Program for Acoustic Echo Simulation

The following main program (Fig.2.10) simulates a simple acoustic echo using the delayline function in Fig.2.2. It reads a sound file and writes a sound file containing a single, discrete echo at the specified delay. For simplicity, utilities from the free Synthesis Tool Kit (STK) (Version 4.2.x) are used for sound input/output [86].^3.2

Figure 2.10: Program in C++ for implementing the echo simulator of Fig.2.9 using the free, open-source Synthesis Tool Kit (STK).

 

/* Acoustic echo simulator, main C++ program.
   Compatible with STK version 4.2.1.
   Usage: main inputsoundfile 
   Writes main.wav as output soundfile
 */

#include "FileWvIn.h"  /* STK soundfile input support */
#include "FileWvOut.h" /* STK soundfile output support */

static const int M = 20000; /* echo delay in samples */
static const int g = 0.8;   /* relative gain factor */

#include "delayline.c" /* defined previously */

int main(int argc, char *argv[]) 
{ 
  long i;
  Stk::setSampleRate(FileRead(argv[1]).fileRate());
  FileWvIn input(argv[1]);  /* read input soundfile */
  FileWvOut output("main"); /* creates main.wav */
  long nsamps = input.getSize();
  for (i=0;i<nsamps+M;i++)   {
    StkFloat insamp = input.tick();
    output.tick(insamp + g * delayline(insamp));
  }
}

In summary, a delay line simulates the time delay associated with wave propagation in a particular direction. Attenuation (e.g., by $1/r$ ) associated with ray propagation can of course be simulated by multiplying the delay-line output by some constant $g$ .