Technical Seminar - 2004 Presented by :- Debabandana Apta (EC200163376) National Institute of Science and Technology [1] “ECHO CANCELLATION” Presented

Technical Seminar - 2004

Presented by :- Debabandana Apta (EC200163376)Nati

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“ECHO CANCELLATION”

Presented by

Debabandana Apta Roll # EC200163376

Under the Guidance of

Mr. G.V. Kiran Kumar



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TYPE OF ECHO

Two types of echo are present : Acoustic echo: Acoustic echo is generated with analog and digital

handsets, with the degree of echo related to the type and quality of equipment used.

This form of echo is produced by poor voice coupling between the earpiece and microphone in handsets and hands-free devices.

Acoustic Echo on Digital Cellular



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Hybrid Echo

Hybrid echo is electrically generated echo is created as voice signals are transmitted across the network via the hybrid connection at the two-wire/four-wire PSTN conversion points, reflecting electrical energy back to the speaker from the four-wire circuit..

Hybrid echo is the primary source of echo generated from the public-switched telephone network (PSTN). .



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CAUSES OF ECHO Acoustic echo apart, background noise is generated

through the network when analog and digital phones are operated in hands-free mode .

As additional sounds are directly and indirectly picked up by the microphone, multi-path audio is created and transmitted back to the talker.

Digital processing delays and speech-compression techniques further contribute to echo generation and degraded voice quality in wireless networks.



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PRINCIPLES OF ECHO CANCELLATION An acoustic echo canceller works in the following fashion: it

records the sound going to the loudspeaker and substract it - in some way - from the signal coming from the microphone.

The sound going through the echo-loop is transformed and delayed, and noise is added, which complicate the substraction process.



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Controlling Complex Echo in a Wireless Digital

Network. The Combined Problem on Digital Cellular Networks. Controlling Acoustic Echo

Controlling Acoustic Echo

THE PROCESS OF ECHO CANCELLATION



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Echo Canceller for Digital/Data Communication

For digital/data communication system to get ride of echo

problem echo canceller used.



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ECHO CANCELLATION TECHNOLOGY Echo suppression:

The module identifies echo and suppresses it by means of gain control. Echo suppression prevents howling effect (positive feedback loop). The module allows one party to interrupt the other party's speech. The algorithm adapts to background noise level and to echo gain and delay.

Echo cancellation: The module removes the echo by means of adaptive filtering. Both parties may talk freely at the same time. Echo cancellation prevents the howling effect (positive feedback loop).



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THE IMPORTANCE OF ECHO CANCELLATION One of the primary challenges faced by service

providers in delivering quality voice communications is the elimination of echo which is ever-present on almost all telephone calls.

The hybrid is not completely efficient in carrying the electrical energy and a certain amount of the electrical energy, or voice signal, is reflected back and may be perceived as echo.



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SUBBAND ACOUSTIC ECHO CANCELLATION

FOR MOBILE & HANDS FREE PHONES IN CAR When a person is on the phone, a sound wave received on the

earpiece enters through mouthpiece of the handset via reflections off objects in the sound path and circulate the feedback loop.



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Technical Issues In AEC systems Multi-path echo, time varying echo, combined echo and

noise reduction and performance of the echo canceller are some of the issues that have to be thoroughly scrutinized when designing the AEC system.

Sub-band adaptive filtering is one of the common solutions for AEC systems



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New digital cellular networks and network scenarios reflect a significant change taking place in the operation of echo cancellers.

Echo cancellers have now become highly sophisticated transmission equipment at the center of highly complex networks.

Network operators and telcos implementing echo cancellation across their networks will hold the key to improved call quality, directly impacting their ability to provide enhanced network performance, increase talk time revenues, and reduce subscriber churn.

Conclusion



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THANK YOU

Documents

Technical Seminar - 2004 Presented by :- Debabandana Apta (EC200163376) National Institute of Science and Technology [1] “ECHO CANCELLATION” Presented