diff -urN midi_prog-/Makefile midi_prog/Makefile
--- midi_prog-/Makefile	Fri Aug  7 00:00:00 2015
+++ midi_prog/Makefile	Wed Aug 12 00:00:00 2015
@@ -9,7 +9,7 @@
 VCD_OBJS = vcd.o in.o filter.o out.o wrt.o util.o
 VOCO_OBJS = voco.o vco.o wave.o in.o filter.o out.o util.o
 MIDTXT_OBJS = midtxt.o rd.o wrt.o util.o
-TOOL_OBJS = tool.o in.o out.o util.o buf.o
+TOOL_OBJS = tool.o in.o out.o util.o buf.o pitch.o
 
 all: $(TARG) vcd voco midtxt tool
 
diff -urN midi_prog-/pitch.c midi_prog/pitch.c
--- midi_prog-/pitch.c	Thu Jan  1 09:00:00 1970
+++ midi_prog/pitch.c	Wed Aug 12 00:00:00 2015
@@ -0,0 +1,69 @@
+#include "pitch.h"
+
+double
+pitch_wn(double freq, double next_freq)
+{
+	/*
+	wn / (2 * freq) = (wn + 1) / (2 * next_freq)
+
+	next_freq * wn = freq * wn + freq
+	(next_freq - freq) * wn = freq
+
+	wn = freq / (next_freq - freq)
+	   = 1 / (next_freq / freq - 1)
+
+
+	440 * e( (69-69)/12 * l(2) ) = 440.00000000000000000000
+	440 * e( (70-69)/12 * l(2) ) = 466.16376151808991640200
+
+	wn = 1 / (466.163761518089916402 / 440 - 1)
+           = 16.81715374510576755683
+	*/
+
+	return freq / (next_freq - freq);
+}
+
+double
+pitch_wsec(double freq, double wn)
+{
+	return 0.5 * wn / freq;
+}
+
+double
+pitch_freq(double wsec, double wn)
+{
+	/*
+	T = 2 * wsec / wn
+	f = wn / (2 * wsec)
+          = 0.5 * wn / wsec
+
+        wsec = 0.5 * wn / freq
+        freq = 0.5 * wn / wsec
+
+	*/
+	return 0.5 * wn / wsec;
+}
+
+void
+pitch_init(struct pitch *p, double smp_freq, double freq, int wn,
+	   double abuf_wsec)
+{
+	p->freq = freq;
+	p->wn = wn;
+	sbuf_init(&p->sb, smp_freq, pitch_wsec(p->freq, wn));
+	abuf_init(&p->ab, 2*96, abuf_wsec);
+}	    
+
+void
+pitch_add(struct pitch *p, double v)
+{
+	struct tbuf *stb = &p->sb.tb;
+	double sec = tbuf_next_sec(stb);
+	double complex arg = I * 2 * M_PI * p->freq * sec;
+
+	sbuf_add(&p->sb, v * cexp(-arg));
+
+	if(tbuf_is_over_sec(&p->ab.tb, sec - stb->wsec * 0.5)){
+		abuf_add(&p->ab, cabs( sbuf_sum_mean_all(&p->sb) ) );
+	}
+}
diff -urN midi_prog-/pitch.h midi_prog/pitch.h
--- midi_prog-/pitch.h	Thu Jan  1 09:00:00 1970
+++ midi_prog/pitch.h	Wed Aug 12 00:00:00 2015
@@ -0,0 +1,21 @@
+#ifndef __PITCH_H__
+#define __PITCH_H__
+
+#include "buf.h"
+
+struct pitch{
+	double freq;
+	int wn;
+	struct sbuf sb;
+	struct abuf ab;
+};
+
+double pitch_wn(double freq, double next_freq);
+double pitch_wsec(double freq, double wn);
+double pitch_freq(double wsec, double wn);
+
+void pitch_init(struct pitch *p, double smp_freq, double freq, int wn,
+		double abuf_wsec);
+void pitch_add(struct pitch *p, double v);
+
+#endif
diff -urN midi_prog-/tool.c midi_prog/tool.c
--- midi_prog-/tool.c	Mon Aug 10 00:00:00 2015
+++ midi_prog/tool.c	Wed Aug 12 00:00:00 2015
@@ -1,6 +1,6 @@
 #include "util.h"
 #include "in.h"
-#include "buf.h"
+#include "pitch.h"
 
 int
 main(int ac, char **av)
@@ -8,19 +8,22 @@
 	in_rec_t in;
 	double v;
 
-	struct sbuf sb;
+	struct pitch p;
 	double freq = 440.0;
-	int wn = 8;
-	double wsec = wn / freq;
+	double next_freq = 440 * pow(2, (70-69)/12.0);
+	int wn = (int) pitch_wn(freq, next_freq);
+	double abuf_wsec = opt_double("-abuf_wsec", ac, av, 0.5);
+	double sec, sec_bak = -1;
 
 	in_init(&in, ac, av);
-	sbuf_init(&sb, in.smp_freq, wsec);
+	pitch_init(&p, in.smp_freq, freq, wn, abuf_wsec);
 
 	while(in_do_mono(&in, &v) != EOF){
-		double complex arg = I * 2 * M_PI * freq * tbuf_next_sec(&sb.tb);
-		sbuf_add(&sb, v * cexp(-arg));
-		v = cabs( sbuf_sum_mean_all(&sb) );
-		printf("v=%f\n", v);
+		pitch_add(&p, v);
+		sec = tbuf_newest_sec(&p.ab.tb);
+		if(sec <= sec_bak) continue;
+		printf("sec=%f v=%f\n", sec, p.ab.sum);
+		sec_bak = sec;
 	}
 	return 0;
 }