guitfx/delay.c

#include <stdint.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include "delay.h"

void delay_init(
    struct delay * delay
) {
    delay->mix = 0.8;
    delay->feedback = 0.8;
    delay->duration = 0;
    delay->buf_idx = 0;
    delay->buf_capacity = 0;
    delay->buf = NULL;
}

void delay_set_time(
    struct delay * delay,
    uint64_t new_duration
) {
    printf("set delay duration to %lu samples\n", new_duration);
    if( new_duration > delay->buf_capacity ) {
        delay->buf_capacity = new_duration;
        delay->buf = realloc( delay->buf, sizeof(float) * new_duration );
    }

    for( int i = delay->duration; i < new_duration; ++i ) {
        delay->buf[i] = delay->buf[i - delay->duration];
    }

    delay->duration = new_duration;
    if( new_duration > 0 ) {
        delay->buf_idx %= new_duration;
    }
}

void delay_process(
    struct delay * delay,
    size_t frame_size,
    float const * in,
    float * out
) {
    for( size_t i = 0; i < frame_size; ++i ) {
        if( delay->duration > 0 ) {
            out[i] =
                0.5 * in[i]
                + 0.5 * delay->mix * delay->buf[ delay->buf_idx ];

            delay->buf[ delay->buf_idx ] *= delay->feedback;
            delay->buf[ delay->buf_idx ] += (1.0 - delay->feedback) * in[i];
            delay->buf_idx = (delay->buf_idx + 1) % delay->duration;
        } else {
            out[i] = 0.5 * in[i];
        }
    }
}