sddsdigfilter performs time-domain digital filtering of columns of data. Filters can be combined in series and/or cascade to produce complex filter characteristics. In addition to allowing simple 1-pole lowpass and highpass filters, filter charateristics can be defined using either digital ’Z’ or analog ’S’ domain transfer functions.
A digital filter has a Z transform given by
while an analog filter has a Laplace transform given by
Pass data through lowpass filter with a -3dB cutoff of 0.01 Hz:
sddsdigfilter data.wf -col=time,value result.wf -low=1,0.01.
Bandstop filter between 10 Hz and 100 Hz:
sddsdigfilter data.wf -col=time,value result.wf -low=1,10 -high=1,100
Bandpass filter between 10 Hz and 100 Hz:
sddsdigfilter data.wf -col=time,value result.wf -low=1,100 -cascade -high=1,10
Analog transfer function:
sddsdigfilter data.wf -col=time,value result.wf -analog=D,1.0,0.01,C,0.1,0.3,1.6
Five-sample digital delay:
sddsdigfilter data.wf -col=time,value result.wf -digital=B,0,0,0,0,0,1
sddsdigfilter [inputFile] [outputFile] [-pipe=[input][,output]] -columns=xName,yName [-proportional=gain] [-lowpass=gain,cutoffFrequency] [-highpass=gain,cutoffFrequency] [-digitalfilter=sddsfile,aCoeffName,bCoeffName [-digitalfilter=[A,a0,a1,..,am][,B,b0,b1,..,bn] [-analogfilter=sddsfile,cCoeffName,dCoeffName [-analogfilter=[C,c0,c1,..,cm][,D,d0,d1,..,dn] [-cascade] [-verbose]
- -pipe[=input][,output] — The standard SDDS Toolkit pipe switch.
- -columns=xName,yName — The names of the input file data columns.
- -proportional=gain — Defines a gain stage, where gain is the multiplier applied to the data.
- -lowpass=gain,cutoffFrequency — Defines a lowpass filter stage, where gain is the mutiplier applied to the data and cutoffFrequency is the -3dB point of the filter in units appropriate to the supplied xName.
- -highpass=gain,cutoffFrequency — Defines a highpass filter stage, where gain is the multiplier applied to the data and cutoffFrequency is the -3dB point of the filter in units appropriate to the supplied xName.
- -digitalfilter=sddsfile,aCoeffName,bCoeffName — Defines a digital filter with coefficients in the supplied SDDS coefficient file. This file must cointain two columns containing the A and B coefficients of a digital ’Z’ transfer function. Note that control theory convention assumes that the A0 coefficient is always 1.0. To ensure consistency with the SDDS file, the a0 coefficient is the first row in the A-column and must be implicitly supplied. Although there is little benefit to setting a0 to anything other than 1.0, it is allowed.
- -digitalfilter=[A,a0,a1,...,am][,B,b0,b1,...,bn] — Defines a digital filter with the A and B coefficients of the digital ’Z’ transfer function supplied on the command line. Either A or B or both coefficients can be supplied. If no A coefficients are supplied, a0 is set to 1.0. Equally, if no B coefficients are supplied, b0 is set to 1.0. If different numbers of A and B coefficients are suppied, the filter order is determined from the largest order.
- -analogfilter=sddsfile,cCoeffName,dCoeffName — Defines an analog filter with coefficients in the supplied sdds cefficient file. This file must cointain two columns containing the C and D coefficients of an analog ’s’ transfer function. Conversion to the digital domain is done using a bilinear transform. Note that the user must ensure adequate data sampled, since the general format does not allow frequency warping based on the filter cutoff frequency.
- -analogfilter=[A,a0,a1,...,am][,B,b0,b1,...,bn] — Defines an analog filter with the C and D coefficients of the analog ’S’ transfer function supplied on the command line. Either C or D or both coefficients can be supplied. If no C coefficients are supplied, then c0 is set to 1.0. Equally, if no D coefficients are supplied, then d0 is set to 1.0. Conversion to the digital domain is done using a bilinear transform. Note that the user must ensure adequate data sampled, since the general format does not allow frequency warping based on the filter cutoff frequency.
- -cascade — Defines the start of a new filter stage. Any number of filter stages can be supplied for a single data set. If more than one filter is defined, then the outputs are summed unless the -cascade switch is supplied between the filter definitions in which case the output of the first filter stage is fed into the input of the subsequent filter stage.
- -verbose — Prints the filter coefficients for each filter stage.