Activity Detection and AGC 50013-54A Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 20 Exhibit A continued. Detailed Signal Processing Algorithm Specification A.1 HDLC Communications Not included as Licensed Technology. A.2 Voice Activity Detection Voice Activity Detection (VAD) detects voice activity, adapts to background ambient or line noise as well as the presence of echo, classifies voice activity as "early" versus "sustained", and assigns an "effort level" to the speaker that is independent of network loss. This module is used to detect voice activity in the CP Detect state. A.2.1 Functional requirements: The Voice Activity Detector discriminates voice activity generated by a caller from background noise (acoustic and line noise) as well as echo and sidetones reflected back to the receive voice path. It also provides an "effort level" quantity that indicates the level of effort of the caller. The functional and performance requirements are specified to cover a wide range of applications, such as voice activated recordings (as in voice messaging), outbound call classification, digital speech interpolation (DSI), and voice conferencing. 1. The Voice Activity Detector classifies every block of voice data (8 ms long) as "port active" (early detect), "speaker active" (port sustained), and "not active". 2. It provides a measurement that approximates the level of effort exerted by the caller. Such an approximation is made by normalizing the short term RMS of the voice signal by a longer term RMS value. The "effort level" varies between -32 dB and 31 dB, and is 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