Introduction

The aim of room acoustics simulation is to simulate the reverberant properties of a space without having to physically build anything. This is useful for a variety of applications: architects need to be able to evaluate the acoustics of a building before construction begins; sound editors for film sometimes need to mix in recordings which were not made on location; electronic musicians like to conjure imaginary or impossible spaces in their music, and virtual-reality experiences must use audio cues to convince the user that they have been transported to a new environment.

Unfortunately, software allowing the synthesis of accurate impulse responses is not currently widely available. Often, software produced for research purposes is not made public. Such software that is available generally suffers from one or more of an array of issues:

• Most software relies only on fast geometric methods, which are inaccurate, especially at low frequencies. Conversely, programs opting to use more accurate wave-modelling methods require long time periods, in the order of days, or significant computing power to run.
• Licensing is also a problem. Most room acoustics packages are the product of years of combined research by multiple contributors, which is only made viable by releasing the software commercially. However, this inhibits further research, as the code is not freely available. This model also limits users to those able to pay, restricting widespread adoption.
• When software is made available freely, often the user experience suffers. Code requires manual compilation, or perhaps can only be run from a textual interface, or else the project is outdated and unmaintained.

The Wayverb project provides a solution to these problems, by making available a graphical tool for impulse response synthesis. It combines geometric and wave-modelling simulation techniques, providing an adjustable balance between speed and accuracy. It is also free to download, can be run immediately on commodity hardware, and the source code can be used and extended under the terms of the GNU General Public License (GPL).

The software has three main simulation engines, each with complementary strengths and weaknesses. Each engine had to be thoroughly researched, and implementation decisions evaluated, in order to balance the dual aims of accuracy and efficiency. This process is described in detail for each engine type, as is the process of automatically combining the engine outputs. Wayverb also implements two extensions to the basic room acoustics model, namely frequency-dependent reflections at boundaries, and microphone modelling, both of which are reviewed in detail.