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82 lines
3.2 KiB
82 lines
3.2 KiB
7 years ago
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/*
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* fir_filterbank.cpp
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*
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* Created: Chip Audette, Creare LLC, Feb 2017
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* Primarly built upon CHAPRO "Generic Hearing Aid" from
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* Boys Town National Research Hospital (BTNRH): https://github.com/BTNRH/chapro
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*
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* License: MIT License. Use at your own risk.
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*
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*/
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#include "AudioConfigFIRFilterBank_F32.h"
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#include "utility/BTNRH_rfft.h"
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void AudioConfigFIRFilterBank_F32::fir_filterbank(float *bb, float *cf, const int nc, const int nw_orig, const int wt, const float sr)
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{
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double p, w, a = 0.16, sm = 0;
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float *ww, *bk, *xx, *yy;
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int j, k, kk, nt, nf, ns, *be;
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int nw = nextPowerOfTwo(nw_orig);
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//Serial.print("AudioConfigFIRFilterBank: fir_filterbank: nw_orig = "); Serial.print(nw_orig);
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//Serial.print(", nw = "); Serial.println(nw);
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nt = nw * 2; //we're going to do an fft that's twice as long (zero padded)
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nf = nw + 1; //number of bins to nyquist in the zero-padded FFT. Also nf = nt/2+1
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ns = nf * 2;
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be = (int *) calloc(nc + 1, sizeof(int));
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ww = (float *) calloc(nw, sizeof(float));
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xx = (float *) calloc(ns, sizeof(float));
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yy = (float *) calloc(ns, sizeof(float));
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// window
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for (j = 0; j < nw; j++) ww[j]=0.0f; //clear
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for (j = 0; j < nw_orig; j++) {
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p = M_PI * (2.0 * j - nw_orig) / nw_orig;
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if (wt == 0) {
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w = 0.54 + 0.46 * cos(p); // Hamming
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} else if (wt==1) {
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w = (1 - a + cos(p) + a * cos(2 * p)) / 2; // Blackman
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} else {
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//win = (1 - cos(2*pi*[1:N]/(N+1)))/2; //WEA's matlab call, indexing starts from 1, not zero
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w = (1.0 - cosf(2.0*M_PI*((float)(j))/((float)(nw_orig-1))))/2.0;
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}
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sm += w;
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ww[j] = (float) w;
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}
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// frequency bands...add the DC-facing band and add the Nyquist-facing band
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be[0] = 0;
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for (k = 1; k < nc; k++) {
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kk = round(nf * cf[k - 1] * (2 / sr)); //original
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be[k] = (kk > nf) ? nf : kk;
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}
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be[nc] = nf;
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// channel tranfer functions
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fzero(xx, ns);
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xx[nw_orig / 2] = 1; //make a single-sample impulse centered on our eventual window
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BTNRH_FFT::cha_fft_rc(xx, nt);
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for (k = 0; k < nc; k++) {
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fzero(yy, ns); //zero the temporary output
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//int nbins = (be[k + 1] - be[k]) * 2; Serial.print("fir_filterbank: chan ");Serial.print(k); Serial.print(", nbins = ");Serial.println(nbins);
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fcopy(yy + be[k] * 2, xx + be[k] * 2, (be[k + 1] - be[k]) * 2); //copy just our passband
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BTNRH_FFT::cha_fft_cr(yy, nt); //IFFT back into the time domain
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// apply window to iFFT of bandpass
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for (j = 0; j < nw; j++) {
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yy[j] *= ww[j];
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}
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bk = bb + k * nw_orig; //pointer to location in output array
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fcopy(bk, yy, nw_orig); //copy the filter coefficients to the output array
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//print out the coefficients
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//for (int i=0; i<nw; i++) { Serial.print(yy[i]*1000.0f);Serial.print(" "); }; Serial.println();
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}
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free(be);
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free(ww);
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free(xx);
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free(yy);
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}
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