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Version 1.73 Copyright © 1997 Link Communications Inc. 1/18/97
Chapter 3: Audio and DTMF configurations
This chapter deals with how the controller handles DTMF digits that are received from a radio
or the reverse autopatch. You can control both what is heard on the repeater while digits are
being entered and what the controller does with those digits - whether it uses them to execute
commands or ignores them.
Background:
The controller has a DTMF decoder that is constantly listening to each receiver. A DTMF
decoder works by watching for 8 tone frequencies, 4 that represent the row and 4 that represent
the column of a 16 key DTMF keypad. If a row frequency and a column frequency are detected
at the same time, the decoder registers it as a valid digit and tells the microprocessor. This
takes about 40 or 50 milliseconds from the time the DTMF digit starts.
DTMF Mute:
If you have the controller set to mute DTMF digits (see command 007), it will turn off the
audio from that receiver to that transmitter as soon as the digit is detected. Normally you will
hear the first few milliseconds of the DTMF digit before it is detected and muted, although you
can avoid hearing it at all with an audio delay module (available from Link Communications).
The audio stays muted until a few seconds (see command 020, DTMF mute timers) after the
digit is released. If you press another digit during those few seconds, the audio will remain off,
so you won't hear any part of the second (or following) digits. So when you key up to enter a
command, those listening to the repeater will hear a short beep when you hit the first digit and
then your digits will be muted (unless you take too long between digits and the timer expires).
DTMF Cover Tone:
If you want to, you can turn on a "cover tone" that is sent while the DTMF digits are muted (see
command 007). This beep-beep-beep over the repeater lets people know that someone is
programming, so they don't just key up and talk over the silence of the DTMF mute. You can
change what the cover tone sounds like by editing macro 293. You can't use a cover tone
unless you have the DTMF mute turned on.
Mute and Cover Tone are set for each Transmitter:
Both the DTMF mute and cover tone are turned on and off for each transmitter (not receiver).
This means that it doesn't matter which receiver the DTMF tones are coming in on. If you have
just one repeater and no remotes or links, the difference doesn't matter. If you have several
connected repeaters, links or remotes, it can be a bit confusing. You almost always will want
DTMF mute to be turned on for the repeater transmitter. This will mute any tones before they
go out on the repeater, whether those tones are entered from the repeater or from one of the
connected links, remotes, or even the autopatch. DTMF tones that are heard by the repeater
receiver will be muted before they go out the repeater, but they can still go out any connected
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