Consonants fricatives

Now we turn to some more problematic cases. In English, the consonants /dh/, /zh/, /ng/ and /h/ are a little more difficult to deal with. There are clearly exactly four unvoiced fricatives /th/, /f/, /s/ and /sh/ in English and of these, /f/ and /s/ have the voiced equivalents /v/ and /z/, and these are unproblematic. The voiced equivalent of /th/ is /dh/ and while /th/ is a common enough phoneme, /dh/ only occurs in very particular patterns. For a start, the number of minimal pairs that occur between /dh/ and /th/ are few real examples include teeth noun, /1 iy th/ and teeth.verb, /t iy dh/, while most are near minimal pairs such as bath /b ae th/ and bathe / b ey dh/ where the quality of the vowel differs. Even if we except /dh/ as a phoneme on this basis, it occurs in strange lexicon patterns. In an analysis of one dictionary, it occurred in only about 100 words out of a total of 25,000. But if we take token count into consideration, we find in fact that it is one of the most common phonemes of all in that it occurs in some of the most common function words... 

The source characteristics of consonants differ depending on the class of sound being produced. All unvoiced sounds use only the noise source nasals and approximants use only the periodic source while voiced obstruents (i.e. voice fricatives, affricates and stops) use both sources. Approximants are generated in much the same way as vowels. Some consonants (such as [h]) can be synthesised in the same way as vowels that is by sending a sound source through the oral cavity resonators. Most other consonants are however more complicated than /h/ because their source is not at one end of the vocal tract. 

Narayanan, S., Alwan, A., and Haker, K. An articulatory study of fricative consonants using mri. Journal of the Acoustical Society of America 98, 3 (1995), 1325-1347. 

Consonants are described in terms of voicing, maimer and place of articulation. The main values manner can take are stop, fricative, nasal, affricate and approximant. 

Many consonant sounds, such as fricatives and stops, have a sound source located in the oral cavity. This is created by the tongne nearing another surface (tiie roof of the moufli. 

The source for vowels and voiced consonants can be generated either as an explicit time-domain periodic function, of the type described in Section 11.4.2, or by an impulse sequence that is fed into a glottal LTI filter. For obstruent sounds a random-noise generator is used. Sounds such as voiced fricatives use both sources. If we adopt the impulse/filter approach, we see that in fact these sources are equivalent to those of the classical impulse/noise LP model (Section 12.6.4). One difference between the impulse/glottal-filter source and LP models is that in the impulse/glottal-filter model the voiced source is... 

Narayanan, S., Alwan, A., and Haker, K. An articulatory study of fricative consonants using MRl. Journal of the Acoustical Society of America 98, 3 (1995), 1325—1347. Narayanan, S., Alwan, A., and Haker, K. Towards articulatory-acoustic models for liquid consonants based on MRl and EPG data. Part I The laterals. Journal of the Acoustical... 

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