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Improve spectrogram accuracy.

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This commit is contained in:
J.D. Purcell 2015-09-05 13:18:22 -04:00
parent 76d96f4309
commit 42565f4c98
1 changed files with 21 additions and 11 deletions
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32
libse/WaveToVisualizer.cs
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@ -526,7 +526,8 @@ namespace Nikse.SubtitleEdit.Core
private readonly FastBitmap.PixelData[] _palette;
private readonly double[] _segment;
private readonly double[] _window;
private readonly double[] _magnitude;
private readonly double[] _magnitude1;
private readonly double[] _magnitude2;
public SpectrogramDrawer(int nfft)
{
@ -536,7 +537,8 @@ namespace Nikse.SubtitleEdit.Core
_palette = GeneratePalette();
_segment = new double[nfft];
_window = CreateRaisedCosineWindow(nfft);
_magnitude = new double[nfft / 2];
_magnitude1 = new double[nfft / 2];
_magnitude2 = new double[nfft / 2];
double scaleCorrection = 1.0 / (raisedCosineWindowScale * _fft.ForwardScaleFactor);
for (int i = 0; i < _window.Length; i++)
@ -553,22 +555,30 @@ namespace Nikse.SubtitleEdit.Core
bmp.LockImage();
for (int x = 0; x < width; x++)
{
// read a segment of the recorded signal
for (int i = 0; i < _nfft; i++)
Action<int, double[]> processSegment = (offset, magnitude) =>
{
_segment[i] = samples[x * _nfft + i] * _window[i];
}
// read a segment of the recorded signal
for (int i = 0; i < _nfft; i++)
{
_segment[i] = samples[x * _nfft + offset + i] * _window[i];
}
// transform to the frequency domain
_fft.ComputeForward(_segment);
// transform to the frequency domain
_fft.ComputeForward(_segment);
// compute the magnitude of the spectrum
MagnitudeSpectrum(_segment, _magnitude);
// compute the magnitude of the spectrum
MagnitudeSpectrum(_segment, magnitude);
};
// process 2 segments offset by -1/4 and 1/4 fft size, resulting in 1/2 fft size
// window spacing (the minimum overlap to avoid discarding parts of the signal)
processSegment(x > 0 ? -_nfft / 4 : 0, _magnitude1);
processSegment(x < width - 1 ? _nfft / 4 : 0, _magnitude2);
// draw
for (int y = 0; y < height; y++)
{
int colorIndex = _mapper.Map(_magnitude[y]);
int colorIndex = _mapper.Map((_magnitude1[y] + _magnitude2[y]) / 2.0);
bmp.SetPixel(x, height - y - 1, _palette[colorIndex]);
}
}