The Lower Limit of Melodic Pitch

An objective melody task was used to determine the lower limit of melodic pitch (LLMP) for harmonic complex tones. The LLMP was defined operationally as the repetition rate below which listeners could no longer recognize that one of the notes in a four-note, chromatic melody had changed by a semitone. In the first experiment, the stimuli were broadband tones with all their components in cosine phase, and the LLMP was found to be around 30 Hz. In the second experiment, the tones were filtered into bands about 1 kHz in width to determine the influence of frequency region on the LLMP. The results showed that whenever there was energy present below 800 Hz, the LLMP was still around 30 Hz. When the energy was limited to higher-frequency regions, however, the LLMP increased progressively, up to 270 Hz when the energy was restricted to the region above 3.2 kHz. In the third experiment, the phase relationship between spectral components was altered to determine whether the shape of the waveform affects the LLMP. When the envelope peak factor was reduced using the Schroeder phase relationship, the LLMP was not affected. When a secondary peak was introduced into the envelope of the stimuli by alternating the phase of successive components between two fixed values, there was a substantial reduction in the LLMP, for stimuli containing low-frequency energy. A computational auditory model that extracts pitch information with autocorrelation can reproduce all of the observed effects, provided the contribution of longer time intervals is progressively reduced by a linear weighting function that limits the mechanism to time intervals of less than about 33 ms.