func findNextCandidate(samples []float64, sampleRate, min, max float64, c0 int) int {
sr := int(sampleRate)
for c := 0; c+sr < len(samples); c += sr {
pxx, freqs := spectral.Pwelch(samples[c:c+sr], sampleRate, pwOpts)
globalPeakPower, globalPeakFreq := findPeak(pxx, freqs, 32, 880)
localPeakPower, localPeakFreq := findPeak(pxx, freqs, min, max)
if !dsputils.Float64Equal(globalPeakPower, localPeakPower) {
if globalPeakFreq < localPeakFreq || !areHarmonic(globalPeakFreq, localPeakFreq) {
continue
}
}
if localPeakPower < purrMinPower {
continue
}
fmt.Printf("Candidate at %v (local peak: %f Hz (%.2f), global peak: %f Hz (%.2f))\n", fmtSeconds(float64(c+c0)/sampleRate), localPeakFreq, localPeakPower, globalPeakFreq, globalPeakPower)
findRepeats(samples[c:], sampleRate, localPeakFreq, true, true)
return c + c0
}
return -1
}
// This example is adapted from Richard Lyon's "Understanding Digital Signal Processing," section 3.1.1.
func ExampleFFTReal() {
numSamples := 8
// Equation 3-10.
x := func(n int) float64 {
wave0 := math.Sin(2.0 * math.Pi * float64(n) / 8.0)
wave1 := 0.5 * math.Sin(2*math.Pi*float64(n)/4.0+3.0*math.Pi/4.0)
return wave0 + wave1
}
// Discretize our function by sampling at 8 points.
a := make([]float64, numSamples)
for i := 0; i < numSamples; i++ {
a[i] = x(i)
}
X := FFTReal(a)
// Print the magnitude and phase at each frequency.
for i := 0; i < numSamples; i++ {
r, θ := cmplx.Polar(X[i])
θ *= 360.0 / (2 * math.Pi)
if dsputils.Float64Equal(r, 0) {
θ = 0 // (When the magnitude is close to 0, the angle is meaningless)
}
fmt.Printf("X(%d) = %.1f ∠ %.1f°\n", i, r, θ)
}
// Output:
// X(0) = 0.0 ∠ 0.0°
// X(1) = 4.0 ∠ -90.0°
// X(2) = 2.0 ∠ 45.0°
// X(3) = 0.0 ∠ 0.0°
// X(4) = 0.0 ∠ 0.0°
// X(5) = 0.0 ∠ 0.0°
// X(6) = 2.0 ∠ -45.0°
// X(7) = 4.0 ∠ 90.0°
}
func getHits() ([]hit, error) {
w, err := wav.New(os.Stdin)
if err != nil {
return nil, err
}
log.Printf("format: %d, channels: %d, sample rate: %d, byte rate: %d, bps: %d, samples: %d, duration: %v\n",
w.Header.AudioFormat, w.Header.NumChannels, w.Header.SampleRate,
w.Header.ByteRate, w.Header.BitsPerSample, w.Samples, w.Duration)
winSize := int(w.Header.SampleRate * uint32(w.Header.NumChannels) / winDenom)
cursor := 0
hits := make([]hit, 0)
for {
rawSamples, err := w.ReadFloats(winSize)
if err != nil {
if err == io.EOF || err == io.ErrUnexpectedEOF {
break
} else {
return nil, err
}
}
if len(rawSamples) < winSize {
break
}
samples := flattenChannels(int(w.Header.NumChannels), rawSamples)
pxx, freqs := spectral.Pwelch(samples, float64(w.Header.SampleRate), &spectral.PwelchOptions{NFFT: 16384, Scale_off: true})
maxPower, maxPowerFreq := findPeak(pxx, freqs, 32, 880)
pMaxPower, pMaxPowerFreq := findPeak(pxx, freqs, 55, 170)
harmonic := true
if !dsputils.Float64Equal(maxPowerFreq, pMaxPowerFreq) {
if maxPowerFreq < pMaxPowerFreq || !areHarmonic(maxPower, pMaxPower) {
fmt.Printf("t = %v: %f !~ %f\n", fmtSeconds(float64(cursor)/float64(w.Header.SampleRate)), maxPowerFreq, pMaxPowerFreq)
harmonic = false
}
}
v1Freq := pMaxPowerFreq * 1.1
v1Pow := powerAtFreq(v1Freq, pxx, freqs)
p1Freq := pMaxPowerFreq * 1.2
p1Pow := powerAtFreq(p1Freq, pxx, freqs)
v2Freq := pMaxPowerFreq * 1.3
v2Pow := powerAtFreq(v2Freq, pxx, freqs)
p2Freq := pMaxPowerFreq * 1.4
p2Pow := powerAtFreq(p2Freq, pxx, freqs)
if harmonic && pMaxPower >= 0.00 && pMaxPowerFreq >= 55.0 && pMaxPowerFreq <= 160.0 && v1Pow < p1Pow && v2Pow < p2Pow {
hits = append(hits, hit{t: float64(cursor) / float64(w.Header.SampleRate), freq: pMaxPowerFreq, pow: pMaxPower})
}
cursor += len(rawSamples) / int(w.Header.NumChannels)
}
return hits, nil
}