Peter Roach
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speaking when it is customary to disguise the speaker's identity. We also find ingressive airflow created by the larynx (see glottalic, implosive) or by the tongue (see click). instrumental phonetics The field of phonetics can be divided up into a number of sub-fields, and the term 'instrumental' is used to refer to the analysis of speech by means of instruments; this may be acoustic (the study of the vibration in the air caused by speech sounds) or articulatory (the study of the movements of the articulators which produce speech sounds). Instrumental phonetics is a quantitative approach - it attempts to characterise speech in terms of measurements and numbers, rather than by relying on listeners' impressions. Many different instruments have been devised for the study of speech sounds. The best known technique for acoustic analysis is spectrography, in which a computer produces a "picture" of speech sounds. Such computer systems can usually also carry out the analysis of fundamental frequency for producing "pitch displays". For analysis of articulatory activity there are many instrumental techniques in use, including radiography (X-rays) for examining activity inside the vocal tract, laryngoscopy for inspecting the inside of the larynx, palatography for recording patterns of contact between tongue and palate, glottography for studying the vibration of the vocal folds and many others. Measurement of airflow from the vocal tract and of air pressure within it also give us a valuable indirect picture of other aspects of articulation. Instrumental techniques are usually used in experimental phonetics, but this does not mean that all instrumental studies are experimental: when a theory or hypothesis is being tested under controlled conditions the research is experimental, but if one simply makes a collection of measurements using instruments this is not the case. intensity Intensity is a physical property of sounds, and is dependent on the amount of energy present. Perceptually, there is a fairly close relationship between physical intensity and perceived loudness. The intensity of a sound depends both on the amplitude of the sound wave and on its frequency. interdental For most purposes in general phonetics it is felt sufficient to describe articulations involving contact between the tongue and the front teeth as 'dental'; however, in some cases it is necessary to be more precise in one's labelling and indicate that the tip of the tongue is protruded between the teeth