Fig. 8. A model of the interaction between the file and plectrum of a cricket during sound production. In both A and B, the phase of the interaction between the file and the plectrum during the cycle is referred to the lowest point in the cycle of oscillation of the file, termed 270°. The horizontal arrows show the directions of the closing movements of the two wings. The horizontal dashed lines act as references for the relative positions of the file and plectrum at the moment of impact and the dotted lines show the up-and-down oscillation of the tips of the file teeth. In A, is it assumed that a file tooth is engaged, that an impulse is given throughout the first half-cycle (270–90°) and that the plectrum is detached from the file during the second half-cycle (90–0°). At the start of the next cycle (right-hand side), the plectrum engages with the next file tooth (shown by denser stipple). In B, where the amplitude of oscillation is larger, file teeth are engaged and an impulse is given only during the first one-third of the cycle (270–30°); during the later two-thirds of the cycle, the plectrum is detached from the file (30–270°). Sounds will be produced by the ‘escapement’ at both the impact and release of the plectrum (shown by asterisks in A and C or filled circles in B and C). In A, this will give rise to sounds at multiples of twice the frequency of oscillation and in B to asymmetrical waveforms of the type seen in Fig. 5E. FD is the dominant frequency of the song pulse.
