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# 9.1.5: The Missing Fundamental

One important auditory phenomena that cannot easily be explained by either theory of hearing is the missing fundamental or virtual pitch. Some sources refer to the effect as residue pitch. As we saw in the chapter on Fourier analysis, musical instruments have overtones which are harmonic, meaning they are multiples of the fundamental frequency. When you hear a guitar play a note with a fundamental frequency of $$100\text{ Hz}$$ there are harmonic frequencies of $$200\text{ Hz}, 300\text{ Hz}, 400\text{ Hz}$$, etc. present in the sound. Your ear-brain system perceives this as a single pitch of $$100\text{ Hz}$$ instead of a collection of individual frequencies. An interesting auditory phenomena is that if you are listening to a series of frequencies of $$200\text{ Hz}, 300\text{ Hz}, 400\text{ Hz}$$, etc. your ear-brain system will ALSO perceive a single note of $$100\text{ Hz}$$ even if the $$100\text{ Hz}$$ fundamental is missing.