Program for Acoustic Echo Simulation

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Program for Acoustic Echo Simulation

The following main program (Fig.1.9) simulates a simple acoustic echo using the delayline function in Fig.1.2. 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]. See Appendix A for an introduction to the STK.^2.2

**Figure:** Program in `C++` for implementing the echo simulator of Fig.1.8.
/* 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)); } }

/* 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 ) associated with ray propagation can of course be simulated by multiplying the delay-line output by some constant .

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.

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Physical Audio Signal Processing
    Acoustic Modeling with Digital Delay
       Acoustic Wave Propagation Simulation
          Program for Acoustic Echo Simulation