Spectral envelope and context effects in the tritone paradox.

In previous studies of the 'tritone paradox' Deutsch has suggested that, when listeners are presented with pairs of octave-complex tones that are equal in average log frequency but differ in chroma by 6 semitones (a tritone), they perceive the direction of the chroma difference according to an individual pitch-class template. However, it has also been found that the perceived direction changes for many listeners when the spectral envelope of the tones is shifted along the frequency axis. Reanalysis of these data indicates a strong tendency to perceive the pitch class corresponding to the frequency on which the spectral envelope is centered as subjectively lowest. In experiment 1 this spectral-envelope effect was replicated with tone pairs presented in isolation, at the rate of one a day, which rules out artifacts of test format. In experiment 2, involving another context-free format, envelope center frequency was varied over a wide range and it was shown that some individuals are totally envelope dependent, whereas others rely more on pitch class, and yet others show mixed patterns. Experiment 3 demonstrated that listeners' judgments of tritone pairs can be swayed easily by preceding context. Finally, experiment 4 showed that strong envelope effects are also obtained with Deutsch's own tritone test (issued on CD). The subjective relative pitch height of octave-complex tones thus depends on several competing factors, only one of which is pitch class.