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PSY2014S Language Notes
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LANGUAGEPSY2014S
OCTOBER 2023
UCT
Chloe Rose Kyle
,Part 1 Hearing and producing sound – Sound waves, hardware and umwelten
Sound is a form of energy that can be transmitted through a medium, such as air, and can be perceived by
humans as a series of vibrations. It is useful to think of sound as taking the form of a wave, and as each
particular sound wave having a unique frequency of oscillation, and unique amplitude. Frequency is a term
that describes how many times a sound wave oscillates or completes a cycle in one second, which we
call hertz (Hz) (frequency describes the rate at which waves pass a fixed point per unit of time, while the
speed of sound is the distance that a wave travels in a given amount of time, approximately 1220 km/h).
Amplitude characterizes the strength or loudness of a sound wave. It refers to the maximum displacement of
particles from their resting equilibrium as the wave oscillates. Amplitude is quantified in units of decibels
(dB). The decibel is a unit of measurement on a logarithmic scale; thus an increase in sound level by 10 dB
is equivalent to a tenfold increase in sound intensity. The starting point, or zero, on the decibel scale
represents the approximate minimum level of sound that the human ear can detect. A sound registering at 0
dB is just within the threshold of audibility. Conversely, a sound at 100 db is exceptionally loud.
Basic properties of a sound wave Sound waves varying in Hz and dB
Physical attributes map to sensory experience
Frequency determines pitch (high vs low); Amplitude determines volume (loud vs quiet); Sound is not
usually a simple frequency, but complex – it has timbre.
Hearing ranges in several different animal species
The range of human hearing spans a wide spectrum of frequencies and amplitudes. On average, most
humans hear sounds in the range of about 20 Hz to 20,000 Hz. This range is often referred to as the audible
spectrum. The spectrum of sounds can be divided into different frequency regions, not all of which are
audible to humans. These regions include the infrasonic, audible, and ultrasonic ranges. Infrasonic waves
have frequencies below the audible range, typically below 20 Hz, and are often felt rather than heard.
Examples of infrasonic sources include earthquakes and large machinery. Above the audible range lies the
ultrasonic range, consisting of frequencies above 20,000 Hz.
Humans are unable to directly perceive ultrasonic sounds, but bats
and dolphins can detect and use these high-frequency waves for
navigation and communication.
Perceptual and physical properties of sound:
, The perceptual equivalent of frequency is pitch. Pitch represents how the human ear subjectively perceives
the highness or lowness of a musical tone. It is directly correlated with the frequency of the underlying
sound waves—the rate at which the waves oscillate. Higher frequency sounds, like a dog whistle, are
perceived as high-pitched. Their rapid vibrations hit our ears more frequently per second. Conversely, low
frequency sounds like a bass guitar produce fewer oscillations per second, leading to a perception of lower
pitch. The perceptual equivalent of amplitude is loudness. Loudness is the subjective impression of how
strong or weak a sound is, and is affected by amplitude of sound waves. A higher amplitude corresponds to a
louder sound, while a lower amplitude results in a softer sound. For instance, a shouting voice has a larger
amplitude compared to a whisper.
A fundamental wave (1f) and 2nd to 4th harmonics
But that is not all there is to the perceptual experience of sound.
Sounds perceived to have the same pitch and loudness might
nevertheless be very different. The concept of timbre helps us
understand this. Timbre is heavily influenced by the harmonics
(or overtones) of a sound wave. The pure tones produced by musical instruments are rarely just single
frequencies. When a guitar string vibrates, for instance, it generates a fundamental frequency that determines
the pitch we hear. But it also produces additional higher frequencies called harmonics or overtones. These
extra frequencies turn out to be integer multiples of the fundamental - for a 100 Hz fundamental tone, the
harmonics would be 200 Hz, 300 Hz, 400 Hz, and so on. The blend of the fundamental and its harmonics
gives each instrument its distinctive timbre. A violin and trumpet playing the same fundamental pitch sound
completely different because of the different harmonic spectra generated by their vibrating strings and air
columns. The richness of an instrument’s sound depends on the number and relative strength of the audible
harmonics. They add ‘texture’ and ‘color’ to the fundamental tone. Even though we classify our auditory
experiences according to pitch, volume, and timbre, sounds are highly changeable. Imagine being in a room
at a party, with lots of people moving around and talking to each other, and to you. Sounds will come at you
in varying degrees of loudness, pitch, and direction, but you will ordinarily be able to cope with the dynamic
nature of this sound, detecting a friend’s voice among the tumult, and knowing where she is located in the
room, and where she is moving to, just from the sounds.
The concept of umwelt
We have just seen that the hearing and voicing ranges across species are markedly different.
• Ranges vary greatly based on evolutionary adaptations
• Many species detect frequencies outside human range
• Bats use ultrasound, elephants infrasound
This has profound implications.
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