Multiband EQ
This is a fairly typical multiband graphical equalizer. It's implemented using a FFT, so it takes quite a lot of CPU power, but should have less phase effects than an equivalent filter implementation.
If the input signal is at too low a sample rate then the top bands will be ignored, the highest useful band will always be a high shelf.
coeffiecnt lookup table
db_table = malloc(1000 * sizeof(float));
for (i=0; i < 1000; i++) {
db = ((float)i/10) - 70;
db_table[i] = pow(10.0f, db/20.0f);
}
// Create FFT bin -> band + delta tables
bin = 0;
while (bin <= bands[0]/hz_per_bin) {
bin_base[bin] = 0;
bin_delta[bin++] = 0.0f;
}
for (i = 1; i < BANDS-1 && bin < (FFT_LENGTH/2)-1 && bands[i+1] < s_rate/2; i++) {
last_bin = bin;
next_bin = (bands[i+1])/hz_per_bin;
while (bin <= next_bin) {
bin_base[bin] = i;
bin_delta[bin] = (float)(bin - last_bin) / (float)(next_bin - last_bin);
bin++;
}
}
for (; bin < (FFT_LENGTH/2); bin++) {
bin_base[bin] = BANDS-1;
bin_delta[bin] = 0.0f;
}
]]>
in_fifo);
free(plugin_data->out_fifo);
free(plugin_data->out_accum);
free(plugin_data->real);
free(plugin_data->comp);
free(plugin_data->window);
free(plugin_data->bin_base);
free(plugin_data->bin_delta);
free(plugin_data->db_table);
]]>
= FFT_LENGTH) {
fifo_pos = fft_latency;
// Window input FIFO
for (i=0; i < FFT_LENGTH; i++) {
real[i] = in_fifo[i] * window[i];
}
// Run the real->complex transform
#ifdef FFTW3
fftwf_execute(plan_rc);
#else
rfftw_one(plan_rc, real, comp);
#endif
// Multiply the bins magnitudes by the coeficients
for (i = 0; i < FFT_LENGTH/2; i++) {
comp[i] *= coefs[i];
comp[FFT_LENGTH-i] *= coefs[i];
}
// Run the complex->real transform
#ifdef FFTW3
fftwf_execute(plan_cr);
#else
rfftw_one(plan_cr, comp, real);
#endif
// Window into the output accumulator
for (i = 0; i < FFT_LENGTH; i++) {
out_accum[i] += 0.9186162f * window[i] * real[i]/(FFT_LENGTH * OVER_SAMP);
}
for (i = 0; i < step_size; i++) {
out_fifo[i] = out_accum[i];
}
// Shift output accumulator
memmove(out_accum, out_accum + step_size, FFT_LENGTH*sizeof(LADSPA_Data));
// Shift input fifo
for (i = 0; i < fft_latency; i++) {
in_fifo[i] = in_fifo[i+step_size];
}
}
}
// Store the fifo_position
plugin_data->fifo_pos = fifo_pos;
*(plugin_data->latency) = fft_latency;
]]>
50Hz gain (low shelving)
100Hz gain
156Hz gain
220Hz gain
311Hz gain
440Hz gain
622Hz gain
880Hz gain
1250Hz gain
1750Hz gain
2500Hz gain
3500Hz gain
5000Hz gain
10000Hz gain
20000Hz gain
Input
Output
latency