=========================preview======================
(comp342)(s)midterm~cs_tcxaa^_10203.pdf
Back to COMP342 Login to download
======================================================

Hong Kong University of Science and Technology
COMP342: Computer Music

Spring 2008
Midterm Examination

Student Name: key

Student ID:

Instructions:
1.
This is a closed-book, closed-notes examination.

2.
Answer all questions in the space provided.

Question
Score

1
/4

2
/6

3
/6

4
/4

5
/4

6
/6

7
/6

8
/5

9
/4

10
/10

11
/4

12
/4

13
/8

14
/8

15
/7

16
/7

17
/7

Total
/100

1
. Acoustics [4 marks]

a)
Choose the BEST answer below. (2 marks) i. If vibrating the whole string will give a tone of certain frequency = f, halving the string length will give a tone of frequency = 0.5f. ii. If vibrating the whole string will give a tone of certain frequency = f, doubling the string length will give a tone of frequency = 2f. iii. The frequency of the tone is inversely proportional to the length of the string. iv. The frequency of the tone is not related to the string length. It is determined by the material of the string. Answer: iii

b)
Which of the below frequencies will not be found in the harmonic series of a given pitch of frequency = f? You may choose MORE THAN ONE answer. (2 marks) i. 3f iii. 0.5f ii. 4f iv. 4.5f Answer: iii, iv (must be exactly these two to receive marks)

2
. Spectrum Analysis and PVan [6 marks]

a
) Choose the BEST answer below. (2 marks) i. Spectrum is the relative amplitudes of the harmonics that make up the waveform. ii. For any periodic waveform, we can find the spectrum of the waveform. iii. i. and ii. are correct iv. i. and ii. are wrong Answer: iii

b
) What is Spectrum analysis? Choose the BEST answer below. (2 marks) i. Do Fourier transform on a waveform, then isolate one period of the result. ii. Isolate one period of the waveform, then do Fourier transform on the period. iii. Just isolate one period of the waveform. iv. Find the attack time, decay time and pitch of a waveform. v. All the above are wrong Answer: ii

c)
Choose ALL the wrong statements below (2 marks) i. Windowing smoothes samples at the window endpoints, when isolating a moment of sound ii. Windowing extracts half a wave period for Fourier analysis iii. If we specify an inaccurate user-specified fundamental frequency, the windowing technique will be useless. iv. All windowing functions are rectangular or square in shape. Answer: ii, iii and iv (Each statement 0.5 mark)

3
. Waveforms [6 marks]

In each of the following cases, write down what is heard; give a brief explanation (in 1-2 sentences) for each.
If you think there is more than one possible answer, list them all.

a)
Using a sampling rate of 10000Hz, to sample a sinewave of 6000Hz (2 marks)

An
swer: A music tone of 10000 C 6000 = 4000Hz is heard since aliasing occurs.

b)