This Recommendation is based on Annex BP.80 and on experience gained from several international experiments [5], [6], [9], [lo], [12], [13], [15] and [17]. Further, this Recommendation defines a specific testing method for evaluating digital processes. This method allows the subjective effects of distortion introduced by the speech coding process to be taken into account when assessing the performance of the evolving international network.This Recommendation contains advice on how to assess the performance of digital codecs. This Recommendation must be read in conjunction with Recommendation P.80. Additional information is available in sources listed in the Bibliography.