Harmonic complex tones with same or alternating phase. Harmonic complex tones with fundamental frequencies 1 octave apart (f0 = 100 Hz and f0 = 50 Hz in this example, harmonics 8–16). For each fundamental frequency, harmonics are either in same (COS) or alternating (ALT) phase (odd harmonics in sine phase, even harmonics in cosine phase). Alternating phase complex tones have twice the envelope repetition rate as their same phase counterpart, and the autocorrelation of the half-wave-rectified acoustic signal indicates a periodicity at twice the fundamental frequency. A, Amplitude spectrum of a harmonic complex tone with f0 = 100 Hz. B, Acoustic waveform and autocorrelation plots (inset) for a same phase harmonic complex (COS stimulus) with f0 = 100 Hz. C, Acoustic waveform and autocorrelation plots (inset) for an alternating phase harmonic complex (ALT stimulus) with f0 = 100 Hz. D, Amplitude spectrum of a harmonic complex tone with f0 = 50 Hz. E, Acoustic waveform and autocorrelation plots (inset) for a COS stimulus with f0 = 50 Hz. F, Acoustic waveform and autocorrelation plots (inset) for an ALT stimulus with f0 = 50 Hz.