mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-19 08:31:11 +00:00
91 lines
2.4 KiB
C++
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
|