Reference

filtergen(3tcl)

Digital filters


        
    

    
        

            
                
NAME

            
            
    
    
        
            
math::filters - Digital filters

        
    


        

    

    
        

            
                
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 (c) 2020 by Arjen Markus



        
    


        

    



        
            

                
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