# Dictionary:Frequency

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**1**. Symbol, *f*. The repetition rate of a periodic waveform, measured in ‘‘per second’’ or Hertz. The reciprocal of period. Compare *spatial frequency*.

**2**.** Angular frequency** ω, measured in radians per second, is to frequency *f* as 2π:

**3**. The **dominant frequency** of wavelets refers to an approximate repetition (the reciprocal of the peak-to-peak time interval) even though the entire wavelet does not repeat. See Figure W-2.

**4**. The **frequency content** of a waveform refers to the amplitudes of the sinusoidal components into which the waveform can be decomposed by Fourier analysis, even where there is nothing repetitive about the waveform itself; **frequency spectrum**. For mathematical symmetry, the Fourier integral is usually written for frequencies from –∞ to +∞. Negative frequencies can be thought of as the repetition rate where one counts backward in time.