1. A computer-implemented process for estimating speech quality of an audio frame in a single-channel audio signal comprising human speech components, comprising: using a computer to perform the following process actions: inputting a frame of the audio signal; transforming the inputted frame from the time domain into the frequency domain; computing a harmonic component of the transformed frame; computing a non-harmonic component of the transformed frame; computing a harmonic to non-harmonic ratio (HnHR); and designating the computed HnHR as an estimate of the speech quality of the inputted frame in the single-channel audio signal.