When you pluck a guitar string, you actually excite many of its possible standing waves simultaneously. Typically, the fundamental is the loudest, so that is the pitch you hear. However, the unique mix of the fundamental plus overtones is what makes a guitar sound different from a violin or a flute, even if they are playing the same note (i.e., producing the same fundamental). This characteristic of a sound is called its timbre (rhymes with amber).

A sound containing just a single frequency is called a pure tone. A complex tone, in contrast, contains multiple frequencies such as a fundamental plus some of its overtones. Interestingly enough, it is possible to fool someone into identifying a frequency that is not present by playing just its overtones. For example, consider a sound containing pure tones at 450 Hz, 600 Hz, and 750 Hz. Here 600 Hz and 750 Hz are not integer multiples of 450 Hz, so 450 Hz would not be considered the fundamental with the other two as overtones. However, because all three frequencies are consecutive overtones of 150 Hz a listener might claim to hear 150 Hz, over an octave below any of the frequencies present. This 150 Hz is called a virtual pitch or a missing fundamental.

A certain sound contains the following frequencies: 400 Hz, 1600 Hz, and 2400 Hz. Select the best description of this sound:

-This is a pure tone.

-This is a complex tone with a fundamental of 400 Hz, plus some of its overtones.

-This is a complex tone with a virtual pitch of 800 Hz.

-These frequencies are unrelated, so they are probably pure tones from three different sound sources.