Auralization

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Model of an auralized space
The corresponding early echogram

Auralization ("making audible" from the Latin auris = dt. 'Ear' = auricular) is a process for artificially making an acoustic situation audible. In room acoustics z. B. using the simulation of mirror sound sources , ray tracing and the calculation of the diffuse sound enables a room to be made audible , taking into account its geometric and acoustic properties. The word auralization is also sometimes used for it.

Origin and meaning

So-called model measuring methods have been common practice in acoustic construction since the early 1950s. Here, at one of wood , plaster and Plexiglas -made model the acoustic situation of the planned space, usually at a scale of 1:20, measured. However, this procedure represents an enormous expenditure of time and money.

The auralization was developed at the end of the 1960s and brought several advantages over the model measurement method.

The auralization process has undergone significant further development in the last ten years, which is directly linked to the ever increasing computing power of modern computers.

Areas of application

Room acoustics

Auralization gives acousticians new opportunities to draw precise conclusions about the effects of their measures in the planning phase and to assess them through subjective listening. Another application of auralization that should not be underestimated is its use to present acoustic planning. Just as a three-dimensional, virtually accessible room model enables the architect to present the planned rooms to his customers, the acoustician now has an equivalent presentation option with the help of auralization. He can let the customer hear what his premises will sound like and in this way clearly demonstrate the benefits of his measures. With conventional means, on the other hand, it is much more complicated to make it clear to an acoustic layman how important it is to plan the sound in a room.

Electroacoustics

Interactions between the sound source (quantity, position, radiation characteristics, amplitudes, etc.) and room acoustics can be tested against each other and the results used as a basis for decision-making when creating a sound system.

Building acoustics

In building acoustics, auralization programs are primarily used to evaluate the sound insulation properties of building components. The degree of absorption and the acoustic behavior of soundproof doors or windows can be tested using virtual models.

Environmental noise

Auralization is used to assess the influence of environmental noise, such as the noise from roads, railways, air traffic, wind farms, etc.

Vehicle acoustics

Auralization is a tool for evaluating acoustic measures in vehicle construction, both in relation to the situation in the passenger cell and to the insulation of the interior.

Convolution reverb

Probably the most exotic "application" of auralization, the convolution reverb, arose from a sound technical motivation. In principle, however, these programs, such as Emagic's Space Designer , work on the same principle as auralization programs: on the convolution of audio material with a room impulse response . One of the oldest convolution reverb plugins is the Acoustic Modeler (DirectX), which has been on the market since 1997.

functionality

The principle of auralization in room acoustics can be described as follows:

input

When entering, information about the following critical factors must be considered:

  • Type of sound source and receiver
  • Position and possible movement of the source and the receiver
  • Transmission routes to be considered
  • Room influences: size, shape and degree of absorption (α; in 1/3 octave or octave band spacing) and degree of scatter of all surfaces and objects.

In most programs, this entry can be made in a text editor as well as in a graphics editor.

The first step is the geometric input of the space. All points in space must be defined in a coordinate system.
Then all boundary surfaces are defined using their corner points. Acoustic properties are then assigned to these surfaces, ie their degrees of absorption in third-octave or octave bands. Finally, the position and type of sound source or receiver are entered.

Example: Source code excerpt from a project with the software Catt-Acoustic v.8 : 

Quelltext:                                      Erklärung:

CORNERS 			
201	0	0	0	               Definition der vier Punkte der
202    -w	0	0	               in der Abbildung (oben, "Modell
203    -w	d	0                      eines auralisierten Raumes") braun
204	0	d	0                      dargestellten Fläche.

PLANES				               Definition der Fläche 1 genannt
[1 floor \ 201 202 203 204 \ CARPET_SOFT ]     “floor” zwischen den 4 Punkten.
                                               Zuordnung eines Absorptionsverhaltens
                                               genannt "Carpet_Soft"

ABS CARPET_SOFT =                              Definition des Absorptionsverhalten
<7 8 21 26 27 37 47 57>                        Absorptionsgrad in Prozent pro Oktavband
                                               125Hz 250Hz 500Hz 1kHz 2kHz  4kHz  8kHz 16kHz
{191 168 155}                                  Definition einer Farbe zur Darstellung

calculation

In the second step, the program calculates a synthetic room impulse response using three main methods :

  1. the simulation of mirror sound sources
  2. the so-called ray tracing
  3. the calculation of the diffuse sound

With the mirror sound source method, the positions of the mirror sound sources are determined "behind" the boundary surfaces, which then all emit an impulse at the same time. Depending on the distance to the receiver and the degree of absorption of the surfaces, the early reflections can be calculated.
However, this process is almost exclusively limited to cuboid rooms.

With ray tracing, a large number of rays (10,000 to 80,000 per octave) are emitted from the sound source and their path is tracked until they reach the receiver. Ray tracing can provide information about the reverb tail of a room or complete the reflectogram . However, it is not suitable for real-time auralization, since it is associated with a computational effort in the range of hours.

With the diffuse sound calculation, the reverberation is calculated on the basis of variables and relationships known from measurements. This is done using filtered, exponentially decaying noise.

Depending on the software in question, the above-mentioned methods are used individually or in combination.

output

Finally, any sound recording can be folded with the acoustic properties of a room (room impulse response ) and the outer ear transmission function. The outer ear transfer function is used to simulate angle-dependent transfer functions of the human ear and is essential for the natural reproduction of the material.
The resulting binaural signal can then be presented and assessed via headphones.

software

Common auralization programs are:

Room acoustics
  • CATT-Acoustic
  • EASE
  • AquA (mirror sound source simulation)
  • AUVIS
  • ODEON (ray tracing)
  • Ulysses
Building acoustics
  • SONarchitect ISO
  • BASTIAN
  • NORA
  • Noise Reduction Auralization (real-time auralization system)

Weaknesses and limits

Neglecting the wave nature of sound

Auralization programs are based on a geometrical consideration of the acoustics . You are all neglecting the wave nature of sound. This means that all diffraction phenomena are not recorded. For the above-mentioned reason, geometric room acoustics have no general validity in small rooms. In large rooms, auralization methods can deliver acceptable results over almost the entire frequency range. In contrast to this, the low-frequency range of the spectrum must not be included in small rooms. “Large” or “small” refers to the wavelength λ .

High computing effort

Higher-order reflections can lead to a high computational effort, especially with ray tracing. This can sometimes be in the range of several hours. In order to shorten the computing time, the process is often terminated prematurely and the room impulse response is supplemented with a statistical reverberation time, which leads to inaccurate results. More recently, ray tracing has been optimized for modern GPUs , resulting in an exponential increase in performance. This further development has so far related to applications in image synthesis; a transfer to the applications in the auralization is in principle possible and nullifies the high computational effort as a counterpoint.

Simplification of the models

The spatial models are often simplified due to the time required to enter the geometric structures. This clearly leads to falsification of the result.

16 bit PC sound cards

With 16 bits the dynamic is limited to 96 dB. In addition, there is a high level of inherent noise from PC sound cards. Therefore, very quiet or very loud results cannot be adequately represented.

Psychoacoustics

Signals that are too short (15 to 20 seconds) are not sufficient to assess their effect, especially in cases of noise pollution. The signal can also be amplified. As a result, signal components that are actually not audible are raised above the hearing threshold, which falsifies the listener's impression.

literature

General
  • Michael Vorländer: Auralization - Fundamentals of Acoustics, Modeling, Simulation, Algorithms and Acoustic Virtual Reality Springer, Berlin 2008, ISBN 978-3-540-48829-3 .
  • Michael Dickreiter: Handbook of recording studio technology: room acoustics, sound sources, sound perception, sound transducers, sound reinforcement technology, recording technology, sound design. 6th edition. 2 volumes. Saur, Munich 1997, ISBN 3-598-11321-8 .
  • Friedrich u. a :: Book of tables for information and communication technology. 8th edition. 1997.
Acoustics
  • W. Fasold, E. Veres: Noise protection and room acoustics in practice. 2nd Edition. Huss Media, 2003.
Auralization
  • M. Vorländer, R. Thaden: Auralization of Airborne Sound Insulation in Buildings. In: Acustica / Acta acustica. Volume 86, No. 1, 2000, pp. 70-76.
  • M. Vorländer, R. Thaden: Making sound insulation in buildings audible. In: magazine for noise abatement. Volume 47, 2000, pp. 169-173.
  • M. Vorländer, HA Metzen: Auralization - A new tool for building acoustics planning. In: Deutsches Architektenblatt. Volume 5, No. 1, 2001, p. 61ff.
  • M. Vorländer: Auralization in Noise Control. Plenary lecture, Proc. Inter-Noise '03, Jeju, Korea, August 2003.
  • N. Korany: Computer Modeling and Auralization of Sound Fields in Rooms- An Overview. Invited paper for ICA, Kyoto / Japan 2004.
  • A. Freudenschuss: Building and room acoustics using the example of the Deutsche Welle Berlin radio studio. Technical work at the SAE Munich, 2004.
  • M. Vorländer: Room Acoustics in Virtual Reality. Plenary lecture, International Symposium on room acoustics - ISRA. Seville, September 2007.

Individual evidence

  1. ↑ For example, described here: http://graphics.stanford.edu/papers/i3dkdtree/gpu-kd-i3d.pdf

Web links