NAME

math::filters - Digital filters

Table Of Contents

• Table Of Contents

• Synopsis

• Description

• PROCEDURES

• Keywords

• Category

• Copyright

SYNOPSIS

package require Tcl 8.6 9
package require TclOO
package require math::filters ?0.3?

::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
  

  • bool lowpass

    Generate a low-pass filter (1) or a high-pass filter (0)

  • integer lowpass

    The order of the filter to be generated

  • double samplefreq

    Sampling frequency of the data series

  • double cutofffreq

    Cut-off frequency for the filter

• ::math::filters::filter coeffs data

  Filter the entire data series based on the filter coefficients.

  • list coeffs

    List of coefficients as generated by filterButterworth (or in fact any similar list of coefficients)

  • list data

    Data to be filtered

• ::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.

  • list coeffs

    List of coefficients as generated by filterButterworth (or in fact any similar list of coefficients)

  • list yinit

    (Optional) initial data for the filter result.

• $filterObj filter x

  Filter a single value and return the result.

  • double x

    The value to be filtered

• $filterObj reset

  Reset the filter object (start anew)

KEYWORDS

digital, filtering

CATEGORY

Mathematics

COPYRIGHT

Copyright © 2020 by Arjen Markus