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Frequency and amplitude are physics; pitch and loudness are how our ears experience them.
- Pitch is how the frequency of a sound is perceived.
- Shrill sounds (whistle, siren) have high pitch (higher frequency).
- Deep sounds (thunder, a rumble) have low pitch (lower frequency).
- Loudness is how the amplitude of a sound is perceived.
- Larger-amplitude sounds are heard louder ; loudness falls with distance.
- Loudness is commonly measured in decibels (dB) and depends on the listener’s hearing.
In this Activity, we will experiment as a class demonstration to listen to how sound changes across different frequencies.
- Open a mobile app that can generate sounds.
- Set the frequency to 100 Hz, play it, and listen carefully.
- Increase the frequency in steps of 100 Hz up to 1000 Hz and describe the change.
- Then lower the frequency from 50 Hz toward 20 Hz until you can no longer hear it.
- Humans hear roughly 20 Hz to 20 kHz (the audible range).
- Infrasonic waves are below 20 Hz (elephants can detect them).
- Ultrasonic waves are above 20 kHz (dogs, cats, bats and dolphins can detect them).
Loudness is measured in decibels (dB) : rustling leaves are a few dB, normal talk about 60 dB, and firecrackers can exceed 100 dB. Unwanted sound is noise ; prolonged exposure to loud sound causes noise pollution and can lead to hearing loss, tested with audiograms. Hearing aids (a microphone, amplifier and speaker) help those with hearing loss.
- Won India’s first Nobel Prize in Science for discovering the Raman Effect in light.
- Also studied the acoustics of Indian percussion instruments like the tabla and mridangam to understand their rich sound.
A tone is a single-frequency sound; a musical note is a fundamental frequency plus higher overtones that make it rich. Even at the same note and loudness, a flute, ektara and tabla sound different — this quality is timbre . An octave is the interval between two notes where one has double the frequency of the other (e.g. 200 Hz and 400 Hz).
- Pitch — the way the human ear perceives the frequency of a sound.
- Loudness — the way the ear perceives the amplitude of a sound, measured in decibels.
- Audible range — the frequencies a human ear can hear, about 20 Hz to 20 kHz.
- Ultrasonic and infrasonic waves — sound above 20 kHz and below 20 Hz, outside the human audible range.
