A Software Delay Line

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

Figure 1.2: The $M$-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.