[0001] The invention relates to a method for reproducing sound of a vehicle using a plurality
of transducers.
[0002] In the current state of the art, simulation devices in vehicle engineering are used
in order to predict acoustic properties of vehicles during the development phase.
Such devices present sound of a possible or a real vehicle to a listener in order
to investigate the subjective impression of certain vehicle sounds and to find an
optimal sound for a certain application. Such simulation devices are including but
not limited to NVH engineering purposes (noise, vibration, harshness) such as disclosed
by
Marc Allman-Ward, Roger Williams, G. Dunne and P. Jennings in "The evaluation of vehicle
sound quality using an NVH simulator", Internoise 2004, 33rd International Congress
and Exposition on Noise Control Engineering, Prag, Czech Republic, August 22-25 2004, and by
Karl Janssens, Hans Coomans, Ismaël Belghit, Antonio Vecchio, Patrick Van de Ponseele
and Herman Van der Auweraer in "A Virtual Sound Synthesis Approach for On-line Assessment
of Interior Car and Aircraft Noise", ICSV Conference, St. Petersburg, Russia, July
2004.
[0003] Vehicle sound simulation systems presented up to now use reproduction over headphones
or stereophonic loudspeaker reproduction e.g. with a loudspeaker installation of 4
loudspeakers and a subwoofer.
[0006] In the past years, several methods have been developed to enable the control of a
wave field in an extended listening area. A first method relies on the recreation
of the curvature of the wave front of an acoustic field emitted by a sound source
by using a plurality of loudspeakers. Such method has been disclosed by
A .J. Berkhout in "A holographic approach to acoustic control", Journal of the Audio
Eng. Soc., Vol. 36, pp 977-995, 1988, and is known under the name of "wave field synthesis". A second method relies on
the decomposition of a wave field into spatially independent wave field components
such as spherical harmonics or cylindrical harmonics. Such method has been disclosed
by
M. A. Gerzon in "Ambisonic in multichannel broadcasting and video", Journal of the
Audio Engineering Society, vol. 33, pp. 859-871, 1985. Both methods are mathematically linked as disclosed by
Jérôme Daniel, Rozenn Nicol and Sébastien Moreau in "Further Investigations of High
Order Ambisonics and Wavefield Synthesis for Holophonic Sound Imaging", Audio Engineering
Society, Proceedings of the 114th AES Convention, Amsterdam, The Netherlands, March
22-25, 2003. In theory, these methods allow the control of a wave field within a certain listening
zone in all three spatial dimensions. In practice, the physical control of the wave
field is limited due to the distance of the loudspeakers, which results in spatial
aliasing, and, in most implementations, due to the restriction of the loudspeaker
set-up to the horizontal plane. This allows no localisation of sound sources outside
of the loudspeaker plane. For these reasons, both methods do not provide a physically
correct wave field but are able to create a perceptively sufficient spatial impression
of virtual sound sources in a virtual room for simulation purposes. Both systems provide
perceptive cues for sound localisation of human hearing without reproducing all physical
properties of the desired wave field.
[0007] In practice, the said simulation approach with headphones using head-related transfer
functions shows several drawbacks. The localization is disturbed by front-back confusions,
out-of-head localization is limited and distance perception does not necessarily match
the intended real image. The feeling of wearing a headphone reduces the feeling of
being present into the virtual environment. In the past years, this method with headphones
has been widely used since in theory it promises to reproduce physically correct ear
input signals in order to create a spatial impression of sound. Practice has shown
that the spatial impression provided by this method does not necessarily match the
intended spatial sonic image and that strong differences in perception may occur from
one listener to another due to mismatches of the used HRTFs in the signal processing
to individual HRTFs of the listener. Such results have been published e.g. by
H. Møller, M. F. Sørensen, C. B. Jensen, D.Hammershøi in "Binaural technique: Do we
need individual recordings?", J. Audio Eng. Soc., Vol. 44, No. 6, pp. 451-469, June
1996 as well as by
H. Møller, D. Hammershoi, C. B. Jensen, M. F. Sørensen in "Evaluation of artificial
heads in listening tests", J. Audio Eng. Soc., Vol. 47, No. 3, pp. 83-100, March 1999. It has to be pointed out that in practice such physically correct sound simulations
do not necessarily provide perceptively correct sound simulations.
[0008] The said simulation approach with stereophonic loudspeaker reproduction shows very
limited possibilities of spatial sound reproduction: Stereophonic reproduction works
only for one specific listening position, the so called "sweet spot". Outside of this
listening position, the stereophonic sound image collapses and the sound seems to
come from the nearest loudspeaker. Taking as an example the simulation of a car interior
where one would like to place the listener not only acoustically into the simulated
environment but also provide a visual and haptical simulation of a car, it is almost
impossible to place a listener correctly between the loudspeakers, because there is
not enough space in a car for an equally distanced loudspeaker installation around
the driver position according to the norms for stereophonic systems such as disclosed
in the recommendation ITU-R BS.775-1 published by the International Telecommunication
Union (ITU).
[0009] Furthermore, in this example of a car simulator, the spatial sound imaging will only
give a correct impression for one single listening position neglecting all other possible
seating positions in the car.
[0010] If we take the example of a car simulation device where only loudspeakers for an
acoustic simulation are used without a mechanical and optical imitation of a car environment,
stereophonic systems still have strong drawbacks, since spatial sound reproduction
is limited due to the relatively small number of loudspeakers. The listener may not
freely move his head due to the small listening zone ("sweet spot") and the perception
of a homogeneous diffuse field is limited since only a few loudspeakers are used and
no further signal processing is applied to account for the loudspeaker position.
[0011] The aim of the invention is to overcome these drawbacks of the state of the art.
More precisely, it is the aim of the invention to use loudspeakers in order to avoid
the feeling of wearing a headphone and to overcome the described problem of a sweet
spot in order to create a spatial impression of sound in an enlarged listening area
using possibly an irregular spatial configuration of loudspeakers. Diffuse sound field
reproduction and localisation of simulated sound sources is to be improved. It is
not the idea to create physically correct ear input signals as described for headphones
reproduction but it is intended to create a perceptive impression that approximates
the impression of a real sound field.
[0012] The invention relies in processing audio signals representing the sound of a vehicle
using a plurality of transducers by calculating a plurality of transducers driving
signals from at least one said audio input signal and transducers positioning data
as well as sound field description data associated to said audio input signal. Methods
for such signal processing have been published for example under the names of "wave
field synthesis" and "ambisonics" as described above but have not been transferred
to such simulation approaches in sound quality assessment up to now since they do
not allow in practice a physically correct sound simulation but are restricted to
a perceptively correct sound simulation. Both exemplary methods do not provide a physically
correct wave field reproduction but allow a correct perception of determining parameters
for sound quality assessment in vehicle engineering. Quality of the simulation does
not rely on the physical approximation of the audio signals to a real or a possible
real signal but on approximating the perceptive properties of the simulation to those
of a real or a possible real signal.
[0013] More precisely the invention relates to a method for reproducing sound of a vehicle
using a plurality of transducers, characterized by calculating a plurality of transducers
driving signals from at least one audio input signal representing sound of a vehicle
using transducers positioning data and sound field description data associated to
said audio input signal.
[0014] Furthermore the method may comprise steps
- wherein the plurality of transducers driving signals drive a plurality of transducers
synthesizing a wave field perceived by a listener.
- wherein sound field description data associated to the audio input signal refer to
the position of a virtual sound source in space in order to synthesize the wave field
of this virtual source using the plurality of transducers.
- wherein the position in space associated to at least one audio input signal is referring
to a position of a virtual sound source in space at least very far distanced from
the plurality of transducers such that the wave field synthesized by the plurality
of transducers contains substantially planar wave fronts. If a sound source is located
at a very far distance, the curvature of the wave front can be considered as almost
planar. For virtual sound sources, this approximation is true in the loudspeaker plane.
At least for virtual sound source at a larger distance than 10m from the loudspeakers,
in most applications the wave front can be considered as planar from a perceptual
point of view.
- wherein the sound field description data associated to an audio input signal refer
to the radiation characteristics and the position of a virtual sound source in space
in order to synthesize the wave field of this virtual sound source using the plurality
of transducers.
- wherein the sound field description data refer to at least one spatially independent
wave field components such as spherical harmonics, or cylindrical harmonics.
- wherein calculating the plurality of transducers driving signals comprises processing
each audio input signal to form output signals associated to each transducer using
filters derived from, at least, the sound field description data, and summing in summing
units, for each transducer, the respective output signals derived from all audio input
signals at the previous step. Furthermore it may comprise a step wherein the filters
are used to compute the plurality of transducers driving signals for each audio input
signal and wherein said filters are calculated in real time using the sound field
description data and the transducers positioning data. Furthermore it may comprise
a step wherein the filters used to compute the plurality of transducers driving signals
for each audio input signal are extracted from a database of precalculated filters
considering transducers positioning data and a set of sound field description data.
[0015] Moreover the invention comprises a device for reproducing sound of a vehicle using
a plurality of transducers, characterized by, a storing unit for storing at least
one audio input signal representing sound of a vehicle and by a wave field computing
device connected to the storing unit calculating a plurality of transducers driving
signals by using the said audio input signal and transducers positioning data as well
as sound field description data associated to said audio input signal, for driving
the plurality of transducers connected to the wave field computing device.
[0016] The invention will be described with more detail hereinafter with the aid of an example
and with reference to the attached drawings, in which
figure 1 shows a possible configuration of the device according to the invention and
figure 2 shows a possible configuration of a wave field computing device.
[0017] Figure 1 shows a possible configuration of the device according to the invention.
A storing unit 7 stores audio input signals 2 representing the sound of a vehicle.
It may also store sound field description data 8 associated to each audio input signal
2. If these sound field description data 8 are not stored in the storing unit 7 they
are directly stored and processed in a wave field computing device 3. The wave field
computing device 3 calculates a plurality of transducers driving signals 4 by using
the said audio input signal 2 and transducers positioning data 15 as well as sound
field description data 8 associated to said audio input signal 2. The transducers
positioning data 15 describe the position of each transducer in space relative to
a reference point 11. The sound field description data may comprise a description
about the position of a virtual sound source 12 in space relative to a reference point
13. The plurality of transducers driving signals 4 drive the plurality of transducers
5 synthesizing a wave field 6. The said wave field 6 may then be perceived by a listener
1.
[0018] Figure 2 shows a possible configuration of the wave field computing device 3. In
this exemplary configuration, two audio input signals 2 are used. They are processed
by set of filters 9 to form output signals 14 associated to each transducer. Then,
a step of summing in summing units 10 is performed on the respective output signals
14 for each transducer to derive the plurality of transducers driving signals 4.
[0019] Applications of the invention are including but not limited to the following domains:
interior noise simulation for car, interior noise simulation for train, interior noise
simulation for aircraft, flyover noise simulation for aircraft, outside noise simulation
for car, etc.
[0020] Vehicles can be any transportation device such as cars, trucks, trains, aircrafts,
motorbikes, etc.
[0021] The invention will hereinafter be more clearly described with the aid of an example
of a simulation of the interior noise of a car or parts of the interior noise of a
car. In such case, the audio input signal 2 representing the sound of a vehicle may
consist of recorded exterior or interior sounds of at least one vehicle or of synthesized
exterior or interior sounds of at least one vehicle, such as road noise, wind noise,
engine noise, warning noises from user interfaces, noise of small electric motors,
etc. Recorded sounds may result from recordings using microphones. Synthesized sounds
may result from models of a vehicle describing the construction and properties of
different parts of the vehicle and their acoustic parameters such as transfer functions.
Such audio input signal 2 does not necessarily need to approximate physically the
properties of a real or a possible vehicle sound but may be a perceptive approximation
to the sound of real or a possible vehicle. For example one can simulate an extended
sound source by using phantom source imaging between two virtual sound sources reproduced
with the said method wave field synthesis, allowing a control of sound source localisation
and source extension as published by
Günther Theile, Helmut Wittek and Markus Reisinger in "Wellenfeldsynthese-Verfahren:
Ein Weg für neue Möglichkeiten der räumlichen Tongestaltung", Proceedings of the 21st
VDT International Audio Convention (Tonmeistertagung), Hanover, Germany, 2002. Therefore the audio input signal 2 represents perceptively the sound of a vehicle
even if the physical properties of the synthesized wave field may be different from
the sound field in a real vehicle. Note that the sound described by one audio input
signal 2 does not necessarily need to describe the whole vehicle sound. It is possible
to use separated signals for different sound sources of the vehicle, especially when
a model for sound synthesis is applied to generate the audio input signals 2. Then,
the spatial sound reproduction of this invention allows an enhanced spatial separation
of different sound sources of the vehicle and separated investigations of different
sources, e.g. for engine noise, road noise, wind noise, warning sounds from user interfaces,
etc.
[0022] In such an exemplary application, the transducers will be loudspeakers.
[0023] In such an exemplary application, the wave field will be an acoustic field (sound
field), which can be perceived by human hearing.
[0024] The transducers positioning data can be derived from measurements of angle and distance
of the loudspeakers in space relative to a given reference point.
[0025] The sound field description data 8 associated to each audio input signal 2 provides
information about how to calculate the plurality of transducers driving signals 4.
[0026] Such information may describe the sound field according to at least one element of
a group of elements comprising the methods of wave field synthesis and ambisonics.
In the case of wave field synthesis, the sound field description data 8 associated
to the audio input signal 2 may refer to the position of a virtual sound source in
space in order to synthesize the wave field of this virtual source using the plurality
of transducers 5. In the case of ambisonics, the sound field description data 8 may
refer to at least one spatially independent wave field component such as spherical
harmonics, or cylindrical harmonics. But also other information may be described by
the sound field description data 8. For example, it is possible to describe the radiation
characteristics of a virtual sound source and to create a sound field according to
this description as disclosed by
Olivier Warusfel, Etienne Corteel, Nicolas Misdariis, Terence Caulkins in "Reproduction
of sound source directivity for future audio applications", Proceedings of the ICA-International
Congress on Acoustics, Kyoto, Japan, 2004. The said sound field description data 8 may also describe parameters such as source
width, dynamic behaviour of radiation characteristics and any other parameter influencing
the sound field emitted by a source.
- 1 listener
- 2 audio input signal (at least one)
- 3 wave field computing device
- 4 plurality of transducers driving signals
- 5 plurality of transducers
- 6 wave field
- 7 storing unit
- 8 sound field description data
- 9 filters
- 10 summing unit
- 11 reference point for loudspeaker position
- 12 virtual sound source
- 13 reference point for virtual sound source position
- 14 output signals
- 15 transducers positioning data
1. A method for reproducing sound of a vehicle using a plurality of transducers (5),
characterized by calculating a plurality of transducers driving signals (4) from at least one audio
input signal (2) representing sound of a vehicle using transducers positioning data
(15) and sound field description data (8) associated to said audio input signal (2).
2. The method of claim 1 wherein the plurality of transducers driving signals (4) drive
a plurality of transducers (5) synthesizing a wave field (6) perceived by a listener
(1).
3. The method of claim 1, wherein sound field description data (8) associated to the
audio input signal (2) refer to the position of a virtual sound source (12) in space
in order to synthesize the wave field of said virtual sound source (12) using the
plurality of transducers (5).
4. The method of claim 3, wherein the position in space associated to at least one audio
input signal (2) is referring to a position of a virtual sound source (12) in space
at least very far distanced from the plurality of transducers (5) such that the wave
field (6) synthesized by the plurality of transducers (5) contains substantially planar
wave fronts.
5. The method of claim 1, wherein the sound field description data (8) associated to
an audio input signal (2) refer to the radiation characteristics and the position
of a virtual sound source (12) in space in order to synthesize the wave field of the
said virtual sound source (12) using the plurality of transducers (5).
6. The method of claim 1, wherein the sound field description data (8) refer to at least
one spatially independent wave field component such as spherical harmonics, or cylindrical
harmonics.
7. The method of claim 1, wherein calculating the plurality of transducers driving signals
(4) comprises processing each audio input signal (2) to form output signals (14) associated
to each transducer using filters (9) derived from, at least, the sound field description
data (8), and summing in summing units (10), for each transducer, the respective output
signals (14) derived from all audio input signals (2) at the previous step.
8. The method of claim 7, wherein the filters (9) are used to compute the plurality of
transducers driving signals (4) for each audio input signal (2) and wherein said filters
(9) are calculated in real time using the sound field description data (8) and the
transducers positioning data (15).
9. The method of claim 7, wherein the filters (9) used to compute the plurality of transducers
driving signals (4) for each audio input signal (2) are extracted from a database
of pre-calculated filters considering transducers positioning data (15) and a set
of sound field description data (8).
10. A device for reproducing sound of a vehicle using a plurality of transducers (5),
characterized by, a storing unit (7) for storing at least one audio input signal (2) representing
sound of a vehicle and by a wave field computing device (3) connected to the storing
unit (7) calculating a plurality of transducers driving signals (4) by using the said
audio input signal (2) and transducers positioning data (15) as well as sound field
description data (8) associated to said audio input signal (2), for driving the plurality
of transducers (5) connected to the wave field computing device (3).