Dynamic Measurement of Binaural Room Impulse Responses Using an Optical Tracking System

The binaural room impulse responses for different head orientations are captured by using a dynamic measurement technique. The system is excited by a so called periodic perfect sequence which exhibits the self-orthogonal property. A head-and-torso simulator is mounted on a turntable and is continuously rotated. During the measurement, the head orientation is also recorded with an optical tracking system. The BRIRs for selected azimuth angles are then computed by using a time-varying system identification method based on spatial interpolation. The performance of the proposed approach is evaluated by comparing the BRIRs obtained from a dynamic measurement and a conventional static measurement. Introduction Binaural room impulse responses (BRIRs) characterize the acoustic transmission from a sound source to the outer ears of a listener. BRIRs can be used for an authentic auralization of a loudspeaker array system that is installed in a room. For each loudspeaker, BRIRs are measured for different head orientations, so that rotational head movements can be included in binaural synthesis. Such a binaural re-synthesis has been often employed in listening experiments for the comparison of sound reproduction systems in different rooms, comparison of different spatial audio techniques, and for the perceptual evaluation in different listening positions, to name only a few [? , 1, 2, 3]. Another application can be found in music production, where the ear signals of a mixing studio are simulated, e.g. Nx 3D Audio plug-in by WAVES. This allows the sound engineer to mix using headphone in a virtual mixing room. Since the temporal and spectral structure of BRIRs strongly depends on the listener’s anthropometry, it is often advised to use individual BRIRs for higher timbral and spatial fidelity [4, 5, 6]. In a typical measurement technique, linearity and time-invariance of the system is assumed. It is thus important to immobilize the listener’s head during the measurement. To obtain a pair (left and right) of BRIRs, an excitation signal (e.g. sine sweep, maximum length sequence) is played back and the responses at the outer ears are captured. This is repeated for every possible combinations of loudspeakers and headorientations. Therefore, the total duration scales with the dimensionality (azimuth-only or azimuth-and-elevation) of the measurement, the spatial resolution of the head orientations, and the number of loudspeakers. To avoid such a tedious and time-consuming procedure, a dynamic measurement technique can be considered. In recent years, various approaches have been proposed for a time-efficient measurement of a large numger of impulse responses, e.g. head-related impulse responses (HRIRs) and spatial room impulse responses [7, 8, 9, 10, 11, 12]. Typically, the loudspeaker or the receiver is continuously moved and an excitation signal is played back during the entire measurement period. The movement has to be either controlled accurately based on a pre-defined trajectory, or captured with a tracking method. The impulse responses are then estimated from the captured signal by using a time-varying system identification method. In the present work, real room BRIRs are measured by using the approach introduced by the authors in [11]. The room is excited by a periodic perfect sequence and the signal captured at each outer ears are considered as a spatio-temporal sampling of the sound field. The original sound field is reconstructed by means of spatial interpolation. The BRIRs are then obtained by deconvolving the sound field with the excitation signal. The performance of the dynamic measurement are evaluated by comparing them with a conventional static measurement. System Identification For a head orientation φ, the acoustic signals (sound pressure) at the left and right ears are represented as