Papers by Claus Lynge Christensen
Ultragarsas "Ultrasound", Sep 22, 2014
The CAHRISMA project (Conservation of the Acoustical Heritage by the Revival and Identification o... more The CAHRISMA project (Conservation of the Acoustical Heritage by the Revival and Identification of the Sinan's Mosques Acoustics) investigates, among other things, the acoustics in some of the old churches and mosques in Istanbul. The present paper deals with acoustic computer simulations and in particular comparison between In-situ recordings and auralization obtained from simulations carried out in the Odeon program. Three of the rooms in the project-Sokullu, Süleymaniye and Saint Irene, were compared. Two types of In-situ recordings have been made, one directly recorded in the room with a person performing, and another where measured binaural room impulse responses (BRIR) have been convolved with anechoic recordings. These two types of recordings have been compared with simulated auralizations in selected positions. The rooms in the comparison vary in size and reverberation time.
The use of sine sweeps is a robust method to measure room impulse responses. One particular advan... more The use of sine sweeps is a robust method to measure room impulse responses. One particular advantage is that the frequency spectrum of the excitation signal can be controlled in the time domain-by changing the rate of frequency change-while keeping the amplitude of the signal virtually constant over time. The sine sweep approach is adopted in the measurement tool of the ODEON software. In this paper, a method to optimize the measurements is introduced. The spectrum of the sweep signal is modified, making use of a previously measured impulse response and its resulting Schroeder decay curve. The maximum dynamic range of the Schroeder curve is defined as the decay range. This decay range is calculated in octave bands, and its deviation from a broadband average is subtracted from the sweep spectrum magnitude. The goal of this approach is to redistribute the power across frequency bands in order to ensure a more uniform signal-to-noise ratio (SNR). The method is evaluated through experimental measurements. The proposed optimization leads to a more constant decay range across octave bands, with an improved SNR in bands with poor decay. Practical aspects including repeatability and sweep duration are discussed.
Proceedings of the ICA congress, 2019
Room acoustic simulation tools based on geometrical acoustics fail to predict accurately the beha... more Room acoustic simulation tools based on geometrical acoustics fail to predict accurately the behaviour of rooms at low frequencies. This inaccuracy can lead to poor acoustic conditions especially in rooms of moderate volume, such as classrooms and meeting rooms. The present paper tackles this problem by introducing a simulation technique for room acoustics based on the Image Source Method and the Equivalent Source Method. These methods are implemented in the time domain to achieve efficient calculations with reliable results for low to medium frequencies. Given a source emitting a pulse signal in a room, image sources up to different orders are defined to determine early reflections. With the direct sound field from the original source and the contributions of the image sources, the remaining part of the sound field is solved by the Equivalent Source Method to account for late reflections and diffraction effects. The results of the test simulations carried out show that this combined Image-Equivalent Source Method is a suitable option for room acoustics.
The correct level of presentation is important for all kinds of auralisation in order to be as re... more The correct level of presentation is important for all kinds of auralisation in order to be as realistic as possible. The method applied in ODEON is approximate, aiming at the A-weighted sound pressure level to match that of the calculation result of the same simulation. A pink noise signal is applied for the calibration. The trick is to create modified versions of the input signals used for auralisation in such a way that the input signals have the same A-weighted level. In order to ensure a proper calibration it is necessary to know the sound power level of the sound source used as input for the auralisation. This can be difficult in some cases and may be the major source of uncertainty in the calibration. Next step is to look at the room simulation that produces the auralisation, and to choose a source-receiver combination to be used for the calibration. The relation between the sound power of the source and the sound pressure level in the receiver position is a result of the roo...
The acoustic illusion of music being performed in any room, being virtual or real, is possible wi... more The acoustic illusion of music being performed in any room, being virtual or real, is possible with today's advanced room acoustic software, Odeon. Recently, a music CD has been released with the simulated acoustics of the famous Hagia Sophia in Istanbul, although the recordings were originally made in an anechoic room. The quality and realism of the 3D sound is believed to be unparalleled. The acoustic simulation technique has also been applied for the simulation of a complete symphony orchestra using multi-source-auralisation and an integrated mixing of the sound from all the instruments.
The measurement of the Sound Strength (G) room acoustic parameter requires a calibration of the m... more The measurement of the Sound Strength (G) room acoustic parameter requires a calibration of the measuring system, so either the sound power of the source or the sound pressure level at a distance of 10 m in free field is known. Two procedures are described in ISO 3382-1: Calibration in a reverberation chamber and calibration in free field in a large anechoic chamber. Both methods require that all conditions in the measuring chain (amplification gains, sound card, cables etc.) remain fixed during calibration and in-situ measurements. This can be impractical mainly because measurements may be performed much later than calibration and at a distant location, and it cannot be guaranteed that the conditions in the measuring chain remain unchanged. In this paper a Two-step calibration procedure is proposed that removes the requirement of fixed conditions of the measuring chain. The procedure adds a second step to the normal reverberation room or free field calibration methods, in order to ...
A common characteristic of religious spaces in Eastern and Western Mediterranean cultures is the ... more A common characteristic of religious spaces in Eastern and Western Mediterranean cultures is the existence of large curved surfaces, usually in form of domes at the ceiling. Modeling of such spaces using geometrical acoustic algorithms typically requires discretisation of curved surfaces into planar elements. The degree of discretisation plays a crucial role in the quality of results, and simulation of several acoustic phenomena such as focusing. In this paper an investigation of the size of discretized elements is performed using the ODEON Room Acoustics Software, version 13. For this investigation a model of the mosque “Selimiye” has been used. Impulse responses of this space were recorded in many positions as part of the CAHRISMA project (Conservation of Acoustical Heritage by the Revival and Identification of the Sinan’s Mosques Acoustics) in 2000 2003. The model has a big central dome and several other surrounding curved surfaces. Measured room acoustic parameters are compared ...
A new method has been developed for the calculation of transmission through walls, including aura... more A new method has been developed for the calculation of transmission through walls, including auralization in the receiving room. This has been made as an option in the room acoustic simulation software Odeon version 9. Transmission through multiple walls can be investigated; even walls with different materials on either side and with thickness can be handled. The influence of partial areas with different transmission losses, the volumes of the rooms, and the reverberation times of the rooms are included in the simulation results.
Proceedings of the Isra 2007 Seville Vol 1 2008 Isbn 9788469082676, 2008
The application of room acoustic simulations to industrial halls with a large number of sound sou... more The application of room acoustic simulations to industrial halls with a large number of sound sources has been known for many years as an efficient means for noise control. However, the application of the auralisation tool to multi-source environments is rather new. The challenges and possibilities are discussed through a number of examples including a symphony orchestra in a concert hall, crowd sounds in a theatre, and the speech privacy in an open plan office. In order to make this technique a useful tool it is important that the quality and realism of the auralisation is very high, but also that the user interface allows a sufficient overview and control of the whole scenario. Good localisation is particularly important in multi-source environments. For some applications the use of headphones is not possible, so it is necessary that the auralisation can be presented through a surround loudspeaker system.
The paper describes the state-of-the-art of room acoustic auralization and the results of two dif... more The paper describes the state-of-the-art of room acoustic auralization and the results of two different ways to validate the quality. The first method is an objective measurement of room acoustic parameters from the simulated impulse response using a monaural auralization filter. The measurement results are compared to the calculation results from the simulation. The other method is a subjective comparison by listening to three different binaural reproductions: The computer simulation, the recording with a dummy head in the real room, and a convolution of the measured binaural impulse response with an anechoic recording. This comparison has been made as part of a large project on Byzantine churches and Sinan's mosques in Istanbul.
Auralisation is a very complicated technique, the quality of which depends on every single part i... more Auralisation is a very complicated technique, the quality of which depends on every single part in a long chain, starting with the anechoic recording of the sound to be used as input, continu- ing through the room acoustic simulation that connects the source and the receiver, and ending in the presentation of the sound to the listening person. The auralisation of a symphony orchestra is an even bigger challenge because of the large number of sound sources distrib- uted over a considerable area. Recently, a number of high quality anechoic recordings of symphonic music aiming at the multi- source auralisation technique have been available. So, the aim of this paper is to give an overview of the auralisation chain with particular reference to the multi-source auralisation of a sym- phony orchestra.
This paper presents an extension to the traditional room acoustic modelling methods allowing comp... more This paper presents an extension to the traditional room acoustic modelling methods allowing computer modelling of huge machinery in industrial spaces. The program in question is Odeon 3.0 Industrial and Odeon 3.0 Combined which allows the modelling of point sources, surface sources and line sources. Combining these three source types it is possible to model huge machinery in an easy and visually clear way.
Introduction The ODEON 4.0 software packages are developed at the Department of Acoustic Technolo... more Introduction The ODEON 4.0 software packages are developed at the Department of Acoustic Technology during an ongoing research project. This manual is intended to serve as an introduction on modelling room geometries and to the facilities in the program. It will not cover in depth all facilities; explanations of displays, calculation parameters, results, etc. are available from within the program. In general through on-line documentation is available from within ODEON, providing context sensitive help from all displays. It is recommended to use the online information to learn about the specific features available from the different displays, the interpretation of results, calculation parameters, etc.. The answer is properly right at your hand. The contents of the manual are as follows: Chapter 1 covers installation of the program, changes from previous versions etc.. Chapter 2 is a Short guided tour, introducing the ODEON program and its facili
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Papers by Claus Lynge Christensen