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Cut off spectrum at 2/3 of nyquist frequency.

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Define SPECTRUM_LOGARITHMIC to get decibel scale rather than power in the spectrum (generally less useful, therefore disabled by default).

Originally committed to SVN as r531.
This commit is contained in:
Niels Martin Hansen 2006-08-27 23:31:20 +00:00
parent df964c78cd
commit a6fca3677f
1 changed files with 25 additions and 10 deletions
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35
core/audio_display.cpp
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@ -520,7 +520,8 @@ protected:
// Prepare constants
const int halfwindow = window/2;
const int posThres = MAX(1,int(double(halfwindow-cutoff)/double(h)*0.5/scale + 0.5));
//const int posThres = MAX(1,int(double(halfwindow-cutoff)/double(h)*0.5/scale + 0.5));
const int maxband = (halfwindow-cutoff) * 2/3;
const float mult = float(h)/float(halfwindow-cutoff)/255.f;
// Calculation loop
@ -539,11 +540,6 @@ protected:
write_ptr = data+i+h*w;
write_ptr16 = ((unsigned short*)data)+(i+h*w);
// Calculate the signal power over frequency
for (int j = 0; j < window; j++) {
power[j] = sqrt(out_r[j]*out_r[j] + out_i[j]*out_i[j]);
}
// According to the formula at http://en.wikipedia.org/wiki/Fast_Fourier_transform:
// X_k = SUM ( n=0, N-1, x_n * e^(-2*pi*i / N * n * k) )
// The maximum output value for our case (real-valued-only input, range -16384 to +16383, N=1024)
@ -559,6 +555,22 @@ protected:
// But scale this by a user amount (vertical zoom0 -- scale is from 0 to 8
int maxpower = window*16384 / (16*256*scale);
// Calculate the signal power over frequency
#ifdef SPECTRUM_LOGAGITHMIC
for (int j = 0; j < window; j++) {
float t = out_r[j]*out_r[j] + out_i[j]*out_i[j];
if (t < 1)
power[j] = 0;
else
power[j] = 10. * log10(t) * 64; // try changing the constant 64 if playing with this
}
maxpower = 10 * log10((float)maxpower);
#else
for (int j = 0; j < window; j++) {
power[j] = sqrt(out_r[j]*out_r[j] + out_i[j]*out_i[j]);
}
#endif
#define WRITE_PIXEL \
if (intensity > 255) intensity = 255; \
if (intensity < 0) intensity = 0; \
@ -578,8 +590,8 @@ protected:
// Iterate over pixels, picking a range of samples for each
for (int j = 0; j < h; j++) {
int sample1 = (halfwindow-cutoff) * j/h + cutoff;
int sample2 = (halfwindow-cutoff) * (j+1)/h + cutoff;
int sample1 = maxband * j/h + cutoff;
int sample2 = maxband * (j+1)/h + cutoff;
float maxval = 0;
for (int samp = sample1; samp <= sample2; samp++) {
if (power[samp] > maxval) maxval = power[samp];
@ -595,11 +607,11 @@ protected:
// Iterate over pixels, picking the nearest power values
for (int j = 0; j < h; j++) {
float ideal = (float)(j+1.)/h * (halfwindow-cutoff);
float ideal = (float)(j+1.)/h * maxband;
float sample1 = power[(int)floor(ideal)+cutoff];
float sample2 = power[(int)ceil(ideal)+cutoff];
float frac = ideal - floor(ideal);
int intensity = int(((1-frac)*sample1 + frac*sample2) / maxpower * 255);
int intensity = int(((1-frac)*sample1 + frac*sample2) / maxpower);
WRITE_PIXEL
}
}
@ -806,6 +818,8 @@ void AudioDisplay::DrawSpectrum(wxDC &finaldc,bool weak) {
////// END OF PARALLELISED CODE //////
// Clear top of image
/*
// not needed with new algo, it always fill the entire image
int filly = h - (halfwindow-cutOff)/posThres;
if (filly < 0) filly = 0;
if (depth == 32) {
@ -828,6 +842,7 @@ void AudioDisplay::DrawSpectrum(wxDC &finaldc,bool weak) {
}
}
}
*/
// Clear memory
delete raw_float;