  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.
