diff -urN midi_prog-/Makefile midi_prog/Makefile
--- midi_prog-/Makefile	2014-01-25 00:00:00.000000000 +0900
+++ midi_prog/Makefile	2014-01-26 00:00:00.000000000 +0900
@@ -1,6 +1,6 @@
 CC = gcc -Wall
 LIB = -lm
-TARG = prog28
+TARG = prog29
 OBJS = main.o vcf.o ch.o delay.o stat.o note.o env.o tone.o filter.o lfo.o modu.o vco.o wave.o out.o rd.o util.o
 
 all: $(TARG)
diff -urN midi_prog-/vco.c midi_prog/vco.c
--- midi_prog-/vco.c	2014-01-24 00:00:00.000000000 +0900
+++ midi_prog/vco.c	2014-01-26 00:00:00.000000000 +0900
@@ -11,9 +11,12 @@
 double
 vco_out(int wave, struct vco_stat_rec *stat, double freq, double sec, double modu_v)
 {
+	double cycle_prev;
+
 	if(modu_v != 0) freq *= pow(2, modu_v);
+	cycle_prev = stat->cycle;
 	vco_stat_update(stat, freq, sec);
-	return wave_out(wave, stat->cycle);
+	return wave_out2(wave, cycle_prev, stat->cycle);
 }
 
 /* EOF */
diff -urN midi_prog-/wave.c midi_prog/wave.c
--- midi_prog-/wave.c	2014-01-24 00:00:00.000000000 +0900
+++ midi_prog/wave.c	2014-01-26 00:00:00.000000000 +0900
@@ -16,8 +16,35 @@
 		return cycle < 0.5 ? 1 : -1;
 	case WAVE_NOISE:
 		return ((double)rand() / RAND_MAX) * 2 - 1;
+
+	case WAVE_INTEGRAL | WAVE_SAW:
+		return cycle < 0.5 ? cycle * cycle : (1 - cycle) * (1 - cycle);
+	case WAVE_INTEGRAL | WAVE_SQUARE:
+		return cycle < 0.5 ? cycle : 1 - cycle;
 	}
 	return 0;
 }
 
+double
+wave_out2(int wave, double cycle_prev, double cycle)
+{
+	double d, v, v_prev;
+
+	switch(wave){
+	case WAVE_SIN:
+	case WAVE_NOISE:
+		return wave_out(wave, cycle);
+	}
+	cycle -= (int)cycle;
+	cycle_prev -= (int)cycle_prev;
+	d = cycle - cycle_prev;
+	if(d < 0) d += 1;
+	if(d == 0) return wave_out(wave, cycle);
+	
+	wave |= WAVE_INTEGRAL;
+	v = wave_out(wave, cycle);
+	v_prev = wave_out(wave, cycle_prev);
+	return (v - v_prev) / d;
+}
+
 /* EOF */
diff -urN midi_prog-/wave.h midi_prog/wave.h
--- midi_prog-/wave.h	2014-01-24 00:00:00.000000000 +0900
+++ midi_prog/wave.h	2014-01-26 00:00:00.000000000 +0900
@@ -7,7 +7,9 @@
 #define WAVE_SAW	1
 #define WAVE_SQUARE	2
 #define WAVE_NOISE	3
+#define WAVE_INTEGRAL	(1<<8)
 
 double wave_out(int wave, double cycle);
+double wave_out2(int wave, double cycle_prev, double cycle);
 
 #endif