← IGCSE Computer Science Paper 1

Analogue sound waves and digital sound

A sound wave is analogue: its amplitude changes smoothly. A computer stores only separate binary numbers, so the wave a microphone captures must be converted into discrete digital values.

Part of: IGCSE Computer Science 0478 — 1.2 Text, Sound and Images — Module 11, ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound — Module 46

Understanding Analogue sound waves and digital sound in IGCSE Computer Science Paper 1

What it does: The microphone picks up the analogue wave, and the conversion step turns it into discrete binary values the computer can store. Sound in the real world is analogue. Its amplitude can take any value and changes smoothly, with no gaps between values. The smooth, continuous change belongs to the analogue wave, while digital sound is stored as separate steps.

Common mistakes: The wave is analogue and continuous, so it cannot be stored as it is. Each item added must be a separate measured number, so it should be samples.append(measure(wave)). The captured wave is still analogue. It must be passed through the converter to become digital values, so the line should be digital = adc.convert(wave).

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This module's key terms are also in a printable crossword (Modules 43–58) and word search (Modules 28–58).

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Learning
Duo
Which describes a real sound wave?
Analogue: its amplitude changes smoothly and continuouslyDigital: its amplitude is stored as separate binary numbers
Matches
A computer stores the analogue wave directly
↓
A computer cannot store an analogue wave directly. It can only store discrete binary values, so the wave must first be converted to digital.
Applying
Meanings
Term
analogue to digital
Meaning
A sound wave is analogue: its amplitude changes smoothly. A computer stores only separate binary numbers, so the wave a microphone captures must be converted into discrete digital values.
Practice
wave ← microphone()
Testing
Gaps
wave ← .capture()
Check Answer
Spots
2samples = []
3samples.append(wave)

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Quick Questions

1. Which describes a real sound wave?
A. Analogue: its amplitude changes smoothly and continuously ✓
B. Digital: its amplitude is stored as separate binary numbers
Sound in the real world is analogue. Its amplitude can take any value and changes smoothly, with no gaps between values.
2. A computer can directly store which kind of data?
A. A smooth, continuous wave
B. Separate (discrete) binary numbers ✓
Computers only store discrete values as 1s and 0s, so a continuous wave cannot be stored as it is.
3. A microphone captures a sound wave. What must happen before the computer can process it?
A. It must be converted into discrete digital values ✓
B. It can be processed straight away as an analogue wave
The captured analogue signal has to be converted to digital (binary) values, which is what analogue to digital conversion does.
4. What does the microphone do in the process of recording sound?
A. It captures the sound wave so it can be measured ✓
B. It stores the sound as binary on the hard drive
The microphone picks up the analogue wave. Converting it to binary and storing it are separate steps.
5. Which statement about amplitude in an analogue wave is correct?
A. It can only jump between a few fixed whole numbers
B. It changes smoothly and can take any value in a range ✓
Analogue means continuous. Only after conversion to digital is the amplitude limited to separate, fixed values.

Match the Pairs

analogue → A signal that changes smoothly and continuously, like the amplitude of a sound wave, with infinitely many possible values
digital → Data stored as separate (discrete) binary values, so a computer can process it
A microphone captures a continuous sound wave, and the wave must then be converted into binary numbers → sound wave -> microphone -> analogue to digital -> binary
A computer can only store separate numbers, so the smooth wave is stored as a list of discrete values → wave = 0.0 ... 1.0 -> stored = 0, 3, 5, 3, 0
A computer stores the analogue wave directly → A computer cannot store an analogue wave directly. It can only store discrete binary values, so the wave must first be converted to digital.
Digital sound has a smoothly changing amplitude → It is analogue sound that has a smoothly changing amplitude. Digital sound is made of separate, discrete values.

Key Term

analogue to digital
A sound wave is analogue: its amplitude changes smoothly. A computer stores only separate binary numbers, so the wave a microphone captures must be converted into discrete digital values.

Fill in the Blanks

1. wave ← microphone.capture()
Hint: Type the device that captures the sound wave.
2. digital ← convert(wave)
Hint: Type the function name that changes the analogue wave into digital values.
3. OUTPUT wave.amplitude
Hint: Type the property of a sound wave that changes smoothly.
4. digital ← [3, 7, 12, 9]
Hint: Type the variable name for separate numbers stored by the computer.
5. computer.store(binary)
Hint: Type the number system a computer uses to store the separate values.

Spot the Error

Question 1
A wave = microphone.capture()
B samples = []
C samples.append(wave)
D print(samples)
Line C — The wave is analogue and continuous, so it cannot be stored as it is. Each item added must be a separate measured number, so it should be samples.append(measure(wave)).
Question 2
A mic = Microphone()
B wave = mic.capture()
C adc = Converter()
D digital = wave
Line D — The captured wave is still analogue. It must be passed through the converter to become digital values, so the line should be digital = adc.convert(wave).
Question 3
A wave = 'analogue'
B computer = 'digital'
C convert = wave == computer
D print(convert)
Line C — Conversion is needed when the wave type is different from the type the computer stores. The test should use != (not equal), not ==.
Question 4
A amplitude = 'separate'
B computer_values = 'separate'
C print(amplitude)
Line A — The amplitude of an analogue sound wave changes smoothly. It is the computer's stored values that are separate, so line 1 should be amplitude = 'smooth'.
Question 5
A mic = Microphone()
B wave = mic.capture()
C levels = measure(wave)
D store(levels, 'analogue')
Line D — A computer can only store digital data as binary numbers. The measured levels must be stored as 'binary', not 'analogue'.

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