3-1
RLC-4 V1.79 Copyright © 1998 Link Communications Inc. 9/18/98
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 20, 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 creating a special macro and changing the event trigger
to call it with command 045. You can't use a cover tone unless you have the DTMF mute turned
on.
Mute and Cover Tone are set for each Transmitter:
You can specify whether the DTMF mute and cover tone are turned on and off for each transmitter
(not receiver). This means that the muting function and cover tone don’t consider which receiver
the DTMF tones are coming in on; if they could be heard on a transmitter (if they are coming in on
a connected receiver) and the mute/cover tone is turned on, they will be muted. 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 transmitters. This will mute any tones before they go out on the
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