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A time–frequency representation (TFR) is a view of a signal (taken to be a function of time) represented over both time ''and'' frequency.〔E. Sejdić, I. Djurović, J. Jiang, “Time-frequency feature representation using energy concentration: An overview of recent advances,” Digital Signal Processing, vol. 19, no. 1, pp. 153-183, January 2009.〕 Time–frequency analysis means analysis into the time–frequency domain provided by a TFR. This is achieved by using a formulation often called "Time–Frequency Distribution", abbreviated as TFD. TFRs are often complex-valued fields over time and frequency, where the modulus of the field represents either amplitude or "energy density" (the concentration of the root mean square over time and frequency), and the argument of the field represents phase. == Background and motivation == A signal, as a function of time, may be considered as a representation with perfect ''time resolution''. In contrast, the magnitude of the Fourier transform (FT) of the signal may be considered as a representation with perfect ''spectral resolution'' but with no time information because the magnitude of the FT conveys frequency content but it fails to convey when, in time, different events occur in the signal. TFRs provide a bridge between these two representations in that they provide ''some'' temporal information ''and'' ''some'' spectral information simultaneously. Thus, TFRs are useful for the representation and analysis of signals containing multiple time-varying frequencies. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Time–frequency representation」の詳細全文を読む スポンサード リンク
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