The fundamental tone often referred to simply as the fundamental, is the lowest frequency in a harmonic series.
The fundamental frequency of a periodic signal is the inverse of the pitch period length. The pitch period is, in turn, the smallest repeating unit of a signal. One pitch period thus describes the periodic signal completely. The significance of defining the pitch period as the smallest repeating unit can be appreciated by noting that two or more concatenated pitch periods form a repeating pattern in the signal. However, the concatenated signal unit obviously contains redundant information.
A 'fundamental bass' is the root note, or lowest note or pitch in a chord or sonority when that chord is in root position or normal form.
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