Vibrant/Tremulant

The IPA articulatory-oriented description of a trill implies repeated
contact between an active articulator (like the tongue tip) and a passive
articulator (like the alveolar ridge) - this description may need some
modification applied to bilabial trills, and for uvular trills the tongue
dorsum is the passive articulator. Note that contact does not imply complete
closure. From an acoustic point of view, the important thing is a series of
successive rapid decreases and increases in amplitude.

I'm completing an acoustic study of trills in 18 languages, and very often
only the first contact shows signs of complete closure - successive contacts
are weaker, with a more approximant-like acoustic structure, occasionally in
a strong-weak pattern if more than 2 occur. I think that incompletely
occluded trills are not only possible, they occur quite commonly in speech,
even relatively carefully articulated word-lists. Overall, trills occur
about 30% of the time in non-spontaneous samples in languages said to have a
trilled /r/. Other realisations are taps (most common), approximants, and
fricatives.

To transcribe this more open trill sound, you could use the IPA symbol for
the apical trill, i.s. [r], with the subscript 'more open' diacritic (looks
like a small capital T).

One final thing: research suggests that apical trills are made in the same
way as the vibration of the vocal folds - not individual neuromuscular
commands for each contact, but an essentially aerodynamically driven
vibration which is helped along by uneven mechanical displacements in the
vibrating structures (so the vocal folds 'wobble' a bit, with some bits
moving faster than others, generating a rhythm due to the internal
vibration), by the elasticity of the articulators, and by the tension in
e.g. the vocal tract walls, which stores energy. Having an incomplete
closure means that the pressure behind the constriction will reach a lower
maximum, so the elastic return forces in the tongue tip would have to play a
bigger role in maintaining vibration (or you up the oral pressure by
contracting the lungs more).

Mark

+++++++++++++++++++++++++++++++

Mark J. Jones
British Academy Post-doctoral Research Fellow
Department of Linguistics
University of Cambridge
http://www.ling.cam.ac.uk/people/mark/
mjj13@cam.ac.uk

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