3 Phonetics: The Sounds of Speech

The Sounds of Speech

Learning Outcomes

After studying this chapter, you should be able to discuss:

  • the three aspects of speech that make up phonetics
  • the International Phonetic Alphabet
  • the theories of speech perception


Think about how you might describe the pronunciation of the English word cat. If you had to tell someone what’s the first sound of the word, what would you tell them?

image of a catSaying “The first sound of cat is a ‘k’ sound” will not be sufficient. Why do you think it’s insufficient? (Hint: can you think of other English words that are written with a “k” but don’t have this same sound? Can you think of other English words that have this sound but aren’t written with a “k”?)

Read this poem out loud:

“Hints on pronunciation for foreigners

by Anonymous (see note)

I take it you already know
of tough and bough and cough and dough.
Others may stumble, but not you,
On hiccough, thorough, lough* and through.
Well done! And now you wish, perhaps,
To learn of less familiar traps.

Beware of heard, a dreadful word
That looks like beard and sounds like bird.
And dead-it’s said like bed, not bead.
For goodness sake, don’t call it deed!
Watch out for meat and great and threat.
They rhyme with suite and straight and debt.

A moth is not a moth in mother,
Nor both in bother, broth in brother,
And here is not a match for there,
Nor dear and fear for pear and bear.
And then there’s dose and rose and lose
Just look them up–and goose and choose.
And cork and work and card and ward.
And font and front and word and sword.
And do and go, then thwart and cart.
Come, come I’ve hardly made a start.

A dreadful language? Man alive,
I’d mastered it when I was five!

*Laugh has been changed to lough, which is pronounced “lock” and is suggested as the original spelling here.

NOTE: For interesting tidbits about the origins of this poem, see the comments on this blog post.

What does this poem show us about the need for phonetic description?

In addition to variations of pronunciation of the same groupings of letters, the same word, with the same spelling, can have different pronunciations by different people (for example, because of different dialects). The point here is that English spelling does not clearly and consistently represent the sounds of language. In fact, English writing is infamous for that problem. There are lots of subtle differences between pronunciations, and we need a very systematic and formal way to describe how every sound is made. That’s what phonetics is for.

What is Phonetics?

Phonetics looks at human speech from three distinct but interdependent viewpoints:

  • Articulatory phonetics (The Production of Speech)…studies how speech sounds are produced.
  • Auditory or Perceptual phonetics (The Perception of Speech)…studies the way in which humans perceive sounds.
  • Acoustic phonetics (The Physics of Speech)…studies the physical properties of speech sounds.

This video gives an overview of these three different phonetics viewpoints:

Articulatory Phonetics

Articulatory phonetics focuses on how we produce speech. When people play a clarinet or similar instrument, they can make different sounds by closing the tube in different places or different ways. Human speech works the same way: we make sound by blowing air through our tube (from the lungs, up the throat, and out the mouth and/or nose), and we change sounds by changing the way the air flows and/or closing the tube in different places or in different ways.

There are three basic ways we can change a sound, and they correspond to three basic phonetic “features”. (The way I am categorizing features here may be different than what’s presented in some readings; there are lots of different theories about how to organize phonetic features.) They are as follows:

  • We can change the way the air comes out of our lungs in the first place, by letting our vocal folds vibrate or not vibrate. This is called voicing.
  • We can change the way that we close the tube—for example, completely closing the tube will create a one kind of sound, whereas than just narrowing it a little to make the air hiss will create a different kind of sound. This aspect of how we make sound is called manner of articulation.
  • We can change the place that we close the tube — for example, putting our two lips together creates a “closure” further up the tube than touching our tongue to the top of our mouth does. This aspect of how we make sound is called place of articulation (“the place that you move to close your mouth”).

Articulatory phonetics involves some basic understanding of the anatomy of speech i.e. the lungs, the larynx, and the vocal tract.

The Anatomy of Speech

Three central mechanisms are responsible for the production of speech:

  • Respiration: The lungs produce the necessary energy in form of a stream of air.
  • Phonation: The larynx serves as a modifier to the airstream and is responsible for phonation.
  • Articulation: The vocal tract modifies and modulates the airstream by means of several articulators.


Before any sound can be produced at all, there has to be some form of energy. In speech, the energy takes the form of a stream of air normally coming from the lungs. Lung air is referred to as pulmonic air.

The respiratory system is used in normal breathing and in speech and is contained within the chest or thorax. Within the thoracic cavity are the lungs, which provide the reservoir for pulmonic airflow in speech.

The lungs are connected to the trachea, by two bronchial tubes which join at the base of the trachea. At the lower end of the thoracic cavity we find the dome-shaped diaphragm which is responsible for thoracic volume changes during respiration. The diaphragm separates the lungs from the abdominal cavity and lower organs.


The larynx consists of a number of cartilages which are interconnected by complex joints and move about these joints by means of muscular and ligamental force. The larynx has several functions:

  • the protective function
  • the respiratory function
  • the function in speech

The primary biological function of the larynx is to act as a valve that closes off air from the lungs and prevents foreign substances from entering the trachea. The principal example of this protective function of the larynx is the glottal closure, during which the laryngeal musculature closes the airway while swallowing.

During respiration, the larynx controls the air-flow. Normally, humans breathe about 15 times per minute, but breathing for speech has a different pattern than normal breathing. Speaking may require a deeper, more full breath than regular inhalation, and such inhalation would be done at different intervals. A speaker’s breathing rate is no longer a regular pattern of fifteen to twenty breaths a minute, but rather is sporadic and irregular, with quick inhalation and a long, drawn out, controlled exhalation (exhaling can last 10 to 15 seconds). The result is various types of phonation:

  • No voice
  • Normal voice
  • Whisper
  • Breathy
  • Creaky
  • Falsetto

The most important effect of vocal fold action is the production of audible vibration – a buzzing sound, known as voice or vibration. Each pulse of vibration represents a single opening and closing movement of the vocal folds. The number of cycles per second depends on age and sex. Average male voices vibrate at 120 cycles per second, while women’s voices average 220 cycles per second.


Once the air passes through the trachea and the glottis, it enters a long tubular structure known as the vocal tract. Here, the airstream is affected by the action of several mobile organs, the active articulators. Active articulators include the lower lip, tongue, and glottis. They are actively involved in the production of speech sounds.image showing the articulatorsThe active articulators are supported by a number of passive articulators, specific organs or locations in the vocal tract which are involved in the production of speech sounds but do not move. These passive articulators include the palate, alveola, ridge, upper and lower teeth, nasal cavity, velum, pharynx, epiglottis, and trachea. The production of speech sounds, or phonemes (sometimes shortened to phones), through these organs is referred to as articulation. (Note which parts in the diagram above are not mentioned here!)

As you think about how the vocal tract is used to make the sounds of language, remember that these same structures can also make other sounds that are not a part of the English language. However, just because they aren’t used in English doesn’t mean that they aren’t used for speaking other languages!

Check your Knowledge


Phonetics helps us to identify how different sounds are articulated. For example, we can use phonetics to help us describe how to make the sounds of consonants and vowels, which can help us to correctly pronounce words. The individual sounds that letters make are called phones or segments.

The following videos demonstrate how consonants and vowels are articulated in North American English:

Introduction to Articulatory Phonetics licensed CC BY.


Introduction to Articulatory Phonetics licensed CC BY.

The International Phonetic Alphabet

Understanding how different sounds are pronounced is an important aspect of using, learning, understanding, and studying language. The International Phonetic Alphabet (IPA) is an alphabetic system of phonetic notation devised by the International Phonetic Association in the late 19th century as a standardized representation of speech sounds in written form. The general principle of the IPA is to provide one letter for each distinctive sound segment represented in every language in the world. The IPA is used by lexicographers, foreign language students and teachers, linguists, speech–language pathologists, singers, actors, and constructed language creators and translators.

Current IPA Chart
IPA Chart licensed CC BY SA.

The IPA is designed to represent those qualities of speech that are part of sounds in oral language: phones, phonemes, intonation, and the separation of words and syllables.

IPA symbols are composed of one or more elements of two basic types, letters and diacritics. For example, the sound of the English letter ⟨t⟩ may be transcribed in IPA with a single letter, [t], or with a letter plus diacritics, [t̺ʰ], depending on how precise one wishes to be. Slashes are used to signal phonemic transcription; thus /t/ is more abstract than either [t̺ʰ] or [t] and might refer to either, depending on the context and language.

The video below provides and introduction to the IPA.

Introduction to Articulatory Phonetics licensed CC BY.


The chart might look complex, and it’s ok if you don’t fully understand it right now. In fact, while this chart can be very useful for a variety of circumstances, it isn’t necessarily required. This video shares an interesting perspective on learning the IPA for people learning to speak English:

Thankfully, there are some great tools that can help you to understand phonetics and make use of the IPA, even if you don’t really understand it. For example, this website shows the sounds from American English represented with the IPA. In addition, you can type in any English word and get the phonetic conversion!


Practice using the Phonetic Conversion tool on EasyPronunciation.com to create the phonetic conversions for about 10 different words, just to get a feel for what some common phonetic spellings look like.

Suprasegmental Features

The IPA chart lists the sounds needed to vocalize all human sounds. These sounds are the basic segments of speech. Together, they form syllables, words, and eventually sentences. In addition to understanding how the basic segments of speech are articulated, there are a number of additional features of speech, known as suprasegmental or prosodic features. The most important suprasegmental features are:

  • loudness
  • pitch
  • length

In a spoken utterance ,the syllables are never produced with the same intensity. Some syllables are unstressed (weaker), while others are stressed (stronger).

Adopting anatomical and physiological criteria, phoneticians define segmental (i.e. the sounds of speech) and suprasegmental (e.g. tonal phenomena).


Food for Thought

Given what you’ve learned so far about the articulation of speech, consider the activity below and think about the distinction that could be made between speech and communication.

Activity 1

The video below suggests that chimpanzees can speak. Is that true? Hint: Think about anatomical reasons that chimpanzees may or may not be able to speak.

Much research has been conducted to determine if primates can speak. The following articles have different ideas about this topic:

While we are pretty familiar with parrots speaking, you might also be interested in learning about other animals who seem to have learned to “speak”:

Kishik the Elephant

Orca Whales

Cats & Dogs


Auditory Phonetics

Auditory phonetics investigates the processes underlying human speech perception. The starting point for any auditory analysis of speech is the study of the human hearing system i.e. the anatomy and physiology of the ear and the brain.

Since the hearing system cannot react to all features present in a sound wave, it is essential to determine what we perceive and how we perceive it. This enormously complex field is referred to as speech perception.

This area is not only of interest to phonetics but is also the province of experimental psychology.

The Auditory System

The auditory system consists of three central components:

  • The outer ear – modifies the incoming sound signal and amplifies it at the eardrum.
  • The middle ear – improves the signal and transfers it to the inner ear.
  • The inner ear – converts the signal from mechanical vibrations into nerve impulses and transmits it to the brain via the auditory nerve.
diagram of ear
Ear licensed CC BY NC SA

Outer Ear

The outer ear consists of the visible part, known as the auricle or pinna, and of the interior part. The auricle helps to focus sound waves into the ear, and supports our ability to locate the source of a sound.

From here, the ear canal, a 2.5 cm long tube, leads to the eardrum.The main function of the ear canal is to filter out tiny substances that might approach the eardrum. Furthermore, it amplifies certain sound frequencies(esp.between 3, 000 and 4, 000 Hz) and protects the eardrum from changes in temperature as well as from damage.

Middle Ear

Behind the eardrum lies the middle ear, a cavity which is filled with air via the Eustachian tube (which is linked to the back of the nose and throat).

The primary function of the middle ear is to convert the sound vibrations at the eardrum into mechanical movements. This is achieved by a system of three small bones, known as the auditory ossicles. They are named after their shape:

  • the malleus (hammer)
  • the incus (anvil)
  • the stapes (stirrup)

When the eardrum vibrates due to the varying air pressure caused by the sound waves, it causes the three small bones, the so-called ossicles, to move back and forth. These three bones transmit the vibrations to the membrane-covered oval opening of the inner ear. Together, the ossicles function as a kind of leverage system, amplifying the vibrations by a factor of over 30 dB by the time they reach the inner ear.

Inner Ear

The inner ear contains the vestibular organ with semi-circular canals, which control our sense of balance, and the cochlea, a coiled cavity about 35 mm long, resembling a snail’s shell. The cochlea is responsible for converting sounds that enter the ear canal from mechanical vibrations into electrical signals. The mechanical vibrations are transmitted to the oval window of the inner ear via the stapes (stirrup). The conversion process, known as transduction, is performed by specialized sensory cells within the cochlea. The electrical signals, which code the sound’s characteristics, are carried to the brain by the auditory nerve.

The cochlea is divided into three chambers by the basilar membrane. The upper chamber is the scala vestibuli and the bottom chamber is the scala tympani. They are both filled with a clear viscous fluid called perilymph. Between these two chambers is the cochlea duct, which is filled with endolymph.

On the basilar membrane rests the organ of Corti which contains a systematic arrangement of hair cells which pick up the pressure movements along the basilar membrane where different sound frequencies are mapped onto different membrane sites from apex to base.

The hair cells bend in wave-like actions in the fluid and set off nerve impulses which then pass through the auditory nerve to the hearing center of the brain. Short hair cell fibres respond to high frequencies and longer fibres respond to lower frequencies.

Speech Perception

Since the hearing system cannot react to all features present in a sound wave, it is essential to determine what we perceive and how we perceive it. This enormously complex field is referred to as speech perception. Two questions have dominated research:

  • Acoustic cues: Does the speech signal contain specific perceptual cues?
  • Theories of Speech Perception: How can the process of speech perception be modeled?

A further important issue in speech perception, which is also the province of experimental psychology, is whether it is a continuous or – as often assumed – a categorical process.

Acoustic Cues

The speech signal presents us with far more information than we need in order to recognize what is being said. Yet, our auditory system is able to focus our attention on just the relevant auditory features of the speech signal – features that have come to be known as acoustic cues:

  • Voice Onset Time (VOT): the acoustic cue for the voiceless/voiced distinction
  • F2-transition : the acoustic cue for place of articulation
  • Frequency cues

The importance of these small auditory events has led to the assumption that speech perception is by and large not a continuous process, but rather a phenomenon that can be described as discontinuous or categorical perception.

Voice Onset Time

The voice onset time (VOT) is the point when vocal fold vibration starts relative to the release of a closure, i.e.the interval of voicing prior to a voiced sound. It is crucial for us to discriminate between clusters such as [ pa ] or [ ba ]. It is a well-established fact that a gradual delay of VOT does not lead to a differentiation between voiceless and voiced consonants. Rather, a VOT-value of around 30 msecs serves as the key factor. In other words:

  • If VOT is longer than 30 msecs, we hear a voiced sound, such as [ ba ],
  • If VOT is shorter than 30 msecs, the perceptual result is [ pa ].

F2 Transition

The formant pattern of vowels in isolation differs enormously from that of vowels embedded in a consonantal context. If a consonant precedes a vowel, e.g. ka/ba/etc, the second formant (F2) seems to emerge from a certain frequency region, the so-called F2-locus. It seems that speech perception is sensitive to the transition of F2 and that F2-transition is an important cue in the perception of speech. In other words, the F2 frequency of the vowel determines whether or not the initial consonant sound is clear.

Frequency Cues

The frequency of certain parts of the sound wave helps to identify a large number of speech sounds. Fricative consonants, such as [s], for example, involve a partial closure of the vocal tract, which produces a turbulence in the air flow and results in a noisy sound without clear formant structure spreading over a broad frequency range. This friction noise is relatively unaffected by the context in which the fricative occurs and may thus serve as a nearly invariant cue for its identification.

However, the value of frequency cues is only relative since the perception of fricatives is also influenced by the fricative’s formant transitions.

Theories of Speech Perception

Speech perception begins with a highly complex, continuously varying, acoustic signal and ends with a representation of the phonological features encoded in that signal. There are two groups of theories that model this process:

  • Passive theories: This group views the listener as relatively passive and speech perception as primarily sensory. The message is filtered and mapped directly onto the acoustic-phonetic features of language.
  • Active theories: This group views the listener as more active and postulates that speech perception involves some aspects of speech production; the signal is sensed and analysed by reference to how the sounds in the signal are produced.
Passive Theories

Passive theories of speech perception emphasize the sensory side of the perceptual process and relegate the process of speech production to a minor role. They postulate the use of stored neural patterns which may be innate. Two influential passive theories have emerged:

  • The Theory of Template Matching
    Templates are innate recognition devices that are rudimentary at birth and tuned as language is acquired.

  • The Feature Detector Theory
    Feature detectors are specialized neural receptors necessary for the generation of auditory patterns.

Active Theories

Active theories assume that the process of speech perception involves some sort of internal speech production, i.e. the listener applies his articulatory knowledge when he analyzes the incoming signal. In other words: the listener acts not only when he produces speech, but also when he receives it.

Two influential active theories have emerged:

  • The Motor Theory of Perception
    According to the motor theory, reference to your own articulatory knowledge is manifested via direct comparison with articulatory patterns.

  • The Analysis-by-Synthesis Theory
    The analysis-by-synthesis theory postulates that the reference to your own articulation is via neurally generated auditory patterns.

The McGurk Effect

The McGurk effect is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. The visual information a person gets from seeing a person speak changes the way they hear the sound. If a person is getting poor quality auditory information but good quality visual information, they may be more likely to experience the McGurk effect.

Activity 2

You are invited to participate in a little experiment on perception. In the video below you see a mouth speaking four items. Your tasks are the following:

  1. Watch the mouth closely, but concentrate on what you hear.
  2. Now close your eyes. Play the clip again.
  3. What did you perceive when you saw and heard the video clip? What did you perceive when you just heard the items?

Acoustic Phonetics

Acoustic phonetics studies the physical properties of the speech signal. This includes the physical characteristics of human speech, such as frequencies, friction noise, etc.

There are numerous factors that complicate the straightforward analysis of the speech signal, for example, background noises, anatomical and physiological differences between speakers, etc.

These and other aspects contributing to the overall speech signal are studied under the heading of acoustic phonetics.

Sound Waves

Sound originates from the motion or vibration of a sound source, e.g. from a tuning fork. The result of this vibration is known as a simple sound wave, which can be mathematically modeled as a sine wave. Most sources of sounds produce complex sets of vibrations. They arise from the combination of a number of simple sound waves.

Speech involves the use of complex sound waves because it results from the simultaneous use of many sound sources in the vocal tract.

The vibration of a sound source is normally intensified by the body around it. This intensification is referred to as resonance. Depending on the material and the shape of this body, several resonance frequencies are produced.

Simple sound waves are produced by a simple source, e.g. the vibration of a tuning fork. They are regular in motion and are referred to as periodic. Two properties are central to the measurement of simple sound waves: the frequency and the amplitude.

Practically every sound we hear is not a pure tone but a complex tone; its wave form is not simple but complex. Complex wave forms are synthesized from a sufficient number of simple sound waves. There are two types of complex wave forms:

  • periodic complex sound waves
  • aperiodic complex sound waves

Speech makes use of both kinds. Vowels, for example, are basically periodic, whereas consonants range from periodic to aperiodic:

  • the vowel [ a ], periodic
  • the consonant [ n ], periodic
  • the consonant [ s ], aperiodic
  • the consonant [ t ], aperiodic


The sound wave created by a sound source is referred to as the fundamental frequency or F0 (US: “F zero”).

On a musical instrument, F0 is the result of the vibration of a string or a piece of reed. In speech, it is the result of vocal fold vibration.

In both cases, F0 is a complex sound wave which is filtered (intensified and damped) by numerous parts of the resonating body. The resulting bundles of resonance frequencies or harmonics are multiples of F0. They are called formants and are numbered F1, F2 and so on.

In speech, these formants can be associated with certain parts of the vocal tract, on a musical instrument they are multiples of F0. For example, on an oboe F0 is the result of the vibration of the reed. This fundamental frequency is intensified (and dampened) by the resonating body. As a result, a number of harmonics or formant frequencies are created as multiples of the frequency of F0.

This video explains how understanding resonance can help singers improve their performance:


The study of phonetics certainly illustrates why linguistics is considered a science. Language is complex, and an important part of understanding how language works is understanding  how our anatomy helps us to create and understand language.

The study of phonetics can help us to understand language acquisition (both by children and second language learners), speech disorders, speech detection technology, voice recognition, and more. Though this chapter might have felt a bit overwhelming, I hope that you come away with a basic understanding of phonetics, as well as the understanding that phonetics is an important building block in our study of language and culture.


This chapter is licensed CC-BY-SA.

Content adapted from the following:

VLC102 – Speech Science by Jürgen Handke, Peter Franke, Linguistic Engineering Team under CC BY 4.0

International Phonetic Alphabet” licensed under CC BY SA.

McGurk Effect” licensed under CC BY SA.

Introduction to Linguistics by Stephen Politzer-Ahles. CC-BY-4.0.



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