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spectral bin

How much of one frequency a window holds, from the Fourier transform.

Bin k of an N-sample DFT, X_k = Σ x_n e^{-2πink/N}, measures the frequency k f_s/N; for a sine of amplitude A on the bin, |X_k| = AN/2.

Examples

  • With a 1 s window at 100 Hz the bins are 1 Hz apart, so the 23 Hz bin measures shaking at about the fan's rotation speed.

  • Adding the 23 Hz and 24 Hz bins of the axis across the shaft takes the fan's feature vector from 12 to 14 numbers.

See also

Goertzel algorithm spectral leakage feature vector
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