4.7.1. Frequency Shift Keying (FSK)

Two-way Frequency Shift Keying (FSK) allows applications to send and receive character or binary data at 1200 bits/second between a server and Analog Display Services Interface (ADSI) compatible devices. The two-way FSK feature supports applications such as off-line Email editing and sending FSK caller ID data to a Customer Premises Equipment (CPE) device through an MSI/SC board.

Adjusting the FSK Receiver Carrier Detect Threshold

Host applications can change the receiver carrier detect threshold from the default value (-44 dBm) to any value in the range of -22 dBm to -44 dBm. Values are adjusted in 2 dB intervals with a hysteresis of +/- 2 dB at each step. Odd numbers are valid values, but they will be rounded up to the next even number, for example, -27 becomes -26.

To edit the Voice.prm file to set the receiver carrier detect threshold, proceed as follows:

1. Open the file \Program Files\Dialogic\Data\Voice.prm using Windows Notepad* (or another text editor).
2. Add parameter 255 and the appropriate value (26 in this example) as shown in bold text in the following example:

#beginning of voice.prm 
AREA=VOICE
SIZE=WORD
BASE=DECIMAL
. . .
PARAM 255 : 26  # set receiver carrier detect threshold  
#end of voice.prm  

3. Save the file.

In order for the added parameter to take effect, run DCM and specify the Voice.prm file as the value for the ParameterFile parameter, which appears on the Misc property sheet for Springware boards.

Adjusting Runtime Volume Control

With analog boards such as the D/41ESC, FSK output volume levels can exceed FCC part 68 specifications. The maximum permitted average volume level is -9.5 dBm for analog boards (D/41ESC, D/160SC-LS) and -13.5 dBm for SCbus operation and T-1 or E-1 network interface boards, in order to have an acceptable margin for compliance purposes. In the case of analog boards, the default transmit output volume level for FSK is approximately -2 dBm.

In order to maintain overall server output signal level compliance, applications need to attenuate the transmit level by approximately -8 dB to comply with FCC part 68 specifications. This 8 dB attenuation applies universally to analog boards (D/41ESC, D/160SD-LS) as well as SCbus operation and also to T-1 or E-1 voice processing boards.

To adjust the output volume level in your application, use the dx_adjsv( ) function, which is documented in the Voice Software Reference - Programmer's Guide. The dx_adjsv( ) function lets applications modify the speed or the volume of playback dynamically. Once the speed or volume level is modified, the new setting holds until dx_adjsv( ) executes again or the system is downloaded again.

The dx_adjsv( ) function uses the Speed and Volume Modification Table to adjust the settings. There are 21 entries that represent different levels of speed or volume. You can specify either an absolute position in this table or a relative position to the current value in the table. You can also toggle between table values. Detailed information about this table is in the Voice Software Reference - Features Guide.

Note: If the default Speed and Volume Modification Table does not provide enough granularity, you can modify the table with the dx_setsvmt( ) function, which is also documented in the Voice Software Reference - Programmer's Guide.

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