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Spectral flatness or tonality coefficient,〔 〕〔 〕 also known as Wiener entropy,〔(The Song Features › Wiener entropy ) "defined as the ratio of geometric mean to arithmetic mean of the spectrum"〕〔(Luscinia parameters ) "Wiener entropy is an alternative measure of the noisiness of a signal. It is defined as the ratio of the geometric mean to the arithmetic mean of the power spectrum."〕 is a measure used in digital signal processing to characterize an audio spectrum. Spectral flatness is typically measured in decibels, and provides a way to quantify how noise-like a sound is, as opposed to being tone-like.〔 The meaning of ''tonal'' in this context is in the sense of the amount of peaks or resonant structure in a power spectrum, as opposed to flat spectrum of a white noise. A high spectral flatness (approaching 1.0 for white noise) indicates that the spectrum has a similar amount of power in all spectral bands — this would sound similar to white noise, and the graph of the spectrum would appear relatively flat and smooth. A low spectral flatness (approaching 0.0 for a pure tone) indicates that the spectral power is concentrated in a relatively small number of bands — this would typically sound like a mixture of sine waves, and the spectrum would appear "spiky".〔(A Large Set of Audio Features for Sound Description ) - technical report published by IRCAM in 2003. Section 9.1〕 The spectral flatness is calculated by dividing the geometric mean of the power spectrum by the arithmetic mean of the power spectrum, i.e.: : where ''x(n)'' represents the magnitude of bin number ''n''. Note that a single (or more) empty bin yields a flatness of 0, so this measure is most useful when bins are generally not empty. The ratio produced by this calculation is often converted to a decibel scale for reporting, with a maximum of 0 dB and a minimum of −∞ dB. The spectral flatness can also be measured within a specified subband, rather than across the whole band. == Applications == This measurement is one of the many audio descriptors used in the MPEG-7 standard, in which it is labelled In birdsong research, it has been used as one of the features measured on birdsong audio, when testing similarity between two excerpts.〔Tchernichovski, O., Nottebohm, F., Ho, C. E., Pesaran, B., Mitra, P. P., 2000. A procedure for an automated measurement of song similarity. Animal Behaviour 59 (6), 1167–1176, .〕 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「spectral flatness」の詳細全文を読む スポンサード リンク
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