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SOFiA Radial Filter Improvement
This function improves the FIR radial filters from SOFiA M/F. The filters are made causal and are windowed in time domain. The DC components are estimated. The R/F/I module should always be inserted to the filter path when treating measured data even if no use is made of the included kernel downscaling or highpass filters.
INFORMATION
If HPF is on (highPass>0) the radial filter kernel is
downscaled by a factor of two. Radial Filters and HPF share the available taps and the latency keeps constant. Be careful using very small signal blocks because there may remain too few taps. Observe the filters by plotting their spectra and impulse responses.
 Be very carefull if NFFT/max(kr) < 25 (Low spectral density)
 Do not use R/F/I if NFFT/max(kr) < 15 (Very low spectral density)
 Do NOT use R/F/I for single open sphere filters (e.g.simulations).
IMPORTANT
Remember to choose a fftoversize factor (F/D/T) large enough to cover all filter latencies and reponse slopes. Otherwise undesired cyclic convolution artifacts may appear in the output signal.
ARGUMENTS
Input
Name 
Type 
Purpose 
Default 
dn 
complex float mtx 
Analytical frequency domain radial filter coeficients from M/F 
 
kernelDownscale 
int 
Downscale filer kernel in powers of 2 
2 
highPass 
float 
Highpass Filter 0:highPass:1,
highPass = 1 corresponds to the max kr available.
highPass = 0 filter off (#default) 
0 
Output
Name 
Type 
Purpose 
dn 
complex float mtx 
Improved frequency domain radial filter coeficients 
kernelSize 
int 
current total size of the filter kernel (in samples) 
latency 
int 
approximated latency due to the filters (in samples) 
FILE(S):
File 
Type 
OS/Matlab 
sofia_rfi.m 
Help header, Function 
All OS 
HEADER
/*
function [dn, kernelSize, latency] = sofia_rfi(dn, kernelDownScale, highPass)


dn 
Improved radial filters 
kernelSize 
Filter kernel size (total) 
latency 
Approximate signal latency due to the filters 
 
dn 
Analytical frequency domain radial filters from SOFiA M/F 
kernelDownScale 
Downscale factor for the filter kernel #default: 2 
highPass 
Highpass Filter 0:highPass:1
HighPass = 1 corresponds to the max kr available
HighPass = 0 filter off (#default) 
*/ 

