I am learning phonetics right now […]. I have a question for you: what is the phonetic difference between a voiceless [b̥] and an unaspirated [p] (as in Spanish pájaro)? I think that there is no phonetic difference between the two. If there is no difference between the two, then why do people ever use the symbol [b̥], when [p] is less complicated and means the same thing? Is this only for phonological reasons? I have looked through many linguistics books and I have not found a clear answer to this seemingly simple question.I replied
Voiceless [b̥] is "lenis", whereas [p] is "fortis". Lenis plosives have less intraoral pressure than fortis ones. See Wikipedia, or see my Longman Pronunciation Dictionary (3rd ed.) p. 881.I might have added that this is presumably because in devoiced lenis obstruents the vocal folds adopt the ‘whisper’ position, i.e. are narrowed, unlike the wide open position that they adopt for fortis obstruents. This reduces the flow of air and therefore reduces the amount of turbulence.
The difference is easily noticed in the English pair "touched" vs. "judged" (said in isolation). The final consonants are pronounced without vocal fold vibration in both cases. But the fricative component of the affricate in "touched" is much noisier (more turbulent) than that of the affricate in "judged".
Try it out. If you’re a NS or have a NS-like command of English, you should have no difficulty in hearing and feeling the difference between the voiceless fortis [tʃt] of touched and the devoiced lenis [d̥ʒ̥d̥] of judged. (Sorry I don’t have any instrumental evidence to hand with which to back this up. I assume experimentalists could easily furnish some.)
In English the fortis/lenis contrast is usually reinforced by other factors. Syllable-initially, before a strong vowel at least, fortis plosives have aspiration, while lenis plosives don’t. Even with fricatives there is a clear difference in VOT. Syllable-finally, fortis obstruents trigger pre-fortis clipping (duration reduction) in the preceding vowel (and sonorant, if there is one), and again lenis ones don’t. Between voiced sounds such as vowels, fortis obstruents have no voicing (always excepting AmE-style /t/), while lenis ones generally have voicing.
Since the presence vs. absence of aspiration is perceptually and instrumentally more salient than force of articulation itself, Spanish-style unaspirated initial p can easily be confused with English initial b in a word in isolation.
In some languages (Icelandic is a good example) all plosives are voiceless, but there is a clear contrast of fortis vs. lenis. See here. In my blog I last touched on the topic of fortis and lenis over four years ago, on 4 April 2007. That was before readers could leave comments. Now you can.