at ratio at 20 ms EIA/TIA-464A echo 45 ms requirements - ------------------------------------------------------------------------------------------------------------------- Dial Tone DTMF Detection in the DTMF Detection in the Pass both Bellcore and presence of dial tone presence of dial tone EIA/TIA-464A at -15 dBm per dial at -16 dBm per dial requirements for tone frequency tone frequency detection of DTMF digits in the presence of dial tone - ------------------------------------------------------------------------------------------------------------------- TABLE A-2: DTMF Performance Requirements Other performance requirements: 1. A leading edge of DTMF digit is signaled during the block in which the minimum duration is met, and the trailing edge is signaled during the block in which the minimum debounce interval is met. 2. Talk-down: DTMF detection must work reliably in the presence of echo (for the maximum allowable output voice level) and with varying levels of DTMF signals (due to network loss). D2's DTMF detector combined with the echo must meet the performance requirements of Figure A-I in the presence echo generated by playing pause-removed voice (male and female) at - 18 dBm ASL (averaged over 3 seconds) over a telephone circuit with 15 dB echo return loss (ERL). INSERT GRAPH Figure A-1: DTMF Talk-down Acceptance Curve 3. Debounce test: Long tones (generated by "hard" key presses) must not be detected as multiple tones in the presence of echo interference or line noise. Combined with the echo canceller, the DTMF detector is required to reliably "debounce" all DTMF digits above -18 dBm in the presence of voice levels below -15 dBm (ASL) and a telephone 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