Audio Signal Processing and Coding

12.5 SUBJECTIVE EVALUATIONS OF 5.1-CHANNEL STANDARDIZED CODECS

In addition to two-channel stereo systems, multichannel perceptual audio coders are increasingly in demand for multimedia, cinema, and home theater applications. As a result, the European Broadcasting Union (EBU) sponsored Deutsche Telekom Berkom in a formal subjective evaluation [Wust98] that compared the output quality for real-time implementations of the 5.1-channel Dolby AC-3 and the matrixed 5.1-channel MPEG-2/BC layer II algorithms at bit rates between 384 and 640 kb/s (Table 12.3). The tests adhered to the methodologies outlined in ITU BS.1116, and the five-channel listening environment was configured according to ITU-R Rec. BS.775 [ITUR93a]. Mean subjective difference grades were computed over the scores from 32 experts after a t-test analysis was used to discard inconsistent results from seven subjects.

Table 12.1. Comparison of standardized two-channel algorithms (after [Soul98]).

Table 12.2. Comparison of standardized two-channel algorithms at 128 kb/s (after [Soul98]).

The resulting difference grades given in Table 12.3 represent averages of the mean grades reported for a collection of eight critical test items. Even though none of the tested codec configurations satisfied “transparency,” the MPEG-2/BC layer ...