofffreq

::math::filters::filter coeffs data

::math::filters::filterObj new coeffs yinit

$filterObj filter x

$filterObj reset

DESCRIPTION¶

The math::filters package implements digital filters, notably Butterworth low-pass and high-pass filters. The procedures allow to filter an entire data series as well as filter data one by one.

PROCEDURES¶

The package defines the following public procedures:

::math::filters::filterButterworth lowpass order samplefreq cutofffreq

Determine the coefficients for a Butterworth filter of given order. The coefficients are returned as a list of the x-coefficients, the y-coefficients and the scale. The formula is (n is the filter order):

                   n             n


    scale * y_k = sum x_(k-i) + sum y_(k-i)


                  i=0           i=1

::math::filters::filter coeffs data

Filter the entire data series based on the filter coefficients.

::math::filters::filterObj new coeffs yinit

Create a filter object. The initial x data are taken as zero. The initial y data can be prescribed. If they are not given, they are taken as zero as well.

$filterObj filter x

Filter a single value and return the result.

$filterObj reset

Reset the filter object (start anew)

KEYWORDS¶

digital, filtering

CATEGORY¶

Mathematics

COPYRIGHT¶

Copyright (c) 2020 by Arjen Markus