Chapter: Digital Signal Processing - Applications of DSP

Important Short Questions and Answers: Applications of DSP

Digital Signal Processing - Applications of DSP - Important Short Questions and Answers: Applications of DSP



1. What is the need for multirate signal processing?

In real time data communication we may require more than one sampling rate for processing data in such a cases we go for multi-rate signal processing which increase and/or decrease the sampling rate.


2. Give some examples of multirate digital systems.

Decimator and interpolator


3. Write the input output relationship for a decimator.

Fy = Fx/D


4. Write the input output relationship for an interpolator.

Fy = IFx


5. What is meant by aliasing?

The original shape of the signal is lost due to under sampling. This is called aliasing.


6. How can aliasing be avoided?

Placing a LPF before down sampling.


7. How can sampling rate be converted by a factor I/D.

Cascade connection of interpolator and decimator.


8. What is meant by sub-band coding?

It is an efficient coding technique by allocating lesser bits for high frequency signals and more bits for low frequency signals.


9. What is meant by up sampling?

Increasing the sampling rate.


10. What is meant by down sampling?

Decreasing the sampling rate.


11. What is meant by decimator?

Down sampling and a anti-aliasing filter.


12. What is meant by interpolator?

An anti-imaging filters and Up sampling.


13. What is meant by sampling rate conversion?

Changing one sampling rate to other sampling rate is called sampling rate conversion.


14. What are the sections of QMF.

Analysis section and synthesis section.


15. Define mean.

Mxn=E[xn]=intg xpxn(x,n) dx


16. Define variance.



17. Define cross correlation of random process.

R xy (n.m)= intxy*pxn,ym(x,n,y,m)dxdy.


18. Define DTFT of cross correlation

Txy(e jw) = x rxy(l) e jwl


19. What is the cutoff frequency of Decimator?

Pi/M where M is the down sampling factor


20. What is the cutoff frequency of Interpolator?

Pi/L where L is the UP sampling factor.


21. What is the difference in efficient transversal structure?

Number of delayed multiplications are reduced.


22. What is the shape of the white noise spectrum?

Flat frequency spectrum.



Sampling Rate:


The No. of samples per cycle given in the signal is termed as sampling rate of the signal .The samples occur at T equal intervals of Time.

Sampling Theorem:


Sampling Theorem states that the no. of samples per cycle should be greater than or equal to twice that of the frequency of the input message signal.


Sampling Rate Conversion:


The Sampling rate of the signal may be increased or decreased as per the requirement and application. This is termed as sampling rate Conversion.





The Decrease in the Sampling Rate are termed as decimation or Downsampling. The No. of Samples per Cycle is reduced to M-1 no. of terms.




The Increase in the Sampling rate is termed as Interpolation or Up sampling. The No. of Samples per Cycle is increased to L-1 No. of terms.


Polyphase Implementation:


If the Length of the FIR Filter is reduced into a set of smaller filters of length k. Usual upsampling process Inserts I-1 zeros between successive Values of x(n). If M Number of Inputs are there, Then only K Number of Outputs are non-zero. These k Values are going to be stored in the FIR Filter.


Narrow band Filters:


If we want to design a narrow passband and a narrow transition band, then a lowpass linear phase FIR filters are more efficiently implemented in a Multistage Decimator – Interpolator.



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