Term	Definition	Demo
Frequency	The number of vibrations or cycles completed by a signal in one second. Frequency is expressed in cycles, or more commonly, Hertz (Hz).
Frequency Modulation	A method of radio broadcasting in which the radio carrier frequency is frequency modulated by the audio signal. Capable of high sound quality, and relatively immune to interference and static. However, it propagates poorly over long distances and suffers from multipath interference and shadow zone problems in cities and hilly areas.
Frequency Response	A measure of the amplitude vs. frequency performance of an audio component, measured from its input to its output. A perfect electronic device should have a flat, or linear, frequency response over its useful frequency range, indicating that it reproduces all frequencies at the correct level. Loudspeakers are more complicated since the output is sound which is radiated in all directions. It is necessary to measure the frequency response at many locations all around the loudspeaker in order to be able to predict how it may sound in a room. For loudspeakers, there is no single frequency response measurement that is completely descriptive of its performance. See: Transfer Function, Spectrum.
Frequency Weighting	Used in measurement of overall sound levels to take account of the frequency-dependent loudness characteristics of ears at different sound levels. A-weighted measurements attenuate sounds below about 1000 Hz (low sound levels), B-weighting rolls off frequencies below about 200 Hz (middle sound levels), and C-weighting rolls off below about 50 Hz (high sound levels). All three weightings roll off high frequencies above about 7 kHz. Sound levels measured using these weightings are designated dB (A), dB(B), dB(C), as opposed to unweighted (linear) measurements of sound pressure level (SPL).