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Fig. 7. A diagram of sonic muscle electromyogram (EMG; 1–5) and acoustic traces from a voluntary disturbance call with a breakdown of dual-waveform sounds produced by each muscle twitch (vertical 1–5). Right and left EMG traces are superimposed on the same trace all deflecting up and the acoustic trace has been simplified to highlight the negative pressure peaks. Note that the 2nd sound waveform (relaxation sound; see text) of a single twitch coincides with the 1st waveform (contraction sound) of the next twitch of that sonic muscle, not the contralateral muscle (compare traces 2 and 4, double arrows, and traces 3 and 5, single arrows). Note also that the first two sound pulses in the call are not reinforced in this manner. Finally, note that the relaxation sounds of the final twitch of the right and left sonic muscles account for the two attenuated sound pulses at the end of the call.





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