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//
// compand_example.c
//
// This example demonstrates the interface to the compand function
// (compression, expansion). The compander is typically used with the
// quantizer to increase the dynamic range of the converter, particularly for
// low-level signals. The transfer function is computed (empirically) and
// printed to the screen.
//
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "compand_example.m"
// print usage/help message
void usage()
{
printf("compand_example\n");
printf(" u/h : print usage/help\n");
printf(" v/q : verbose/quiet, default: verbose\n");
printf(" n : number of samples, default: 31\n");
printf(" m : companding parameter: mu > 0, default: 255\n");
printf(" r : range > 0, default: 1.25\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int n=31;
float mu=255.0f;
float range = 1.25f;
int verbose = 1;
int dopt;
while ((dopt = getopt(argc,argv,"uhvqn:m:r:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'v': verbose = 1; break;
case 'q': verbose = 0; break;
case 'n': n = atoi(optarg); break;
case 'm': mu = atof(optarg); break;
case 'r': range = atof(optarg); break;
default:
exit(1);
}
}
// validate input
if (mu < 0) {
fprintf(stderr,"error: %s, mu must be positive\n", argv[0]);
usage();
exit(1);
} else if (range <= 0) {
fprintf(stderr,"error: %s, range must be greater than zero\n", argv[0]);
usage();
exit(1);
}
// 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");
float x = -range;
float y, z;
float dx = 2.0*range/(float)(n-1);
unsigned int i;
for (i=0; i<n; i++) {
y = compress_mulaw(x,mu);
z = expand_mulaw(y,mu);
if (verbose)
printf("%8.4f > %8.4f > %8.4f\n", x, y, z);
fprintf(fid,"x(%3u) = %12.4e;\n", i+1, x);
fprintf(fid,"y(%3u) = %12.4e;\n", i+1, y);
fprintf(fid,"z(%3u) = %12.4e;\n", i+1, z);
x += dx;
}
// plot results
fprintf(fid,"\n\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(x,y,'-b','LineWidth',2,x,z,'-r');\n");
fprintf(fid,"axis square\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"xlabel('x');\n");
fprintf(fid,"ylabel('f(x)');\n");
// close debug file
fclose(fid);
printf("results wrtten to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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