8. Apparatus operable to provide a single-end speech quality Measurement, comprising: a feature extraction module which extracts, frame-by-frame, perceptual features from a received speech signal that has been processed by network equipment, transmitted on a communications link, or both; a time segmentation module which classifies each frame based on the perceptual features into a class selected from a set of classes including voiced and unvoiced; a statistical reference model generated prior to extraction of the perceptual features, the reference model including at least one statistical model for each class of the set of classes; a consistency calculation module which, for the frames of each class, operates in response to output from the feature extraction module to assess the perceptual features with a statistical model of that class to form indicators of subjective speech quality without reference to a corresponding speech signal that has not been processed by network equipment, transmitted on a communications link, or both, including assessing at least some unvoiced frames; and a scoring module which employs the indicators of speech quality from different classes to produce a speech quality score without reference to a corresponding speech signal that has not been processed by network equipment, transmitted on a communications link, or both.
8. Apparatus operable to provide a single-end speech quality Measurement, comprising: a feature extraction module which extracts, frame-by-frame, perceptual features from a received speech signal that has been processed by network equipment, transmitted on a communications link, or both; a time segmentation module which classifies each frame based on the perceptual features into a class selected from a set of classes including voiced and unvoiced; a statistical reference model generated prior to extraction of the perceptual features, the reference model including at least one statistical model for each class of the set of classes; a consistency calculation module which, for the frames of each class, operates in response to output from the feature extraction module to assess the perceptual features with a statistical model of that class to form indicators of subjective speech quality without reference to a corresponding speech signal that has not been processed by network equipment, transmitted on a communications link, or both, including assessing at least some unvoiced frames; and a scoring module which employs the indicators of speech quality from different classes to produce a speech quality score without reference to a corresponding speech signal that has not been processed by network equipment, transmitted on a communications link, or both. 14. The apparatus of claim 8 wherein the statistical reference model includes Gaussian Mixture Models.