Spatial Audio Processing: MPEG Surround and Other Applications

10.5 Subjective evaluation

Informal listening indicated that the scheme described here offers a benefit over conventional stereo playback, especially for off-sweet-spot listening. The goal for the subjective test was not to gain specific psychophysically interesting data, but to get some evidence that the scheme is preferred by listeners compared with conventional stereo playback.

10.5.1 Subjects and playback setup

Eight subjects participated in the tests. Six of these subjects had already participated in the past in subjective tests for audio quality evaluation. The subjects all had an age between 26 and 37 years and reported normal hearing. The test was carried out in a sound insulated room mimicking a typical living room. For audio playback a laptop computer (Apple PowerBook G4) was used with an external D/A converter (MOTU 896) connected directly to eight active loudspeakers (Genelec 1029A).

The loudspeakers were arranged in front of the subject, as illustrated in Figure 10.14. All loudspeakers were always switched on and the subjects had no explicit knowledge from which loudspeakers sound was emitted.

10.5.2 Stimuli

Eleven different stereo music clips were selected. The clips were obtained from CDs and were of lengths between 10 and 15. In order to demonstrate that the described scheme performs well for audio material which is encoded with a typical audio coder, the clips were encoded using MP3 [40] at 192 kb/s. The MP3 encoder integrated with Apple QuickTime 6 was used.