/// <summary>
/// Convolves the specified finite signal with an infinite signal.
/// </summary>
/// <param name="s1">The finite signal.</param>
/// <param name="s2">The infinite signal.</param>
/// <returns></returns>
/// <exception cref="SamplerateMismatchException"></exception>
public static ISignal Convolve(this IFiniteSignal s1, ISignal s2)
{
if (s1.SampleRate != s2.SampleRate)
{
throw new SamplerateMismatchException();
}
return(new InfiniteSignal(
(start, length) =>
{
var l = s1.Length + Math.Max(s1.Length, length) - 1;
var n = Fft.NextPowerOfTwo(l);
var spectrum1 = Fft.RealFft(s1.Signal, n);
var signal2A = s2.GetWindowedSignal(start - s1.Length - s1.Start, s1.Length);
var spectrum2A = Fft.RealFft(signal2A, n);
var signal2B = s2.GetWindowedSignal(start - s1.Start, length);
var spectrum2B = Fft.RealFft(signal2B, n);
var spectrumA = spectrum1.Multiply(spectrum2A);
var spectrumB = spectrum1.Multiply(spectrum2B);
var signalA = Fft.RealIfft(spectrumA).Skip(s1.Length).Take(Math.Min(length, s1.Length - 1));
var signalB = Fft.RealIfft(spectrumB).Take(length);
var signal = signalA.AddFull(signalB);
return signal;
},
s1.SampleRate)
{
DisplayName = "convolution result"
});
}
/// <summary>
/// Initializes a new instance of the <see cref="FftSpectrum" /> class.
/// </summary>
/// <param name="timeSignal">The finite time domain signal.</param>
/// <param name="sampleRate">The sample rate.</param>
/// <param name="start">The start.</param>
public FftSpectrum(IReadOnlyList <double> timeSignal, double sampleRate, int start = 0)
: this(new FftSeries(sampleRate, timeSignal.Count), Fft.RealFft(timeSignal.CircularShift(start)))
{
this.TimeDomainSignal = timeSignal.CircularShift(start).ToReadOnlyList();
}
/// <summary>
/// Initializes a new instance of the <see cref="FftSpectrum" /> class.
/// </summary>
/// <param name="timeSignal">The time domain signal.</param>
/// <param name="fftLength">Length of the FFT.</param>
/// <param name="sampleRate">The sample rate.</param>
/// <param name="start">The start sample time of the signal.</param>
public FftSpectrum(IEnumerable <double> timeSignal, int fftLength, double sampleRate, int start = 0)
: this(new FftSeries(sampleRate, fftLength), Fft.RealFft(timeSignal.CircularShift(start), fftLength))
{
}