Sound Waves: Characteristics and Applications · Lesson 9 of 14
Human Perception of Sound
“Pitch, loudness and timbre describe how humans experience measurable wave properties.”
• Distinguish physical wave properties from human perception. • Define pitch and relate it to frequency. • State the human audible range. • Define infrasonic and ultrasonic frequency ranges. • Explain loudness and its relation to amplitude. • Distinguish loudness from intensity. • Describe tone musical note timbre and octave. • Summarise the basic pathway of hearing in the human ear.
Frequency, wavelength, amplitude and speed are measurable physical quantities. Human hearing transforms these physical vibrations into subjective experiences such as pitch and loudness.
Human Perception of Sound
Pitch
The way humans perceive frequency.
A whistle or siren is commonly described as high-pitched, while thunder or an aircraft rumble is described as low-pitched. In general, higher frequency is perceived as higher pitch and lower frequency as lower pitch, although the exact relationship between physical frequency and perception is not simply linear.
Human Hearing Range
The typical human audible range extends from about 20 Hz to 20,000 Hz, or 20 kHz. The exact range varies between people and tends to decrease with age.
Sound waves with frequencies below 20 Hz.
Sound waves with frequencies above 20 kHz.
Humans normally cannot hear infrasonic or ultrasonic frequencies. Some animals can: dogs, cats, bats and dolphins can detect ultrasound, while elephants can detect infrasound.
Loudness
The human perception associated with sound amplitude; larger-amplitude sounds are generally heard as louder.
Loudness decreases as the listener moves farther from the source because sound intensity decreases with spreading. Intensity is a measurable physical quantity, whereas loudness depends on the listener's hearing ability.
Sound level is commonly expressed in decibels. The chapter gives rustling leaves at a few decibels, normal conversation at about 60 dB and firecrackers as capable of exceeding 100 dB.
Noise and Hearing
Unwanted or harmful sound.
Long exposure to excessive sound can affect health, sleep and hearing. Hearing loss can be investigated using audiograms. A hearing aid commonly contains a microphone, amplifier and speaker.
How the Ear Detects Sound
Incoming sound causes the eardrum to vibrate. Tiny bones amplify the vibrations, and the cochlea converts them into electrical signals that travel to the brain. Two ears also help the brain estimate the direction of a source using very small arrival-time differences.
Tone, Musical Note and Timbre
A sound consisting essentially of a single frequency, such as the nearly single-frequency sound from a tuning fork.
A sound containing a fundamental frequency together with higher frequencies called overtones.
The quality that allows different instruments or voices to sound different even when they play the same note at the same loudness.
The shape, material and construction of an instrument influence the pattern and strengths of its overtones, producing its characteristic timbre. Indian instruments such as the sarangi, sitar and veena can use additional strings to enrich the sound.
The interval between two notes whose fundamental frequencies differ by a factor of two.
For example, 200 Hz and 400 Hz are separated by an octave. The chapter also highlights C. V. Raman's acoustic study of Indian percussion instruments. The central black patch called syaahi on instruments such as tabla or mridangam alters membrane vibration and contributes to their rich sound.
Keep physical quantity and perception separate: frequency is measured in hertz and is perceived mainly as pitch; amplitude is a physical wave property and is perceived mainly as loudness; intensity measures energy flow and is not identical to loudness.
Quiz
Which description best matches Pitch?
Which description best matches Infrasonic Waves?
Which term matches this description: The way humans perceive frequency.
Which term matches this description: Sound waves with frequencies below 20 Hz.
Which statement is a key takeaway from this lesson?
Practice Problems
- State the usual human hearing range.
- Classify 10 Hz and 30 kHz as infrasonic, audible or ultrasonic.
- Explain the difference between frequency and pitch.
- Explain the difference between intensity and loudness.
- Distinguish tone, musical note and timbre.
- What does it mean for two notes to be one octave apart?
Key Takeaways
• Humans perceive different properties of sound as pitch, loudness and quality or timbre. • Pitch is mainly related to frequency: higher frequency produces a higher-pitched sound. • Loudness is strongly influenced by the amplitude and intensity of the sound reaching the ear. • Timbre allows us to distinguish sounds produced by different sources even when their pitch and loudness are similar.