Cancelled harmonics—How high does the effect go?

Demonstration Number 1 in the IPO-NIU-ASA collection of auditory demonstrations (compact disk) periodically cancels and reinserts a harmonic of a complex tone having a 200-Hz fundamental and 20 equal-amplitude harmonics. This procedure causes a listener to hear out the manipulated harmonic as a separate tone. In this way, the demonstration exposes harmonics 1 through 10. The following question arises: What is the highest harmonic that can be made audible, and what is responsible for the limitation? Listening experiments, using random harmonic phases, fundamental frequencies (f0) from 50 to 2000 Hz, and a maximum harmonic frequency of 20 kHz, show that for high fundamental frequencies (f0>200 Hz) the highest audible harmonic frequency is insensitive to f0 and is only about 10 percent less than the highest audible sine frequency in quiet. For lower fundamental frequencies, the highest audible harmonic number tends to be insensitive to f0 and is 50–70 for normal hearing listeners. In this region the highest audible harmonic number can be predicted from noise-masked threshold data, but with a large uncertainty. [Work supported by NIDCD.]