郑大计算机应用基础试题7章,多媒体信号处理(郑大中澳班考试卷最强总结)

Q1.a)Briefly explain the advantage of logarithm b)the main steps performed in a audio coder.

quantification.

Ans: logarithm quantification provides quantification errors for low amplitude values. b)The advantage of backward adaptive

quantification .

Ans:Don’t require transmission and has lower delay .

Q2.a)The difference between Lossless and lossy compression . Ans:Lossless compression reconstructs original signal

while lossy compression produces an accurate representation of the original signal . Q3.a)The source filter model of speech production . Ans:The source filter model consists of filter,the input of

which is either a periodic pulse train or random noise .The source is chosen using a switch .This model is used synthesis speech and model speech production . b)With regard to human hearing ,define simultaneous masking . Ans:This is where a tone is masked by another tone or set of tones occurring in the same frequency region as the single tone and at same time. c)Which type of speech signal are most suited to

linear prediction and explain why.

Ans:Voiced speech signals are most suited due to the presence of short term correlations. d)How is the performance of speech and audio coders evaluated?Why SNR\subjective measures? Ans:The performance can be evaluated using subjective and objective measures.This is because there is no fixed correlation between objective and subjective error ----a large mathematical error such as measured with the SNR may not result in a perceivable error. Q4.a)The method represented the LP excitation

signal in 3 broad methods . Ans:Direct ---G721 uses ADPCM ; Analysis-by-Synthesis---Quantise each sample ; Parametric ---Modelling the excitation using e.g. pulses for voiced speech and random noise. b)What is the pitch period of a speech signal ? Ans:the pitch period of a speech signal corresponds to

the measured period of the quasi-periodic voiced sections of a speech signal.This periodic nature is caused by the periodic opening and closing of the vocal folds in the vocal tract. Q5.a)MP3 is based on the perceptual coding paradigm.Explain how audio coders operating. ANS:Audio coders operate by using a psychoacoustic model.The most important components are represented more accurately than the masked components. bands. Perceptual Model:Calculate a psychoacoustic model for the input spectrum. Quantization and coding:Quantise the spectral

components falls below the masking threshold . Encoding of Bitstream:Use entropy ending to further reduce the bit rate. c)two key difference between MP3 and AAC? ANS:TNS ; Joint stereo coding . Q1B:a)the difference between a grey scale digital image and a colour digital image . ANS:Grey scale image is black and white .Only one colour component per pixel with a range of values form 0

to 255.colour images have multiple components per pixel ,representing red,green and blue. b)the purpose of transforming in image compression ? ANS:transforming aims to compact the energy . c)What criteria should be used when choosing the resolution for a digital image ? ANS:the subjective distortion is minimised. d)compare RGB colour space with YCrCb colour space. ANS:Y is made up of all R,G,B components.Cr and Cb is

one of the colour components.They represent colour. e)explain the term critical flicker . ANS:the minimum frame rate below which the human eye will detect flicker. Q2B:a)Which coefficients are the most important in DCT image compression ? ANS:The coefficients with the highest magnitude .These

are the first few coefficients obtained from a 2D DCT of the image . b)What is the zigzag scanning pattern ? ANS:This is designed to order the coefficients in magnitude.It will lead to long sequences of zeros. Q3B:a)Compare the DWT-based image compression and DCT-based image compression . ANS:DWT-based image compression will result in blurred distortion whereas DCT-based image compression will result in blocky distortions.