jlaudio/lib/extractfreq/harmonicwindow.go

package extractfreq

import (
	"log"

	"gonum.org/v1/gonum/floats"
	"gonum.org/v1/gonum/stat"
)

type HarmonicWindow struct {
	Harmonic       float64 // 0.25, 0.5, 1, 2, 3, ...
	Amps           []float64
	Freqs          []float64
	IdxPeak        int
	IdxPeakInterp  float64
	FreqPeakInterp float64
	AmpPeak        float64
	AmpMean        float64
	AmpStd         float64
}

func NewHarmonicWindow(
	fFundamental float64,
	harmonic float64,
	rawAmps []float64,
	rawFreqs []float64,
) *HarmonicWindow {
	deltaF := rawFreqs[1] - rawFreqs[0]

	// TODO: At higher harmonic numbers, the harmonics are going to be spaced
	// more cloesly together. That means that the window size must shrink.
	//winSizeCents := float64(150)

	// To start, we create a window around the approximate harmonic location.
	idxPeak := int((fFundamental * harmonic) / deltaF)
	winSize := int(0.5 * fFundamental / deltaF)
	amps := rawAmps[idxPeak-winSize : idxPeak+winSize]
	freqs := rawFreqs[idxPeak-winSize : idxPeak+winSize]

	// Next, we refine the window be centering it on the actual peak.
	idxPeak += (floats.MaxIdx(amps) - winSize)
	amps = rawAmps[idxPeak-winSize : idxPeak+winSize]
	freqs = rawFreqs[idxPeak-winSize : idxPeak+winSize]
	idxPeak = winSize

	// Next we compute statistical properties to determine if this peak is worth
	// using.
	mean, std := stat.MeanStdDev(amps, nil)
	ampPeak := amps[idxPeak]

	log.Printf("%0.2f: %0.4f", harmonic, (ampPeak-mean)/std)
	// TODO: Actual interpolation.

	return &HarmonicWindow{
		Harmonic:       harmonic,
		Amps:           amps,
		Freqs:          freqs,
		IdxPeak:        idxPeak,
		IdxPeakInterp:  float64(idxPeak),
		FreqPeakInterp: freqs[idxPeak],
		AmpPeak:        ampPeak,
		AmpMean:        mean,
		AmpStd:         std,
	}
}