A Software Delay Line

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A Software Delay Line

In software, a delay line is often implemented using a circular buffer. Let D denote an array of length . Then we can implement the -sample delay line in the C programming language as shown in Fig.1.2.

**Figure 1.2:** The -sample delay line.
/* delayline.c */ static double D[M]; // initialized to zero static long ptr=0; // read-write offset double delayline(double x) { double y = D[ptr]; // read operation D[ptr++] = x; // write operation if (ptr >= M) { ptr -= M; } // wrap ptr return y; }

Figure 1.2: The

-sample delay line.

    /* delayline.c */
    static double D[M];  // initialized to zero
    static long ptr=0;   // read-write offset

    double delayline(double x)
    {
      double y = D[ptr];    // read operation 
      D[ptr++] = x;         // write operation
      if (ptr >= M) { ptr -= M; } // wrap ptr 
      return y;
    }

Delay lines of this type are typically used in digital reverberators and other acoustic simulators involving fixed propagation delays. Later, in Chapter 3, we will consider time-varying delay lengths.

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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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Chapters

Physical Audio Signal Processing
    Acoustic Modeling with Digital Delay
       Delay Lines
          A Software Delay Line