Devoicing vs voiceless fricative

Question

I was reading a session in the book Introducing Phonetics and Phonology (by Davenport and Hannahs, 4th ed.) about the articulatory variation in pronouncing the phoneme [w] when it follows voiceless obstruents (p37). I quote the relevant part to my question as follows,

Following voiceless obstruents [w] devoices, and as with [j], this may result in friction being audible, especially after voiceless stops; 't[w̥]it' (devoicing) or t[ʍ]it' (voiceless labial-velar fricative).

My question is, what is the difference between the [w̥] (devoicing) and the [ʍ] (voiceless labial-velar fricative)? Is the difference like that between the 'w' as in 'wet' and the 'wh' as in 'wHite (aspirated h)'?

Thank you so much to whoever is kind enough to pitch in.

Answer 1

Whether there is a meaningful difference between a devoiced approximant and a voiceless fricative is an unsettled question in phonetics. No language is found to make a phonemic contrast between such categories, and phoneticians are divided over whether to admit such things as voiceless approximants.

For those who do, a voiceless approximant is simply a voiceless sound with the same supraglottal articulatory configurations as the homorganic voiced approximant. So, to them, the difference between a voiceless fricative and approximant lies in whether turbulent noise would be produced if the vocal cords were vibrating but everything above the glottis were the same. For those who don't, devoicing an approximant automatically makes it a fricative even without any change above the glottis (Ohala & Solé 2010: 43).

It looks like Davenport & Hannahs are taking the position that any friction necessitates classifying the sound as a fricative, which is odd given I'm sure the devoiced glides in twit, pewter, etc. are almost always accompanied by at least some audible friction. I'd never heard of such a position even though I've read quite a few authors on the matter (see this question).

Answer 2

The usage difference between [w̥] and [ʍ] is primarily in the phonological status of the segment. Given a choice between representing a phoneme with a bare symbol versus with a symbol plus diacritic, the bare symbol is preferred. If the language in question phonemically contrasts [w̥] and [ʍ] then you have to use both. If there is just one always-voiceless phoneme, which contrasts with [w], it is preferred to use [ʍ]. If there is a single phoneme that has both voiced and voiceless allophones, it is preferred to write [w̥] for the voiceless allophone. In English "twit", devoicing is an allophonic variant of the phoneme /w/, therefore preferred usage is to write [w̥]. This is reinforced by consideration of the full set of facts of devoicing, where there is also devoicing or /r, l, j, m, n/ (e.g. "clay, snore, p[j̥]ewter" – there is no bare symbol for voiceless nasals or r so the diacritic is mandatory).

Some dialects of English have a phoneme /ʍ/, found in which, when, whim. This would support using ʍ for the autonomous phoneme and w̥ for the contextual allophone. Since the two sounds never appear in the same context, you can't establish that the sounds are physically the same or physically different.

The usual phonetic treatment of post-voiceless "devoicing" in English words like slip, small, snake, shrimp etc is that there is gestural overlap between the spread glottis of the preceding obstruent and the sonorant phoneme, that is, even the treatment as [w̥] is linguist's over-phonologization of coarticulation – whereas in the case of "which", we have a clearly voiceless phoneme. Davenport & Hannahs are simply engaging in common over-phonologization of articulatory detail.