Fig. 2.

(A) Spectrogram of a male calling song (upper panel) and a synthetic model song (lower panel) with a f_c of 4.9 kHz and 600 Hz downward FM. (B) Power spectrum of model songs for each tested f_c and depth of FM. Note that even a downward modulation of 800 Hz does not result in a corresponding increase in the width of the spectrum towards lower frequencies, but approximately only to 400 Hz, when measured 20 dB below the maximum at the f_c (dashed line).