mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-11-15 21:01:45 -05:00
96 lines
3.2 KiB
C++
96 lines
3.2 KiB
C++
/*
|
|
July 15, 2015
|
|
Iowa Hills Software LLC
|
|
http://www.iowahills.com
|
|
|
|
If you find a problem with this code, please leave us a note on:
|
|
http://www.iowahills.com/feedbackcomments.html
|
|
|
|
Source: ~Projects\Common\BasicFIRFilterCode.cpp
|
|
|
|
This generic FIR filter code is described in most textbooks.
|
|
e.g. Discrete Time Signal Processing, Oppenheim and Shafer
|
|
|
|
A nice paper on this topic is:
|
|
http://dea.brunel.ac.uk/cmsp/Home_Saeed_Vaseghi/Chapter05-DigitalFilters.pdf
|
|
|
|
This code first generates either a low pass, high pass, band pass, or notch
|
|
impulse response for a rectangular window. It then applies a window to this
|
|
impulse response.
|
|
|
|
There are several windows available, including the Kaiser, Sinc, Hanning,
|
|
Blackman, and Hamming. Of these, the Kaiser and Sinc are probably the most useful
|
|
for FIR filters because their sidelobe levels can be controlled with the Beta parameter.
|
|
|
|
This is a typical function call:
|
|
BasicFIR(FirCoeff, NumTaps, PassType, OmegaC, BW, wtKAISER, Beta);
|
|
BasicFIR(FirCoeff, 33, LPF, 0.2, 0.0, wtKAISER, 3.2);
|
|
33 tap, low pass, corner frequency at 0.2, BW=0 (ignored in the low pass code),
|
|
Kaiser window, Kaiser Beta = 3.2
|
|
|
|
These variables should be defined similar to this:
|
|
double FirCoeff[MAXNUMTAPS];
|
|
int NumTaps; NumTaps can be even or odd, but must be less than the FirCoeff array size.
|
|
TPassTypeName PassType; PassType is an enum defined in the header file. LPF, HPF, BPF, or NOTCH
|
|
double OmegaC 0.0 < OmegaC < 1.0 The filters corner freq, or center freq if BPF or NOTCH
|
|
double BW 0.0 < BW < 1.0 The filters band width if BPF or NOTCH
|
|
TWindowType WindowType; WindowType is an enum defined in the header to be one of these.
|
|
wtNONE, wtKAISER, wtSINC, wtHANNING, .... and others.
|
|
double Beta; 0 <= Beta <= 10.0 Beta is used with the Kaiser, Sinc, and Sine windows only.
|
|
It controls the transition BW and sidelobe level of the filters.
|
|
|
|
|
|
If you want to use it, Kaiser originally defined Beta as follows.
|
|
He derived its value based on the desired sidelobe level, dBAtten.
|
|
double dBAtten, Beta, Beta1=0.0, Beta2=0.0;
|
|
if(dBAtten < 21.0)dBAtten = 21.0;
|
|
if(dBAtten > 50.0)Beta1 = 0.1102 * (dBAtten - 8.7);
|
|
if(dBAtten >= 21.0 && dBAtten <= 50.0) Beta2 = 0.5842 * pow(dBAtten - 21.0, 0.4) + 0.07886 * (dBAtten - 21.0);
|
|
Beta = Beta1 + Beta2;
|
|
|
|
*/
|
|
|
|
#ifndef _WFIR_H_
|
|
#define _WFIR_H_
|
|
|
|
#include "export.h"
|
|
|
|
class SDRBASE_API WFIR
|
|
{
|
|
public:
|
|
enum TPassTypeName
|
|
{
|
|
LPF, HPF, BPF, NOTCH
|
|
};
|
|
|
|
enum TWindowType
|
|
{
|
|
wtNONE,
|
|
wtKAISER,
|
|
wtSINC,
|
|
wtHANNING,
|
|
wtHAMMING,
|
|
wtBLACKMAN,
|
|
wtFLATTOP,
|
|
wtBLACKMAN_HARRIS,
|
|
wtBLACKMAN_NUTTALL,
|
|
wtNUTTALL,
|
|
wtKAISER_BESSEL,
|
|
wtTRAPEZOID,
|
|
wtGAUSS,
|
|
wtSINE,
|
|
wtTEST
|
|
};
|
|
|
|
static void BasicFIR(double *FirCoeff, int NumTaps, TPassTypeName PassType,
|
|
double OmegaC, double BW, TWindowType WindowType, double WinBeta);
|
|
|
|
private:
|
|
static void WindowData(double *Data, int N, TWindowType WindowType,
|
|
double Alpha, double Beta, bool UnityGain);
|
|
static double Bessel(double x);
|
|
static double Sinc(double x);
|
|
};
|
|
|
|
#endif
|