fréquences

Frequency, or fréquences in French usage, denotes how often an event repeats per unit of time. The basic measure is cycles per second, or hertz (Hz); f equals the number of cycles per second. The reciprocal of frequency is the period T = 1/f. This relationship applies to any periodic phenomenon, including mechanical vibrations, electrical signals, and electromagnetic waves. For light, frequency determines color; for sound, it determines pitch. Energy of a photon is proportional to frequency via E = h f, linking frequency to quantum energy.

In different domains, frequencies can be temporal or spatial. Temporal frequency counts how rapidly a signal oscillates over time; spatial frequency describes how quickly a wavefront varies across space and is central in imaging and diffraction.

Measurement and analysis: Frequency can be measured with counters, spectrum analyzers, or by transforming signals into the frequency domain using Fourier analysis. The discrete Fourier transform and fast Fourier transform yield a spectrum showing amplitude versus frequency. Important concepts include the Nyquist frequency, related to sampling rate, and aliasing when sampling is insufficient.

Statistics and linguistics: In statistics, frequency refers to how often an event occurs within a dataset; a frequency distribution summarizes counts or proportions. In language and music, frequencies influence perception and structure: word frequency in corpora, and musical pitch corresponding to a specific frequency. The term fréquences is used in French-language contexts to describe these same concepts.