A Method for Capturing and Reproducing Directional Reverberation in Six Degrees of Freedom

TL;DR

A framework that extracts directional decay properties from a set of captured spatial impulse responses to characterize a directional feedback delay network is proposed and acquired in the main auditorium of the Finnish National Opera and Ballet in Helsinki from multiple source-listener positions.

Abstract

The reproduction of acoustics is an important aspect of the preservation of cultural heritage. A common approach is to capture an impulse response in a hall and auralize it by convolving an input signal with the measured reverberant response. For immersive applications, it is typical to acquire spatial impulse responses using a spherical microphone array to capture the reverberant sound field. While this allows a listener to freely rotate their head from the captured location during reproduction, delicate considerations must be made to allow a full six degrees of freedom auralization. Furthermore, the computational cost of convolution with a high-order Ambisonics impulse response remains prohibitively expensive for current real-time applications, where most of the resources are dedicated towards rendering graphics. For this reason, simplifications are often made in the reproduction of reverberation, such as using a uniform decay around the listener. However, recent work has highlighted the importance of directional characteristics in the late reverberant sound field and more efficient reproduction methods have been developed. In this article, we propose a framework that extracts directional decay properties from a set of captured spatial impulse responses to characterize a directional feedback delay network. For this purpose, a data set was acquired in the main auditorium of the Finnish National Opera and Ballet in Helsinki from multiple source-listener positions, in order to analyze the anisotropic characteristics of this auditorium and illustrate the proposed reproduction framework.

Figures (10)

• Figure 1: EDD analysis of a measured SRIR, illustrating directional decay deviations on the lateral plane. The radius is the time axis and the areas in red represent directions with more energy in the decay, while directions in blue have less.
• Figure 2: Flow diagram of the DFDN alary_frequency-dependent_2020. The delay paths are organized into delay groups. The thick lines represent multichannel signal paths.
• Figure 3: Main auditorium at the National Finnish Opera and Ballet in Helsinki, Finland. The positions of the loudspeaker ($S$) and microphones (circles numbered from 1 to 15) are shown. The point $v$ is the location of a virtual point used to illustrate the interpolation of parameters in Fig. \ref{['fig:InterpolationTest']}.
• Figure 4: Distribution of $\mathrm{EDC}_0$ values on the top hemisphere, representing the total energy in the decay of the sound field from the various captured microphones locations.
• Figure 5: Estimated directional decay times for the captured SRIRs in the frequency range of $200\,$Hz-$800\,$Hz, the values are centered around a mean decay times with red representing longer decay times, and blue shorter ones.