Fig. 6. Unilateral biphonation in two syllables produced by mockingbird m130. (A) Two independent frequencies produced by a single side of the syrinx. Arrows a and b indicate biphonic sounds concurrent with airflow through only the left side of the syrinx. Similar, but less dramatic, biphonation events also occur during the first syllable in A. At arrow a, sound energy is present at 990 Hz (f₀) and 1505 Hz (g₀), and their harmonics, 2f₀ (1980 Hz) and 2g₀ (3010 Hz). (B) An expanded view of the sound waveform at arrow a (spectrogram, A), showing a change from the biphonation event to a single f₀ tone. (C) Power spectrum taken at arrow b, in spectrogram (A), showing the two fundamental frequencies (f₀ and g₀), as well as sound energy at various linear combinations of the two fundamentals. Abbreviations as in Fig. 3.