public const double HIGHPASS = 7000.0; //HZ
public static double[] DistortionMask(int maskLength, double distortionStrength, WaveFormat format)
{
double lowpass, highpass;
double nyquist = SoundProcessing.NyquistRate(format);
lowpass = LOWPASS / (nyquist / SoundProcessing.Constants.FFT_LENGTH / 2.0);
highpass = HIGHPASS / (nyquist / SoundProcessing.Constants.FFT_LENGTH / 2.0);
double[] mask = new double[maskLength];
for (int i = 0; i < maskLength; ++i)
{
double rampDown = 1.0;
if (i < lowpass)
{
rampDown = MathUtils.Clamp(Math.Sqrt(i), -distortionStrength, distortionStrength);
}
else if (i > highpass)
{
rampDown = MathUtils.Clamp(Math.Sqrt(i / 2), -distortionStrength, distortionStrength);
}
mask[i] = rampDown;
}
return(mask);
}
public static double[] ApplyDistortion(double[] samples, double distortionStrength, WaveFormat fmt)
{
List <double> processedSamples = new List <double>();
//list containing overlapping sound frames
List <double> savedTimeDomain = new List <double>(SoundProcessing.Constants.FFT_FRAME_LENGTH);
SoundProcessing.PadZeroes(savedTimeDomain, SoundProcessing.Constants.FFT_FRAME_LENGTH);//pad zeroes to have required container size
//build a filter mask specified for the distortion
double[] filterMask = FilterMasks.DistortionMask(
SoundProcessing.Constants.FREQUENCY_DOMAIN_LENGTH,
distortionStrength,
fmt
);
for (int i = 0; i < samples.Length; i += SoundProcessing.Constants.FFT_FRAME_LENGTH)
{
//cut out a data frame from samples
var data = samples.Slice(i, SoundProcessing.Constants.FFT_LENGTH);
//prepare a buffer for FFT
var complices = new Complex[SoundProcessing.Constants.FREQUENCY_DOMAIN_LENGTH];
//arrays containing the input samples, the result of FFT and the result of IFFT
PinnedArray <double> input = new PinnedArray <double>(data);
PinnedArray <Complex> frequencyDomain = new PinnedArray <Complex>(complices);
PinnedArray <double> timeDomain = new PinnedArray <double>(data.Length);
//convert time domain to frequency domain
DFT.FFT(input, frequencyDomain);
//mask the frequencies using a mask created earlier
for (int j = 0; j < frequencyDomain.Length; ++j)
{
frequencyDomain[j] *= filterMask[j];
}
//mask negative frequencies
for (int j = frequencyDomain.Length - 1; j > frequencyDomain.Length / 2; --j)
{
frequencyDomain[j] *= filterMask[frequencyDomain.Length - j];
}
//convert back to time domain
DFT.IFFT(frequencyDomain, timeDomain);
//overlapping of the frames
for (int j = 0; j < SoundProcessing.Constants.OVERLAP; ++j)
{
timeDomain[j] *= (j + 0.0) / SoundProcessing.Constants.OVERLAP;
timeDomain[j] += savedTimeDomain[j] * (1.0 - (j + 0.00) / (double)SoundProcessing.Constants.OVERLAP); //overlap with previous samples to avoid stuttering
}
//add overlapping sound samples
savedTimeDomain.Clear();
for (int j = SoundProcessing.Constants.FFT_FRAME_LENGTH; j < timeDomain.Length; ++j)
{
savedTimeDomain.Add(MathUtils.Clamp(timeDomain[j], -1.0, 1.0));
}
//add the actual samples
for (int j = 0; j < SoundProcessing.Constants.FFT_FRAME_LENGTH; ++j)
{
processedSamples.Add(MathUtils.Clamp(timeDomain[j], -1.0, 1.0));
}
//dispose of the PinnedArray objects
input.Dispose();
frequencyDomain.Dispose();
timeDomain.Dispose();
}
return(processedSamples.ToArray());
}