tcdweb/js/analyzer.js

const Analyzer = {

  detectBPM(pcmData, sampleRate, channels) {
    const frameSize = 2048;
    const hopSize = 256;
    const maxSecs = 60;
    const totalSamples = pcmData.length / channels;
    const limitSamples = Math.min(totalSamples, Math.floor(sampleRate * maxSecs));

    if (limitSamples < sampleRate * 3) return 0;

    const numFrames = Math.max(1, Math.floor((limitSamples - frameSize) / hopSize) + 1);

    const onset = new Float64Array(numFrames);
    for (let f = 0; f < numFrames; f++) {
      let energy = 0;
      const start = f * hopSize * channels;
      const end = Math.min(start + frameSize * channels, limitSamples * channels);
      for (let i = start; i < end; i += channels) {
        const s = pcmData[i];
        energy += s * s;
      }
      onset[f] = energy;
    }

    const odf = new Float64Array(numFrames);
    for (let f = 1; f < numFrames; f++) {
      const d = onset[f] - onset[f - 1];
      odf[f] = d > 0 ? d : 0;
    }

    let maxOdf = 0;
    for (let i = 0; i < numFrames; i++) if (odf[i] > maxOdf) maxOdf = odf[i];
    if (maxOdf > 0) for (let i = 0; i < numFrames; i++) odf[i] /= maxOdf;

    let meanOdf = 0;
    for (let i = 0; i < numFrames; i++) meanOdf += odf[i];
    meanOdf /= numFrames;
    for (let i = 0; i < numFrames; i++) odf[i] -= meanOdf;

    const minBPM = 30;
    const maxBPM = 300;
    const secsPerHop = hopSize / sampleRate;
    const minLag = Math.ceil(60 / (maxBPM * secsPerHop));
    const maxLag = Math.floor(60 / (minBPM * secsPerHop));

    if (minLag >= numFrames || maxLag < minLag) return 0;

    const acLen = maxLag - minLag + 1;
    const ac = new Float64Array(acLen);

    for (let lag = minLag; lag <= maxLag; lag++) {
      let s = 0;
      const n = numFrames - lag;
      for (let i = 0; i < n; i++) s += odf[i] * odf[i + lag];
      ac[lag - minLag] = n > 0 ? s / n : 0;
    }

    const interpAC = (lag) => {
      const idx = lag - minLag;
      const i = Math.floor(idx);
      const f = idx - i;
      if (i < 0 || i + 1 >= acLen) return 0;
      return ac[i] + f * (ac[i + 1] - ac[i]);
    };

    const peaks = [];
    for (let i = 1; i < acLen - 1; i++) {
      if (ac[i] > ac[i - 1] && ac[i] >= ac[i + 1]) {
        const a = ac[i - 1];
        const b = ac[i];
        const c = ac[i + 1];
        const denom = a - 2 * b + c;
        if (Math.abs(denom) < 1e-12) continue;

        const p = 0.5 * (a - c) / denom;
        const peakLag = (i + minLag) + p;
        if (peakLag <= 0) continue;

        const bpm = 60 / (peakLag * secsPerHop);
        if (bpm >= minBPM && bpm <= maxBPM) {
          const interpVal = b + 0.25 * (a - c) * p;
          peaks.push({ bpm, lag: peakLag, score: interpVal });
        }
      }
    }

    if (peaks.length === 0) return 0;

    peaks.sort((a, b) => b.score - a.score);

    const fastBPM = (lag) => 60 / (lag * secsPerHop);

    let bestBPM = peaks[0].bpm;
    let bestScore = peaks[0].score;

    for (const pk of peaks) {
      const lag = pk.lag;
      const acBase = pk.score;
      let hScore = acBase;

      for (let div = 2; div <= 8; div *= 2) {
        const fl = lag / div;
        if (fl >= minLag && fl <= maxLag) {
          hScore += interpAC(fl) * (1.0 / div);
        }
      }

      if (hScore > bestScore) {
        bestScore = hScore;
        bestBPM = pk.bpm;
      }
    }

    for (const pk of peaks) {
      const lag = pk.lag;
      for (let div = 2; div <= 8; div *= 2) {
        const fl = lag / div;
        if (fl >= minLag && fl <= maxLag) {
          const acDiv = interpAC(fl);
          if (acDiv > pk.score * 0.35) {
            const candBPM = fastBPM(fl);
            if (candBPM >= minBPM && candBPM <= maxBPM) {
              bestBPM = candBPM;
              return bestBPM;
            }
          }
        }
      }
    }

    return bestBPM;
  },

  applyHann(buf) {
    const n = buf.length;
    for (let i = 0; i < n; i++)
      buf[i] *= 0.5 * (1.0 - Math.cos(2.0 * Math.PI * i / (n - 1)));
  },

  fftRadix2(re, im, n, inv) {
    for (let i = 1, j = 0; i < n; i++) {
      let bit = n >> 1;
      for (; j & bit; bit >>= 1)
        j ^= bit;
      j ^= bit;
      if (i < j) {
        let tr = re[i]; re[i] = re[j]; re[j] = tr;
        let ti = im[i]; im[i] = im[j]; im[j] = ti;
      }
    }
    for (let len = 2; len <= n; len <<= 1) {
      const ang = 2.0 * Math.PI / len * (inv ? -1 : 1);
      const wr = Math.cos(ang), wi = Math.sin(ang);
      for (let i = 0; i < n; i += len) {
        let cr = 1.0, ci = 0.0;
        for (let j = 0; j < len / 2; j++) {
          const a = i + j, b = a + len / 2;
          const tr = cr * re[b] - ci * im[b];
          const ti = cr * im[b] + ci * re[b];
          re[b] = re[a] - tr; im[b] = im[a] - ti;
          re[a] += tr; im[a] += ti;
          const ncr = cr * wr - ci * wi;
          const nci = cr * wi + ci * wr;
          cr = ncr; ci = nci;
        }
      }
    }
    if (inv)
      for (let i = 0; i < n; i++) { re[i] /= n; im[i] /= n; }
  },

  analyzeAudio(pcmData, sampleRate, channels, fftSize) {
    const power = new Float64Array(fftSize / 2);
    let count = 0;
    const frame = pcmData;

    const buf = new Float64Array(fftSize);
    const re = new Float64Array(fftSize);
    const im = new Float64Array(fftSize);
    const overlap = 2;
    const step = fftSize / overlap;

    for (let ch = 0; ch < channels; ch++) {
      for (let pos = 0; pos + fftSize <= frame.length / channels; pos += step) {
        for (let i = 0; i < fftSize; i++)
          buf[i] = frame[(pos + i) * channels + ch];
        this.applyHann(buf);
        re.set(buf);
        im.fill(0);
        this.fftRadix2(re, im, fftSize, 0);
        for (let i = 0; i < fftSize / 2; i++)
          power[i] += re[i] * re[i] + im[i] * im[i];
        count++;
      }
    }

    if (count === 0) return null;
    return { power, count, sampleRate, channels, fftSize };
  },

  detectCutoff(a, thresholdDb, sensitivity) {
    const n = a.fftSize / 2;
    const sr = a.sampleRate;

    const mag = new Float64Array(n);
    let peak = 0.0;
    for (let i = 0; i < n; i++) {
      mag[i] = Math.sqrt(a.power[i] / a.count);
      if (mag[i] > peak) peak = mag[i];
    }
    if (peak < 1e-12) return { score: 0, cutoff: 0 };

    const threshold = peak * Math.pow(10.0, thresholdDb / 20.0);

    let cutoffHz = 0;
    for (let i = n - 1; i >= 0; i--) {
      if (mag[i] >= threshold) { cutoffHz = i * sr / a.fftSize; break; }
    }

    const lowThresh60 = peak * 0.001;
    let cutoff60Hz = 0;
    let cutoff60Bin = n - 1;
    for (let i = n - 1; i >= 0; i--) {
      if (mag[i] >= lowThresh60) { cutoff60Hz = i * sr / a.fftSize; cutoff60Bin = i; break; }
    }

    const highThresh = peak * 0.1;
    let cutoffHighHz = 0;
    const startBin = cutoff60Bin > 0 ? cutoff60Bin : n - 1;
    for (let i = startBin; i >= 0; i--) {
      if (mag[i] >= highThresh) { cutoffHighHz = i * sr / a.fftSize; break; }
    }

    let transitionBw = (cutoff60Hz > 0) ? cutoff60Hz - cutoffHighHz : 0;
    if (transitionBw < 0) transitionBw = 0;
    const steepness = transitionBw;

    let noiseSum = 0, noiseCount = 0;
    for (let i = n * 3 / 4; i < n; i++) {
      if (mag[i] > 0) { noiseSum += mag[i]; noiseCount++; }
    }
    const noiseFloor = (noiseCount > 0) ? (noiseSum / noiseCount) : 1e-12;
    const noiseDb = 20.0 * Math.log10(noiseFloor / peak);

    let extDb = noiseDb + 6.0;
    const minExtDb = thresholdDb - 30.0;
    if (extDb < minExtDb) extDb = minExtDb;
    const extPeak = peak * Math.pow(10.0, extDb / 20.0);
    let extCutoff = 0;
    for (let i = n - 1; i >= 0; i--) {
      if (mag[i] >= extPeak) { extCutoff = i * sr / a.fftSize; break; }
    }
    const extendedCutoff = extCutoff;

    let roughCutoff = cutoffHz;
    if (noiseDb > thresholdDb) {
      const adjDb = noiseDb + 10.0;
      const adjThresh = peak * Math.pow(10.0, adjDb / 20.0);
      let adjCutoff = 0;
      for (let i = n - 1; i >= 0; i--) {
        if (mag[i] >= adjThresh) { adjCutoff = i * sr / a.fftSize; break; }
      }
      if (adjCutoff > 0) roughCutoff = adjCutoff;
    }

    let roughness = 0.0;
    const cutoffIdx = roughCutoff * a.fftSize / sr;
    let lo = Math.floor(cutoffIdx * 0.60);
    let hi = Math.floor(cutoffIdx * 0.95);
    if (hi >= n) hi = n - 1;
    if (lo < 1) lo = 1;

    const noiseMag = Math.pow(10.0, noiseDb / 20.0) * peak;
    const regionTotal = hi - lo + 1;
    let aboveNoise = 0;
    for (let i = lo; i <= hi; i++) {
      if (mag[i] > noiseMag * 2.0) aboveNoise++;
    }
    if (aboveNoise / regionTotal < 0.30) {
      roughness = 0.01;
    } else if (hi > lo) {
      let sum = 0;
      for (let i = lo; i <= hi; i++) sum += mag[i];
      const mean = sum / (hi - lo + 1);
      if (mean > 1e-12) {
        let varSum = 0;
        for (let i = lo; i <= hi; i++) {
          const dev = (mag[i] - mean) / mean;
          varSum += dev * dev;
        }
        roughness = Math.sqrt(varSum / (hi - lo));
      }
    }
    if (roughness < 0.01) roughness = 0.01;

    let energyLow = 0, energyHigh = 0;
    let elCount = 0, ehCount = 0;
    for (let i = 0; i < n; i++) {
      const f = i * sr / a.fftSize;
      if (f >= 12000 && f < 16000) { energyLow += mag[i]; elCount++; }
      if (f >= 16000 && f < 20000) { energyHigh += mag[i]; ehCount++; }
    }
    const bandRatio = (elCount > 0 && ehCount > 0)
      ? (energyHigh / ehCount) / (energyLow / elCount + 1e-12)
      : 0.5;

    const nyquist = sr / 2.0;

    let decisionCutoff = cutoffHz;
    if (noiseDb > thresholdDb) {
      const dcDb = noiseDb + 10.0;
      const dcThresh = peak * Math.pow(10.0, dcDb / 20.0);
      let dc = 0;
      for (let i = n - 1; i >= 0; i--) {
        if (mag[i] >= dcThresh) { dc = i * sr / a.fftSize; break; }
      }
      if (dc > 0) decisionCutoff = dc;
    }
    const cutoffRatio = decisionCutoff / nyquist;
    const effCutoffRatio = (extendedCutoff > cutoffHz && noiseDb >= -100.0)
      ? extendedCutoff / nyquist : cutoffRatio;

    const bwFactor = Math.max(0.25, 2.0 * (1.0 - sensitivity));
    const r1 = 0.40 * (1.0 + (0.5 - sensitivity) * 1.5);
    const r2 = 0.30 * (1.0 + (0.5 - sensitivity) * 1.5);
    const r3 = 0.20 * (1.0 + (0.5 - sensitivity) * 1.5);
    const b1 = 0.90 - (0.5 - sensitivity) * 0.10;
    const b2 = 0.85 - (0.5 - sensitivity) * 0.10;
    const bypass = 0.99 - (0.5 - sensitivity) * 0.02;

    let score = 0;

    if (decisionCutoff <= 0 || cutoffRatio >= bypass) {
      if (roughness > r1) score = 1;
      else if (roughness > r2 && bandRatio < b1) score = 1;
      else if (roughness > r3 && bandRatio < b2) score = 1;
      return { score, cutoff: cutoffHz, steepness, noiseDb, roughness, bandRatio, extendedCutoff,
               cutoffRatio, bypassed: true, mag, peak };
    }

    let maxBw;
    if (cutoffRatio < 0.50) maxBw = 4000.0 * bwFactor;
    else if (cutoffRatio < 0.70) maxBw = 3000.0 * bwFactor;
    else if (cutoffRatio < 0.80) maxBw = 2000.0 * bwFactor;
    else if (cutoffRatio < 0.90) maxBw = 1200.0 * bwFactor;
    else maxBw = 500.0 * bwFactor;

    if (transitionBw < maxBw) score = 1;

    if (!score && cutoffRatio > 0.80) {
      if (roughness > r1) score = 1;
      else if (roughness > r2 && bandRatio < b1) score = 1;
      else if (roughness > r3 && bandRatio < b2) score = 1;
    }

    return { score, cutoff: cutoffHz, steepness, noiseDb, roughness, bandRatio, extendedCutoff,
             cutoffRatio, maxBw, transitionBw, bypassed: false, mag, peak };
  },

  computeConfidence(cutoffRatio, steepness, roughness, bandRatio, isNativeLossy) {
    let conf = 0;
    let count = 0;

    if (isNativeLossy) {
      if (cutoffRatio < 0.70) {
        const margin = Math.min(1, (0.70 - cutoffRatio) / 0.70);
        conf += 0.50 + 0.50 * margin;
        count++;
      } else if (cutoffRatio < 0.80) {
        const margin = Math.min(1, (0.80 - cutoffRatio) / 0.80);
        conf += 0.40 + 0.60 * margin;
        count++;
      } else if (cutoffRatio < 0.85) {
        const margin = Math.min(1, (0.85 - cutoffRatio) / 0.85);
        conf += 0.20 + 0.60 * margin;
        count++;
      } else {
        conf += 0.70;
        count++;
      }
    } else {
      if (cutoffRatio < 0.50) {
        const margin = Math.min(1, (0.50 - cutoffRatio) / 0.50);
        const sMargin = Math.max(0, Math.min(1, (4000.0 - steepness) / 4000.0));
        conf += 0.50 + 0.50 * (margin * 0.5 + sMargin * 0.5);
        count++;
      } else if (cutoffRatio < 0.70) {
        const rMargin = Math.min(1, (0.70 - cutoffRatio) / 0.70);
        const sMargin = Math.max(0, Math.min(1, (3000.0 - steepness) / 3000.0));
        conf += 0.30 + 0.70 * (rMargin * 0.4 + sMargin * 0.6);
        count++;
      } else if (cutoffRatio < 0.80) {
        const rMargin = Math.min(1, (0.80 - cutoffRatio) / 0.80);
        const sMargin = Math.max(0, Math.min(1, (2000.0 - steepness) / 2000.0));
        conf += 0.20 + 0.80 * (rMargin * 0.4 + sMargin * 0.6);
        count++;
      } else if (cutoffRatio < 0.90) {
        const rMargin = Math.min(1, (0.90 - cutoffRatio) / 0.90);
        const sMargin = Math.max(0, Math.min(1, (1200.0 - steepness) / 1200.0));
        conf += 0.10 + 0.90 * (rMargin * 0.4 + sMargin * 0.6);
        count++;
      } else {
        const sMargin = Math.max(0, Math.min(1, (500.0 - steepness) / 500.0));
        conf += 0.20 + 0.80 * sMargin;
        count++;
      }

      if (cutoffRatio > 0.80) {
        if (roughness > 0.40) {
          const margin = Math.min(1, (roughness - 0.40) / 0.40);
          conf += 0.40 + 0.60 * margin;
          count++;
        } else if (roughness > 0.30 && bandRatio < 0.90) {
          const rMargin = Math.min(1, (roughness - 0.30) / 0.10);
          const bMargin = Math.min(1, (0.90 - bandRatio) / 0.90);
          conf += 0.20 + 0.80 * (rMargin * 0.5 + bMargin * 0.5);
          count++;
        } else if (roughness > 0.20 && bandRatio < 0.85) {
          const rMargin = Math.min(1, (roughness - 0.20) / 0.10);
          const bMargin = Math.min(1, (0.85 - bandRatio) / 0.85);
          conf += 0.10 + 0.90 * (rMargin * 0.5 + bMargin * 0.5);
          count++;
        }
      }
    }

    if (count === 0) return 0;
    return Math.max(0, Math.min(100, conf / count * 100.0));
  }
};