diff -urN midi_prog-/Makefile midi_prog/Makefile
--- midi_prog-/Makefile	Thu Jun 25 00:00:00 2015
+++ midi_prog/Makefile	Fri Aug  7 00:00:00 2015
@@ -9,8 +9,9 @@
 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
 
-all: $(TARG) vcd voco midtxt
+all: $(TARG) vcd voco midtxt tool
 
 $(TARG): $(OBJS)
 	$(CC) -o $@ $(OBJS) $(LIB)
@@ -24,9 +25,13 @@
 midtxt: $(MIDTXT_OBJS)
 	$(CC) -o $@ $(MIDTXT_OBJS)
 
+tool: $(TOOL_OBJS)
+	$(CC) -o $@ $(TOOL_OBJS) -lm
+
 clean:
 	rm -f $(TARG) $(OBJS) *~
 	rm -f vcd $(VCD_OBJS) voco $(VOCO_OBJS)
 	rm -f midtxt $(MIDTXT_OBJS)
+	rm -f tool $(TOOL_OBJS)
 
 # EOF
diff -urN midi_prog-/buf.c midi_prog/buf.c
--- midi_prog-/buf.c	Thu Jan  1 09:00:00 1970
+++ midi_prog/buf.c	Fri Aug  7 00:00:00 2015
@@ -0,0 +1,153 @@
+#include "buf.h"
+
+void
+rbuf_init_alloc(struct rbuf *rb, int n, int is_complex)
+{
+	int sz = ( is_complex ? sizeof(rb->c[0]) : sizeof(rb->d[0]) ) * n;
+	rb->n = n;
+	rb->n_bak = rb->n;
+	rb->is_cpx = is_complex;
+	if((rb->buf = malloc(sz)) == NULL) ERR("No Mem");
+	rb->d = !is_complex ? rb->buf : NULL;
+	rb->c = is_complex ? rb->buf : NULL;
+
+	rbuf_init(rb);
+}
+
+void
+rbuf_init_alloc_dbl(struct rbuf *rb, int n)
+{
+	rbuf_init_alloc(rb, n, 0);
+}
+
+void
+rbuf_init_alloc_cpx(struct rbuf *rb, int n)
+{
+	rbuf_init_alloc(rb, n, 1);
+}
+
+void
+rbuf_init(struct rbuf *rb)
+{
+	int i;
+	rb->n = rb->n_bak;
+	rb->cnt = 0;
+	for(i=0; i<rb->n; i++){
+		if(rb->is_cpx) rb->c[i] = 0;
+		else rb->d[i] = 0;
+	}
+}
+
+void
+rbuf_init_n(struct rbuf *rb, int n)
+{
+	rbuf_init(rb);
+	rb->n = n;	
+}
+
+void
+rbuf_copy_init(struct rbuf *rb, struct rbuf *src)
+{
+	int i;
+	rb->cnt = src->cnt;
+	for(i=0; i<rb->n; i++){
+		if(rb->is_cpx) rb->c[i] = src->c[i];
+		else rb->d[i] = src->d[i];
+	}
+}
+
+void
+rbuf_free(struct rbuf *rb)
+{
+	if(rb->buf){
+		free(rb->buf);
+		rb->buf = NULL;
+		rb->d = NULL;
+		rb->c = NULL;
+	}
+}
+
+
+double
+rbuf_get_arr_dbl(struct rbuf *rb, int i)
+{
+	if(rb->is_cpx) ERR("is_cpx");
+	return rb->d[i];
+}
+
+double complex
+rbuf_get_arr_cpx(struct rbuf *rb, int i)
+{
+	if(!rb->is_cpx) ERR("not is_cpx");
+	return rb->c[i];
+}
+
+void
+rbuf_set_arr_dbl(struct rbuf *rb, int i, double v)
+{
+	if(rb->is_cpx) ERR("is_cpx");
+	rb->d[i] = v;
+}
+
+void
+rbuf_set_arr_cpx(struct rbuf *rb, int i, double complex v)
+{
+	if(!rb->is_cpx) ERR("not is_cpx");
+	rb->c[i] = v;
+}
+
+void
+rbuf_add_dbl(struct rbuf *rb, double v)
+{
+	rbuf_set_arr_dbl(rb, rb->cnt++ % rb->n, v);
+}
+
+void
+rbuf_add_cpx(struct rbuf *rb, double complex v)
+{
+	rbuf_set_arr_cpx(rb, rb->cnt++ % rb->n, v);
+}
+
+int
+rbuf_oldest(struct rbuf *rb)
+{
+	return rb->cnt - rb->n;
+}
+
+int
+rbuf_newest(struct rbuf *rb)
+{
+	return rb->cnt - 1;
+}
+
+int
+rbuf_next(struct rbuf *rb)
+{
+	return rb->cnt;
+}
+
+static int
+arr_idx(int si, int n)
+{
+	return (si + (si < 0 ? n : 0)) % n;
+}
+
+double
+rbuf_get_dbl(struct rbuf *rb, double sridx)
+{
+	int si = (int) sridx;
+	double d = sridx - si;
+	double v = rbuf_get_arr_dbl(rb, arr_idx(si, rb->n));
+	if(d == 0) return v;
+	return v + (rbuf_get_arr_dbl(rb, arr_idx((si + 1), rb->n)) - v) * d;
+}
+
+double complex
+rbuf_get_cpx(struct rbuf *rb, double sridx)
+{
+	int si = (int) sridx;
+	double d = sridx - si;
+	double complex v = rbuf_get_arr_cpx(rb, arr_idx(si, rb->n));
+	if(d == 0) return v;
+	return v + (rbuf_get_arr_cpx(rb, arr_idx((si + 1), rb->n)) - v) * d;
+}
diff -urN midi_prog-/buf.h midi_prog/buf.h
--- midi_prog-/buf.h	Thu Jan  1 09:00:00 1970
+++ midi_prog/buf.h	Fri Aug  7 00:00:00 2015
@@ -0,0 +1,39 @@
+#ifndef __BUF_H__
+#define __BUF_H__
+
+#include <complex.h>
+#include "util.h"
+
+struct rbuf{
+	int n, cnt, is_cpx, n_bak;
+	void *buf;
+	double *d;
+	double complex *c;
+};
+
+void rbuf_init_alloc(struct rbuf *rb, int n, int is_complex);
+void rbuf_init_alloc_dbl(struct rbuf *rb, int n);
+void rbuf_init_alloc_cpx(struct rbuf *rb, int n);
+
+void rbuf_init(struct rbuf *rb);
+void rbuf_init_n(struct rbuf *rb, int n);
+void rbuf_copy_init(struct rbuf *rb, struct rbuf *src);
+void rbuf_free(struct rbuf *rb);
+
+double rbuf_get_arr_dbl(struct rbuf *rb, int i);
+double complex rbuf_get_arr_cpx(struct rbuf *rb, int i);
+void rbuf_set_arr_dbl(struct rbuf *rb, int i, double v);
+void rbuf_set_arr_cpx(struct rbuf *rb, int i, double complex v);
+
+void rbuf_add_dbl(struct rbuf *rb, double v);
+void rbuf_add_cpx(struct rbuf *rb, double complex v);
+
+/* return sridx : serial index */
+int rbuf_oldest(struct rbuf *rb);
+int rbuf_newest(struct rbuf *rb);
+int rbuf_next(struct rbuf *rb);
+
+double rbuf_get_dbl(struct rbuf *rb, double sridx);
+double complex rbuf_get_cpx(struct rbuf *rb, double sridx);
+
+#endif
diff -urN midi_prog-/in.c midi_prog/in.c
--- midi_prog-/in.c	Wed Apr 29 00:00:00 2015
+++ midi_prog/in.c	Fri Aug  7 00:00:00 2015
@@ -1,5 +1,14 @@
 #include "in.h"
 
+void
+in_init(in_rec_t *inp, int ac, char **av)
+{
+	struct out_rec otr;
+	out_init(&otr, ac, av);
+	*inp = otr;
+	inp->fp = stdin;
+}
+
 int
 in_do(in_rec_t *inp, double *vp)
 {
@@ -17,5 +26,17 @@
 {
 	int i;
 	for(i=0; i<inp->ch_num; i++) if(in_do(inp, &vp[i]) == EOF) return EOF;
+	return 0;
+}
+
+int
+in_do_mono(in_rec_t *inp, double *vp)
+{
+	double v[2];
+	int i;
+	if(in_do2(inp, v) == EOF) return EOF;
+	*vp = 0;
+	for(i=0; i<inp->ch_num; i++) *vp += v[i];
+	*vp /= inp->ch_num;
 	return 0;
 }
diff -urN midi_prog-/in.h midi_prog/in.h
--- midi_prog-/in.h	Wed Apr 29 00:00:00 2015
+++ midi_prog/in.h	Fri Aug  7 00:00:00 2015
@@ -5,7 +5,9 @@
 
 typedef struct out_rec in_rec_t;
 
+void in_init(in_rec_t *inp, int ac, char **av);
 int in_do(in_rec_t *inp, double *vp);
 int in_do2(in_rec_t *inp, double *vp);
+int in_do_mono(in_rec_t *inp, double *vp);
 
 #endif
diff -urN midi_prog-/tool.c midi_prog/tool.c
--- midi_prog-/tool.c	Thu Jan  1 09:00:00 1970
+++ midi_prog/tool.c	Fri Aug  7 00:00:00 2015
@@ -0,0 +1,16 @@
+#include "util.h"
+#include "in.h"
+
+int
+main(int ac, char **av)
+{
+	in_rec_t in;
+	double v;
+
+	in_init(&in, ac, av);
+
+	while(in_do_mono(&in, &v) != EOF){
+		printf("v=%f\n", v);
+	}
+	return 0;
+}