Acoustics research centre
Measuring auditory spaciousness in reproduced sound
Development and Perception of Spatial Sound Reproduction Systems
Bill Davies & Peter Philipson (supervisors), Jos Hirst (student)
EPSRC PhD studentship, 1.10.99 - 30.9.03
Spatial impression in both concert halls and reproduced sound has been identified as an important attribute of the perceptual listening experience. In this study, the synthesis and objective measurement of spatial impression in reproduced sound was examined.
A novel, multichannel spatializing technique for musical synthesis was developed that entailed the separation of the individual harmonics of a musical note that were spatially distributed over multichannel surround systems. Subjective testing of the techniques revealed that the perceived degree of spatial impression significantly increased as the angular spread of harmonics increased, however, extending the spatial spread beyond 90° did not significantly increase the perception of spatial impression.
The concert hall measure of spatial impression, the interaural cross correlation coefficient (IACC) was used to objectively measure the effects of the spatializing techniques. The IACC measurements displayed a strong correlation to the subjective results. Further examination of the IACC measurement indicated the possibility of it's adaptation to multichannel surround sound in general.
A method of adapting IACC to reproduced sound was further developed. The method involved comparing IACC measurements taken in a concert hall to IACC measurements taken in reproduced versions of the same concert hall. The method was first conducted as a simulation using basic auralisation techniques. Real concert hall measurements and reproduction systems were then employed. Results showed that the method was able to discriminate between the spatial capabilities of a number of different surround sound systems and rank them in a predictable order. The results were further validated by means of a subjective test.
In an attempt to sensitise the IACC measurement, the frequency dependency of IACC was investigated by means of a subjective test. The results indicated that a perceptually more accurate indication of spatial impression may be gained by applying a frequency-dependent weighting (especially at low frequencies) to IACC measurements. This may be useful in the spatial measurement of both reproduced sound and concert halls.
- Hirst, J.M., Davies, W.J. and Phiipson, P.J., "Multichannel spatialization techniques for musical synthesis," Proc. Institute of Acoustics 22(6), 117-128, (2000).
- Hirst, J.M., Davies, W.J. and Philipson, P.J., "The Adaptation of Concert Hall Measures of Spatial Impression to Reproduced Sound", Audio Engineering Society Preprint, 120th Convention, Paris. (2006)