A new hybrid simulation method for room acoustics is presented. It is grounded on two well known numerical simulation techniques for room acoustics. The hybrid method takes geometric acoustics for granted and uses an improved version of the classical ray-tracing technique for computing the specular reflections and a slightly modified energy transition method for simulating the diffuse reflections. The impulse responses (IRs) are then computed by superposition of the specular and diffuse ones. The reverberant part of the IRs gains a much more realistic aspect than the one obtained from either ones method alone. Both the ray-tracing technique and the energy transition method are reviewed and some improved features are discussed. The sound source and the receiver modeling are presented, including a new method for simulating the head related transfer functions (HRTFs), and based on the wavelet technique, which provides a shorter time computation of the binaural impulse responses for auralization purposes. In a companion paper, entitled Hybrid method for numerical simulation of room acoustics: Part 2 - Validation of the computational code RAIOS 3, a validation of the method in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones

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Nowadays, with the increasing capacity of personal computers, software in room acoustics simulation is being developed all over the world by strong architectural acoustic groups, as a practical and reliable way to evaluate the sound quality of a room. However, software must be exaustively tested in order to be recognized as a trustworthy tool for modern acoustical design. In this paper, a new software tool in room acoustics simulation, RAIOS, is presented. A hybrid technique, which uses the ray-tracing method to simulate the first part of the impulse response and an energy transition algorithm to compute its reverberant tail, for a room with arbitrary geometry is described. All the parameters for room acoustics quality, following ISO 3382 standard, are also computed. The effects of filtering, reflection, and absorption on the walls and in the air are considered in the model. The software has participated in Round Robin 3, promoted by PTB, Germany. The results of phase three of RR3 (the most complex one) are presented in this paper. Comparison with other software is given. If the experimental data of the PTB studio are available before the end of this year, then comparisons will be made.