Fig. 2. (A) Oscillogram of two 3.2 kHz tone bursts, each of four cycles duration. An asymmetric waveform was generated so as to introduce second and third harmonic distortion. (B) Oscillogram to show the effect of electronic filtering by Canary software on the waveform shown in A. Frequencies below 5 kHz were filtered out; an oscillation at this frequency built up before the start of the broad-band waveform and decayed after it had ended. The vertical dotted lines show the beginnings and ends of the two four-cycle tone bursts used as a test signal. (C) Graphs of the cycle-by-cycle frequency of the waveforms in A and B plotted by zero-crossing analysis. The frequencies remained approximately constant within the tone bursts but that of the broad-band waveform fell during the gap between the first and second tone bursts (left-hand scale and filled circles). The frequency of the without-FD waveform (the song pulse after filtering out the peak at the dominant frequency FD of the song pulse) was approximately twice that of the broad-band waveform within the tone bursts (right-hand scale and open circles). Before and after the tone bursts, the plot shows the 5 kHz frequency at which the signal was filtered. The inset shows the convention used to define the phase of a sine wave.
