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(a) A waveform and spectrogram of a song stimulus pair used in the age discrimination experiment, (b) with an enlargement of two trill notes of each song. On the left a song from an individual in its first breeding season, and on the right the same song type from the same individual in its third breeding season. Spectrogram settings: fast Fourier transform (FFT) size=512 Hz, Hamming window, time resolution=2.67 ms, frequency resolution=94 Hz.
