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Noises are characterized in the time domain by Allan deviation, σy(τ), or in the frequency domain by the power spectra of fractional frequency fluctuations, Sy(f). These are related by
      ∫ ∞ σ2(τ) = 4 Sy(f)sin4(πτf)df, y 0 (πτf)2
where Sy (f) is the two-sided spectrum [23*].