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  2. Spectral density - Wikipedia

    en.wikipedia.org/wiki/Spectral_density

    Electronic instruments called spectrum analyzers are used to observe and measure the power spectra of signals. The spectrum analyzer measures the magnitude of the short-time Fourier transform (STFT) of an input signal. If the signal being analyzed can be considered a stationary process, the STFT is a good smoothed estimate of its power spectral ...

  3. Fourier transform - Wikipedia

    en.wikipedia.org/wiki/Fourier_transform

    An example application of the Fourier transform is determining the constituent pitches in a musical waveform.This image is the result of applying a constant-Q transform (a Fourier-related transform) to the waveform of a C major piano chord.

  4. Fourier series - Wikipedia

    en.wikipedia.org/wiki/Fourier_series

    A Fourier series (/ ˈ f ʊr i eɪ,-i ər / [1]) is an expansion of a periodic function into a sum of trigonometric functions. The Fourier series is an example of a trigonometric series. [2] By expressing a function as a sum of sines and cosines, many problems involving the function become easier to analyze because trigonometric functions are ...

  5. Square wave - Wikipedia

    en.wikipedia.org/wiki/Square_wave

    (Odd) harmonics of a 1000 Hz square wave Graph showing the first 3 terms of the Fourier series of a square wave. Using Fourier expansion with cycle frequency f over time t, an ideal square wave with an amplitude of 1 can be represented as an infinite sum of sinusoidal waves: = = ⁡ (()) = (⁡ + ⁡ + ⁡ + …

  6. Spectral density estimation - Wikipedia

    en.wikipedia.org/wiki/Spectral_density_estimation

    The Fourier transform of a function produces a frequency spectrum which contains all of the information about the original signal, but in a different form. This means that the original function can be completely reconstructed ( synthesized ) by an inverse Fourier transform .

  7. Periodogram - Wikipedia

    en.wikipedia.org/wiki/Periodogram

    Two power spectra (magnitude-squared) (rectangular and Hamming window functions plus background noise), calculated by the periodogram method. For sufficiently small values of parameter T, an arbitrarily-accurate approximation for X ( f ) can be observed in the region − 1 2 T < f < 1 2 T {\displaystyle -{\tfrac {1}{2T}}<f<{\tfrac {1}{2T}}} of ...

  8. Fourier analysis - Wikipedia

    en.wikipedia.org/wiki/Fourier_analysis

    A number of authors, notably Jean le Rond d'Alembert, and Carl Friedrich Gauss used trigonometric series to study the heat equation, [20] but the breakthrough development was the 1807 paper Mémoire sur la propagation de la chaleur dans les corps solides by Joseph Fourier, whose crucial insight was to model all functions by trigonometric series ...

  9. Frequency domain - Wikipedia

    en.wikipedia.org/wiki/Frequency_domain

    The modulus of the number is the amplitude of that component, and the argument is the relative phase of the wave. For example, using the Fourier transform, a sound wave, such as human speech, can be broken down into its component tones of different frequencies, each represented by a sine wave of a different amplitude and phase. The response of ...