NEC 128 manual Video & Audio Interfaces, Echo Canceller, H.320 Codec

3-2 Technical Description

Video & Audio Interfaces

These circuits provide the correct electrical and protocol connections for video sources, video outputs and display monitors, audio sources, and audio outputs. Connections are provided for microphones, headset, line-level audio inputs/outputs, and video inputs/outputs. VisuaLink supports S-video which allows the transmission and reception of higher image resolutions.

Echo Canceller

Echo can be a real problem on audio circuits. Some systems communicating over long distances can create an echo effect that is very distracting for videoconferencing participants. So distracting, it is considered unacceptable in videoconferencing.

A special Echo Canceller circuit eliminates echo effects caused by long distance lines and signal clipping caused by narrow bandwidth equipment. This built-in echo canceller supports a wide range of frequencies from 50 Hz to 7 KHz.

H.320 Codec

The Codec is the heart of the VisuaLink system; digitizing and compressing video/audio signals, and preparing the signals to be transmitted over digital lines.

The Codec, along with the Echo Canceller circuits are designed to support the latest International Telecommunications Union (ITU-T) H.320 standard for videoconferencing. These H.320 options are supported in VisuaLink:

Video:

•H.261 - supports older low resolution systems with video compression for wide bandwidth transmissions. (This ensures VisuaLink is compatible with these older systems.)

•H.263 - supports newer high resolution systems with video compression technology for low bandwidth transmissions. (This provides better picture quality over standard ISDN BRI lines.)

Audio:

•G.711 - for narrowband transmission (at 48-56 Kbps)

•G.722 - for wideband transmission (at 48-56 Kbps)

•G.728 - for narrowband transmission (at 16 Kbps)

(For additional information, see the section more on H.320 Videoconferencing at the end of this Technical Description.)

VisuaLink 128/384 General Description