note.c

dsp AD公司ADSP21的代码,里面有FFT FIR IIR EQULIZER G722_21F 等可以在项目中直接应用的代码.此代码的来源是ADI公司自己出版的书籍,此书在美国购得

#include <libap.h>

/* Function to generate samples from a second order oscillator.
          key  = 0-127 "MIDI" note number (69 = 440 Hz).
          rate = envelope rate of change parameter (close to 1).
   change_flag = indicates that key and/or rate have changed.

10-31-94 CAC adapted to CAC boards
*/

#define PI 3.14159265358979323846

#ifdef KHZ8
#define SAMPLE_RATE 8e3
#else
#ifdef KHZ16
#define SAMPLE_RATE 16e3
#else
#define SAMPLE_RATE 32e3
#endif
#endif

/* key constant is 1/12 */
#define KEY_CONSTANT 0.083333333333333

/* this set the A above middle C reference frequency of 440 Hz */
/* calculate this as a globable so it never happens again */
#define TWO_PI_DIV_FS_440  (880.0 * PI / SAMPLE_RATE)

/*
 key:
     semi-tone pitch to generate,
     number 69 will give A above middle C at 440 Hz.
 voice:
     voice number from 0 to MAX_VOICES-1
 change_flag:
    -1 = start new sequence from t=0
     0 = no change, generate next sample in sequence
     1 = change rate after start
 rate:
     rate constant determines the decay or rise of envelope
*/

/* cw is the cosine constant required for fast changes of envelope */
/* a and b are the coefficients for the difference equation */
/* y1 and y0 are the history values */
/* t is time index for this note */
/* cindex is the index into rate and ts arrays (reset when t=0) */

typedef struct {
    int key,t,cindex;
    float cw,a,b;
    float y1,y0;
} NOTE_STATE;

/* NOTE_STATE structure, time break point array, rate parameter array */

float note(sparm,tbreak_array,rate_array)
NOTE_STATE *sparm;
int *tbreak_array;
float *rate_array;
{
    register NOTE_STATE *s = sparm;
    register int ti,ci;
    register float rate,out;
    float wosc;

    ti = s->t;
/* t=0 re-start case, set state variables */
    if(!ti) {
        wosc = TWO_PI_DIV_FS_440 * xtoy(2.0,(s->key-69) * KEY_CONSTANT);
        s->cw = 2.0 * qcos(wosc);
        rate = rate_array[0];
        s->a = s->cw * rate;     /* rate change */
        s->b = -rate * rate;
        s->y0 = 0.0;
        out = rate*qsin(wosc);
        s->cindex = 0;
    }
    else {
        ci = s->cindex;
    /* rate change case */
        if(ti == tbreak_array[ci]) {
            rate = rate_array[++ci];
            s->a = s->cw * rate;
            s->b = -rate * rate;
            s->cindex = ci;
        }

    /* make new sample */
        out = s->a * s->y1 + s->b * s->y0;
        s->y0 = s->y1;
    }
    s->y1 = out;
    s->t = ++ti;
    return(out);
}