pitch.cpp.hpp

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#include "fl/audio/detector/pitch.h"
#include "fl/audio/audio_context.h"
#include "fl/math/math.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
namespace audio {
namespace detector {
 
Pitch::Pitch()
    : mCurrentPitch(0.0f)
    , mSmoothedPitch(0.0f)
    , mConfidence(0.0f)
    , mIsVoiced(false)
    , mPreviousVoiced(false)
    , mPreviousPitch(0.0f)
    , mMinFrequency(80.0f)     // Typical low male voice / bass guitar
    , mMaxFrequency(1000.0f)   // Upper range for most melodic instruments
    , mConfidenceThreshold(0.5f)  // Require 50% confidence minimum
    , mPitchChangeSensitivity(5.0f)  // 5 Hz threshold for pitch change events
    , mMinPeriod(0)
    , mMaxPeriod(0)
    , mSampleRate(44100.0f)    // Standard audio sample rate
{
    updatePeriodRange();
    // Reserve space for autocorrelation buffer (worst case: max period)
    mAutocorrelation.reserve(static_cast<size>(mMaxPeriod + 1));
}
 
Pitch::~Pitch() FL_NOEXCEPT = default;
 
void Pitch::update(shared_ptr<Context> context) {
    // Get PCM data from context
    span<const i16> pcm = context->getPCM();
    size numSamples = pcm.size();
 
    // Compute dt from actual audio buffer duration
    mLastDt = computeAudioDt(pcm.size(), static_cast<int>(mSampleRate));
 
    // Need at least 2x max period for autocorrelation
    if (numSamples < static_cast<size>(mMaxPeriod * 2)) {
        // Not enough samples for reliable pitch detection
        mConfidence = 0.0f;
        mIsVoiced = false;
 
        mVoicedStateChanged = (mIsVoiced != mPreviousVoiced);
        return;
    }
 
    // Calculate autocorrelation and find pitch
    float detectedPitch = calculateAutocorrelation(pcm.data(), numSamples);
 
    // Check if pitch is valid and confidence is sufficient
    if (detectedPitch > 0.0f && mConfidence >= mConfidenceThreshold) {
        mIsVoiced = true;
        mCurrentPitch = detectedPitch;
        updatePitchSmoothing(detectedPitch);
        mFirePitch = true;
 
        if (shouldReportPitchChange(detectedPitch)) {
            mFirePitchChange = true;
            mPreviousPitch = detectedPitch;
        }
    } else {
        mIsVoiced = false;
        mCurrentPitch = 0.0f;
        mFirePitch = false;
    }
 
    mVoicedStateChanged = (mIsVoiced != mPreviousVoiced);
}
 
void Pitch::fireCallbacks() {
    if (mFirePitch) {
        if (onPitch) onPitch(mSmoothedPitch);
        if (onPitchWithConfidence) onPitchWithConfidence(mSmoothedPitch, mConfidence);
        mFirePitch = false;
    }
    if (mFirePitchChange) {
        if (onPitchChange) onPitchChange(mSmoothedPitch);
        mFirePitchChange = false;
    }
    if (mVoicedStateChanged) {
        if (onVoiced) onVoiced(static_cast<u8>(mConfidence * 255.0f));
        mPreviousVoiced = mIsVoiced;
        mVoicedStateChanged = false;
    }
}
 
void Pitch::reset() {
    mCurrentPitch = 0.0f;
    mSmoothedPitch = 0.0f;
    mConfidence = 0.0f;
    mIsVoiced = false;
    mPreviousVoiced = false;
    mPreviousPitch = 0.0f;
    mAutocorrelation.clear();
    mPitchSmoother.reset();
}
 
void Pitch::updatePeriodRange() {
    // Convert frequency range to period range (in samples)
    // Period (samples) = SampleRate / Frequency
    mMinPeriod = frequencyToPeriod(mMaxFrequency);
    mMaxPeriod = frequencyToPeriod(mMinFrequency);
}
 
float Pitch::calculateAutocorrelation(const i16* pcm, size numSamples) {
    // Clear and resize autocorrelation buffer
    mAutocorrelation.clear();
    mAutocorrelation.resize(static_cast<size>(mMaxPeriod + 1), 0.0f);
 
    // Normalize input to float range [-1, 1]
    const float normFactor = 1.0f / 32768.0f;
 
    // Calculate autocorrelation for all lags in the period range
    // ACF[k] = sum(signal[n] * signal[n + k]) for all valid n
    for (int lag = mMinPeriod; lag <= mMaxPeriod; lag++) {
        float sum = 0.0f;
        int validSamples = 0;
 
        for (size i = 0; i + lag < numSamples; i++) {
            float s1 = static_cast<float>(pcm[i]) * normFactor;
            float s2 = static_cast<float>(pcm[i + lag]) * normFactor;
            sum += s1 * s2;
            validSamples++;
        }
 
        // Normalize by number of samples
        if (validSamples > 0) {
            mAutocorrelation[static_cast<size>(lag)] = sum / static_cast<float>(validSamples);
        }
    }
 
    // Find the lag with maximum autocorrelation (best period match)
    int bestLag = findBestPeakLag(mAutocorrelation);
 
    // Calculate confidence based on autocorrelation peak
    if (bestLag > 0) {
        mConfidence = calculateConfidence(mAutocorrelation, bestLag);
 
        // Convert period (lag) to frequency
        return periodToFrequency(bestLag);
    }
 
    // No reliable pitch found
    mConfidence = 0.0f;
    return 0.0f;
}
 
int Pitch::findBestPeakLag(const vector<float>& autocorr) const {
    // Find the lag with maximum autocorrelation value
    // (excluding lag 0, which is always maximum by definition)
 
    float maxValue = -1.0f;
    int bestLag = 0;
 
    for (int lag = mMinPeriod; lag <= mMaxPeriod && lag < static_cast<int>(autocorr.size()); lag++) {
        float value = autocorr[static_cast<size>(lag)];
 
        // Look for positive peaks
        if (value > maxValue && value > 0.0f) {
            maxValue = value;
            bestLag = lag;
        }
    }
 
    return bestLag;
}
 
float Pitch::calculateConfidence(const vector<float>& autocorr, int peakLag) const {
    // Confidence based on:
    // 1. Strength of the autocorrelation peak
    // 2. Ratio of peak to nearby values (peak clarity)
 
    if (peakLag <= 0 || peakLag >= static_cast<int>(autocorr.size())) {
        return 0.0f;
    }
 
    float peakValue = autocorr[static_cast<size>(peakLag)];
 
    // Confidence is primarily based on peak strength
    // Autocorrelation ranges from -1 to 1, but we only care about positive peaks
    float confidence = fl::max(0.0f, fl::min(1.0f, peakValue));
 
    // Calculate clarity by comparing peak to surrounding values
    // Look at ±10% of the period
    int windowSize = fl::max(2, peakLag / 10);
    float neighborSum = 0.0f;
    int neighborCount = 0;
 
    for (int offset = -windowSize; offset <= windowSize; offset++) {
        if (offset == 0) continue;  // Skip the peak itself
 
        int lag = peakLag + offset;
        if (lag >= mMinPeriod && lag <= mMaxPeriod && lag < static_cast<int>(autocorr.size())) {
            neighborSum += fl::max(0.0f, autocorr[static_cast<size>(lag)]);
            neighborCount++;
        }
    }
 
    if (neighborCount > 0) {
        float neighborAvg = neighborSum / static_cast<float>(neighborCount);
 
        // Peak should be significantly higher than neighbors
        // If peak is 2x higher, that's good; if it's similar, reduce confidence
        if (neighborAvg > 1e-6f) {
            float clarity = fl::min(1.0f, (peakValue - neighborAvg) / neighborAvg);
            confidence *= (0.7f + 0.3f * clarity);  // Weight clarity at 30%
        }
    }
 
    return confidence;
}
 
float Pitch::periodToFrequency(int period) const {
    if (period <= 0) {
        return 0.0f;
    }
    return mSampleRate / static_cast<float>(period);
}
 
int Pitch::frequencyToPeriod(float frequency) const {
    if (frequency <= 0.0f) {
        return 0;
    }
    return static_cast<int>(mSampleRate / frequency);
}
 
void Pitch::updatePitchSmoothing(float newPitch) {
    // OneEuroFilter: adaptive — low jitter when pitch stable, low lag on changes
    mSmoothedPitch = mPitchSmoother.update(newPitch, mLastDt);
}
 
bool Pitch::shouldReportPitchChange(float newPitch) const {
    // Check if pitch has changed significantly from previous detection
    if (mPreviousPitch == 0.0f) {
        // First pitch detection
        return true;
    }
 
    // Calculate absolute difference in Hz
    float pitchDiff = fl::abs(newPitch - mPreviousPitch);
 
    // Report change if difference exceeds sensitivity threshold
    return pitchDiff >= mPitchChangeSensitivity;
}
 
} // namespace detector
} // namespace audio
} // namespace fl