public void SaveSnippet(string filename, int startIndex, int endIndex)
{
List <Complex[]> snippet = CopyFFTs(startIndex, endIndex - startIndex);
FFTs stft_snippet = new FFTs(snippet, sampleRate, stepSize, window);
stft_snippet.SaveToWav(filename);
}
private static int[] createFreqShiftMap(FFTs stft, int indexShift, SelectedWindowIndices indices = null, int order = 0, double thresh = 0.9)
{
(_, _, int freqIndex1, int freqIndex2) =
indices != null?indices.Indices() : (0, stft.Count, 0, stft.fftSize);
/**
* Explanation of algorithm:
* We basically want one half cycle of a cos(ang_freq * (centerIndex-i))^(order)
* First we calculation the attenuation we want at the window boundaries, ie
* cos(ang_freq*(centerIndex-freq1))^(order) = thresh
* Then we solve for ang_freq to find the angular frequency of the window
* Then we use that angular frequency for arbitrary values of i
*
* And then, depending on the shift direction, we don't care about shifts on the opposite side of the direction
*
* If order is zero, it results in a Linear Frequency Shifter
*/
int centerIndex = (freqIndex2 + freqIndex1) / 2;
int[] shift_map = new int[stft.fftSize];
for (int i = 0; i < shift_map.Length / 2; i++)
{
double angular_freq = Math.Acos(Math.Pow(thresh, (1d / ((double)order)))) / (centerIndex - freqIndex1);
double angle = angular_freq * (i - centerIndex);
double mod = Math.Pow(Math.Cos(angle), order);
//Don't care about values outside of the half period window
if (Math.Abs(angle) >= Math.PI / 2)
{
mod = 0;
}
//Don't care about values past the window in the direction it's not shifting
else if (indexShift > 0 && i < freqIndex1)
{
mod = 0;
}
else if (indexShift < 0 && i > freqIndex2)
{
mod = 0;
}
int shift = (int)(indexShift * mod);
if (i >= freqIndex1 && i < freqIndex2)
{
shift_map[i] = indexShift; //first side
shift_map[shift_map.Length - i - 1] = -indexShift; //mirrored side
}
else
{
shift_map[i] = shift;
}
}
return(shift_map);
}
private static double[] createFreqShiftModulation(FFTs stft, int shiftIndex, SelectedWindowIndices indices, bool freqDependent = false)
{
if (freqDependent)
{
; //todo, implement createFreqDependentShiftMap first
}
double[] shift_mod = new double[stft.fftSize];
Array.Fill(shift_mod, 1);
return(shift_mod);
}
public static void AddGain(FFTs stft, double gain = 0, SelectedWindowIndices indices = null, bool dB = true)
{
(int timeIndex1, int timeIndex2, int freqIndex1, int freqIndex2) =
indices != null?indices.Indices() : (0, stft.Count, 0, stft.fftSize);
//Defaults to dB
//Converts to linear gain for multiplying gain to data
gain = dB ? Math.Pow(10, gain / 20) : gain;
List <Complex[]> data = stft.GetFFTs();
for (int n = timeIndex1; n < timeIndex2; n++)
{
for (int k = freqIndex1; k < freqIndex2; k++)
{
data[n][k].Real *= gain;
data[n][k].Imaginary *= gain;
}
}
}
public static void WhiteNoiseFilter(FFTs stft, double threshold, SelectedWindowIndices indices = null, bool dB = true)
{
List <Complex[]> data = stft.GetFFTs();
(int timeIndex1, int timeIndex2, int freqIndex1, int freqIndex2) =
indices != null?indices.Indices() : (0, data.Count, 0, stft.fftSize);
threshold = dB ? Math.Pow(10, threshold / 20) : threshold;
for (int n = timeIndex1; n < timeIndex2; n++)
{
for (int k = freqIndex1; k < freqIndex2; k++)
{
if (data[n][k].Magnitude < threshold)
{
data[n][k].Real = 0;
data[n][k].Imaginary = 0;
}
}
}
}
private static void HighPassFilter(FFTs stft, double cutoff, SelectedWindowIndices indices = null)
{
(int timeIndex1, int timeIndex2, int freqIndex1, int freqIndex2) =
indices != null?indices.Indices() : (0, stft.Count, 0, stft.fftSize / 2);
List <Complex[]> data = stft.GetFFTs();
int index_cutoff = (int)(cutoff / stft.FreqResolution);
for (int n = timeIndex1; n < timeIndex2; n++)
{
for (int k = freqIndex1; k < freqIndex2; k++)
{
if (k <= index_cutoff)
{
data[n][k] = new Complex();
data[n][stft.fftSize - 1 - k] = new Complex(); //Mirrored side
}
}
}
}
public static void FrequencyShifter(FFTs stft, int freq_shift, SelectedWindowIndices indices = null, int order = 0, double thresh = 0.9)
{
int indexShift = freq_shift / stft.FreqResolution;
if (indexShift == 0)
{
return;
}
(int timeIndex1, int timeIndex2, int freqIndex1, int freqIndex2) =
indices != null?indices.Indices() : (0, stft.Count, 0, stft.fftSize);
//Shift map tells how far each index is going to shift
//Order of 0 results in a linear shifter
//shift_mod gives a scaling factor to each shifted index
int[] shift_map = createFreqShiftMap(stft, indexShift, indices, order, thresh);
double[] shift_mod = createFreqShiftModulation(stft, indexShift, indices);
List <Complex[]> ffts = stft.GetFFTs();
for (int n = timeIndex1; n < timeIndex2; n++)
{
Complex[] fft = ffts[n];
Complex[] shifted_fft = new Complex[fft.Length];
for (int k = 0; k < fft.Length; k++)
{
if (k + shift_map[k] >= 0 && k + shift_map[k] < fft.Length) //Ignore the ones that get shifted too far
{
shifted_fft[k + shift_map[k]] += fft[k] * shift_mod[k];
}
}
Array.Copy(shifted_fft, fft, fft.Length);
}
}
private static int[] createRecursiveBandShiftMap(FFTs stft, int indexShift, SelectedWindowIndices indices = null)
{
throw new NotImplementedException();
}
public static void SaveFFTsToWav(string filename, FFTs stft)
{
float[] audio = stft.GetAudioFloat();
using WaveFileWriter writer = new NAudio.Wave.WaveFileWriter(filename, new WaveFormat(stft.sampleRate, 1));
writer.WriteSamples(audio, 0, audio.Length);
}