1. A method for measuring distortion in a noise-reduced signal, comprising: receiving a noise component which does not contain speech; receiving a speech component which does not contain noise; receiving a combined signal by a noise reduction module, the combined signal formed from the combination of the noise component and the speech component; generating a noise reduced signal by the noise reduction module, the noise reduction module performing noise reduction to the combined signal to generate the noise reduced signal; constructing an estimated idealized noise reduced reference from the noise component, the speech component and the noise-reduced signal; and comparing the noise-reduced signal and the estimated idealized noise reduced reference to calculate a measure of distortion produced by the noise reduction module, the distortion calculated as at least one of the voice energy added, voice energy lost, noise energy added, and noise energy lost in the noise-reduced signal.