digital_audio.c

一些经典的数字信号处理算法方面的c源代码。

/* allpass.c - allpass reverberator with circular delay line */

double tap();
void cdelay();

double allpass(D, w, p, a, x)                   /* usage: y=allpass(D,w,&p,a,x); */
double *w, **p, a, x;                           /* \(p\) is passed by address */
int D;
{
       double y, s0, sD;

       sD = tap(D, w, *p, D);                   /* \(D\)th tap delay output */
       s0 = x + a * sD;
       y  = -a * s0 + sD;                       /* filter output */
       **p = s0;                                /* delay input */
       cdelay(D, w, p);                         /* update delay line */

       return y;
}



/* lowpass.c - lowpass reverberator with feedback filter G(z) */

double tap(), can();
void cdelay();

double lowpass(D, w, p, M, a, b, v, x)
double *w, **p, *a, *b, *v, x;                   /* \(v\) = state vector for \(G(z)\) */
int D;                                           /* \(a,b,v\) are \((M+1)\)-dimensional */
{
       double y, sD;

       sD = tap(D, w, *p, D);                    /* delay output is \(G(z)\) input */
       y = x + can(M, a, M, b, v, sD);           /* reverb output */
       **p = y;                                  /* delay input */
       cdelay(D, w, p);                          /* update delay line */

       return y;
}


/* plain.c - plain reverberator with circular delay line */

double tap();
void cdelay();

double plain(D, w, p, a, x)                     /* usage: y=plain(D,w,&p,a,x); */
double *w, **p, a, x;                           /* \(p\) is passed by address */
int D;
{
       double y, sD;

       sD = tap(D, w, *p, D);                   /* \(D\)th tap delay output */
       y = x + a * sD;                          /* filter output */
       **p = y;                                 /* delay input */
       cdelay(D, w, p);                         /* update delay line */

       return y;
}



/* tapi.c - interpolated tap output of a delay line */

double tap();

double tapi(D, w, p, d)                   /* usage: sd = tapi(D, w, p, d); */
double *w, *p, d;                         /* \(d\) = desired non-integer delay */
int D;                                    /* \(p\) = circular pointer to \(w\) */
{
       int i, j;
       double si, sj;

       i = (int) d;                       /* interpolate between \(s\sb{i}\) and \(s\sb{j}\) */
       j = (i+1) % (D+1);                 /* if \(i=D\), then \(j=0\); otherwise, \(j=i+1\) */

       si = tap(D, w, p, i);              /* note, \(s\sb{i}(n) = x(n-i)\) */
       sj = tap(D, w, p, j);              /* note, \(s\sb{j}(n) = x(n-j)\) */

       return si + (d - i) * (sj - si);
}



/* tapi2.c - interpolated tap output of a delay line */

double tap2();

double tapi2(D, w, q, d)                  /* usage: sd = tapi2(D, w, q, d); */
double *w, d;                             /* \(d\) = desired non-integer delay */
int D, q;                                 /* \(q\) = circular offset index */
{
       int i, j;
       double si, sj;

       i = (int) d;                       /* interpolate between \(s\sb{i}\) and \(s\sb{j}\) */
       j = (i+1) % (D+1);                 /* if \(i=D\), then \(j=0\); otherwise, \(j=i+1\) */

       si = tap2(D, w, q, i);             /* note, \(s\sb{i}(n) = x(n-i)\) */
       sj = tap2(D, w, q, j);             /* note, \(s\sb{j}(n) = x(n-j)\) */

       return si + (d - i) * (sj - si);
}