Speech segments are classified by abstract classes, concrete sounds, and transition units

Evidence

Phoneme: an abstract unit of speech, a class that includes all such instances that don’t cause meaning to change if used instead of another member of the same phoneme class. In this sense, the phoneme is a minimal linguistic unit. When a phoneme is referred to in text, the symbols are enclosed in a pair of slashes, as in /i/. • Phone (speech sound): a concrete unit of speech sound, including details of producing the sound. Based on context, the properties of phones vary due to coarticulation, which is the continuity of articulatory movements and ease of pronounciation causing the change. Also based on context, a phoneme can be pronounced differently, and the alternative pronunciations for a phoneme are called allophones. Sequences of phones constitute syllables that are further composed into words, phrases, and so on. When the text discusses phones, they are referred to by enclosing them within square brackets, as in [i]. • Diphone: a unit providing another view to a sequence of phones. While a phone covers the time span from the previous phone boundary to the next, a diphone is understood as the time span from the middle of a phone to the middle of the next one, including the phone transition in the centre of the diphone. A phone boundary is typically the moment of the fastest transition between phones or the beginning of a transition. The duality of phones and diphones reflects the fact that some phones are quite static, carrying information in their central part, while in other cases the transition (diphone nucleus) carries the main phonetic information. • Triphone: a temporal unit that covers two diphones. Longer units include more coarticulation within them, which is favourable in speech technology applications (recognition and synthesis), but on the other hand the combinatory explosion of the number of possible units makes them more problematic than short units. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 571

Categorization

• DEFINE: Clear technical definitions distinguishing phoneme, phone, allophone, diphone, and triphone units of speech analysis.