There are a wide variety of spatial audio reproduction systems available, from a single loudspeaker to many spatially distributed loudspeakers. An important factor in the selection, development, or optimization of such systems is listener preference and the important perceptual characteristics that contribute to this. An experiment was performed to determine the attributes that contribute to listener preference for a range of spatial audio reproduction methods. Experienced and inexperienced listeners made preference ratings for combinations of seven program items replayed over eight reproduction systems and reported the reasons for their judgments. Automatic text clustering reduced redundancy in the responses by approximately 90%, facilitating subsequent group discussions that produced clear attribute labels, descriptions, and scale end-points. Twenty-seven and twenty-four attributes contributed to preference for the experienced and inexperienced listeners respectively. The two sets of attributes contain a degree of overlap (ten attributes from the two sets were closely related); however, the experienced listeners used more technical terms while the inexperienced listeners used more broad descriptive categories.

It is desirable to determine which of the many different spatial audio reproduction systems listeners prefer, and the perceptual attributes that are most important to listener experience, so that future systems can be perceptually optimized. A paired comparison preference rating experiment was performed alongside a free elicitation task for eight reproduction methods (consumer and professional systems with a wide range of expected quality) and seven program items (representative of potential broadcast material). The experiment was performed by groups of experienced and inexperienced listeners. Thurstone Case V modeling was used to produce preference scales. Both listener groups preferred systems with increased spatial content; nine-and five-channel systems were most preferred. The use of elicited attributes was analyzed alongside the preference ratings, resulting in an approximate hierarchy of attribute importance: three attributes (amount of distortion, output quality,andbandwidth) were found to be important for differentiating systems where there was a large preference difference; sixteen were always important (most notably enveloping and horizontal width); and seven were used alongside small preference differences. INTRODUCTIONThere is a wide range of spatial audio reproduction methods used for domestic or professional audio replay. Systems include mono and two-channel stereo, channelbased surround sound methods (5.1, 7.1, 9.1, 11.1, and 22.2 [1] are all used domestically or within the audio industry), "one box" solutions such as sound bars, and reproduction over headphones. With such a wide range of methods in use, it is important to discover what aspects of spatial audio reproduction particularly enhance the listener experience.A previous study by the authors [2] identified the perceptual attributes that contribute to preference judgments made between alternative reproduction systems. The research described in the current paper aimed to determine which of these attributes are most important to listeners-that is, which of them have a strong relationship with listener preference. With this knowledge, these attributes can then be targeted in the design of new reproduction systems and the improvement of existing ones, and perceptual models of the important attributes can be developed and used to meter and optimize spatial audio reproduction. The problem was approached from two directions: determining listener preference for certain systems and ascertaining the perceptual characteristics of the differences between the systems. By collecting both quantitative and qualitative data, the relationship between the attributes and preference scores could be investigated. This facilitated analysis of the perceptual attributes that most contribute to creating a positive listener experience. EXPERIMENT BACKGROUNDThere have been previous attempts to understand the relationship between audio attributes and listener preference. Choisel and Wickelmaier [3] performed a spatial audio elicitation experiment and determined a set o...

Envelopment is an important attribute of listener preference for spatial audio reproduction. Object-based audio offers the possibility of altering the rendering of an audio scene in order to modify or maintain perceptual attributes-including envelopment-if the relationships between attributes and mix parameters are known. In a method of adjustment experiment, mixing engineers were asked to produce mixes of four program items at low, medium, and high levels of envelopment in 2-channel, 5-channel, and 22-channel reproduction systems. The participants could vary a range of level, position, and equalization parameters that can be modified in object-based audio systems. The parameters could be varied separately for different semantic object categories. Nine parameters were found to have significant relationships with envelopment; parameters relating to the horizontal and vertical spread of sources were shown to be most important. A follow-on experiment demonstrated that these parameters can be adjusted to produce a range of envelopment levels in other program items.

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