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4
Audio
ICT Focus
• AAC and WMA
• Data in analogue audio is accessed mostly by sequential access. Data in digital
audio is accessed by direct access. Exact copies can be made by digital audio
easily while analogue audio cannot.
Activity 1
2. VoiceA.wav
3. VoiceA.wav, VoiceC.wav
File
Sampling rate (Hz)
Sample size (bit)
Channels
File size (KB)
VoiceA.wav
44,100
16
2
1,723
VoiceB.wav
22,050
8
1
216
VoiceC.wav
11,025
8
1
108
Activity 3
File
File format
Encoding bit
rate (kbps)
File size (KB)
Compression
ratio
RomanceA
WAV
(Uncompressed)
1,411 kbps
6,363
-
RomanceB
MP3
128 kbps
578
11: 1
RomanceC
RealAudio
128 kbps
592
10.75: 1
RomanceD
WMA
128 kbps
614
10.36: 1
RomanceE
AAC
128 kbps
578
11: 1
Concept Map
1. F
2. B
3. J
4. G
5. D
6. H
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NSS ICT Elective C1 Textbook Answers
7. A
8. C
9. E
10. I
Concept Checker
1. T
2. T
3. F
4. T
5. F
Multiple Choice Questions
1. B
2.
3.
4.
5.
6.
7.
8.
C
D
C
D
B
D
C
9. B
10. A
11. B
12. D
Short Questions
1. •WAV–Windows Media Player
•MP3–Windows Media Player
•MIDI–Windows Media Player
•RealAudio–RealPlayer
•WMA–Windows Media Player
(any three × 2)
2. (a) •WAV files are used to record any sound including speech but MIDI files are
principally a sequence of notes (or MIDI events).
•WAV files usually have a larger file size but MIDI files usually have a
smaller file size.
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NSS ICT Elective C1 Textbook Answers
•WAV files are difficult to edit but MIDI files are easy to edit.
(any two × 1)
(b) The quality of the ringing tone increases with both the sampling rate and
sample size. (2)
(c) Uncompressed file size =
1  22,050  8  10
KB (1)  215.3 KB (1)
1,024  8
(d) Maximum length of ring tone
=
1,024 KB
 10 seconds (1)  47.6 seconds (1)
215.3 KB
3. (a) •A portable MP3 player has a smaller physical size as it is not governed by
the size of a CD.
•A portable MP3 player can store more music files.
•A user can create a list of favourite music files and store it in an MP3
player easily.
(any two × 1)
(b) M4V / MP4 / MOV (any two × 1)
(c) The length of audio
=
8 GB
8  1,024  1,024  1,024  8 bits
(1) 
 536,870.9 s  149.1 hours (1)
128,000 bps
128,000 bps
(d) It may cause permanent hearing loss. (1)
Long Questions
1. (a) (i) Sampling rate is the number of samples used to record a one-second
analogue audio signal. (1)
(ii) File size = 44.1 Hz × 1,000 × 16 bits × 2 × 3 × 60 s (1)
= 254,016,000 bits
 30.28 MB (1)
(b) File format: MP3 / WMA (any one × 1)
Reason: Save storage space / high compression ratio (any one × 2)
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NSS ICT Elective C1 Textbook Answers
(c) (i) File size = 128 bps × 1,000 × 3 × 60 s (1)
= 23,040,000 bits
 2.75 MB (1)
23,040,000 bits
(ii) Time required =
(1)  400 s (1)
57,600 bps
(d) (i) Streaming audio (1)
(ii) MP3 / RA (RealAudio) / WMA (Windows Media Audio) / Ogg Vorbis
(any one × 1)
(e) (i) MIDI format (1)
(ii) MIDI format has a much smaller file size. (2)
2. (a) Hardware: microphone, (1) sound card (1) and speakers (1)
Software: audio recording / editing software (any one × 1)
(b) Increase the volume level of the narration using audio editing software. (2)
(c) Lower the sampling rate. (1) Decrease the sample size. (1) Reduce the
number of channels. (1)
(d) He should mix his narration with the background music using audio
editing / mixing software. (2)
(e) File size = 22,050 Hz × 8 bits × 1 × 5 × 60 s (1)
= 52,920,000 bits
= 6.31 MB (1)
(f)
Reason: The audio file is too large and has not been automatically attached
or embedded in the presentation file. (1)
Solution: Send both the presentation file and the audio file to the e-mail
account and resemble the two files at school. / Embed the audio
file in the presentation file manually. (any one × 1)
© Pearson Education Asia Limited 2010
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NSS ICT Elective C1 Textbook Answers