/// <summary>
/// Gets a zero-delay convolution filter with minimally sacrificed phase 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[] GetConvolution(this Equalizer eq, int sampleRate, int length = 1024, float gain = 1,
Complex[] initial = null)
{
length <<= 1;
Complex[] filter = new Complex[length];
if (initial == null)
{
for (int i = 0; i < length; ++i)
{
filter[i].Real = gain; // FFT of DiracDelta(x)
}
}
else
{
for (int i = 0; i < length; ++i)
{
filter[i].Real = initial[i].Magnitude * gain;
}
}
eq.Apply(filter, sampleRate);
using (FFTCache cache = new FFTCache(length)) {
Measurements.MinimumPhaseSpectrum(filter, cache);
filter.InPlaceIFFT(cache);
}
return(Measurements.GetRealPartHalf(filter));
}
