9618 · 1.2.2

Multimedia - Sound — practice questions

Practice and worked examples for 9618 Multimedia - Sound. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

Calculate the file size in kilobytes (KB) for a 25-second mono audio clip sampled at 22,050 Hz with a 16-bit sampling resolution. Give your answer to one decimal place. (Assume 1 KB = 1024 bytes).

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Identify the formula:
File Size (bits) = Sampling Rate $\times$ Resolution $\times$ Time $\times$ Channels
Substitute the values:
File Size (bits) = 22,050 Hz $\times$ 16 bits $\times$ 25 s $\times$ 1 (mono)
Calculate the total bits:
File Size = 8,820,000 bits
Convert bits to bytes:
File Size (bytes) = 8,820,000 / 8 = 1,102,500 bytes
Convert bytes to kilobytes (KB):
File Size (KB) = 1,102,500 / 1024 = 1076.66... KB
Round to one decimal place:
Final Answer: 1076.7 KB

Worked example 2

A 4-minute stereo music track is recorded with a sampling rate of 48 kHz and a bit depth of 24 bits. Calculate the file size in megabytes (MB). Give your answer to two decimal places. (Assume 1 MB = 1024 KB, 1 KB = 1024 bytes).

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Convert all units to base units:
Time: 4 minutes $\times$ 60 seconds/minute = 240 s
Sampling Rate: 48 kHz $\times$ 1000 = 48,000 Hz
Channels: 2 (stereo)
Resolution: 24 bits
Use the formula:
File Size (bits) = 48,000 $\times$ 24 $\times$ 240 $\times$ 2
Calculate total bits:
File Size = 552,960,000 bits
Convert bits to bytes:
File Size (bytes) = 552,960,000 / 8 = 69,120,000 bytes
Convert bytes to kilobytes (KB):
File Size (KB) = 69,120,000 / 1024 = 67,500 KB
Convert kilobytes to megabytes (MB):
File Size (MB) = 67,500 / 1024 = 65.9179... MB
Round to two decimal places:
Final Answer: 65.92 MB

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