Acoustics

A common property of rhotics is that they have a low F3 (around 1800 Hz). Because most versions of rhotics involve movement of the tongue body, which is relatively massive and slow to move, their acoustic properties tend to be very extensive in the time domain.

We illustrate this with the approximants [ɹ] and [l]. Figure 6.6 shows two utterances: ‘to lead’, [tə li:d], and ‘to read’, [tə ɹi:d]. The portion of laterality is marked LAT. Notice that it has more or less clear boundaries on the spectrogram, corresponding to the fairly abrupt onset and offset of lateral airflow. [ɹ], like [j] and [w], has no clear beginning or end. The portion marked RHO surrounds obvious formant transitions where F3 moves downwards, and the point marked ‘1’ is the place where F3 is lowest on the spectrogram.

Without either labialization or valorization, [ɹ] has a low F3. With these secondary articulations, F3 is lowered still further. So one explanation for the secondary articulations is that they enhance the low F3 of [ɹ] and so make it more perceptually salient.