This level of representation distinguishes every portion of speech that is recognisably a separate segment of the acoustic waveform or spectrogram. Hence stop closures, release bursts, and aspiration phases will all be segmented separately, as will glottal onset of a vowel, or separate voiced and voiceless portions of a fricative , nasal or stop. The labelling will be done in terms of these well-established articulatory categories, which can be easily related to the labels at higher linguistic levels. The boundaries of some segment types (glides and vowels) will to some extent be arbitrary, and a criterion for homogeneity such as ``sameness of change'' will have to be employed (e.g. in the falling second formant for a palatal glide).