Subjective and objective quality evaluation of watermarked audio tracks

This paper presents methods for the quality evaluation of watermarked audio data. Subjective and objective methods used in testing transparency as well as approaches rating the quality of the watermarked copies with regard to the original ones are presented. The various methods are discussed and detailed with regard to their applicability. According to the discussions two different kinds of tests were performed to test the quality of watermarked items. During the tests different settings of the so-called Noise-to-Mask-Ratio (NMR) were used. The first test is a subjective listener test which compares the quality of the original audio track with the watermarked one. The second test uses objective methods to rate the quality of watermarked audio tracks as well as compressed original audio tracks with the so-called objective difference grade (ODG). The results are compared to rate the quality of the watermarked items with respect to the compressed ones.