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:

${\displaystyle \omega =2\pi f}$

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.

Figure W-2. Wave definitions. For sinusoids, (a) how displacement at one point varies with time; (b) how wave looks at different places at a given instant. (c) If wavefront approaches at an angle, the apparent wavelength differs from the true wavelength. For nonperiodic waves, (d) dominant period is based on the time between principal adjacent troughs (or peaks); (e) dominant wavelength is measured similarly.

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.