at 0 dB when the speaker is speaking at his/her "normal" level. 3. The Voice Activity Detector adapts to background noise up to -24 dBm. Adaptation is 200 ms when the noise level drops, and is approximately 1000 ms when noise rises. 4. The Voice Activity Detector screens out sidetone or echo as speech up to an ERL of -26 dB. Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 21 A.2.2 Performance Requirements: The accuracy of the voice Activity detector is measured by the rate of "false detection" (i.e. classifying noise or echo as voice activity) and "clipping" (i.e. classifying voice activity as noise or echo) under different ambient noise and echo conditions. "Port active" detection under different ambient noise conditions: 1. No perceptible clipping at quiet to modest noise levels of -50 dBm to -40 dBm with nominal levels of speech activity (-20 dBm average power over 2 seconds of speech). No more than 5% of voice onsets is clipped for noisy conditions (noise level from -40 dBm to -30 dBm). 2. No more than 1% of "silence" periods is detected as speech for the modest noise condition. No more than 2% of "silence" is detected as port active for noisy conditions. 3. The performance goals above is met when noise levels change during the test. "Speaker active" detection under different ambient noise conditions: 1. Speech activity that lasts more than tSUSTAIN is detected as "Sustained" or "Speaker Active". 2. The clipping requirements is better than "Port Activity" detection. Fewer than 0.5% of onsets/hour (2.5 per hour) for modest noise condition (-45 dBm) and fewer than 2% (10 per hour) for high noise condition (-35 dBm) have perceptible clipping. 3. False detection performance (i.e., detecting noise as "speaker active") exceeds those of "port activity" due