Method and apparatus for determining the acoustic spatial characteristics particularly of a vehicle occupant compartment in a motor vehicle

This application claims the priority of German patent document 199 33 317.3, filed Jul. 16, 1999, the disclosure of which is expressly incorporated by reference herein.

The invention relates to a method and an apparatus for determining the acoustic spatial characteristics of an enclosure, particularly of a vehicle occupant compartment in a motor vehicle.

For example, in the case of audio and video receivers for hi-fi playback, methods are known which permit one-time manual or automatic adjustments to be made at the equipment which is playing back the useful sound, for a spatial adaptation. In one known manual adjustment technique, for example, the spatial measurements, the locations of the loudspeakers and/or the reflection condition of the walls can be input to the equipment. In a known automatic adjustment arrangement, a special test sound is emitted when the hi-fi equipment is installed, and the analysis sound then received by means of a microphone, is analyzed to determine the spatial sound parameters. The latter are then correspondingly stored by means of a spatial sound processor, for the playback of a space-adapted useful sound.

When using the known methods in motor vehicles, the problem arises that the spatial acoustics in the vehicle occupant compartment change constantly; for example, as a function of the number and movement of the vehicle occupants, noise-affecting environmental influences (e.g., wind noise), temperature fluctuations, road conditions, or operating parameters of the motor vehicle, (e.g., vehicle speed or rotational engine speed).

Furthermore, methods are known for the active sound compensation by means of digital adaptive filters which, however, usually adapt too slowly to compensate the disturbing noises which often change very rapidly in the vehicle.

It is an object of the invention to optimize the sound quality of acoustic systems in motor vehicles, such as CD and radio playback equipment or handsfree telephone systems, in a simple manner in the sense of a dynamic space adaptation.

This and other objects and advantages are achieved by the method and apparatus according to the invention for determining acoustic spatial characteristics (particularly in a vehicle occupant compartment in a motor vehicle), in which a piece of equipment which normally emits a useful sound (such as music) also emits a test sound, in a psycho-acoustic masking range of the useful sound. Subsequently, the total sound, consisting of the reflected useful sound and the reflected test sound, is recorded as analysis sound. Finally, the reflected test sound fraction of the analysis sound is analyzed (in a known manner) with respect to the acoustic spatial characteristics. Preferably, particularly post-masking in the time domain and/or simultaneous masking in the frequency domain are utilized. Although the utilization of the pre-masking is a possible alternative, it is too complicated.

The test sound can be emitted simultaneously with the useful sound (for example, during a piece of music), the test sound becoming inaudible as a result of the so-called masking effect of the useful sound.

For background information on the nature of the psychoacoustic masking, reference is made to the “Psychoacoustics” Textbook by E. Zwicker, Springer Publishers, 1982, particularly Pages 35, and on, and Pages 94, and on.

In one embodiment of the invention, the masking range of the useful sound is determined in a useful-sound analysis block. A test sound is then defined which is adapted for the determined masking range, before the useful sound and the test sound are emitted. For example, within a piece of music, as a function of individual sections of the piece of music (the useful sounds), for example, with particularly wide covering ranges, several test sounds are emitted several times.

By means of the invention, the spatial characteristics, and thus the spatial transmission characteristics, are dynamically adaptively determined and compensated. This takes place by means of arbitrarily frequent test sound emission during a useful sound playback which can take place by the selection of the respective test sound in the inaudible range.

Also, as a result of the invention, simultaneous compensation of dispersions of the electroacoustic components (such as the loudspeaker, the microphone, the transducer or the amplifier) is possible.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

FIG. 1 is a conceptual block diagram of a system for implementing the method according to the invention;

FIG. 2 is a graphic depiction of a test sound in the aftercovering range according to the method of the invention;

FIG. 3 shows a test sound in the simultaneous covering range according to the method of the invention.

FIG. 1 illustrates, for example, a handsfree telephone system or a CD player in a motor vehicle as a piece of equipment 1 emitting a useful sound. From the piece of equipment 1 , the useful-sound signal is first sent to a useful-sound analysis block 2 . In the useful-sound analysis block 2 , the psychoacoustic covering range, particularly the aftercovering range (FIG. 2) and/or the simultaneous covering range (FIG. 3) of the (audible) useful sound is determined which results from the (first digital or analog electric) useful-sound signal.

Subsequently, the test sound (T; TS) is defined in at least one of the two determined covering ranges ( 6 , FIG. 2; 7 , FIG. 3 ), which test sound preferably consists of orthogonal excitation sequences. The selection of the test sound in the covering range is essential to the invention; that is, in a frequency range and/or in a level range which is inaudible to the human ear because of the masking effect of the useful sound.

The covering range of the useful sound is determined in the useful-sound analysis block 2 , before the useful sound and the test sound are emitted; that is, the useful sound emitted by the piece of equipment 1 (together with the test sound) is emitted in a delayed manner by the useful-sound analysis block 2 to the loudspeaker 3 .

For determining the acoustic spatial characteristics of the vehicle occupant compartment, the thus defined test sound is emitted from the useful-sound analysis block 2 by way of the loudspeaker 3 together with the useful sound into the vehicle occupant compartment. Subsequently, the analysis sound is recorded by means of a microphone 5 , which may, for example, be the handsfree microphone, which is present anyhow, or an additional reference microphone, and analyzed in the test sound analysis block 4 . Although the analysis sound contains both the reflected useful sound and the reflected test sound, as a result of the connection of the useful-sound analysis block 2 , which emits the useful sound and the test sound, with the test sound analysis block 4 , the test source can be isolated and considered separately. The special analysis takes place by a corresponding comparison of the emitted test sound with the recorded test sound, for example, similar to known correlation techniques. As a result, the spatial characteristics can be determined in the form of a spatial transmission function and can be taken into account during the further playback of the useful sound.

The useful-sound analysis block 2 and the test sound analysis block 4 can also be integrated in the piece of equipment 1 .

In FIG. 2, the time t is plotted on the abscissa and the sound level (in dB) is plotted on the ordinate. Until the point in time t 0 , a useful sound or a useful-sound signal, such as a section of a piece of music, is played back by the piece of equipment 1 (FIG. 1) at a medium level P. At the point in time t 0 , a pause follows. In the pause range (t>t 0 ), the sound level of the aftercovering range 6 is illustrated. In this aftercovering range 6 , the test sound T is defined which particularly has a level that is below the level of the sound signal in aftercovering range 6 .

In FIG. 3, the frequency f is shown on the abscissa and the sound level (in dB) on the ordinate. The useful sound in this example has two frequencies with comparatively high levels which define the dash-dotted simultaneous covering range 7 . In this case, the test sound is formed, for example, of a broad-band noise-type test signal (TS) which has a level below that of the simultaneous covering range 7 but above the level of the useful sound.

Thus, in the above-mentioned embodiments, both the test sound T according to FIG. 2 and the test sound TS according to FIG. 3 are in a momentarily inaudible range of the human ear, so that the useful sound can be emitted simultaneously with the test sound. However, on the other hand, the test sound has a sufficiently high level to be utilized for dynamic determination of the spatial characteristics according to the method of the invention.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.