close to frequency range may be detected. Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 30 INSERT GRAPH Figure A-2: Frequency Domain Representation of tone parameters for a Single Tone If the Power Level of the detected parameter is greater than the minimum power specified by the parameters, the signal shall not be rejected by Power Level heuristics. Duration parameters are used to set the allowable duration of a tone. Minimum and maximum tone durations may be specified (make durations). Also, minimum and maximum silence durations between tones may be specified. A.5.3.1.2 Dual Tones Dual tones are created by summing two sinusoids. Since each tone can be isolated in the frequency domain, dual tones are specified as a pair of single tones. Parameters for each tone of a dual pair use the same constraints as single tones. Namely, frequency1 is the center frequency of the lower tone, and bandwidth1 specifies its frequency tolerance. The same is true for frequency2 and bandwidth2 for the high tone. Figure A-3 shows the definition of the frequency and bandwidth parameters for a dual tone. INSERT GRAPH Figure A-3: Frequency Domain Representation of Tone Parameters for a Dual Tone Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 31 Not all dual tones are detectable by UTD. A dual tone shall detected only when the difference between the two component frequencies is greater than 10 Hz and less than 230Hz. A.5.3.1.3 Amplitude Modulated Tones Amplitude modulated tones are created by multiplying two sinusoids. When analyzed in the frequency domain, a modulated tone looks like three tones. Figure A-4 shows the frequency spectrum for a modulated tone. The tone whose frequency is the average of the other tones is the carrier. The other two tones can be referred to