Get VoIP Voice and Fax Signal Processing now with O’Reilly online learning. In general, these interfaces work as four-wire interfaces.
IP phone acoustic interfaces are extended through headsets and Bluetooth terminals. In speakerphone mode, acoustic echo is created and an acoustic echo canceller is used to cancel it. The normal headset mode works as a four-wire digital phone. IP phone acoustics are used as a normal headset, speakerphone, and headset interface. This level is sufficient for VoIP calls up to delays of 400 ms. Echo generated by reflections at Phone 2 and contained in the far end signal reaching Phone 1 can be cancelled by Phone 1.
Echo cancellation can be done in two modes: a. In digital phones, TCLw from the handset is 45 dB. Echo Cancellation is based on the principle of cancelling by using a filter to estimate the echo and removing it from the signal. In summary, the IP phone works as a four-wire digital phone in regular handset mode. In the IP phone, sidetone has to be created as an internal electrical signal provided from the microphone path to the speaker path, and this function will be limited as sidetone and will not be continued as electrical echo. In a normal analog phone, sidetone is generated in the design of hybrids and coupling at two-to-four-wire interfaces. The microphone and speaker are used as electrically separate units.
The IP phone works as a four-wire interface without using a two-to-four wire hybrid. 6.9.1 Echo Cancellation in IP and WiFi Handsets The sound frequency is 16 kHz mono and 16 bits PCM frame. This AEC will help to cancel the echo (coming from Speaker) in microphone input at the same PC. The echo cancellation for these VoIP systems is given in this section. I am trying to implement a Acoustic Echo cancellation algorithm in Java for a VoIP system. 6.9 ECHO CANCELLATION IN MULTIPLE VOIP TERMINALSĪs explained in Chapter 2, VoIP deployment makes use of several user interface devices such as IP phones, WiFi phones, personal computers (PCs) as soft IP phones, residential gateways with FXO interfaces, and VoIP-to-PSTN gateways.