circuit with echo return loss (ERL) of 15 dB. Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 25 4. Double-talk talk-off: Many voice processing hardware or semiconductor manufacturers significantly degrade the "talk-off' performance of their detector in the presence of voice echo or sidetone to achieve a high level of talk-down performance. This strategy is acceptable in a pure digit-in-voice-out scenario, but for voice conferencing or voice recognition applications, voice could be present in the both the transmit and receive path. In such cases, the DTMF detector must be very robust against "talk-off" in double-talk situations. The talk-off requirements for D2's DTMF detector under double-talk is fewer than 66 talkoffs for the Bellcore talk-off tape. A.4 Tone Generation The tone generation module can be programmed to generate any single, dual or amplitude modulated tone required to meet international telecommunications specifications. This functionality is provided by the GENF module, which produces the sum or product of two independently generated sine waves as its output. Each sine wave can be individually parameterized. A.4.l Functional requirements: The GENF module is designed to generate a wide range of DTMF, Call Progress Signals, MF Rl/R2, and miscellaneous tones. In order to meet or exceed international telecommunication specifications, GENF must meet or exceed the following functional requirements. 1. Independent arguments shall be supplied for each frequency for dual tones that GENF generates. Single tones are generated by specifying that one of the dual tone's frequencies is 0 Hz. 2. Independent arguments shall be supplied for the carrier and modulation frequencies for amplitude modulated tones that GENF generates. 3. Arguments shall be supplied that allow the frequency of a tone to be set in the range of 0 to 4000 Hz in 1 Hz units. 4. Arguments shall be supplied that allow the