diff --git a/delay.c b/delay.c
index d878fd1..c73889f 100644
--- a/delay.c
+++ b/delay.c
@@ -1,17 +1,36 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include "delay.h"
 
 void delay_init(
     struct delay * delay
 ) {
-    delay->duration = 15000;
     delay->mix = 0.8;
     delay->feedback = 0.6;
-
+    delay->duration = 0;
     delay->buf_idx = 0;
-    delay->buf = calloc( delay->duration, sizeof(float) );
+    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;
+    delay->buf_idx %= new_duration;
 }
 
 void delay_process(
@@ -21,12 +40,16 @@ void delay_process(
     float * out
 ) {
     for( size_t i = 0; i < frame_size; ++i ) {
-        out[i] =
-            (1.0 - delay->mix) * in[i]
-            + delay->mix * delay->buf[ delay->buf_idx ];
+        if( delay->duration > 0 ) {
+            out[i] =
+                (1.0 - delay->mix) * in[i]
+                + 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;
+            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] = in[i];
+        }
     }
 }
diff --git a/delay.h b/delay.h
index fc004e6..4ed2cf5 100644
--- a/delay.h
+++ b/delay.h
@@ -9,6 +9,7 @@ struct delay {
     float mix;
 
     uint64_t buf_idx;
+    size_t buf_capacity;
     float * buf;
 };
 
@@ -16,6 +17,11 @@ void delay_init(
     struct delay * delay
 );
 
+void delay_set_time(
+    struct delay * delay,
+    uint64_t new_duration
+);
+
 void delay_process(
     struct delay * delay,
     size_t frame_size,
diff --git a/guitfx.c b/guitfx.c
index ad35445..71bd06a 100644
--- a/guitfx.c
+++ b/guitfx.c
@@ -29,6 +29,7 @@ struct data {
 	struct port * out_port;
 
 	//! effect data
+	uint64_t last_tap;
 	struct delay delay;
 
 	//! elapsed time in number of samples
@@ -71,10 +72,18 @@ static void on_process(void *userdata, struct spa_io_position *position)
 						unsigned sec =
 						      (frame + c->offset)
 							/ (float) position->clock.rate.denom;
-						char * data = SPA_POD_BODY(&c->value);
+						char * midi_data = SPA_POD_BODY(&c->value);
 						unsigned size = SPA_POD_BODY_SIZE(&c->value);
 
-						printf("[%d] MIDI message (%d bytes) : %x, %x, %x\n", sec, size, data[0], data[1], data[2]);
+						uint64_t cur_tap = frame + c->offset;
+						uint64_t duration = cur_tap - data->last_tap;
+						data->last_tap = cur_tap;
+
+						printf("duration = %lu\n", duration);
+						if( duration < (4*position->clock.rate.denom) ) {
+						  delay_set_time( &data->delay, duration );
+						}
+						printf("[%d] MIDI message (%d bytes) : %x, %x, %x\n", sec, size, midi_data[0], midi_data[1], midi_data[2]);
 					} else {
 					    printf("on_process(): non midi-control\n");
 					}