The pitch of a periodic tone depends on its fundamental frequency (F0), and the brightness of its timbre depends on the centroid of its power spectrum (Fc). The goal of the present study was to determine whether small shifts in F0 and in Fc are detected independently of each other. The standard tone used had an F0 of 400 Hz, five harmonics (400-2000 Hz), and a triangular spectral envelope peaking at an Fc of 1000 Hz. With a forced-choice adaptive procedure, detection thresholds were measured for (1) shifts in F0 alone (Fc being fixed), (2) shifts in Fc alone (F0 being fixed), and (3) combined shifts in F0 and Fc. The two components of the combined shifts were chosen to have the same level of detectability when presented alone. Overall, as expected from the independence model, the combined shifts were not better detected when their two components had the same direction (F0 and Fc both increase, or both decrease) than when they had opposite directions. However, substantial differences between subjects were observed with respect to the perceptual integration of shifts in F0 and in Fc.
Ten musicians were presented with a transposable melodic sequence of two monaural pure tones and were required to set the pitch of the higher tone in the sequence just above the upper limit of "musical" pitch. The overall mean of the frequency adjustments was 4.7 kHz, but subjects' individual means consistently differed from each other; their standard deviation was about three semitones. Subjects' adjustments depended on the range of possible adjustments and thus were influenced by context factors. However, the effect of range was 2.7 times smaller than it should have been if the upper limit of musical pitch had no perceptual reality. No consistent frequency differences were found between adjustments made for tones heard through the left ear and the right ear. However, in an additional study on six nonmusicians, one subject displayed a systematic interaural frequency difference amounting to about one semitone. Control measurements showed that this difference could not be explained by the subject's binaural diplacusis. Thus, as suggested by Bachem in 1937, it seems that the upper limit of musical pitch can be a different pitch for the two ears of the same subject.