← ACARA Digital Technologies Years 7–8

Reading a sound waveform

A graph of a sound. Time runs left to right and volume goes up and down. Louder sounds make taller waves and silence is a flat line.

Part of: ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound — Module 47

Understanding Reading a sound waveform in ACARA Digital Technologies Years 7–8

What it does: The horizontal (x) axis of a waveform shows time moving forward from left to right. The height of the wave up and down shows the volume at that moment, so taller waves are louder. A flat line means there is no volume at that time, so the recording is silent. A shout is loud so it makes tall waves. A whisper is quiet so it makes short waves. The shout comes first, so the tall waves are on the left. An audio editor shows your recording as a waveform. You can see loud parts, quiet parts and silence. A flat line is silence. The loudest part would be where the waves are tallest.

Common mistakes: Silence has no volume, so its waveform is a flat line, not a tall wave. It should be: silence ← flat line. The height of the wave shows volume, not time. Time runs left to right. It should be: height ← ABS(sample).

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 153–172) and word search (Modules 153–188).

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Learning
Duo
In a waveform, what does the left-to-right direction show?
Time passingVolume getting louder
Matches
y-axis = time
↓
Time is on the horizontal x-axis, running left to right. The vertical y-axis shows volume.
Applying
Meanings
Term
waveform
Meaning
A graph of a sound. Time runs left to right and volume goes up and down. Louder sounds make taller waves and silence is a flat line.
Practice
quiet ← [0, 2, 0, -2, 0]
Testing
Gaps
xAxis =
Check Answer
Spots
3loud ← tall wave
4silence ← tall wave

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Quick Questions

1. In a waveform, what does the left-to-right direction show?
A. Volume getting louder
B. Time passing ✓
Time runs left to right across a waveform. The up and down direction shows volume.
2. In a waveform, what does the up and down height show?
A. Length of the recording
B. Volume of the sound ✓
The height of the wave at each point shows how loud the sound is at that moment. Time is the left-to-right direction.
3. Which waveform shows a louder sound?
A. Tall waves ✓
B. Short waves
Louder sounds make taller waves. Quieter sounds make shorter waves.
4. What does a flat line in a waveform mean?
A. Silence ✓
B. A very loud sound
A flat line means there is no volume at that time, so the recording is silent.
5. A friend shouts, then whispers. What happens to the waveform?
A. Tall waves, then short waves ✓
B. Short waves, then tall waves
A shout is loud so it makes tall waves. A whisper is quiet so it makes short waves. The shout comes first, so the tall waves are on the left.

Match the Pairs

[0, 0, 0, 0, 0] → A flat line on the waveform, which means silence
[9, -9, 9, -9] → Tall waves, which means a loud sound
Time runs from left to right along a waveform → x-axis = time
The taller the wave, the louder the sound → height = volume
y-axis = time → Time is on the horizontal x-axis, running left to right. The vertical y-axis shows volume.
silence = tall waves → Silence is a flat line, not tall waves. Tall waves mean a loud sound.

Key Term

waveform
A graph of a sound. Time runs left to right and volume goes up and down. Louder sounds make taller waves and silence is a flat line.

Fill in the Blanks

1. xAxis = time yAxis = volume
Hint: Type what the left-to-right axis of a waveform shows
2. IF sound is louder THEN wave is taller
Hint: Type the word describing how a louder sound changes the wave's height
3. IF volume = 0 THEN wave is a flat line
Hint: Type the volume number that means silence
4. heights = [2, 8, 5, 1] loudest = MAX(heights)
Hint: Type the function name that finds the biggest (tallest) value
5. timeDirection = left TO right
Hint: Type the direction that time moves across a waveform

Spot the Error

Question 1
A x_axis ← time
B y_axis ← volume
C loud ← tall wave
D silence ← tall wave
Line D — Silence has no volume, so its waveform is a flat line, not a tall wave. It should be: silence ← flat line
Question 2
A FOR each sample in recording
B height ← time of sample
C DRAW bar of that height
Line B — The height of the wave shows volume, not time. Time runs left to right. It should be: height ← ABS(sample)
Question 3
A FOR each sample in recording
B IF sample is zero THEN
C DISPLAY 'tall wave'
D END IF
Line B — A zero sample is silence, which is flat, so it cannot give a tall wave. The test should be: IF sample is large THEN
Question 4
A x_axis ← time
B y_axis ← volume
C start ← left of graph
D end ← top of graph
Line D — Time runs from left to right, so the end of the sound is at the right of the graph. The top shows loud volume. It should be: end ← right of graph
Question 5
A x_axis ← volume
B y_axis ← volume
C peak ← highest point
Line A — On a waveform, time runs along the horizontal x-axis. Volume goes on the vertical y-axis. It should be: x_axis ← time

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