Tutorial on Critical Listening of Multi-channel Audio Codec Performance

Listening for impairments introduced by multichannel audio codecs is an important task. Classical objective methods are not adequate in assessing audio coding schemes. Accordingly, the ITU-R BS.1116 & 1534 recommendations provide guidelines for subjective evaluation of codecs. This paper provides a tutorial on the proper conditions to do reliable codec testing. Several key components covered are, proper experimental design, selection of listening panel and training of listeners, developing the test methodology, selecting balanced program material, loudspeaker/room and sound-field requirements, listening for artifacts, and statistical analysis. This paper addresses these various components including the sound-field requirements since, as per the ITU: "The characteristics of the reference sound field at the listening area are most important for the subjective perception of, or the quality assessment of, auditory events and their reproducibility at other listening places or rooms. These characteristics result from the interaction of the loudspeaker(s) and the listening room”.