.\" $NetBSD: dtmfdecode.1,v 1.7 2014/03/18 18:20:46 riastradh Exp $
.\"
.\" Copyright (c) 1999 Hellmuth Michaelis.  All rights reserved.
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.\"	$Id: dtmfdecode.1,v 1.7 2014/03/18 18:20:46 riastradh Exp $
.\"
.\" $FreeBSD$
.\"
.\"	last edit-date: [Mon Dec 13 22:53:13 1999]
.\"
.\"
.Dd February 15, 1999
.Dt DTMFDECODE 1
.Os
.Sh NAME
.Nm dtmfdecode
.Nd decodes DTMF tones from A-law audio data
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm
is part of the isdn4bsd package and is used to detect DTMF tones in the
audio stream.
.Pp
It reads audio G.711 A-law coded data from stdin and outputs the detected
numbers values as ASCII characters to stdout.
.Pp
The detector is implemented as 8 narrow band-pass filters realized with
an integer double-cross recursive algorithm.  Various ad-hoc methods are
employed to provide hysteresis and anti-bounce for the detected signals.
.Sh EXAMPLES
The command:
.Bd -literal -offset indent
dtmfdecode \*[Lt] beep.al
.Ed
.Pp
will print a "1" to stdout.
.Sh STANDARDS
ITU Recommendations G.711
.Sh AUTHORS
The
.Nm
utility was written by
.An Poul-Henning Kamp Aq Mt phk@freebsd.org .
This man page was written by
.An Hellmuth Michaelis Aq Mt hm@freebsd.org .