Table 2 Song characteristics included in a principal components analysis used to choose purring exemplars.

Peak frequency

Frequency with the greatest acoustic power.

Peak frequency bandwidth

Difference between upper and lower frequencies 10 dB below the peak frequency band’s apex.

Number of peaks (frequency bands)

Number of frequency bands between 1.5 and 20 kHz that fall within 10 dB of the peak frequency band’s apex.

Broadbandedness

Range (in Hz) of frequency bands 10 dB below the peak frequency band’s apex.

Relative amplitude of 6 frequency ranges

dB difference between each defined frequency range and the song’s total amplitude. Frequency ranges include: 2–3.5, 3.5–6, 6–9.5, 9.5–12.5, 12.5–17.5, 17.5–20 kHz. Ranges determined based on cricket hearing ability⁵⁰.

Proportion long chirp

Length of the long chirp (in ms) divided by the sum of the long and short chirp lengths.