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.\" Copyright (c) 1999 Hellmuth Michaelis.  All rights reserved.
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.\"	$Id: dtmfdecode.1,v 1.4 1999/04/26 11:42:33 hm Exp $
.\"
.\"	last edit-date: [Mon Apr 26 13:42:15 1999]
.\"
.\"
.Dd February, 15 1999
.Dt dtmfdecode 1
.Sh NAME
.Nm dtmfdecode
.Nd decodes DTMF tones from A-law audio data
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm dtmfdecode
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 charcters 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 < beep.al 
.Ed
.Pp
will print a "1" to stdout.

.Sh STANDARDS
ITU Recommendations G.711

.Sh AUTHOR
The
.Nm
utility was written by Poul-Henning Kamp, phk@freebsd.org. This man page
was written by Hellmuth Michaelis, hm@freebsd.org.