diff -urN midi_prog-/buf.c midi_prog/buf.c
--- midi_prog-/buf.c	Fri Aug  7 00:00:00 2015
+++ midi_prog/buf.c	Mon Aug 10 00:00:00 2015
@@ -151,3 +151,144 @@
 	if(d == 0) return v;
 	return v + (rbuf_get_arr_cpx(rb, arr_idx((si + 1), rb->n)) - v) * d;
 }
+
+
+/* tbuf */
+
+void
+tbuf_init(struct tbuf *tb, double smp_freq, double wsec, int is_complex)
+{
+	int n = (int) ceil(smp_freq * wsec + 1);
+	rbuf_init_alloc(&tb->rb, n, is_complex);
+	tb->smp_freq = smp_freq;
+	tb->wsec = wsec;
+}
+
+double
+tbuf_sec_to_sridx(struct tbuf *tb, double sec)
+{
+	return tb->smp_freq * sec;
+}
+
+double
+tbuf_sridx_to_sec(struct tbuf *tb, double sridx)
+{
+	return sridx / tb->smp_freq;
+}
+
+double
+tbuf_oldest_sec(struct tbuf *tb)
+{
+	int sridx = rbuf_oldest(&tb->rb);
+	return tbuf_sridx_to_sec(tb, sridx);
+}
+
+double
+tbuf_newest_sec(struct tbuf *tb)
+{
+	int sridx = rbuf_newest(&tb->rb);
+	return tbuf_sridx_to_sec(tb, sridx);
+}
+
+double
+tbuf_next_sec(struct tbuf *tb)
+{
+	int sridx = rbuf_next(&tb->rb);
+	return tbuf_sridx_to_sec(tb, sridx);
+}
+
+int
+tbuf_is_over_sec(struct tbuf *tb, double sec)
+{
+	return tbuf_next_sec(tb) <= sec;
+}
+
+void
+tbuf_add_dbl(struct tbuf *tb, double v)
+{
+	rbuf_add_dbl(&tb->rb, v);
+}
+
+void
+tbuf_add_cpx(struct tbuf *tb, double complex v)
+{
+	rbuf_add_cpx(&tb->rb, v);
+}
+
+double
+tbuf_get_dbl(struct tbuf *tb, double sec)
+{
+	double sridx = tbuf_sec_to_sridx(tb, sec);
+	return rbuf_get_dbl(&tb->rb, sridx);
+}
+
+double complex
+tbuf_get_cpx(struct tbuf *tb, double sec)
+{
+	double sridx = tbuf_sec_to_sridx(tb, sec);
+	return rbuf_get_cpx(&tb->rb, sridx);
+}
+
+
+/* sbuf */
+
+void
+sbuf_init(struct sbuf *sb, double smp_freq, double wsec)
+{
+	int is_complex = 1;
+	tbuf_init(&sb->tb, smp_freq, wsec, is_complex);
+	sb->sum = 0;
+}
+
+void
+sbuf_add(struct sbuf *sb, double complex v)
+{
+	sb->sum += v;
+	tbuf_add_cpx(&sb->tb, sb->sum);
+}
+
+double complex
+sbuf_sum(struct sbuf *sb, double from_sec, double to_sec)
+{
+	return tbuf_get_cpx(&sb->tb, to_sec) - tbuf_get_cpx(&sb->tb, from_sec);
+}
+
+double complex
+sbuf_sum_mean(struct sbuf *sb, double from_sec, double to_sec)
+{
+	double wsec = to_sec - from_sec;
+	double dn = tbuf_sec_to_sridx(&sb->tb, wsec);
+	return sbuf_sum(sb, from_sec, to_sec) / dn;
+}
+
+double complex
+sbuf_sum_mean_all(struct sbuf *sb)
+{
+	double from_sec = tbuf_oldest_sec(&sb->tb);
+	double to_sec = tbuf_newest_sec(&sb->tb);
+	return sbuf_sum_mean(sb, from_sec, to_sec);
+}
+
+
+/* abuf */
+
+void
+abuf_init(struct abuf *ab, double smp_freq, double wsec)
+{
+	int is_complex = 0;
+	tbuf_init(&ab->tb, smp_freq, wsec, is_complex);
+	ab->max_v = 0;
+	ab->sum = 0;
+}
+
+void
+abuf_add(struct abuf *ab, double v)
+{
+	int sridx = rbuf_oldest(&ab->tb.rb);
+	double ov = rbuf_get_dbl(&ab->tb.rb, sridx);
+
+	tbuf_add_dbl(&ab->tb, v);
+
+	if(ab->max_v < v) ab->max_v = v;
+	ab->sum += v - ov;
+}
diff -urN midi_prog-/buf.h midi_prog/buf.h
--- midi_prog-/buf.h	Fri Aug  7 00:00:00 2015
+++ midi_prog/buf.h	Mon Aug 10 00:00:00 2015
@@ -36,4 +36,50 @@
 double rbuf_get_dbl(struct rbuf *rb, double sridx);
 double complex rbuf_get_cpx(struct rbuf *rb, double sridx);
 
+
+struct tbuf{
+	struct rbuf rb;
+	double smp_freq;
+	double wsec;
+};
+
+void tbuf_init(struct tbuf *tb, double smp_freq, double wsec, int is_complex);
+
+/* sridx : serial index, rb->cnt scale */
+double tbuf_sec_to_sridx(struct tbuf *tb, double sec);
+double tbuf_sridx_to_sec(struct tbuf *tb, double sridx);
+
+double tbuf_oldest_sec(struct tbuf *tb);
+double tbuf_newest_sec(struct tbuf *tb);
+double tbuf_next_sec(struct tbuf *tb);
+int tbuf_is_over_sec(struct tbuf *tb, double sec);
+
+void tbuf_add_dbl(struct tbuf *tb, double v);
+void tbuf_add_cpx(struct tbuf *tb, double complex v);
+
+double tbuf_get_dbl(struct tbuf *tb, double sec);
+double complex tbuf_get_cpx(struct tbuf *tb, double sec);
+
+
+struct sbuf{
+	struct tbuf tb;
+	double complex sum;
+};
+
+void sbuf_init(struct sbuf *sb, double smp_freq, double wsec);
+void sbuf_add(struct sbuf *sb, double complex v);
+double complex sbuf_sum(struct sbuf *sb, double from_sec, double to_sec);
+double complex sbuf_sum_mean(struct sbuf *sb, double from_sec, double to_sec);
+double complex sbuf_sum_mean_all(struct sbuf *sb);
+
+
+struct abuf{
+	struct tbuf tb;
+	double max_v;
+	double sum;
+};
+
+void abuf_init(struct abuf *ab, double smp_freq, double wsec);
+void abuf_add(struct abuf *ab, double v);
+
 #endif
diff -urN midi_prog-/tool.c midi_prog/tool.c
--- midi_prog-/tool.c	Fri Aug  7 00:00:00 2015
+++ midi_prog/tool.c	Mon Aug 10 00:00:00 2015
@@ -1,5 +1,6 @@
 #include "util.h"
 #include "in.h"
+#include "buf.h"
 
 int
 main(int ac, char **av)
@@ -7,9 +8,18 @@
 	in_rec_t in;
 	double v;
 
+	struct sbuf sb;
+	double freq = 440.0;
+	int wn = 8;
+	double wsec = wn / freq;
+
 	in_init(&in, ac, av);
+	sbuf_init(&sb, in.smp_freq, 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);
 	}
 	return 0;