Question
What is the difference between noise and music? How do frequency and amplitude explain pitch and loudness?
Solution — Step by Step
Every sound is a vibration — something moves back and forth, and that disturbance travels through air to reach your ear. The pattern of that vibration is what separates music from noise.
Music comes from regular, periodic vibrations — the vibrating object repeats its pattern at equal time intervals. A guitar string plucked cleanly does this. Noise comes from irregular, non-periodic vibrations — no fixed pattern, no repeating cycle. A crumpled paper, a car horn in traffic, chalk screeching on a blackboard.
Frequency is how many vibrations happen per second (measured in Hz). High frequency = more vibrations per second = high pitch (shriller sound). Low frequency = fewer vibrations per second = low pitch (deeper sound).
A female voice typically has higher frequency than a male voice. A whistle (high pitch) has much higher frequency than a drum (low pitch).
Amplitude is how far the vibrating object moves from its rest position — basically the “size” of each vibration. Large amplitude = more energy = loud sound. Small amplitude = less energy = soft sound.
When you tap a table lightly vs. bang it hard, the frequency stays roughly the same but the amplitude changes — that’s why one is louder.
| Property | Determined by | Unit |
|---|---|---|
| Pitch | Frequency | Hz |
| Loudness | Amplitude | — |
| Noise vs Music | Pattern (irregular vs regular) | — |
Music = regular vibrations with controlled frequency and amplitude. Noise = irregular vibrations with no fixed pattern.
Why This Works
Think of frequency as the rhythm of the vibration. A regular rhythm means your ear can process it as a note with a definite pitch. An irregular rhythm — random jumps, no pattern — is what your brain registers as unpleasant noise.
Amplitude is simply the energy of the vibration. The more violently something vibrates, the more air molecules it displaces, the more pressure reaches your ear, and the louder it sounds. This is why a sound doubles in perceived intensity when amplitude increases significantly — more energy, more disturbance.
The distinction between noise and music isn’t always sharp in everyday life — a very loud music system can become noise for your neighbour — but physically, the definition is precise: regularity of vibration.
Alternative Method
Use a graphical approach — this is how your NCERT textbook shows it and is worth knowing for diagrams in exams.
Draw a sound wave on a time-amplitude graph:
- Music: a smooth, repeating wave — peaks and troughs at equal intervals. The shape repeats exactly.
- Noise: a jagged, random graph — no two sections look the same, peaks appear at irregular intervals.
When comparing pitch on such a graph: two waves with the same amplitude but different frequencies — the one with more cycles crammed into the same time span has higher pitch.
When comparing loudness: two waves with same frequency but different amplitudes — the taller wave is louder.
This graphical method makes NCERT diagram-based questions straightforward.
Common Mistake
Many students write: “Loud sounds have high frequency and soft sounds have low frequency.” This is wrong — loudness depends on amplitude, not frequency. Frequency controls pitch only. A low-pitched (low frequency) foghorn can be extremely loud (large amplitude). A high-pitched whistle can be very soft (small amplitude). These are independent properties. Mixing them up costs marks on both MCQs and short-answer questions in CBSE Class 8 and 9 exams.
A quick memory trick: Frequency → Pitch (both have a “high/low” quality), Amplitude → Loudness (Amplitude = how Large the vibration is). Two separate properties, two separate letters to remember.