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CLK/SignalProcessing/FIRFilter.hpp
2017-03-26 14:34:47 -04:00

91 lines
2.4 KiB
C++

//
// LinearFilter.h
// Clock Signal
//
// Created by Thomas Harte on 01/10/2011.
// Copyright 2011 Thomas Harte. All rights reserved.
//
#ifndef FIRFilter_hpp
#define FIRFilter_hpp
/*
The FIR filter takes a 1d PCM signal with
a given sample rate and filters it according
to a specified filter (band pass only at
present, more to come if required). The number
of taps (ie, samples considered simultaneously
to make an output sample) is configurable;
smaller numbers permit a filter that operates
more quickly and with less lag but less
effectively.
FIR filters are window functions; expected use is
to point sample an input that has been subject to
a filter.
*/
#ifdef __APPLE__
#include <Accelerate/Accelerate.h>
#endif
namespace SignalProcessing {
class FIRFilter {
public:
/*!
Creates an instance of @c FIRFilter.
@param number_of_taps The size of window for input data.
@param input_sample_rate The sampling rate of the input signal.
@param low_frequency The lowest frequency of signal to retain in the output.
@param high_frequency The highest frequency of signal to retain in the output.
@param attenuation The attenuation of the discarded frequencies.
*/
FIRFilter(unsigned int number_of_taps, float input_sample_rate, float low_frequency, float high_frequency, float attenuation);
~FIRFilter();
/*! A suggested default attenuation value. */
constexpr static float DefaultAttenuation = 60.0f;
/*!
Applies the filter to one batch of input samples, returning the net result.
@param src The source buffer to apply the filter to.
@returns The result of applying the filter.
*/
inline short apply(const short *src) {
#ifdef __APPLE__
short result;
vDSP_dotpr_s1_15(filter_coefficients_, 1, src, 1, &result, number_of_taps_);
return result;
#else
int outputValue = 0;
for(unsigned int c = 0; c < number_of_taps_; c++) {
outputValue += filter_coefficients_[c] * src[c];
}
return (short)(outputValue >> kCSKaiserBesselFilterFixedShift);
#endif
}
inline unsigned int get_number_of_taps() {
return number_of_taps_;
}
void get_coefficients(float *coefficients);
private:
short *filter_coefficients_;
unsigned int number_of_taps_;
static void coefficients_for_idealised_filter_response(short *filterCoefficients, float *A, float attenuation, unsigned int numberOfTaps);
static float ino(float a);
};
}
#endif