A method for determining unbiased signal amplitude estimates () after cepstral variance modification of a discrete time domain signal (s(t)), wherein the cepstrally-modified spectral amplitudes () of the discrete time domain signal (s(t)) are χ-distributed with 2{tilde over (μ)} degrees of freedom. A bias reduction factor (r) is determined using the equation r 2 = μ μ ~ ⁢ ⅇ ψ ⁡ ( μ ~ ) - ψ ⁡ ( μ ) , where 2μ are the degrees of freedom of the χ-distributed spectral amplitudes of the discrete time domain signal (s(t)) and ψ ⁡ ( x ) = - 0.5772 - ∑ n = 0 ∞ ⁢ ( 1 x + n - 1 1 + n ) ; then the unbiased signal amplitude estimates () are determined by multiplying the cepstrally-modified spectral amplitudes () with the bias reduction factor (r) according to the equation =r. A method for speech enhancement and a hearing aid use the method for determining unbiased signal amplitude estimates () in order to offer the advantage of spectral modification, such as smoothing, of spectral quantities without affecting their signal power.