Task 4.Answer the questions to Text C.

1. What is the primary function performed by the Adaptive Filter?

2.What two different models of adaptive filter operation are applied?

3.What practical examples that illustrate adaptive filter operation do you know?

4.What is a further area where adaptive filters are applied?

5. How can you describe the scheme of noise cancellation?

Scheme A and common words can be used.

Scheme A. Noise cancellation.

* spurious – мешающий;

Common words to be used to describe the scheme:

1. to contain

2. to be applied

3. to produce

4. to be applied

5. to form

6. to substract the unwanted component

7. to leave the desired signal

Task 5. Put all possible questions to the following statements to discover all the details.

Liner distortions arise in many different ways in telephony networks. Three distinct types can be identified: amplitude distortion, group-delay distortion, and echoes.

Task 6. Translate the text into English.

Адаптивные фильтры применяются для устранения шумов двигателя в микрофоне пилота в кабине самолета.

Также адаптивные фильтры могут использоваться для подавления акустических шумов окружающей среды, например, на крупных электростанциях.

Еще одно применение адаптивных фильтров - это реализация самонастраивающегося фильтра. Этот фильтр используется для выделения синусоиды из широкополосного шума.

Task 7. Grammar Training. Translate the following sentences. Pay attention to the “Complex Object”.

1. We know the primary function of Adaptive Filters to be a system modeling.

2. They believe the primary signal to be input to a system with impulse response H (n) and its output to be connected to the other adaptive filter input.

3. He thinks a practical example of the 1-th mode to be echo cancellation across a telephone line hybrid.

4. The specialist assumed the adaptive filter to model the inverse of the line response to output equalized (distortion-free) data.

5. The students heard the adaptive filter be applied for noise cancellation.

6. Scientists know an example that may be used to illustrate operation of the adaptive filter in the inverse response modeling mode of operation to be equalization for distortion in data transmission over telephone lines.

7. They found the input to the telephone line to be excited by a known signal and the distorted line output of the adaptive filter.

8. We supposed them to use the adaptive filters for realizing a self-tuning filter which can be used to detect a sinusoid that is obscured by wideband noise.

UNIT 2. PROGRAMMABLE FILTER DESIGNS

 

Text A. Recursive Filters

Text B. Nonrecursive Filters

Text C. Transformed-Based Filters

Text A. Recursive Filters

 

Essential Vocabulary

feed forward multiplier feedback multiplier weighted samples present (previous) output sample   present (previous) input sample   pole-zero filter design pole (zero) location delay stages input sample rates   unconditionally stable inclusion of…. sharp cutoff filter characteristics   a low transmission bandwidth   low filter complexity straying poles

- умножитель прямой связи - умножитель обратной связи - взвешенные выборки - выборка на выходе в данный (предыдущий) момент времени - выборка на входе в данный (предыдущий) момент времени - полосно-нулевой тип фильтра - размещение полюсов (нулей) - (зд.) элементы задержки - скорости передачи входных импульсов - неограниченно устойчивый - наличие (чего-либо) - фильтры с крутым срезом характеристики - малая ширина полосы пропускания - фильтры малой сложности - (зд.) паразитные полюса

Read and translate Text A using Essential Vocabulary

Text A. Recursive Filters

There are several types of programmable filters /Hamming/ that can be used in the design of the adaptive filters. Here we summarize initially the two basic filter designs and then expand them into the processors.

The most generalized digital filter structure is the recursive filter design. This comprises both feed-forward multipliers, whose weights are controlled by the «a» coefficients, and feedback multipliers, which are controlled by the «b» coefficients. The response of this n-stage filter is governed by the nth-order difference equation which shows that the value of present filter output sample is given by a linear combination of the weighted present and past input samples as well as the previous output samples. This structure results in a pole-zero filter design where the pole locations are controlled by the «b» coefficients and the zero locations by the «a» coefficients. The number of poles and zeros, or order of the filter, is given by the number of delay stages. Second-order integrated filters are commercially available for input sample rates (64 kilobaud), which are compatible with digital telephony systems.

This recursive structure has theoretically an infinite memory and hence it is referred to as an infinite impulse response (IIR) filter design. It is not unconditionally stable unless restrictions are placed on the values of the «b» coefficients.

However, the inclusion of poles as well as zeros makes it possible to realize sharp cutoff filter characteristics incorporating a low transition bandwidth with only a modest number of delay stages (i.e., low filter complexity). One drawback of the IIR design is that no control is offered on the phase (group delay) response of the filter. However, the major problem, with adaptive IIR filter design is the possible instability of the filter due to poles straying outside the stable region.

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