/// <summary>
/// Performs the convolution of two real signals. The real result is returned.
/// </summary>
/// <remarks>Requires <paramref name="excitation"/> and <paramref name="impulse"/>
/// to match in a length of a power of 2.</remarks>
public static float[] Convolve(float[] excitation, float[] impulse, FFTCache cache = null)
{
Complex[] result = cache != null?
ConvolveFourier(excitation, impulse, cache) :
ConvolveFourier(excitation, impulse);
result.InPlaceIFFT();
return(Measurements.GetRealPart(result));
}
/// <summary>
/// Gets a linear phase convolution filter that results in this EQ when applied.
/// </summary>
/// <param name="eq">Source <see cref="Equalizer"/></param>
/// <param name="sampleRate">Sample rate of the target system the convolution filter could be used on</param>
/// <param name="length">Length of the convolution filter in samples, must be a power of 2</param>
/// <param name="gain">Signal voltage multiplier</param>
/// <param name="initial">Custom initial spectrum to apply the EQ on - phases will be corrected, this is not convolved,
/// and has to be twice the size of <paramref name="length"/></param>
public static float[] GetLinearConvolution(this Equalizer eq, int sampleRate, int length = 1024, float gain = 1,
Complex[] initial = null)
{
Complex[] filter = new Complex[length];
if (initial == null)
{
for (int i = 0; i < length; ++i)
{
filter[i].Real = i % 2 == 0 ? gain : -gain; // FFT of DiracDelta(x - length/2)
}
}
else
{
for (int i = 0; i < length; ++i)
{
filter[i].Real = initial[i].Magnitude * (i % 2 == 0 ? gain : -gain);
}
}
eq.Apply(filter, sampleRate);
filter.InPlaceIFFT();
return(Measurements.GetRealPart(filter));
}