The mixing time of room impulse responses denotes the moment when the diffuse reverberation tail begins. A diffuse sound field can physically be defined by 1) equidistribution of acoustical energy and 2) a uniform acoustical energy flux over the complete solid angle. Accordingly, the perceptual mixing time is the moment when the diffuse tail cannot be distinguished from that of any other position in the room. This provides an opportunity for reducing the length of binaural impulse responses that are dynamically exchanged in virtual acoustic environments (VAEs). Numerous model parameters and empirical features for the prediction of perceptual mixing time in rooms have been proposed. This study aims at a perceptual evaluation of all potential estimators. Therefore, binaural impulse response data sets were collected with an adjustable head and torso simulator for a representative sample of rectangularly shaped rooms. Prediction performance was evaluated by linear regression using results of a listening test where mixing times could be adaptively altered in real time to determine a just audible transition time into a homogeneous diffuse tail. Regression formulae for the perceptual mixing time are presented, conveniently predicting perceptive mixing times to be used in the context of VAEs.
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