lpladder.h

/*
 * Copyright © 2015-2023 Synthstrom Audible Limited
 *
 * This file is part of The Synthstrom Audible Deluge Firmware.
 *
 * The Synthstrom Audible Deluge Firmware is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program.
 * If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "dsp/filter/filter.h"
#include "dsp/filter/ladder_components.h"
#include "util/fixedpoint.h"
 
namespace deluge::dsp::filter {
 
class LpLadderFilter : public Filter<LpLadderFilter> {
public:
    LpLadderFilter() = default;
    // returns a compensatory gain value
    q31_t setConfig(q31_t hpfFrequency, q31_t hpfResonance, FilterMode lpfMode, q31_t lpfMorph, q31_t filterGain);
    void doFilter(std::span<q31_t> buffer);
    void doFilterStereo(std::span<StereoSample> buffer);
    void resetFilter() {
        l.reset();
        r.reset();
    }
 
private:
    struct LpLadderState {
        q31_t noiseLastValue;
        BasicFilterComponent lpfLPF1;
        BasicFilterComponent lpfLPF2;
        BasicFilterComponent lpfLPF3;
        BasicFilterComponent lpfLPF4;
 
        void reset() {
            lpfLPF1.reset();
            lpfLPF2.reset();
            lpfLPF3.reset();
            lpfLPF4.reset();
        }
    };
 
    [[gnu::always_inline]] q31_t scaleInput(q31_t input, q31_t feedbacksSum) {
        q31_t temp;
        if (morph > 0 || processedResonance > 510000000) {
            temp = multiply_32x32_rshift32_rounded(
                       (input - (multiply_32x32_rshift32_rounded(feedbacksSum, processedResonance) << 3)),
                       divideByTotalMoveabilityAndProcessedResonance)
                   << 2;
            q31_t extra = 2 * multiply_32x32_rshift32(input, morph);
            temp = getTanHUnknown(temp + extra, 2);
        }
        else {
            temp = multiply_32x32_rshift32_rounded(
                       (input - (multiply_32x32_rshift32_rounded(feedbacksSum, processedResonance) << 3)),
                       divideByTotalMoveabilityAndProcessedResonance)
                   << 2;
        }
 
        return temp;
    }
 
    [[gnu::always_inline]] inline q31_t do24dBLPFOnSample(q31_t input, LpLadderState& state);
    [[gnu::always_inline]] inline q31_t do12dBLPFOnSample(q31_t input, LpLadderState& state);
    [[gnu::always_inline]] inline q31_t doDriveLPFOnSample(q31_t input, LpLadderState& state);
    // all ladders are in this class to share the basic components
    // this differentiates between them
    FilterMode lpfMode;
 
    // state
    LpLadderState l;
    LpLadderState r;
 
    // configuration
    q31_t processedResonance;
    q31_t divideByTotalMoveabilityAndProcessedResonance;
 
    // moveability is tan(f)/(1+tan(f))
    q31_t moveability;
 
    q31_t morph;
 
    // All feedbacks have 1 represented as 1073741824
    q31_t lpf1Feedback;
    q31_t lpf2Feedback;
    q31_t lpf3Feedback;
 
    bool doOversampling;
};
} // namespace deluge::dsp::filter