In most sounds several frequencies are present. It is usually the lowest, frequency, the fundamental, that determines the pitch. There is a very interesting phenomenon that happens when the fundamental is removed, or even several of the lowest harmonics as well. The pitch does not change. The frequency that supposedly causes the pitch is absent, but the pitch does not change. The sound changes timbre because of the change in harmonics, though.
You can also experience another interesting phenomenon that shows that in our hearing we do something akin to Fourier Analysis. Try turngin off and on any on of the components. You can pick out that component when, for most listeners, it is lost in the total tone most of the time. It is called Ohm's Acoustical Law and shows,when are attention is drawn to a single frequency, we can pick it out of a complex waveform, much like Fourier Analysis.
In this illustration, you can play a tone and remove the fundamental and the next four harmonics. By humming, you can convice yourself that the pitch does not change.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Play: start the sound. The button will then change to Pause and
pressing it again will stop the sound.
Fundamental Frequency: Change the fundamental frequency of the combined tone.
All other components will change proportionally.
#: Intensity: Change the intensity of the indicated component of the fundamental frequency (0 is the fundamental and it counts up from there).
Flute, Violin, Clarinet, Trumpet: set the relative intensities to the simulations for these instruments.
Pressing this button restores the settings to their default values.