mindball/Source/DelayEngine.h

#pragma once

#include "DelayLine.h"

#include <algorithm>
#include <array>
#include <cmath>
#include <cstdlib>

namespace mindball
{

class DelayEngine
{
public:
    enum Mode
    {
        normal = 0,
        invert,
        pingpong,
        superpong
    };

    struct Params
    {
        float feedback = 0.35f;
        float loCutHz  = 100.0f;
        float hiCutHz  = 12000.0f;
        float dryWet   = 0.4f;
        float timeMs   = 300.0f;
        int   timeSyncIndex = 0;
        int   mode     = normal;
        bool  sync     = false;
        bool  doubleTap = false;
        bool  center   = false;
        bool  autoPan  = false;
        float panDepth = 1.0f;
        double bpm     = 120.0;
    };

    void prepare (double sampleRate, double maxDelaySeconds)
    {
        sr = static_cast<float> (sampleRate);
        dl.prepare (static_cast<float> (maxDelaySeconds * sampleRate));
        dr.prepare (static_cast<float> (maxDelaySeconds * sampleRate));
        clear();

        sFeedback   = 0.0f;
        sLoCut      = 20.0f;
        sHiCut      = 18000.0f;
        sDryWet     = 0.0f;
        head1       = 1.0f;
        head2       = 1.0f;
        blend       = 0.0f;
        lfoPhase    = 0.0f;
    }

    void clear()
    {
        dl.clear();
        dr.clear();

        lpL.reset(); hpL.reset();
        lpR.reset(); hpR.reset();

        lfoPhase = 0.0f;
    }

    void process (const float* inL, const float* inR,
                  float* outL, float* outR,
                  int numSamples, const Params& p,
                  float* wetLOut = nullptr, float* wetROut = nullptr)
    {
        constexpr float pi = 3.14159265358979f;

        const float kPar  = 1.0f - std::exp (-1.0f / (0.02f * sr));

        const float fadeInc = 1.0f / (0.012f * sr);

        float targetTimeSamples;
        if (p.sync)
        {
            const int idx = std::clamp (p.timeSyncIndex, 0, numDivisions - 1);
            const double secondsPerBeat = 60.0 / std::max (1.0, p.bpm);
            targetTimeSamples = static_cast<float> (divisionBeats[static_cast<std::size_t> (idx)]
                                                    * secondsPerBeat * sr);
        }
        else
        {
            targetTimeSamples = p.timeMs * 0.001f * sr;
        }
        targetTimeSamples = std::max (2.0f, targetTimeSamples);

        const float targetFeedback = p.feedback;
        const float targetLoCut    = p.loCutHz;
        const float targetHiCut    = p.hiCutHz;
        const float targetDryWet   = p.dryWet;

        const bool dbl = p.doubleTap;
        const bool ctr = p.center;
        const bool needB = dbl || (ctr && (p.mode == pingpong || p.mode == superpong));

        const float lfoRate = p.autoPan ? (p.sync ? static_cast<float> (p.bpm / 240.0) : 0.25f) : 0.0f;

        for (int i = 0; i < numSamples; ++i)
        {
            sFeedback  += (targetFeedback - sFeedback) * kPar;
            sLoCut     += (targetLoCut    - sLoCut)    * kPar;
            sHiCut     += (targetHiCut    - sHiCut)    * kPar;
            sDryWet    += (targetDryWet   - sDryWet)   * kPar;

            // Delay time changes are done with two stationary read heads and a
            // short crossfade, never by gliding a read position. This avoids the
            // pitch-bend "sped up / slowed down" artifacts that come from a
            // moving read head. When the target moves, snap head2 to it and fade
            // between the two fixed heads; once blended, head2 takes over.
            if (blend == 0.0f && std::fabs (targetTimeSamples - head1) > 0.5f)
                head2 = targetTimeSamples;

            if (blend < 1.0f)
            {
                blend += fadeInc;
                if (blend >= 1.0f)
                {
                    head1 = head2;
                    blend = 0.0f;
                }
            }

            lpL.setFc (sHiCut, sr);  hpL.setFc (sLoCut, sr);
            lpR.setFc (sHiCut, sr);  hpR.setFc (sLoCut, sr);

            const float h1L = dl.read (head1);
            const float h2L = dl.read (head2);
            const float h1R = dr.read (head1);
            const float h2R = dr.read (head2);
            const float aL = h1L + (h2L - h1L) * blend;
            const float aR = h1R + (h2R - h1R) * blend;

            float bL = 0.0f, bR = 0.0f;
            if (needB)
            {
                const float two1 = 2.0f * head1;
                const float two2 = 2.0f * head2;
                bL = dl.read (two1) + (dl.read (two2) - dl.read (two1)) * blend;
                bR = dr.read (two1) + (dr.read (two2) - dr.read (two1)) * blend;
            }

            float fbL = 0.0f, fbR = 0.0f;
            float wetL = 0.0f, wetR = 0.0f;

            switch (p.mode)
            {
                case normal:
                    fbL = aL;
                    fbR = aR;
                    wetL = aL + bL;
                    wetR = aR + bR;
                    break;

                case invert:
                    fbL = aL;
                    fbR = -aR;
                    wetL = aL + bL;
                    wetR = -(aR + bR);
                    break;

                case pingpong:
                    fbL = aR;
                    fbR = aL;
                    wetL = aL + bL;
                    wetR = aR + bR;
                    break;

                case superpong:
                {
                    const float sumA  = aL + aR;
                    const float sumAB = sumA + (needB ? bL + bR : 0.0f);
                    fbL = 0.5f * sumA;
                    fbR = 0.5f * sumA;
                    wetL = sumAB * 0.5f;
                    wetR = sumAB * 0.5f;
                    break;
                }
            }

            if (ctr && (p.mode == pingpong || p.mode == superpong))
            {
                const float c = 0.5f * (aL + aR);
                wetL = c + (needB ? bL : 0.0f);
                wetR = c + (needB ? bR : 0.0f);
            }

            if (p.autoPan)
            {
                const float pan = std::sin (2.0f * pi * lfoPhase);
                lfoPhase += lfoRate / sr;
                if (lfoPhase >= 1.0f)
                    lfoPhase -= std::floor (lfoPhase);

                const float s = std::clamp (p.panDepth, 0.0f, 1.0f);
                const float angle = (1.0f - s) * pi * 0.25f + s * (pan + 1.0f) * pi * 0.25f;
                const float gL = std::cos (angle);
                const float gR = std::sin (angle);
                wetL *= gL;
                wetR *= gR;
            }

            const float g = sFeedback * (1.0f + 0.002f * std::pow (sFeedback, 100.0f));
            dl.write (inL[i] + softClip (lpL.processLP (hpL.processHP (fbL * g))));
            dr.write (inR[i] + softClip (lpR.processLP (hpR.processHP (fbR * g))));

            const float w = sDryWet;
            float dryGain, wetGain;
            if (w <= 0.5f)
            {
                dryGain = 1.0f;
                wetGain = 2.0f * w;
            }
            else
            {
                dryGain = 2.0f * (1.0f - w);
                wetGain = 1.0f;
            }
            outL[i] = inL[i] * dryGain + wetL * wetGain;
            outR[i] = inR[i] * dryGain + wetR * wetGain;
            if (wetLOut != nullptr)
                wetLOut[i] = wetL * wetGain;
            if (wetROut != nullptr)
                wetROut[i] = wetR * wetGain;
        }
    }

    static float syncTimeMs (int index, double bpm)
    {
        const int idx = std::clamp (index, 0, numDivisions - 1);
        const double secondsPerBeat = 60.0 / std::max (1.0, bpm);
        return static_cast<float> (divisionBeats[static_cast<std::size_t> (idx)] * secondsPerBeat * 1000.0);
    }

private:
    static float softClip (float x)
    {
        const float ax = std::fabs (x);
        if (ax < 0.8f)
            return x;
        return std::copysign (0.8f + 0.2f * std::tanh ((ax - 0.8f) / 0.2f), x);
    }

    struct OnePole
    {
        float alpha = 0.0f;
        float state = 0.0f;
        float xPrev = 0.0f;

        void reset() { state = 0.0f; xPrev = 0.0f; }

        void setFc (float fc, float sr)
        {
            constexpr float pi = 3.14159265358979f;
            alpha = 1.0f - std::exp (-2.0f * pi * fc / sr);
        }

        float processLP (float x) { state += alpha * (x - state); return state; }
        float processHP (float x) { state = x - xPrev + (1.0f - alpha) * state; xPrev = x; return state; }
    };

    static constexpr int numDivisions = 12;
    static constexpr std::array<float, numDivisions> divisionBeats = {
        1.0f / 16.0f, 1.0f / 8.0f, 1.0f / 4.0f, 1.0f / 3.0f, 1.0f / 2.0f, 3.0f / 4.0f,
        1.0f, 3.0f / 2.0f, 2.0f, 3.0f, 4.0f, 8.0f
    };

    DelayLine dl, dr;
    OnePole lpL, hpL, lpR, hpR;

    float sr = 48000.0f;
    float lfoPhase = 0.0f;

    float sFeedback = 0.0f;
    float sLoCut = 0.0f;
    float sHiCut = 0.0f;
    float sDryWet = 0.0f;
    float head1 = 1.0f;
    float head2 = 1.0f;
    float blend = 0.0f;
};

}