mirror of https://github.com/TomHarte/CLK.git
103 lines
3.3 KiB
C++
103 lines
3.3 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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#pragma once
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// Use the Accelerate framework to vectorise, unless this is a Qt build.
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// Primarily that avoids gymnastics in the QMake file; it also eliminates
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// a difference in the Qt build across platforms.
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#if defined(__APPLE__) && !defined(TARGET_QT)
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#include <Accelerate/Accelerate.h>
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#define USE_ACCELERATE
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#endif
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#include <cstddef>
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#include <vector>
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namespace SignalProcessing {
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/*!
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The FIR filter takes a 1d PCM signal with a given sample rate and applies a band-pass filter to it.
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The number of taps (ie, samples considered simultaneously to make an output sample) is configurable;
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smaller numbers permit a filter that operates more quickly and with less lag but less effectively.
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*/
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class FIRFilter {
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private:
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static constexpr float FixedMultiplier = 32767.0f;
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static constexpr int FixedShift = 15;
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public:
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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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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(std::size_t number_of_taps, float input_sample_rate, float low_frequency, float high_frequency, float attenuation = DefaultAttenuation);
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FIRFilter(const std::vector<float> &coefficients);
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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, size_t stride = 1) const {
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#ifdef USE_ACCELERATE
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short result;
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vDSP_dotpr_s1_15(filter_coefficients_.data(), 1, src, vDSP_Stride(stride), &result, filter_coefficients_.size());
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return result;
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#else
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int outputValue = 0;
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for(std::size_t c = 0; c < filter_coefficients_.size(); ++c) {
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outputValue += filter_coefficients_[c] * src[c * stride];
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}
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return short(outputValue >> FixedShift);
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#endif
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}
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/*! @returns The number of taps used by this filter. */
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inline std::size_t get_number_of_taps() const {
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return filter_coefficients_.size();
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}
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/*! @returns The weighted coefficients that describe this filter. */
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std::vector<float> get_coefficients() const;
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/*!
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@returns A filter that would have the effect of adding (and scaling) the outputs of the two filters.
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Defined only if both have the same number of taps.
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*/
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FIRFilter operator+(const FIRFilter &) const;
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/*!
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@returns A filter that would have the effect of applying the two filters in succession.
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Defined only if both have the same number of taps.
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*/
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FIRFilter operator*(const FIRFilter &) const;
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/*!
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@returns A filter that would have the opposite effect of this filter.
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*/
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FIRFilter operator-() const;
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private:
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std::vector<short> filter_coefficients_;
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static void coefficients_for_idealised_filter_response(short *filterCoefficients, float *A, float attenuation, std::size_t numberOfTaps);
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static float ino(float a);
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};
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}
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