📄️ Solver concept
Covering the entire audible spectrum with the wave-based solver requires substantial compute resources and it is in most cases considered impractical, but also to some extend, unnecessary to do. Therefore Treble's state-of-the-art Geometrical Acoustics (GA) solver is used to compute the high frequency part of the acoustic response, which is later combined with the wave-based results via hybridization.
📄️ The Image-Source Method
The image-source method (ISM) is a widely used method to model the propagation and reflection of acoustic waves[1,2]. The basic concept is to mirror the original source across each of the planes in the model, thereby creating an image source. The geometrical model of the space generally consists of many planes, that each will create an image source. After mirroring the original source point across all planes, the visibility of the reflection path to the receiver can be verified by tracing a ray backward. This process begins from the receiver point toward the image source, followed by tracing from the intersection point of the ray and the plane back to the original source.
📄️ The Ray-Radiosity Method
The traditional method of acoustic ray tracing involves tracing rays throughout the environment while detecting intersections with a small detection sphere. While this method is conceptually straightforward and intuitive, it typically requires a large number of rays to generate a sufficient number of hits for constructing a meaningful energy histogram.
📄️ Scattering
In acoustic simulations, scattering is used to describe how sound interacts with surfaces in a non-specular manner. Real-world surfaces are rarely perfectly smooth, causing reflections to scatter in multiple directions rather than following a purely specular path.
📄️ Directivity
The Treble GA solver can model the directional characteristics of sources. Currently, directivity is represented by magnitude only, per octave band, for both the Image-Source method (ISM) and the Ray-Radiosity (RR) solver.
📄️ Hybridization (GA)
When integrating ISM with the stochastic energy particle model of RR, two key considerations must be addressed. First, to avoid double counting of reflections, specular reflections already accounted for by ISM must be excluded from RR to ensure a correct energy balance. Consequently, RR should only track energy particles that have undergone scattering, as purely specular reflections are fully handled by ISM. However, beyond the maximum reflection order of ISM, no further restrictions apply, allowing all possible combinations of reflection types (e.g., diffuse, specular, scatter) to be considered in the RR process.