Objective measure of sound colouration in rooms

The growing interest in assisted reverberation systems for multipurpose halls has highlighted the need for new objective measures of particular artifacts due to these systems, such as colouration caused by acoustic feedback from loudspeakers to microphones. A simple method based on the analysis of the distribution of the modulus of the frequency response is presented. The distribution is compared to the theoretical Rayleigh distribution and the difference is expressed in terms of a limited number of indices. A numerical analysis of this method is presented, and the accuracy of the indices estimated. Results obtained from objective and subjective evaluation of colouration with measured impulse response show that the objective indices can distinguish clearly diffusive from non-diffusive passive rooms, and are a relevant measure of colouration in active rooms equipped with assisted reverberation systems.