what is a speech unit

The Sounds of Speech and Phonemes

In order to really understand phonetics and phonology, it is extremely helpful – if not even essential – to understand how sounds are physically produced and transmitted from speaker to hearer. We will therefore begin by taking a very brief look at the physical reality behind speech sounds and how their characteristics can be measured and explained.

What are speech sounds?

Speech sounds are vibrations that travel through a medium (usually air) by displacing the molecules of this medium, pushing them against one another so that they move each other along in the direction of the hearer(s).

Depending on the consistency of the given medium, the sounds move at different speeds and have varying intensities. This is why we sound different when we speak under normal circumstances from when we try to talk underwater and also why it is completely impossible for speech sounds to travel through a vacuum.

Speech sounds propagate in the shape of waves, similar to the ripples that arise when we throw an object – such as a stone – into the water. The degree of displacement corresponds to the height (amplitude) of the wave. Amplitude in sound waves corresponds to intensity – measured in decibel, or dB for short – which, in turn, corresponds to our subjective impression of loudness.

A pure tone is made up of a single sine wave with a fixed frequency or pitch. This means that each cycle of the wave occurs at regular intervals, so that the same pattern is repeated again and again. The following illustration shows a sine wave with a 300 Hz pitch. Hz is the abbreviation for Hertz , which is the unit in which frequency is measured, so named in honour of the physicist Heinrich Hertz.

However, each speech sound is made up of complex waves,

i.e. a complex mix of different frequencies, where it is far more difficult to recognize any regularity, although these often do exist. It is these regularities in the frequency patterns which allow us to first classify the individual speech sounds phonetically and then establish classes of sounds.

Speech sounds are grouped into language units called phonemes . So what actually are phonemes? Probably the simplest explanation is that a phoneme is an abstract concept used to represent a group of sounds or sound combinations that are similar enough to each other to be preceived as performing the same function in a speech chain.

A phoneme is the smallest contrastive language unit that exists in the speech of all people belonging to the same language community in the form of speech sounds and may bring about a change of meaning.

The phoneme is realized in a speech in the material form of speech sounds of different types.

A phoneme is a functional unit. That means that being opposed to other phonemes in the same phonetic context it is capable of differentiating the meaning: /pɪt/ and /bɪt/, the ‘classic’ /ʃɪp/ and /ʃi:p/, /kap/ and /kat/, etc.

The idea of the phoneme is mainly based upon the fact that we can establish distinctions of meaning between words by replacing certain elements, i.e. sounds, by one another. One way in which we can distinguish the elements that can replace each other is to use a minimal pair test in the way we have just seen in the examples above.

Another way of identifying the inventory of phonemes used in a language is to look at their distribution. Another classic example here is the difference between the occurrences of /h/ & /ŋ/ in English, where the first can never occur at the end of a word – other than in the form of aspiration – and the second never at the beginning.

Of course, the two units we can distinguish in this way also need to be sufficiently different from one another in the way they are produced; otherwise, it would not make any sense. So, returning to our example of the voiceless plosives above, we could say that the absence of voicing and same place and manner of articulation in all examples, including the positional variant after the fricative, makes these sounds sufficiently similar to each other to count them as one phoneme.

On the other hand, if we add the voicing to e.g., the bilabial plosive, we do get a distinction in meaning between minimal pairs like /pɪt/ and /bɪt/, so that we can assume that there are two different phonemes.

In cases where we have instances of the same phoneme, but marginally different realizations, we speak of allophonic variation or allophones . This term comes from the Greek word αλλο, which simply means other . Further examples for this are the occurrence of ‘clear’ (/l/) and ‘dark l’ (/ɫ/) in (many, if not most, accents of) English, where the latter only occurs in the final position and the difference in the pronunciation of /k/ in the words key and coo , where the obstacle for the plosive in the former is made considerably further to the front than for the latter articulation, due to the nature of the following vowel.