Phone Call Recorder

echo cancellation

Elimination of side-tone from a return signal. The transmitted signal is used as a reference. The term echo cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call. In addition to improving quality, this process improves bandwidth savings achieved through silence suppression by preventing echo from traveling across a network. There are two types of echo of relevance in telephony: acoustic echo and hybrid echo. Speech compression techniques and digital processing delay often contribute to echo generation in telephone networks. Echo cancellation involves first recognizing the originally transmitted signal that re-appears, with some delay, in the transmitted or received signal. Once the echo is recognized, it can be removed by 'subtracting' it from the transmitted or received signal. This technique is generally implemented using a digital signal processor (DSP), but can also be implemeted in software. Echo cancellation is done using either echo suppressors or echo cancellers. Echo cancellation may have the unwanted side-effect of removing valid signal from the transmission. This can cause signal loss or distortion. For that reason, echo cancellation is usually an option that can be turned on or off on telephony devices. Echo cancellation on fax calls may cause data corruption. Some telephony devices disable echo cancellation when they detect the 2100Hz tones associated with fax calls, in accordance with ITU-T Recommendation G.165. Acoustic echo is generated through a telephone set when sounds directly picked up by the microphone also travel within the location of the microphone, reflect on objects at that location, and are then indirectly picked up again, with a certain amount of delay, by the microphone. The sounds may initiate from either party as well as from any other ambient noise in the location, including the telephone set speaker (ear piece). Hybrid echo is generated by the public-switched telephone network (PSTN) through the reflection of electrical energy by a device called a hybrid (hence the term hybrid echo).

List of telephony terms:

3gpp - a-law - abbreviated dialing - adsl - ani - answering machine - apn - automatic ring back - b-channel - baud - bell 202 modem - bit rate - bonding - bri - busy signal - cable modem - call-progress tones - call accounting - call capture - call forwarding - call originator - call park - call pick-up - call transfer - call waiting - call waiting deluxe - called party - caller id - caller id spoofing - calling party - carrier wave - cbr - ccitt - cdma - cdma2000 - cellular repeater - celp - channel - clec - clock rate - codec - collect call - conference - conference call - crc - csd - d-channel - data compression - device driver - dial-up - dial - dial tone - direct-inward-dialing - direct distance dialing - distinctive ring - dnis - dsl - dsp - dtmf - dtr - duplex - echo cancellation - edge - extension - fax - fcc - fdma - fidonet - follow-me - g.711 - g.723.1 - g.723 - g.726 - g.lite - gprs - gps - gsm - h.323 - harmonic - headphones - hscsd - hspda - iad - idsn - internet call waiting - isp - ivr - jack plug - local loop - long distance - microcontroller - mobile phone - modem - modulation - mu-law - music-on-hold - night service - off-hook - on-hook - pabx - pager - payphone - pbx - pcm - pots - prank call - precise tone plan - pstn - pulse dialling - push to talk - ring modulation - ring tone - ringback - ringing signal - rj11 - roaming - serial communications - serial port - signal noise - sim - simplex - sit - sms - softmodem - switchboard operator - tapi - tdma - telecommunications - telemarketing - telephone - telephone call - telephone card - telephone company - telephone exchange - telephone line - telephone number - telephone numbering plan - telephone operator - telephone switchboard - telephony - tts - twisted pair - umts - v.32 - v.32bis - v.34 - v.42bis - vbr - vertical service code - voicemail - voip - vox - wap - wav - wi-fi - wimax - wire