The acoustics of labiovelar approximants

The portion labelled ‘LV approx’ is the portion where there are clear signs of labiovelar approximation. As the lips are rounded and the tongue back is raised towards the velum, the first formant moves downwards ([u], like [i], has a low F1), while F2 gets much lower, because of both tongue backing and lip-rounding. As the approximations are made, the vocal tract narrows, and the amplitude diminishes: it can be seen from the spectrogram that there is almost no visible information much above 1000 Hz

Notice that for both [j] and [w] the formants are moving throughout the labelled portions. The point labelled ‘1’ for [j] is where F2 is highest and F1 is lowest: this is the most ‘[j]-like’ part of the portion. The point labelled ‘1’ for [w] is where F1 and F2 are lowest: the most ‘[w]-like’ part of the portion.

Auditorily, as visually, the phonetics associated with [j] and [w] is distributed over a long stretch of time: this is a recurrent property of approximants, and it is most clearly visible when we look at spectrograms, or listen to very short stretches of speech where the ‘blending’ of sounds into one another is very obvious. Notice that the formants are constantly moving: there is no ‘steady state’, because in making an approximant, the articulators are gliding into and out of a kind of articulatory target.