Chapter 10 - Voice Mode Operation
10-2
Automatic Detection of Voice, Data, Fax
Since there is no way to standardize the way a human voice should behave in
telephone calling and answering, it is nearly impossible to automatically
distinguish a voice call from a fax call from a data call. One common way of
accomplishing this task is to combine the use of a digitally recorded voice
message with DTMF tone detection. The voice message instructs the caller to
press one number on the touch-tone keypad if they want to send a fax, or another
number if they want to talk. By detecting which DTMF tone was sent, the modem
and software can switch to the appropriate mode and handle your call
accordingly. If no tone is received by the timeout, the Omni 288S will assume it is
a data call and begin its modem handshaking process.
The shortcoming of this process is that some modems will be confused by the
initial voice message portion, and will not be able to connect. Even if the data
call is successfully connected, the long delay before handshaking may not be
acceptable in some applications.
Some software packages use an initial period of silence when answering, and
detect if there is voice energy to decide if it is a voice call.
The Omni 288S can recognize a fax or data call more quickly if a calling tone is
received. In this case, the voice announcement can be omitted.
Voice Input/Output Devices

Microphone and Speaker Jacks

On the back of the Omni 288S, there are two jacks for external microphone and
speaker connections. These jacks are convenient means for voice input/output.
The speaker jack is capable of directly driving an 8 ohm speaker. When an
external speaker is plugged into the speaker jack, the internal speaker is
automatically shut off. The speaker jack only drives one speaker. If you have two
speakers with a stereo plug, use a plug adapter that will enable both speakers to
be driven by one source out of the speaker jack. If you are connecting the
speaker jack output to an amplifier, insert some attenuation in between. The
speaker jack output signal may be too strong for the amplifier.

Voice Input/Output Device Selection

To take advantage of the voice functions of the Omni 288S, you can use either the
speaker and microphone jacks or the handset of any telephone. The voice
input/output device selection is controlled by voice AT commands. Generally,
the user makes input/output selection through application software packages
according to the program’s instructions. The user need not worry about using AT
commands to make the selection. Below are some specific directions for cases
where manual selection through AT commands are necessary.