Improvements of sound 3D auralisation by means of nonlinear convolution (plenary lecture)

In this paper, the improvement of nonlinear convolution is shown and applied in 3D auralisation of rooms. The most-used methods to recreate the acoustics of a room are based on measuring or simulating its impulse responses (3D or binaural). Once the IRs have been obtained, it is possible to recreate, by using linear convolution, the output signal that the system will generate when it is physically driven by any input signal. This method gives great results if the system is linear and time-invariant but it is not satisfactory in other cases, when it cannot be considered completely linear, such as during the emulation of musical instruments, which could be used in the 3D auralisation of rooms. The Arlecchino listening room at University of Bologna, based on stereo-dipole and Ambisonic systems, has been upgraded to nonlinear convolution, by means of a new numerical tool which uses the Volterra series. This new technique has been utilised during the acoustic design of the new Teatro Galli in Rimini, which is going to be reconstructed after its destruction during II World War. The acoustics of the new theatre, which follows the rule “where it was, how it was”, has been studied and virtually presented in the listening room by means of binaural IRs, considering the linear and nonlinear convolution with IRs of musical instruments previously measured at CIARM. A special VST plug-in has been realised for real-time calculation and is presented in the paper.