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Echo cancellation and applications - Essay Example

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Cancelling the effect of echo is called echo cancellation.Echo is the delayed and distorted voice of the original sound.There are certain techniques for the echo cancellation called the echo canceller, corresponding to the field of adaptive filtering…
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Download file to see previous pages Cancelling the effect of echo is called echo cancellation.Echo is the delayed and distorted voice of the original sound.There are certain techniques for the echo cancellation called the echo canceller, corresponding to the field of adaptive filtering Their scope lies in the full duplex data transmission over wire to wire circuits. Echo is observed in telecommunications. Certain filter structures are used including FIR, IIR, lattice structure, frequency domain structure, memory type structure, among which FIR is of most use. Standard bodies such as CCITT evaluate methods and performance requirements for echo cancellers. Two algorithms such as Least squares method and Least Mean square (LMS) methods are used among both, the LMS is most widely used due to its characteristics. But its drawback is that it is correlation of the reference signal dependent. Echo is controlled from the delayed voices resulting from the hybrid transformers (two wire to four wire conversion) and from acoustics resulting from reflection or coupling of sound waves from loud speaker and microphone. The placement of the echo canceler largely depends on the frequency of the echo produced and the amount of echo cancelation required. For the telephone circuits, the FIR is widely used as an echo canceler, whereas for full duplex data models the echo canceler is placed where hybrid connects modem to two wire loop. In the acoustic echoes, signals are converted into many frequency bands due to long durations of the echo as FIR used as an echo canceler will require more complexities, whereas IIR and other cancellers are under study. For ISDN digital loop transmission, due to limited echo duration, either FIR is used or memory type echo cancelors are used. Hence we can conclude that the Echo cancellers provide an effective way for the echo cancelation and voice disturbances, and different type of echo cancelers are used in different cases and scenarios. The VLSI technology is opening new doors for the study. Whereas more study is needed regarding the acoustic echoes. Blind Signal separation using Steepest Descent Method:- Speech enhancers such as microphone arrays are used widely in the communication, consisting of two techniques, such as blind signal separation and beam forming technique. However there is a difference in two techniques because of which, the blind signal separation has a competitive advantage over the beam forming technique due to which, the blind signal separation is widely used compared to the beam forming technique. Because source localization and array geometry is required in the beam forming technique and unlike this technique, the sources are statistically independent. Two blind signal approaches are higher ordered based blind signal approaches and second order based blind signal approach. Due to the slow rate of convergence of the gradient based blind signal system, and for the convoluted mixture, a method is proposed that follows the steepest decent algorithm that improves the convergence characteristics. For optimum size, parabolic interpretation and modified Golden search procedure was observed. The Brent’s method was used for calculating the optimized step size. The Binary signal system is combined with adaptive noise canceler reducing further noise. Compared to the fixed step size gradient based algorithm, the binary signal system contributed to the higher convergence. The result also showed that the hybrid of binary signal system and the adaptive noise canceler provided higher noise suppressions. It was also concluded that the convergence rate was faster along with the desired cost function value. The experiments were performed in the simulated environments and the real room environments. Hence, we can conclude that the binary signal system is an effective technique to achieve the higher convergence. Whereas, a hybrid experiment also, was an effective effort when the binary signal system was combined with the adaptive nois ...Download file to see next pagesRead More
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