vibe.cpp.hpp

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// Vibe - Self-normalizing audio analysis
//
// Algorithm ported from MilkDrop v2.25c by Ryan Geiss.
// Three-stage processing: immediate fft::FFT → asymmetric EMA → slow EMA normalization.
//
// Uses 3 LINEAR fft::FFT bins that map directly to bass/mid/treb bands.
// Linear bins at 20-11025 Hz with 3 bins gives ~3668 Hz per bin:
//   bin 0: 20-3688 Hz (bass), bin 1: 3688-7356 Hz (mid), bin 2: 7356-11025 Hz (treb)
 
#include "fl/audio/detector/vibe.h"
#include "fl/audio/audio_context.h"
#include "fl/math/math.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
namespace audio {
namespace detector {
 
static int sVibeFFTCount = 0;
int Vibe::getPrivateFFTCount() { return sVibeFFTCount; }
void Vibe::resetPrivateFFTCount() { sVibeFFTCount = 0; }
 
 
Vibe::Vibe() {
    // Tau chosen for LED visualizer feel: ~0.3s gives ~1 second of silence
    // to fully gate, matching user expectation that beats decay quickly when
    // music stops. The envelope targets 0.0 — full silence on the metric.
    SilenceEnvelope::Config cfg;
    cfg.decayTauSeconds = 0.3f;
    cfg.targetValue = 0.0f;
    for (int i = 0; i < 3; ++i) {
        mImmRelEnv[i].configure(cfg);
        mAvgRelEnv[i].configure(cfg);
        // Seed cached "last audio" value at 1.0 to match the detector's
        // initial public state (getBass()/getMid()/getTreb() return 1.0
        // before any update()). Without this, the first silent update
        // would immediately decay from 0 — no visible change, but semantic.
        mImmRelEnv[i].reset(1.0f);
        mAvgRelEnv[i].reset(1.0f);
    }
}
 
Vibe::~Vibe() FL_NOEXCEPT = default;
 
void Vibe::update(shared_ptr<Context> context) {
    if (!context) {
        return;
    }
 
    mFrameCount++;
    mSampleRate = context->getSampleRate();
 
    // --- Step 1: Get 3-band energy from shared context ---
    BandEnergy energy = context->getBandEnergy();
    sVibeFFTCount++;
 
    span<const i16> pcm = context->getPCM();
 
    // --- Step 2: Read bass/mid/treb directly ---
    mImm[0] = energy.bass;
    mImm[1] = energy.mid;
    mImm[2] = energy.treb;
 
    // --- Step 3: Temporal blending (MilkDrop v2.25c algorithm) ---
    // Compute effective FPS from audio buffer duration
    float dt = computeAudioDt(pcm.size(), mSampleRate);
    float actualFps = (dt > 0.0f) ? (1.0f / dt) : mTargetFps;
 
    if (mFrameCount == 1) {
        // MilkDrop first-frame initialization: set averages directly
        // Prevents false spikes and startup transients
        for (int i = 0; i < 3; i++) {
            mAvg[i] = mImm[i];
            mLongAvg[i] = mImm[i];
        }
    } else {
        // Pre-compute FPS-adjusted rates (avoids redundant powf in loop)
        float attackRate = adjustRateToFPS(0.2f, 30.0f, actualFps);
        float decayRate = adjustRateToFPS(0.5f, 30.0f, actualFps);
        float longRate = adjustRateToFPS(0.992f, 30.0f, actualFps);
 
        for (int i = 0; i < 3; i++) {
            // Short-term average: asymmetric attack/decay
            // Fast attack (rate=0.2 at 30fps → ~80% new signal on beats)
            // Slow decay  (rate=0.5 at 30fps → graceful fadeout)
            float rate = (mImm[i] > mAvg[i]) ? attackRate : decayRate;
            mAvg[i] = mAvg[i] * rate + mImm[i] * (1.0f - rate);
 
            // Long-term average: slow symmetric EMA (MilkDrop v2.25c algorithm)
            // Rate = 0.992 at 30fps → tau ≈ 4.2 seconds
            // Tracks the overall energy level for self-normalization.
            // Unlike a running maximum, this centers relative levels around 1.0,
            // giving beats proper excursions above 1.0 and quiet sections below 1.0.
            mLongAvg[i] = mLongAvg[i] * longRate + mAvg[i] * (1.0f - longRate);
        }
    }
 
    // --- Step 4: Self-normalizing relative levels ---
    // Division by long-term average makes levels independent of volume/genre.
    // Values hover around 1.0; >1 means louder than average, <1 means quieter.
    for (int i = 0; i < 3; i++) {
        if (mLongAvg[i] < 0.001f) {
            mImmRel[i] = 1.0f;
            mAvgRel[i] = 1.0f;
        } else {
            mImmRel[i] = mImm[i] / mLongAvg[i];
            mAvgRel[i] = mAvg[i] / mLongAvg[i];
        }
    }
 
    // --- Step 4b: Silence gate ---
    // MilkDrop's self-normalization drives mImmRel toward 1.0 when input is
    // silent (noise / noise → 1.0), and the < 0.001f clamp above also pins
    // to 1.0. Neither is what LED effects want when music stops. Route each
    // band through its SilenceEnvelope: pass-through during audio, exponential
    // decay toward 0 during silence. The Context::isSilent() flag is populated
    // by Processor/Reactive from NoiseFloorTracker. Re-uses dt computed above.
    const bool silent = context->isSilent();
    for (int i = 0; i < 3; i++) {
        mImmRel[i] = mImmRelEnv[i].update(silent, mImmRel[i], dt);
        mAvgRel[i] = mAvgRelEnv[i].update(silent, mAvgRel[i], dt);
    }
 
    // --- Step 5: Spike detection ---
    // When immediate exceeds smoothed, energy is rising — a beat is in progress.
    mPrevBassSpike = mBassSpike;
    mPrevMidSpike = mMidSpike;
    mPrevTrebSpike = mTrebSpike;
 
    mBassSpike = mImmRel[0] > mAvgRel[0];
    mMidSpike = mImmRel[1] > mAvgRel[1];
    mTrebSpike = mImmRel[2] > mAvgRel[2];
}
 
void Vibe::fireCallbacks() {
    if (onVibeLevels) {
        VibeLevels levels;
        levels.bass = mImmRel[0];
        levels.mid = mImmRel[1];
        levels.treb = mImmRel[2];
        levels.vol = (mImmRel[0] + mImmRel[1] + mImmRel[2]) / 3.0f;
        levels.bassSpike = mBassSpike;
        levels.midSpike = mMidSpike;
        levels.trebSpike = mTrebSpike;
        levels.bassRaw = mImm[0];
        levels.midRaw = mImm[1];
        levels.trebRaw = mImm[2];
        levels.bassAvg = mAvg[0];
        levels.midAvg = mAvg[1];
        levels.trebAvg = mAvg[2];
        levels.bassLongAvg = mLongAvg[0];
        levels.midLongAvg = mLongAvg[1];
        levels.trebLongAvg = mLongAvg[2];
        onVibeLevels(levels);
    }
 
    // Fire spike callbacks on rising edge (transition from no-spike to spike)
    if (mBassSpike && !mPrevBassSpike && onBassSpike) {
        onBassSpike();
    }
    if (mMidSpike && !mPrevMidSpike && onMidSpike) {
        onMidSpike();
    }
    if (mTrebSpike && !mPrevTrebSpike && onTrebSpike) {
        onTrebSpike();
    }
}
 
void Vibe::reset() {
    mFrameCount = 0;
    for (int i = 0; i < 3; i++) {
        mImm[i] = 0.0f;
        mAvg[i] = 0.0f;
        mLongAvg[i] = 0.0f;
        mImmRel[i] = 1.0f;
        mAvgRel[i] = 1.0f;
        // Match the mImmRel/mAvgRel defaults of 1.0 so the silence gate
        // picks up from the public state after reset().
        mImmRelEnv[i].reset(1.0f);
        mAvgRelEnv[i].reset(1.0f);
    }
    mBassSpike = false;
    mMidSpike = false;
    mTrebSpike = false;
    mPrevBassSpike = false;
    mPrevMidSpike = false;
    mPrevTrebSpike = false;
}
 
// FPS-independent rate adjustment:
// Converts a per-frame smoothing rate tuned at fps1 to the equivalent rate
// at actualFps, preserving the per-second behavior.
//
// At 30fps with rate=0.5: per-second retention = 0.5^30 ≈ 9.3e-10
// At 60fps the per-frame rate adjusts to ~0.707 so 0.707^60 ≈ 9.3e-10 (same)
float Vibe::adjustRateToFPS(float rateAtFps1, float fps1,
                                     float actualFps) {
    if (actualFps <= 0.0f) {
        return rateAtFps1;
    }
    float perSecond = fl::powf(rateAtFps1, fps1);
    return fl::powf(perSecond, 1.0f / actualFps);
}
 
} // namespace detector
} // namespace audio
} // namespace fl