Ratio-scaling of listener preference of multichannel reproduced sound

Sound quality is often assessed by means of direct ratings on a numerical preference scale. The validity of direct rating scales relies on many implicit assumptions, one of them being the unidimensionality of the judgments. While unidimensionality might hold for simple stimuli, this is a non-trivial assumption in the case of complex spatial sounds. In the present study the Bradley-Terry-Luce (BTL) model was employed to investigate the unidimensionality of preference judgments made by 40 listeners on multichannel reproduced sound. Short musical excerpts played back in eight reproduction modes (mono, stereo and various multichannel formats) served as stimuli. On each trial, the task of the subjects was to choose the format they preferred, proceeding through all the possible pairs of the eight reproduction modes. This experiment was replicated with four types of programme material (pop and classical music). As a main result, the BTL model was found to predict the choice frequencies well. This implies that listeners were able to integrate the complex nature of the sounds into a unidimensional preference judgment. It further implies the existence of a preference scale on which the reproduction modes can not only be ordered, but also their ratios are meaningful. There were significant differences between the reproduction modes (some ratios exceeding ten). Also the programme material was found to have a significant effect on the listener preferences. It is concluded that the BTL scaling may be more useful than direct scaling for obtaining quantitative information regarding the quality of reproduced sound.