// Algorithm: first interpolate the spectral peak corresponding to fApprox,
// then locate the (near-)integer multiples of its frequency
Spectrum Analyzer::findHarmonics(const Spectrum spectrum, qreal fApprox) const
{
Spectrum harmonics;
if (fApprox <= 0 || std::isinf(fApprox))
return harmonics;
const auto peaks = spectrum.findPeaks(0.01);
if (peaks.isEmpty())
return harmonics;
harmonics.reserve(peaks.size());
const auto iFund = std::floor(fApprox / m_binFreq) + 1;
const auto fundamental = quadraticInterpolation(&spectrum[iFund]);
harmonics.append(fundamental);
for (const auto peak : peaks) {
if (peak->frequency > fundamental.frequency) {
const Tone t = quadraticInterpolation(peak);
const qreal ratio = t.frequency / fundamental.frequency;
if (qAbs(1200 * std::log2(ratio / qRound(ratio))) < 10)
harmonics.append(t);
}
}
return harmonics;
}
Tone Analyzer::determineSnacFundamental(const Spectrum snac) const
{
Tone result;
const auto peaks = snac.findPeaks();
if (peaks.isEmpty())
return result;
// First find the highest peak other than the first SNAC value, which
// should be 1.0, then pick the first peak after the first zero crossing
// that exceeds 0.8 times that value
const auto maxPeak = *std::max_element(peaks.constBegin(), peaks.constEnd(), [](const Tone *t1, const Tone *t2) {
return *t1 < *t2;
});
const auto zeros = snac.findZeros(1);
auto pick = std::find_if(peaks.begin(), peaks.end(), [&](const Tone *t) {
return t > zeros.first() && t->amplitude > 0.8 * maxPeak->amplitude;
});
if (pick != peaks.end()) {
result = quadraticInterpolation(*pick);
Q_ASSERT(result.frequency > 0);
}
return result;
}