to-back discriminations to be made. Alternatively, stereo, surround or three dimensional microphone techniques can encode directly positional information using one or all of these techniques. Often studio recordings may make use of both recorded positional information, and virtual positioning, for instance by adding an instrument recorded using a stereo technique to a panned mix.
Simply listening to any commercial production of suitably high standard provides ample evidence of the care and attention that goes into the spatial treatment of recorded sound. The ongoing discourse surrounding the technical aspects and merits of surround sound in the AES in particular points toward the importance with which spatial treatment is held amongst recording professionals. It has been claimed that up to one third of the perceived quality of a recording comes from its spatial qualities(Rumsey 2006). Very little however has been written as to the affect this spatial treatment has on the listener’s emotional response to the recorded music. This paper seeks to tie together conceptually, some of the current research from seemingly disparate fields relevant to this question. It will then describe and discuss results from a pilot study designed to establish a methodology for testing the affect of spatial treatment on listeners using the measurement of Electro Dermal Activity (EDA) also known as Galvanic Skin Response (GSR). Finally it will propose some potential explanations for the effect spatial treatment has on our experience of recorded music.
Context
The study of emotion in music psychology has experienced significant growth in recent years. The question of whether and how emotion may be induced by music continues to be debated (see Juslin, Vastfjall 2008, Scherer 2004) and a number of frameworks have been suggested which may be useful in investigating the influence of spatial properties on musical listening. One difficulty is in defining what is meant by emotion in this context. Juslin and Sloboda (2001) outline a number of approaches to classifying emotions, and point to some problems with adopting general approaches to emotion from psychology. Juslin (2009) provides six subcomponents for the definition of emotion, of which physiological response is one. It is assumed by Juslin and Vastfjall (2008) that musical emotions share the same mechanisms as normal emotions, and thus the same emotions should be elicited. They do however point out that emotions induced by music are different in that they lack a goal orientation. The assumption that basic emotions require cognitive appraisal may instead indicate that a different mechanism is used for musical emotion induction.
A more modest approach may be to study feeling as a subset of emotion. Scherer (2004) considers feeling using a valence versus arousal model, a two dimensional approach similar to examples of dimensional models of emotion (Sloboda, Juslin 2001). This simplification aids the development of experiment methodologies by providing a useful measure for quantitative analysis.
The most complete framework of psychological mechanisms for emotional induction presented thus far (Juslin, Vastfjall 2008) provides six such mechanisms. Of these, evaluative conditioning, visual imagery, episodic memory and musical expectancy would seem to have some relevance to spatial treatment of music, particularly where some form of architectural acoustic may be associated with a musical piece or genre.
For a space to be detected or experienced aurally, it is fairly obvious that there must be a sound to stimulate the acoustic environment. A model of production rules for emotional induction by music in which various features are part of a multiplicative function is proposed by Scherer and Zentner (2001). This model provides a framework to allow for quantitative measurement of the various factors so that appropriate weighting can be applied. Of the four main categories of features put forward, spatial characteristics fit within the contextual features. Conceptually, this allows for spatial characteristics to mediate in some way, the induction of emotion by recorded music.
The various theories advanced within music psychology provide a number of possible explanations for any effects resulting from changes in spatial treatment, depending on the mechanisms involved in the emotion elicitation.
Spatial treatment has been studied from the perspective of quality evaluation. Berg (2002) analysed the responses of listeners using their own terms to describe the spatial attributes of recordings, creating useful clusters of terms. For instance, the term envelopment clustered with ‘positiveness’, naturalness and presence. This analysis provides a useful look at how basic attributes of spatial characteristics (such as source localisation or apparent source width) contribute to higher order conceptions such as presence. Rumsey (2006) gives a useful summary of the research to date in this area, and points out that the ultimate goal of this research should be to develop models such that physical attributes of sound can be mapped accurately to perceptual attributes. The measures of quality suggested all appear to rely on self-reporting, and the questions raised revolve around what sort of scales and language should be standardised to make useful comparisons of spatial quality.
Useful studies for this topic have also come from the field of Virtual Environments (VE). The end goal of a VE is to create a sense of presence, of actually being in a virtual world. In a very relevant experiment, Vastfjall et. al. (V2002) asked listeners to rate their emotional reactions as well as the expressed emotions of recordings with various levels of added reverberation. The listeners were also given the visual stimuli of a (computer generated) concert hall. His rating scale was based on a circumplex model of arousal and pleasantness, very similar to the two dimensional feeling construct suggested by Scherer (2004). Correlation was found between the level of both reverberation and pleasantness, and also of arousal. Vastfjall claims that this provides evidence that high levels of arousal corresponds to a higher level of presence. A further study (Vastfjall 2003) looked at self-reported measures of presence and emotional reactions resulting from the use of mono, stereo and six channel reproduction systems. This study provided further evidence of the correlation between reported presence and levels of emotional reaction. Interestingly, a later study which tested for increased levels of reported presence as a result of accurate spatial rendering for a given visual stimuli, found no such correlation (although the investigators cited possible methodological reasons for this)(Larsson, Västfjäll et al. 2007).
Much of the existing research into the reproduction of spatial audio therefore focuses on the ability to create a sense of presence, a sense that the virtual experience is not being mediated. The self-reported data seem to indicate that presence has a correlation with arousal, potentially mediating the arousal caused by the auditory stimulus. It is not clear however, that totally accurate rendering of acoustic environments is necessary, or in fact ideal, for a sense of presence to occur. It does not seem to be clear at this stage whether the correlation of presence to emotional arousal reflects causality in one direction or another, however arousal has been shown to correlate with other musical characteristics.
In physiological theories of emotion, arousal is understood to provide the strength of emotional response, though not its character (Rickard 2004). A good measure of physiological arousal is Electro Dermal Activity (EDA), a measure of changes to skin conductance. Another reaction, known as the chills or thrills response, is also shown to correlate well with arousal, although not always with changes in EDA (Rickard 2004, Guhn, Hamm et al. 2007, Grewe, Nagel et al. 2007, Panksepp 1995, Craig 2005). Measurements of EDA and the discrete nature of chills/thrills provide useful quantitative data for testing for stimuli that elicit changes in arousal and therefore indicate strong emotional responses. For instance, Sloboda (1991) used a survey to identify structural attributes in music which participants reported as eliciting the chills/thrills response. These features fit well with Meyer’s musical expectancy theory. Guhn et. al. (2007) found a different set of features in a continuous response experiment which took physiological measurements along with self-reported data.
Whilst there are a number of promising indications, it has yet to be shown directly that manipulation of spatial characteristics of recorded music can have a measurable effect on the arousal component of an emotional response. The present study is designed to test whether a significant correlation can be measured between the spatial manipulation of a recorded piece and the arousal arising from listening to that piece.
Method
For this investigation, two stimuli that differed only in respect of their spatial characteristics were presented to a sample of listeners in a counterbalanced, repeated measures design. A studio recording was therefore produced so that all of the recorded parameters of the stimuli could be controlled.
The music recorded as the stimuli in this experiment was Schubert’s Stänchen D920a for contralto and male chorus. This music was chosen because the ensemble (piano and voices) was available to me quickly, because it was small enough to fit inside the recording studios at the University and because anecdotal evidence suggested that it would elicit at least some arousal response. It also has a sufficient number of parts to make the spatial manipulation obvious. To make the process of learning the piece more straightforward, an English translation of the piece was chosen.
In order to control all spatial aspects of the piece, it was recorded in the main studio at the University of Hull’s Salmon Grove Studios. The main studio is a very ‘dead’ space acoustically, with highly absorptive panels on all of the walls and on the ceiling, such that reflections of the vocal sounds were minimised.
The piano part of the piece was recorded initially as MIDI data from a Kurzweil digital stage piano directly onto a MIDI track in Pro Tools. This was subsequently processed using the Native Instruments Akoustic Piano plugin which allowed for the synthesis of a Steinway grand piano sound without any acoustic reinforcement.
The contralto part was recorded simultaneously with the piano to allow for elastic interpretations of tempo. An AKG C414 XLS large capsule condenser microphone was used to capture the voice. The pre-amplification came from the Audient ACS 8024 console and the signal was bussed without further