PhysicsICSE Class 10 · Loudness, Pitch and Quality of Sound

Quality (Timbre) of Sound: Waveforms and Overtones (ICSE Class 10)

Updated 15 October 2026 · Fact-checked

Quality, or timbre, is the characteristic that lets us tell apart two sounds of the same loudness and pitch coming from different sources, such as a flute and a violin playing the same note. It depends on the waveform, which is decided by the number and relative strengths of the overtones present along with the fundamental.

Understand Quality (Timbre) of Sound and Waveforms

The third characteristic. Two sounds can have the same loudness (amplitude) and the same pitch (frequency) and still sound different: a flute and a violin playing the same note, or two friends saying the same word equally loudly. The characteristic that distinguishes them is quality (also called timbre).

Why sources differ: fundamental and overtones. A real source does not vibrate at just one frequency. Along with its main, lowest frequency, called the fundamental (which fixes the pitch), it also vibrates weakly at certain higher frequencies, called overtones. Different instruments, because of their different shapes, materials and ways of playing, produce different overtones with different relative strengths.

Waveform. When the fundamental and its overtones combine, they give a wave of a particular shape (waveform). The quality of a sound depends on this waveform:

A tuning fork gives an almost pure note: a smooth, sine-shaped wave with hardly any overtones.
A flute gives a fairly smooth wave with a few weak overtones.
A violin, sitar or human voice gives a complex wave with many overtones.

On a displacement–time graph, two notes of the same quality have the same shape; same pitch shows as the same period; same loudness as the same height (amplitude).

Characteristic	Depends on	Seen on a graph as
Loudness	Amplitude	Height of the wave
Pitch	Frequency	Period (horizontal spacing)
Quality	Waveform (overtones)	Shape of the wave

Subjective and objective. Quality is a subjective sensation; the waveform that causes it is objective and can be recorded on an oscilloscope or a computer.

Everyday examples of quality.

We recognise a friend's voice on the telephone, without seeing them, because every voice has its own waveform.
We can tell a sitar from a guitar playing the same note.
A mimic imitates someone by copying the overtone pattern of their voice.
A cracked bell or a cracked glass sounds different from a sound one, because the crack changes its overtones.

Music and noise. A musical sound is pleasant to hear; it has a regular, repeating waveform, produced by regular periodic vibrations. Noise is unpleasant; it has an irregular waveform with no regular repeating pattern, often with sudden changes in loudness (traffic, a drill, a crowd). The same idea, a regular or irregular waveform, decides whether we hear music or noise.

Reading three graphs. When a question gives several traces and asks which pair shows 'same loudness and pitch but different quality', look for the pair with equal heights and equal periods but different shapes.

Quality (Timbre) of Sound and Waveforms: formulas and key facts

Characteristic and its cause: Loudness amplitude, the height of the wave
Pitch frequency, the spacing (period) of the wave
Quality waveform, the shape of the wave; Each subjective characteristic has an objective cause.
Frequency from a trace: $f = \frac{1}{T} = \frac{n}{t}$; Same period on two traces means same pitch.
Overtones: $f_{overtone} > f_{fundamental}$; The fundamental sets the pitch; the overtones set the quality.
Music and noise: Music regular repeating waveform, pleasant
Noise irregular waveform, unpleasant
Pure note smooth sine-shaped wave, as from a tuning fork; Waveform decides the character of the sound.

Loudness	amplitude, the height of the wave
Pitch	frequency, the spacing (period) of the wave
Quality	waveform, the shape of the wave

Music	regular repeating waveform, pleasant
Noise	irregular waveform, unpleasant
Pure note	smooth sine-shaped wave, as from a tuning fork

How to solve Quality (Timbre) of Sound and Waveforms questions

Quality questions are about explanations and about comparing displacement–time graphs.

1Check what is equal: if loudness and pitch are equal but the sounds still differ, the answer is quality (timbre).
2Give the cause: different waveforms, because the sources produce different overtones with different strengths.
3On graphs, compare height (loudness), period (pitch) and shape (quality) one at a time.
4For pitch on a trace, find the period and use $f = \frac{1}{T}$ .
5Use 'characteristic of sound' words (loudness, pitch, quality), not 'amplitude', 'frequency' or 'waveform', when a characteristic is asked for.

Quality (Timbre) of Sound and Waveforms in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Knowing who is calling

Suppose your phone rings from an unknown number and the caller just says 'Hello'. You recognise your cousin at once.

Which characteristic of sound lets you do this, and what causes it?

Try it first, then show the solutionSolution

Many people could say 'Hello' at the same loudness and pitch.
Your cousin's voice has its own pattern of overtones, giving a unique waveform: its quality (timbre).

Answer: Quality (timbre), caused by the voice's particular waveform.

Memory hook: Same words, same pitch, different shape: that's quality.

Testing a cup for cracks

Imagine a shopkeeper taps each china cup gently with a pencil before packing it. A cracked cup gives a dull sound instead of a clear ring.

What changes in the sound of a cracked cup?

Try it first, then show the solutionSolution

The crack changes how the cup vibrates, so the overtones present and their strengths change.
The waveform changes and the cup sounds dull: its quality is different.

Answer: Its quality (waveform and overtones) changes, so it sounds dull.

Memory hook: A crack changes the character, not just the volume.

Tricks to remember Quality (Timbre) of Sound and Waveforms

Short memory aids. Say each one aloud once, then use it on a question the same day.

L-P-Q = A-F-W
Loudness–Amplitude, Pitch–Frequency, Quality–Waveform: 'Loud People Quarrel About Funny Words'.
Use it when: Matching characteristics to causes.
Height, spacing, shape
On a trace, height is loudness, spacing is pitch, shape is quality.
Use it when: Graph questions.
Fork is plain, violin is rich
Tuning fork: pure sine wave, no overtones. Violin: rich in overtones.
Use it when: Examples of waveforms.
Regular is music
Regular repeating wave = music; ragged wave = noise.
Use it when: Music vs noise.

Quality (Timbre) of Sound and Waveforms: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Same note, different instrument · 1 mark · MCQBoard level

A harmonium and a flute play the same note equally loudly. We can still tell them apart because of the difference in their:
(a) loudness
(b) quality
(c) pitch
(d) speed in air

Try it first, then show the solutionSolution

Same note means same pitch; equally loud means same loudness; the remaining difference is quality.

Answer: (b) quality

Example 2: Defining quality · 3 marks · Short answerBoard level

(a) Define quality (timbre) of sound. (b) On what does it depend? (c) Give one example from daily life.

Try it first, then show the solutionSolution

(a) The characteristic of sound that distinguishes two sounds of the same loudness and pitch produced by different sources. (1)
(b) On the waveform, which depends on the number and relative intensities of the overtones accompanying the fundamental. (1)
(c) Recognising a friend's voice on the telephone, or telling a sitar from a guitar playing the same note. (1)

Answer: (a) Distinguishes sounds of equal loudness and pitch (b) Waveform (overtones) (c) Recognising a voice

Example 3: Two traces, same pitch · 3 marks · Short answerHarder board level

Traces of a note from a violin and from a flute each show 6 complete waves in 15 ms, with equal heights but different shapes. (a) Find the frequency of each. (b) What is the same and what is different about the two sounds? (c) Name the characteristic that differs and its cause.

Try it first, then show the solutionSolution

(a) $f = \frac{6}{15 \times 1 0 ^{- 3}} = 400$ Hz for both. (1)
(b) Same pitch (same period) and same loudness (same height); different waveform shape. (1)
(c) Quality (timbre), caused by the different overtones of the two instruments. (1)

Answer: (a) 400 Hz each (b) Same pitch and loudness; different shape (c) Quality, due to different overtones

Example 4: Music or noise? · 2 marks · Short answerBoard level

(a) Distinguish between a musical sound and noise in terms of the waveform. (b) Classify: the sound of a pressure cooker's whistle, a tanpura, a road drill.

Try it first, then show the solutionSolution

(a) A musical sound has a regular, repeating waveform and is pleasant; noise has an irregular waveform and is unpleasant. (1)
(b) Tanpura: music; road drill: noise; pressure cooker's whistle: usually heard as noise (shrill and unpleasant), though its wave is fairly regular. Accept a reasoned answer. (1)

Answer: (a) Regular vs irregular waveform (b) Tanpura music; drill noise; whistle usually noise

Example 5: Fundamental and overtones · 4 marks · Short answerHarder board level

A string sounds a fundamental of 220 Hz together with weaker overtones at 440 Hz and 660 Hz. (a) Which frequency decides the pitch of the note? (b) What decides its quality? (c) Find the period of the fundamental in ms. (d) What would the trace of a tuning fork of 220 Hz look like by comparison?

Try it first, then show the solutionSolution

(a) The fundamental, 220 Hz. (1)
(b) Which overtones are present (440 Hz, 660 Hz) and their relative strengths, which together fix the waveform. (1)
(c) $T = \frac{1}{220} \approx 4.55 \times 1 0^{- 3}$ s $\approx 4.55$ ms. (1)
(d) A smooth sine wave with the same period: the fork gives almost no overtones. (1)

Answer: (a) 220 Hz (b) Overtones and their strengths (c) About 4.55 ms (d) A smooth sine wave of the same period

Example 6: Why a mimic can fool you · 2 marks · Short answerHOTS / competency

A mimic on a radio show imitates a famous singer so well that listeners are fooled. Which characteristic of sound is the mimic copying, and why is it hard for most people to do?

Try it first, then show the solutionSolution

Matching pitch and loudness is easy; the mimic also copies the quality (timbre) of the singer's voice. (1)
That means reproducing the same pattern of overtones and so the same waveform, which depends on the shape of the vocal tract and how it is used, so it needs great skill. (1)

Answer: Quality (timbre), by copying the singer's overtone pattern and waveform

Example 7: Case study: the school band · 4 marks · Case-basedHOTS / competency

A music teacher records four sounds on a screen. Trace P: smooth sine wave, period 2 ms, height 3 units. Trace Q: complex wave, period 2 ms, height 3 units. Trace R: smooth sine wave, period 1 ms, height 3 units. Trace S: smooth sine wave, period 2 ms, height 6 units.
(a) Which pair shows sounds of the same loudness and pitch but different quality?
(b) Which pair shows the same pitch and quality but different loudness?
(c) Which trace has the highest pitch? Find its frequency.
(d) Which trace probably came from a tuning fork, and which from a violin?

Try it first, then show the solutionSolution

(a) P and Q: same height and period, different shape. (1)
(b) P and S: same period and shape, different height. (1)
(c) R: shortest period; $f = \frac{1}{1 \times 1 0 ^{- 3}} = 1000$ Hz. (1)
(d) A smooth sine wave (P, R or S) is typical of a tuning fork; the complex wave Q is typical of a violin. (1)

Answer: (a) P and Q (b) P and S (c) R, 1000 Hz (d) Fork: P (or R, S); violin: Q

Where students lose marks in Quality (Timbre) of Sound and Waveforms

The slips examiners see most often, and what to write instead.

Mistake: Saying quality depends on frequency or amplitude
Quality is what remains different when frequency (pitch) and amplitude (loudness) are the same; it depends on the waveform.
Wrong working
'The flute and violin sound different because they have different frequencies.'
Right working
'They have the same frequency but different waveforms (overtones), so different quality.'
Do this: Check what the question says is equal first.
Usually costs: 1 to 2 marks.
Mistake: Choosing the wrong pair of graphs
For 'same loudness and pitch, different quality', heights and periods must match, shapes must differ.
Wrong working
Picking two smooth waves of different heights.
Right working
Pick two waves of equal height and period, one smooth and one complex.
Do this: Compare height, then spacing, then shape.
Usually costs: The 2027 specimen paper tests exactly this (Q2(iii)).
Mistake: Naming 'waveform' when a characteristic is asked
The characteristics of sound are loudness, pitch and quality.
Wrong working
'The characteristic that differs is waveform.'
Right working
'Quality (timbre), which depends on the waveform.'
Do this: Give the characteristic, then its cause.
Usually costs: CISCE examiners made the same point for pitch in 2025 Q2(iii), where candidates gave frequency instead of pitch.
Mistake: Describing noise only as 'loud sound'
Noise is defined by its irregular waveform and unpleasantness, not just its loudness.
Wrong working
'Noise is a loud sound; music is a soft sound.'
Right working
'Noise has an irregular waveform and is unpleasant; music has a regular waveform and is pleasant.'
Do this: Mention the waveform.
Usually costs: The distinction mark.

Exam tips

Define quality using the phrase 'same loudness and same pitch'.
State the cause as 'waveform, which depends on the number and relative intensities of the overtones'.
In a graph item, write which feature you compared: 'same amplitude, same period, different shape'.
Recognising a voice on the telephone is the standard everyday example.

Practice questions on Quality (Timbre) of Sound and Waveforms

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Two recorded sounds differ only in the shape of their waves. The characteristic in which they differ is:
(a) intensity
(b) quality
(c) pitch
(d) loudness
Hint
Shape of the wave.
Answer
(b) quality
Q2 · 1 mark · Very short answerBoard level
What is another name for the quality of sound?
Hint
A French-origin word.
Answer
Timbre.
Q3 · 2 marks · Short answerHarder board level
Why can a blind person recognise people by their voices?
Hint
Waveform.
Answer
Each person's voice has its own pattern of overtones and so its own waveform, giving it a distinct quality (timbre), even at the same pitch and loudness.
Q4 · 2 marks · Short answerHarder board level
A violin string sounds its fundamental at 330 Hz and also its first overtone at twice this frequency. Find the overtone's frequency and its wavelength in air (speed 340 m/s).
Hint
Double, then $λ = \frac{v}{f}$ .
Answer
$f = 2 \times 330 = 660$ Hz; $λ = \frac{340}{660} \approx 0.515$ m.
Q5 · 2 marks · Short answerHarder board level
Draw two displacement–time graphs to show two sounds of the same pitch and loudness but different quality.
Hint
Change only the shape.
Answer
Two graphs with the same period and the same maximum height: one a smooth sine wave, the other a wave of the same period with an irregular (complex) shape within each cycle.
Q6 · 2 marks · Short answerHarder board level
Match each characteristic of sound with what it depends on: loudness, pitch, quality; frequency, waveform, amplitude.
Hint
L-P-Q = A-F-W.
Answer
Loudness: amplitude; pitch: frequency; quality: waveform.
Q7 · 3 marks · Short answerHOTS / competency
A flute and a violin play the same note; on a trace, one complete wave of each takes 1.25 ms and both traces are equally tall. (a) Find the frequency. (b) The violin's trace is more jagged. What does this tell you about its overtones? (c) Would the two notes have the same pitch? Explain.
Hint
Period → pitch; shape → overtones.
Answer
(a) $f = \frac{1}{1.25 \times 1 0 ^{- 3}} = 800$ Hz. (b) The violin produces more (and stronger) overtones, giving a more complex waveform. (c) Yes: both have the same period and so the same fundamental frequency.
Q8 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A note from a tuning fork sounds 'plain' compared with the same note on a sitar.
Reason (R): A tuning fork produces almost no overtones, while a sitar produces many.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
Hint
Overtones set quality.
Answer
(c) Both are true, and (R) explains (A).
Q9 · 3 marks · Short answerHarder board level
A cracked bell and an identical sound bell are struck equally hard. Their notes have about the same pitch and loudness, yet the cracked one sounds harsh. (a) Name the characteristic that differs. (b) Explain what the crack does. (c) Why is this used in testing china and glassware?
Hint
Overtones and waveform.
Answer
(a) Quality (timbre). (b) The crack changes the way the bell vibrates, altering its overtones and so its waveform. (c) Tapping an article and listening for a dull or harsh sound reveals hidden cracks, because the quality of a cracked article differs from that of a sound one.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Quality of sound depends on?Show answer
Waveform (overtones).
2.Other name for quality?Show answer
Timbre.
3.Source of an almost pure note?Show answer
Tuning fork.
4.What sets the pitch of a note with overtones?Show answer
The fundamental frequency.
5.Waveform of noise?Show answer
Irregular.

Quality (Timbre) of Sound and Waveforms: frequently asked questions

What is the quality of sound?

Quality (timbre) is the characteristic that distinguishes two sounds of the same loudness and pitch from different sources, such as the same note on a piano and on a flute.

On what does the quality of sound depend?

On the waveform of the sound, which is decided by the overtones present along with the fundamental and by their relative strengths.

Why do different musical instruments sound different when playing the same note?

Each instrument produces a different set of overtones with different strengths, so its waveform, and hence its quality, is different even at the same pitch and loudness.