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//
// quantize_example.c
//
// Demonstrates the quantizer/compander combo.
//
#include <stdlib.h>
#include <stdio.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "quantize_example.m"
// print usage/help message
void usage()
{
printf("quantize_example [options]\n");
printf(" u/h : print usage\n");
printf(" b : number of bits, 0 < b <= 16 [default: 4]\n");
printf(" m : mu, compression factor, mu > 0 [default: 255.0]\n");
}
int main(int argc, char*argv[]) {
unsigned int num_bits=4;
float mu = 255.0f;
unsigned int num_samples = 64;
int dopt;
while ((dopt = getopt(argc,argv,"uhb:m:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'b': num_bits = atoi(optarg); break;
case 'm': mu = atof(optarg); break;
default:
exit(1);
}
}
// validate input
if (num_bits > 16 || num_bits < 1) {
fprintf(stderr,"error: %s, quantizer bits must be in [1,16]\n", argv[0]);
exit(1);
} else if (mu < 0.0f) {
fprintf(stderr,"error: %s, mu must be greater than 0\n", argv[0]);
exit(1);
}
unsigned int i;
float x[num_samples];
float y[num_samples];
float v; // compressed sample
unsigned int q; // quantized sample
float u; // uncompressed sample
float e; // error
float rmse = 0.0f;
printf(" input ADC output\n");
printf(" ----- --- ------\n");
float phi = 0.0f;
float dphi = 0.02f * 256.0f / (float) num_samples;
for (i=0; i<num_samples; i++) {
// generate windowed pulse
x[i] = 0.5f*cosf(2.0f*M_PI*phi) + 0.5f*cosf(2.0f*M_PI*phi*0.57f);
x[i] *= 0.5f * liquid_kaiser(i, num_samples, 10.0f);
phi += dphi;
// compress sample
v = compress_mulaw(x[i],mu);
// quantize: analog to digital converter
q = quantize_adc(v,num_bits);
// quantize: digital to analog converter
u = quantize_dac(q,num_bits);
// expand sample
y[i] = expand_mulaw(u,mu);
// compute error
e = y[i] - x[i];
rmse += e*e;
printf("%4u : %12.8f > 0x%4.4x > %12.8f\n", i, x[i], q, y[i]);
}
rmse = sqrtf(rmse / (float)num_samples);
printf("-----------------------\n");
printf("rmse : %12.4e\n", rmse);
// open debug file
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"num_samples = %u;\n", num_samples);
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %16.8e; y(%4u) = %16.8e;\n", i+1, x[i], i+1, y[i]);
}
fprintf(fid,"figure;\n");
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid,"%% generate stairs-like plot\n");
fprintf(fid,"t0 = reshape([t(1:num_samples-1)(:) t(1:num_samples-1)(:)]',1,2*(num_samples-1)) + 0.5;\n");
fprintf(fid,"y0 = reshape([y(1:num_samples-1)(:) y(2:num_samples)(:)]', 1,2*(num_samples-1));\n");
fprintf(fid,"hold on;\n");
fprintf(fid,"plot(t,x,t0,y0);\n");
fprintf(fid,"xlabel('sample index');\n");
fprintf(fid,"ylabel('signal');\n");
fprintf(fid,"legend('original','reconstructed',1);\n");
fprintf(fid,"grid on;\n");
// close debug file
fclose(fid);
printf("results wrtten to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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