A psycho-acoustical experiment using a stereo dipole for spatial impression of music signals

Acoustic performance of concert halls and opera houses is usually assessed by measuring the BIRs (Binaural Impulse Responses). Anechoic music convoluted with BIRs constitutes the virtual sound in the way it is played in the sound field, i.e. the room. From BIRs, the IACC (Inter-Aural Cross Correlation) can be computed. This parameter makes it possible to evaluate the spaciousness of the hall. However, the calculation of the IACC value is affected by the convolution technique used as well as the kind of musical motif. For example, in the same concert hall, the BIR provides three different IACC values in the case of three different motifs played in it. This study has conducted a psycho-acoustic experiment by using a virtual sound field representation produced by the stereo dipole technique in a listening room. In the experimental set-up there were two or four loudspeakers, corresponding to the single stereo-dipole or the dual stereo-dipole, respectively. By cancelling the cross-talk pathways (i.e. from left loudspeaker to right ear), the parallel sound presentation creates a 3D sound field for listeners sitting in the target point. The invert Kirkeby method was adopted to determine the inverse filters. Finally, the auralization technique with measured BIRs in theatres was utilized and the virtual sound field was generated in the Arlecchino listening room (Bologna, Italy), a low reverberation room equipped with an Ambisonic system. In the virtual sound field, the BIR was recorded again by the same dummy head used during the measurement in the theatres. The similarity between real and virtual sound fields was evaluated by comparing some acoustic parameters. The stereo-dipole technique demonstrates a good degree of accuracy of the sound field appearance. Moreover, the accuracy of the sound field appearance was analysed using two musical motifs and three musical instruments, comparing the values of the IACC calculated by echoic music with the virtual echoic music.