public override void ReadFrame(float[] fftResult)
{
// Check output array size
switch (outputFormat)
{
case OutputFormat.Decibel:
case OutputFormat.Magnitudes:
case OutputFormat.MagnitudesSquared:
if (fftResult.Length != fft.Size / 2)
{
throw new ArgumentException("the provided FFT result array has an invalid size");
}
break;
default:
if (fftResult.Length != fft.Size)
{
throw new ArgumentException("the provided FFT result array has an invalid size");
}
break;
}
base.ReadFrame(frameBuffer);
// do fourier transform
fft.Forward(frameBuffer, fftBuffer);
// normalize fourier results
switch (outputFormat)
{
case OutputFormat.Decibel:
// TODO check if calculation corresponds to Haitsma & Kalker paper
FFTUtil.Results(fftBuffer, fftResult);
break;
case OutputFormat.Magnitudes:
FFTUtil.CalculateMagnitudes(fftBuffer, fftResult);
break;
case OutputFormat.MagnitudesSquared:
// TODO check if consumers of this mode really want it or if they want unsquared magnitudes instead
// (e.g. OLTW; this code path returns CalculateMagnitudesSquared for some time, as a temp test for OLTW,
// but originally returned CalculateMagnitudes)
FFTUtil.CalculateMagnitudesSquared(fftBuffer, fftResult);
break;
case OutputFormat.MagnitudesAndPhases:
FFTUtil.CalculateMagnitudes(fftBuffer, fftResult, 0);
FFTUtil.CalculatePhases(fftBuffer, fftResult, fft.Size / 2);
break;
case OutputFormat.Raw:
// Nothing to do here, result is already in raw format, just copy it to output buffer
Buffer.BlockCopy(fftBuffer, 0, fftResult, 0, fft.Size * 4);
break;
}
OnFrameReadSTFT(fftResult);
}
/// <summary>
/// Calculates a normalization offset for the current window function. Every window function leads to
/// a different FFT result peak value, and since the peak value of each windowed FFT means 0dB, this
/// offset can be used to adjust the calculated dB values.
/// </summary>
private void CalculateWindowFunctionNormalizationOffset()
{
if (windowFunction == null)
{
windowFunctionNormalizationDecibelOffset = 0;
}
else
{
SineGeneratorStream sine = new SineGeneratorStream(1024, 16, new TimeSpan(0, 0, 1));
float[] input = new float[WindowSize];
float[] output = new float[input.Length / 2];
WindowFunction wf = WindowUtil.GetFunction(windowFunction.Type, input.Length);
sine.Read(input, 0, input.Length);
wf.Apply(input);
fft.Forward(input);
int maxIndex = FFTUtil.Results(input, output);
float maxValue = output[maxIndex];
windowFunctionNormalizationDecibelOffset = 1f - maxValue;
}
}
private static void FrequencyDistributionBlockProcess(float[] buffer, double[] target, IFFT fft)
{
windowFunction.Apply(buffer);
fft.Forward(buffer);
for (int i = 0; i < buffer.Length; i += 2)
{
buffer[i / 2] = FFTUtil.CalculateMagnitude(buffer[i], buffer[i + 1]) / buffer.Length * 2;
}
for (int i = 0; i < target.Length; i++)
{
target[i] += buffer[i];
}
}