EP0642292A2 - Device for sonic stereo reproduction - Google Patents

Abstract

In a device for stereophonic reproduction in a closed space, preferably in a motor vehicle, having a number of loudspeakers and at least one listening location which can be located at different distances from the loudspeakers, audio signals provided for reproduction with the aid of the individual loudspeakers pass through delay devices, the delay time of which is adjustable. Means for measuring the sound propagation times from the individual loudspeakers to the listening location are provided, the delay times being automatically adjustable in such a manner that the sum of the sound propagation time and the delay time set in each case is identical for all loudspeakers. <IMAGE>

Description

The invention relates to a device according to the preamble of the main claim.

The human ear receives its directional information from the evaluation of level and transit time differences between the acoustic signals received by the right and left ear. With an ideal listening location in the middle of a so-called stereo triangle consisting of the left speaker, the right speaker and listeners, the directional information corresponds to the stereo recording.

If, on the other hand, the listener is at a location that is asymmetrical to a two or more loudspeaker system, the sound impression is spatially strongly shifted to the next loudspeaker.

While level differences can be compensated for manually by conventional balance controls and faders, the runtime differences of the sound signals of the individual loudspeaker systems are usually not compensated for. However, these are for directional hearing according to the psycho-acoustic Law of the first wavefront essential.

Car radios with runtime compensation are already known, but they require manual measurement and subsequent input of the distances between the listening location and the loudspeakers.

The object of the present invention is to facilitate the setting of the delay times in a device according to the type of the main claim.

In the device according to the invention, this object is achieved in that audio signals provided for playback with the aid of the individual loudspeakers pass through delay devices whose delay time is adjustable, that means for measuring the sound propagation times from the individual loudspeakers to the listening location are provided, and in that the delay times are so automatic can be set so that the sum of the sound propagation time and the respectively set delay time is the same for all speakers.

In addition to simplifying operation, the device according to the invention also has the advantage that the actual sound propagation time is taken into account while the manual measurement for an assumed path of the sound is carried out between the loudspeaker in question and the listening location. In the latter case, for example, reflection or deflection of the sound waves is not taken into account.

Level differences at the listening location are taken into account according to a further development of the device according to the invention in that means are also provided for measuring the sound level caused by the reproduction of a measurement signal, preferably a noise signal, by the individual loudspeakers at the listening location and that the volume of the individual Loudspeaker can be preset automatically in order to compensate for level differences.

Another development of the device according to the invention is that the set delay times and, if appropriate, the stored presets of the volume can be stored in a non-volatile manner for several listening locations. It is preferably provided that information about which of the stored delay times and, if applicable, the stored presets of the volume are supplied to the delay devices each time the device is switched on, can also be stored in a non-volatile manner.

With this development, for example, a car radio can be programmed with the device according to the invention after measuring the sound propagation times for the individual seating positions in such a way that the playback can be optimized by pressing a button on the individual seating positions and that when the device is switched on, the delay times assigned to a predetermined seating position can be set. This will generally be the driver's seating position.

Modern receiving devices, in particular car radios, often include digital signal processing. It is advantageous here if it is provided according to an embodiment of the invention that the delay devices are formed by digital memories from which the audio signals to be delayed are read out with a time delay compared to the writing.

berechnet wird, wobei Ta die einzustellende Verzögerungszeit in Abtastzyklen der digitalen Audiosignalverarbeitungseinrichtung, x den jeweiligen Lautsprecher und k das Verhältnis zwischen der Prozessor-Zyklusdauer, in welcher die Schall-Laufzeiten T_x bzw. T_max gemessen wurden, und der Abtastzyklusdauer bezeichnet.An advantageous embodiment of this embodiment is that the digital memories are part of a digital audio signal processing device that according to the Measurement of the sound propagation times (T _x ) for all loudspeakers (1 ... x) from which the maximum sound propagation time (T _max ) is selected and that the individual delay times according to ${\text{Ta}}_{\text{x}}{\text{= (T}}_{\text{Max}}{\text{-T}}_{\text{x}}\text{) · K}$

is calculated, where Ta denotes the delay time to be set in sampling cycles of the digital audio signal processing device, x the respective loudspeaker and k the ratio between the processor cycle duration in which the sound propagation times T _x or T _{max were} measured and the sampling cycle duration.

An adaptation of the device according to the invention to the respective arrangement of the loudspeakers and the listening location is advantageously possible in that a pulse signal is supplied to each loudspeaker in succession for measuring the sound propagation time, a timer being simultaneously measured which measures the time until on a measuring microphone the sound level exceeds a predetermined threshold. In order to avoid overloading high-frequency loudspeakers, it can be provided that the pulse signal is fed to the loudspeaker via a low-pass filter, preferably a third-order filter with a cut-off frequency of 11 kHz. The pulse signal itself is implemented, for example, by a rectangular pulse of approximately 3 ms duration.

In addition to the automatic adjustment to the sound propagation times, other adjustments can also be made and stored in the device according to the invention. For example, a further development is characterized in that the audio signals also go through frequency response equalizer circuits, that means for measuring the frequency response are provided between the loudspeakers and a measuring microphone and that the frequency response equalizers are adjustable according to the results of the measurement, the respective set frequency responses of the individual speakers for different Listening locations can be saved.

Fig. 1

ein Blockschaltbild einer erfindungsgemäßen Einrichtung,

Fig. 2

ein Ablauf-Diagramm zur Erläuterung der Messung der Schall-Laufzeiten und der Schallpegel sowie der anschließenden Einstellung der Verzögerungszeiten und Lautstärke und

Fig. 3

eine schematische Darstellung eines Autos mit vier Lautsprechern und einem Fahrer und mit den durch die Verzögerungszeiten für diese Hörposition entstehenden scheinbaren Lagen der Lautsprecher.

Exemplary embodiments of the invention are shown in the drawing using several figures and are explained in more detail in the following description. It shows:

Fig. 1

2 shows a block diagram of a device according to the invention,

Fig. 2

a flow chart to explain the measurement of the sound transit times and the sound level as well as the subsequent setting of the delay times and volume and

Fig. 3

is a schematic representation of a car with four speakers and a driver and with the apparent positions of the speakers resulting from the delay times for this listening position.

Identical parts are provided with the same reference symbols in the figures. In Fig. 3, signal lines are shown as solid lines and control lines as dashed lines.

The block diagram according to FIG. 1 represents the LF part of, for example, a car radio with inputs 1, 2, 3 for a receiving part, a cassette player and a CD player. Signals of a microphone amplifier 5 are fed to a further input 4, which is designed only for one of the stereo signals, for example the right signal R. During an operating mode "measuring" the input switch 6 is in the position 4, so that the signals of the microphone amplifier 5 are passed on. In a "playback" operating mode, signals from one of the inputs 1, 2 or 3 are fed to a stereo analog / digital converter 7 via the input switch 6. Of the Input changeover switch 6 and further changeover switches described later can be controlled by a control device 8.

The outputs of the analog / digital converter 7 are connected to inputs of a two-way switch 9, which can also be controlled by the control device 8. In the upper position of the two-way switch 9, the digitized audio signals L and R reach two controllable delay devices 10, 11; 12, 13. These can be implemented as read-write memory (RAM) on a digital signal processor or connected externally to this. The memory is accessed via the internal address and data management of the digital signal processor. The sequence, switchover and level control can be carried out by the digital signal processor itself or by an external microcontroller.

The output signals of the controllable delay devices are provided for the left front loudspeaker, for the left rear loudspeaker, for the right front loudspeaker and for the right rear loudspeaker and are therefore designated with LF, LR, RF and RR. These signals are fed to inputs of a four-way switch 14 and, in the upper position of the four-way switch, are passed on to two stereo digital / analog converters 15, 16.

The output signals LF ', LR', RF 'and RR' of the digital / analog converter 15, 16 arrive via controllable volume controls 17, 18, 19, 20 and power amplifiers 21, 22, 23, 24 as signals LF '', LR '',RF''andRR''to the loudspeakers 25, 26, 27, 28. A measuring microphone 29 can be brought to the different listening locations, in different positions in a motor vehicle, and is connected to the input of the microphone amplifier 5 connected.

An operating and possibly display unit 30 is connected to the control device 8, with which, in addition to the usual operating functions, the measurement of the transit times and the sound level can be initiated by a corresponding key input. For this "measuring" operating mode, the double changeover switch 9 is controlled into the lower position. Furthermore, the individual switches of the four-way switch 14 can be controlled independently of one another during the “measuring” operating mode in such a way that one of the switches one after the other assumes the middle position (connection to test signal pulse or noise) and the other switches assume the lower position, in which the respective Speakers received no signals. The measuring signal MESS arriving via the signal chain 29, 5, 4, 6, 7, 9 is then fed to a level meter 31 and then to a threshold discriminator 32. Its output is connected to a transit time meter 33, which essentially consists of a counter, which is started by the control device together with a pulse generator 34 and is stopped by the output signal of the threshold discriminator 32.

The output of the pulse generator is connected via a low-pass filter 35 to a first input of a changeover switch 36. A noise generator 37, which can also be controlled by the control device 8, is connected to the second input of the changeover switch 36.

FIG. 2 shows the flow chart of a program for the control device 8 (FIG. 1) during the "measuring" operating mode and in abbreviated form during the "playback" operating mode. In the "Playback" operating mode or in normal operation, the usual functions, such as manual control of the volume controls 17 to 20 and the selection between inputs 1, 2 or 3, are possible. Furthermore, in the "Playback" mode Read runtime and volume settings previously stored for a plurality of listening locations from a non-volatile memory of control device 8 and are supplied to actuators 10 to 13 and 17 to 20. The two-way switch 9 and the four-way switch 14 are in the upper position o.

The program part 41, which effects these functions, is run through cyclically, with a query being carried out before each repetition as to whether an acoustic measurement should take place. If this has been entered with the aid of the operating device 30, the operating mode "measure" is activated after branching 42. In a program part 43, the volume controls 17 to 20 (FIG. 1) are set to a defined standard value (average volume). In this part of the program it is also waited for the operator to bring the measuring microphone 29 (FIG. 1) to the first listening location to be measured.

Thereafter, the input switch to input 4 and the double switch 6 to the lower position are controlled in program part 44. The four-way switch 14 is brought to the middle position m for the respective channel to be measured and to the lower position u for the other channels, in which the connected loudspeakers are muted.

At 45, the switch 36 is set to the left position 1, while the pulse generator 34 and the time meter 33 are started. As soon as the sound level at the measuring microphone exceeds a certain threshold value, the transit time meter 33 is stopped at 46 and the measured value is stored in the control device 8 (FIG. 1).

Thereafter, the changeover switch 36 is brought into the right position r in the program part 47 and the noise generator is put into operation for a time of about 500 ms. With the aid of the level meter 31, the average noise level at the microphone is determined at 48 over part of the time window, for example over 200 ms. This value is also saved.

At 49 the program branches depending on whether all four channels have been measured. If this is not yet the case, the program parts 44 to 49 are repeated for the next channel. However, if all four channels have been measured, the measured values T _LF , T _RF , T _LR , T _RR (T _x ) for the runtimes of the four channels and the measured values L _LF , L _RF , L _LR , L _RR (L _x ) before.

berechnet, wobei Ta die einzustellende Verzögerungszeit in Abtastzyklen der digitalen Audiosignalverarbeitungseinrichtung, x den jeweiligen Lautsprecher (LF, RF, LR, RR) und k das Verhältnis zwischen der Prozessor-Zyklusdauer, in welcher die Schall-Laufzeiten T_x gemessen wurden, und der Abtastzyklusdauer bezeichnet. Zuvor wurde aus den gemessenen Schall-Laufzeiten die maximale Schall-Laufzeit T_max (in Prozessor-Zyklen) ermittelt. Ferner erfolgt im Programmteil 49 die Einstellung der Verzögerungseinrichtungen 10 bis 13 auf die errechneten Werte und eine Speicherung der vier Werte zusammen mit einer Angabe des zugehörigen Hörortes in einem nicht-flüchtigen Speicher der Steuereinrichtung.In the subsequent program part 50, the delay times to be set for the delay devices 10 to 13 are shown in FIG ${\text{Ta}}_{\text{x}}{\text{= (T}}_{\text{Max}}{\text{-T}}_{\text{x}}\text{) · K}$

where Ta is the delay time to be set in sampling cycles of the digital audio signal processing device, x the respective loudspeaker (LF, RF, LR, RR) and k is the ratio between the processor cycle duration in which the sound propagation times T _{x were} measured and the sampling cycle duration designated. The maximum sound propagation time T _max (in processor cycles) was previously determined from the measured sound propagation times. Furthermore, in program part 49 the delay devices 10 to 13 are set to the calculated values and the four values are stored together with an indication of the associated listening location in a non-volatile memory of the control device.

für die verschiedenen Lautsprecher berechnet. Die vier Ausgleichspegel La_x werden als fester Offset zum jeweiligen vom Benutzer eingestellten Lautstärkepegel in den einzelnen Kanälen hinzuaddiert. Die Ausgleichspegel werden nach ihrer Berechnung im nicht-flüchtigen Speicher für den zugehörigen Hörort abgelegt.In program part 51, the corresponding steps for the measured volume level L _x follow. First L _{max is} formed. After that ${\text{La}}_{\text{x}}{\text{= L}}_{\text{Max}}{\text{-L}}_{\text{x}}$

calculated for the different speakers. The four equalization levels La _x will be added as a fixed offset to the respective volume level set by the user in the individual channels. After their calculation, the compensation levels are stored in the non-volatile memory for the associated listening location.

A branch 52 takes place depending on whether further listening locations are to be measured. If this is not the case, the volume controls are set at 53 to the values existing before activation of the "measuring" operating mode plus the offset determined in program part 51. At 53, the input 1, 2 or 3 that was active before the calibration is set again. In addition, the other switches are switched according to the "playback" mode. The program then continues at 41. If, however, further listening locations are to be measured, which is done by an appropriate input, the program is repeated after branching 52 at 43.

3 schematically shows a car 60 with a driver 61 and four loudspeakers 25, 26, 27, 28. The distances a, b, c and d from the driver's head to the individual loudspeakers are of different sizes. As a result, the above-mentioned adverse effects occur. In the device according to the invention, the distance to all loudspeakers, which is effective for the psycho-acoustic listening impression, is made the same size by the delay time compensation with the aid of controllable delay devices 10 to 13 (FIG. 1). The loudspeaker 28 which is furthest away from the driver 61 maintains its distance d. The other loudspeakers also have a spacing of d due to the delay time equalization and are apparently in positions 25 ', 26' and 27 ', which lie on a circle around driver 61.

Claims (10)

Device for stereophonic reproduction in a closed space, preferably in a motor vehicle, with several loudspeakers and at least one listening location, which can be at different distances from the loudspeakers, characterized in that for reproduction with the aid of the individual loudspeakers (25, 26, 27, 28) provided audio signals pass through delay devices (10, 11, 12, 13) whose delay time can be set such that means (5, 29, 31, 32, 33, 34, 35) for measuring the sound propagation times of the individual loudspeakers (25 , 26, 27, 28) are provided to the listening location and that the delay times can be set automatically such that the sum of the sound propagation time and the respectively set delay time is the same for all loudspeakers (25, 26, 27, 28). Device according to claim 1, characterized in that further means (5, 29, 31, 37) for measuring the sound caused by the reproduction of a measurement signal, preferably a noise signal, through the individual loudspeakers (25, 26, 27, 28) at the listening location -Levels are provided and that the volume of the individual speakers (25, 26, 27, 28) automatically in the sense of a compensation of level differences can be preset. Device according to one of claims 1 or 2, characterized in that the set delay times and possibly pre-settings of the volume for several listening locations can be stored non-volatile. Device according to claim 3, characterized in that information about which of the stored delay times and, if applicable, the stored pre-settings of the volume when the device is switched on are supplied to the delay devices (10, 11, 12, 13) can also be stored in a non-volatile manner. Device according to one of the preceding claims, characterized in that the delay devices (10, 11, 12, 13) are formed by digital memories from which the audio signals to be delayed are read out with a time delay compared to the writing. Device according to claim 5, characterized in that the digital memories are part of a digital audio signal processing device, that after the measurement of the sound propagation times (T _x ), the maximum sound propagation time (T _max ) is selected therefrom for all loudspeakers and that the individual delay times according to ${\text{Ta}}_{\text{x}}{\text{= (T}}_{\text{Max}}{\text{-T}}_{\text{x}}\text{) · K}$

is calculated, where Ta denotes the delay time to be set in sampling cycles of the digital audio signal processing device, x the respective loudspeaker and k the ratio between the processor cycle duration in which the sound propagation times T _x or T _{max were} measured and the sampling cycle duration. Device according to one of the preceding claims, characterized in that in order to measure the sound propagation time, a pulse signal is supplied to a loudspeaker in succession, at the same time starting a timer (33) which measures the time until a measuring microphone (29) the sound level exceeds a predetermined threshold. Device according to claim 7, characterized in that the pulse signal is realized by a rectangular pulse of at least 3 ms in length. Device according to one of claims 7 or 8, characterized in that the pulse signal is fed to the loudspeaker (25, 26, 27, 28) via a low-pass filter (35), preferably of the third order with a cut-off frequency of 11 kHz. Device according to one of the preceding claims, characterized in that the audio signals also pass through frequency response equalizer circuits, that means for measuring the frequency response are provided between the loudspeakers and a measuring microphone and that the frequency response equalizers are adjustable according to the results of the measurement, wherein the frequency responses set for the individual loudspeakers can be stored for different listening locations.

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