Finally factor of speech clearence (C50) and still more to go.
C50 (factor of clearness) determines sound clearness and clarity. It is computed as near echo/far echo ratio. The method is based on the fact, that echo reduces signal intelligibility. The near echo/far echo ratios in several frequency bands are calculated. They consider near echo (less than 33 ms) as useful signal and far echo (more than 33 ms) as disturbing signal.
Disadvantage of the approach is that the factor of clearness takes into account only one kind of the possible distortions and it is worth to apply it only as one of the speech quality estimations.
So, as promised we would like to clarify what this and the previous posts were about… It seems it’s time to develop new methods and to improve existing ones and it is caused by desire to bring together objective and subjective estimation of quality and to explicitly use in quality of service (QoS) and quality of experience (QoE) systems the knowledge about hearing, human perception and speech production, and therefore the next post will be devoted to ITU standard P.862 also known as PESQ that stands for Perceptual Evaluation of Speech Quality
