Digital Signal Processing interview Questions4

VII – Multi rate digital signal processing

1). What is multirate signal processing?

Ans: The theory of processing signal at different sampling rates is called multirate signal processing.

2). Define down sampling.

Ans: Down sampling a sequence x(n) by a factor M is the process of picking every Mth sample and discarding the rest.

3). What si meant by upsampling?

Ans: Upsampling by a factor L is the process of inserting L-1 zeros between two consecutive samples.

4). If the spectrum of a sequence x(n) is X(), then what is the spectrum of a signal down sampled by a factor 2.

Ans: Y()=

5). If the z-transform of a sequence x(n) is X(z), then what is the z-transform of a s down sampled by a factor M.

Ans:  Y(z)=

6). What are the applications of multirate signal processing?

Ans: i. In high quality signal data acquisition and storage systems.

        ii. In audio signal processing

       iii. In transmultiplexers

7). The output signal y(n) is a down sampled signal of the input signal x(n) and can be represented as y(n)=x(Mn)

8). The output signal y(n) is a up sampled signal of the input signal x(n) and can be represented as y(n)=x(n/L)

9). Upsampler and down sampler are time variant type of systems.

10). What is the spectrum of up-sampled signal?

Ans: Y()= X()

11). The M-branch poly phase decomposition of H(z) is given by H(z)=

12). The operation of  is known as poly phase convolution.

13). To change the sampling rate of a digital signal, multi rate digital signal processing systems use down sampler and up sampler.

14). The discrete-time systems with unequal sampling rates at various parts of the system are called multi rate system.

15). The block diagram representation of the up-sampler is also called as sampling rate expander

16).what is perfect reconstruction  multirate system?

Ans: A multirate structure in which the output sequence is a delayed and scaled replica of the input sequence then the system is said to be perfect reconstruction  multirate system.

17). Aliasing due to a factor-of-M down sampling is absent if and only if the signal x[n] is band limited to

18). Nyquist fikters is also known as Lth band filters.

19). An Lth band filter for L=2 is called a half-band filter.

20). The transfer function of a zero-phase half-band filter is H(z)=

VIII – Apllications of digital signal processing

1).Non-stationary signals means always vary with time.

2). What are the examples of non-stationary signals?

Ans: The examples of non-stationary signals Speech, radar and sonar signals.

3). What is the purpose of STFT?

Ans: The purpose of STFT is to find the spectrum analysis of non-stationary signals.

4). The short time Fourier transform is also known as Time-dependent Fourier transform.

5). The magnitude of the STFT is usually referred to as the spectrogram.

6). A decreases in the window length increases the time-resolution property of the STFT.

7). A increases in the window length increases the frequency-resolutionproperty of the STFT.     

8). The equation for STFT is  . In this equation, if the window sequence w[m]=1, then STFT becomes DFT.

9). What are the  Commonly used time-domain operations carried on musical sound signals?

Ans: The  Commonly used time-domain operations carried on musical sound signals are echo generation, reverberation, flanging, chorus generation and phasing.

10). What is flanging effect?

Ans: There are number of special sound effects that are often used in the mix-down process. One such effect is called flanging effect.

11). How the chorus effect can be achieved?

Ans: The chorus effect is achieved when several musicians are playing the same musical piece at the same time but with small changes in the amplitudes and small timing differences between their sounds.

12). What is the necessity of signal compression?

Ans: For efficient storage of digital signals.

13). A signal in compressed form requires less band width for transmission.

14). A signal coding system consist of encoder and decoder.

15). The signal compression methods can be classified into two basic groups. such aslossless and lossy

16). What is lossless compression?

Ans: In the lossless compression methods, no information is lost due to compression, and the original signal can be recovered exactly from the compressed data by the decoder.

17). What is lossy compression?

Ans: In the lossy compression methods, some amount of information is lost, due to compression and the signal reconstructed by the decoder is not exact replica of original signal.

18). What is the goal of compression?

Ans: The goal of compression is to reduce the volume of data while retaining the information content of the original signal with some acceptable fidelity.

19). What is FDM telephone system?

Ans: In this, multiple analog voice signals are first modulated by single sideband (SSB) modulators onto several subcarriers, combined, and transmitted simultaneously over a common wide-band channel. To avoid cross-talk, the subcarriers are chosen to ensure that the spectra of the modulated signals do not overlap. At the receiving end, the modulated subcarrier signals are separated by analog band pass filters and demodulated to reconstruct the individual voice signals.

20). What is TDM telephone system?

Ans: In this, the voice signals are first converted into digital signals by sampling and A/D conversion. The samples of the digital signals are time-interleaved by a digital multiplexer, and the combined signal is transmitted. At the receiving end, the digital voice signals are separated by a digital demultiplexer and the passed through a D/A converter and an analog reconstruction filter to recover the original analog voice signals.