new acoustic echo pptVBHJN

8/7/2019 new acoustic echo pptVBHJN

1/30

ACOUSTIC ECHO

CANCELLATION FOR DOUBLETALK

BYS IMRANA 07H81A0417

FATIMA TAYYBA


2/30

INTRODUCTION

The purpose of this project is to cancel

Acoustic echo.Before implementing in real

time on DSP kit.

we have simulated in Matlab and found theresponse for different speech signals.


3/30

BACKGROUND

SPEECH SIGNAL.

ECHO SIGNAL

Echo is a phenomenon in which a delayed and

distorted version of an original sound or electrical

signal is reflected back to the source.


4/30

Adaptive Filter

The general adaptive filter ,filters the input signal

so that it resembles (in some sense) the desired

signal input. An adaptive FIR or IIR filter designs

itself based on the characteristics of the input

signal to the filter.

It iteratively alter its parameters.

It minimizes the error between some desiredsignal and some reference signal.As shown in

figure.


5/30

Block Diagram Of AdaptiveFilter


6/30


7/30

Diagram Explanation

we are considering that the desired signal(d) is corr-

upted and our aim is to eliminate the undesired part to

get signal.For this purpose we are using adaptive

filter.It uses algorithm which provides a set of taps.The tap

weights could then be implemented as the correspond-

ing filter, inversed and applied to the received signal

thus producing the original signal in its original

form.


8/30

Adaptive Filtering System

Configurations

There are four major types of adaptive filtering

configurations.

Adaptive system identification. Adaptive echo/noise cancellation.

Inverse system identification.

Linear predictive coding.

Note:

All of the above systems are similar in the implementation ofthe algorithm, but different in system Configuration.


9/30

ACOUSTIC ECHO

Acoustic echo occurs when an audio signal is

reverberated in a real environment, resulting in

the original intended signal plus attenuated, time

delayed images of this signal.

When a signal is received by the system, it is

output through the loudspeaker into an acoustic

environment. This signal is reverberated within

the environment and returned to the system via

the microphone input.


10/30

Cont..

These reverberated signals contain time

delayed images of the original signal, which are

then returned to the original sender. The

occurrence of acoustic echo in speechtransmission causes signal interference and

reduced quality of communication.

The method used to cancel the echo signal is

known as adaptive filtering.


11/30

SOURCES OF ACOUSTIC

ECHO


12/30

ACOUSTIC ECHO

CANCELLER

The echo canceller mimics the transfer function of theecho path (or room acoustic) to synthesize a replica ofthe echo, and then subtracts that replica from the

combined echo and near-end speech (or disturbance)signal to obtain the near-end signal alone.

However, the transfer function is unknown in practice,and so it must be identified. The solution to thisproblem is to use an adaptive filter

An adaptive filter algorithmically alters its parametersin order to minimize a function of the differencebetween the desired output d(n) and its actual outputy(n). This function is known as the cost function of theadaptive algorithm.


13/30

ACOUSTIC ECHO

CANCELLER


14/30

CONT

Here the filter H(n) represents the impulse response of

the acoustic environment, W(n) represents the adaptive

filter used to cancel the echo signal. The adaptive filteraims to equate its output y(n) to the desired output d(n)

(the signal reverberated within the acoustic

environment). At each iteration the error signal,

e(n)=d(n)-y(n), is fed back into the filter, where thefilter characteristics are altered accordingly.


15/30

Conventional block diagram

microphone ejnj

uj

dj pn

n

xjloudspeaker

Adaptive

filter

Step size

control

+


16/30

`block diagram

Main

ADF

StepSize

Control

+

+ +

Sub adf

microphone

Loud speaker

nj

pn

n

dj

UbjUcj

xj

ej

j


17/30

Contd..

In addition to the main adaptive filter in our project

we are using the sub adaptive filter to cancel the

echo.


18/30

LMS ALGORITHM

The LMS algorithm is a linear adaptive filter algorithm,which in general consists of two basic processes.

1. A filter process, which involves

a.Computing the output of a linear filter inresponse to an input signal.

b.Generating an estimation error bycomparing this output with a desiredresponse.

2. An adaptive process, which involves theautomatic adjustment of the parameters of thefilter in accordance with the estimation error.


19/30

IMPLEMENTATION OF LMS

ALGORITHM

Each iteration of the LMS algorithm requires 3 distinct

steps in this order:

1. The output of the FIR filter, y(n) is calculated

using equation

2. The value of the error estimation is calculated

using equation


20/30

CONT..

3. The tap weights of the FIR vector are updated in

preparation for the next iteration, by


21/30

REAL TIME

IMPLEMENTATION

Real Time Processing:

Real-time processing means that the processingmust keep pace with some external event .

Real Time Implementation involves:

A/D converter is used to take the input Thisinput signal is processed by the processor and

the output is send through D/A.To read and write data multi channel buffer

serial port is used


22/30


23/30


24/30


25/30


26/30


27/30


28/30


29/30


30/30

Thank you

new acoustic echo pptVBHJN

Documents

Transcript of new acoustic echo pptVBHJN