Objective measurement of voice quality for cellular mobile phones

Abstract

Objective voice quality assessment in digital cellular mobile phone systems can be achieved using a new methodology based on a weighted calculation of signal to noise ratio (WSNR). Using the new method, the WSNR is calculated by taking into account, in each frequency sub-band, the intensity of the signal (loudness level), frequency sensitivity to noise in each sub-band, and finally the age of the listener. This new method of calculating SNR is based on loudness contours by Robinson and Dadson [1956]. Weights are assigned by setting the perceived loudness level of any tone equal to the perceived intensity level of a 1 kHz tone. Contrary to the conventional SNR, the weighted SNR, directly relates to voice quality by taking into account the four main factors effecting voice quality: (1) frequency sensitivity, (2) intensity (3) ratio of the signal to noise energy and (4) age. Initial experiments indicate that the new objective measure is easy to implement in hardware, yet correlates well with subjective mean opinion scores (MOS).