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