EP3697108A1

EP3697108A1 - Car audio system

Info

Publication number: EP3697108A1
Application number: EP19157678.4A
Authority: EP
Inventors: Tomasz Twardowski; Grzegorz Golabek
Original assignee: Aptiv Technologies Ltd
Current assignee: Aptiv Technologies Ltd
Priority date: 2019-02-18
Filing date: 2019-02-18
Publication date: 2020-08-19

Abstract

A method for operating a car audio system comprising a loudspeaker setup connected to control means for reproducing audio information is described, with said loudspeaker setup comprising a left loudspeaker arrangement and a right loudspeaker arrangement activated by said control means via a left channel and a right channel, respectively. For generating a fader function as to a rear/front audio directivity for the car occupants via only the left channel and right channel spectral subbands of the audio information are formed by FIR filtering.

Description

FIELD

The present disclosure relates to a method for operating a car audio system comprising a loudspeaker setup connected to control means for reproducing audio information, with said loudspeaker setup comprising a left loudspeaker arrangement and a right loudspeaker arrangement activated by said control means via a left channel and a right channel, respectively. The disclosure further relates to a respective car audio system in particular for carrying out the method.

BACKGROUND

Previous car audio systems require left and right loudspeakers activated by left and right channels for providing a left/right sound directivity, and additional front and rear loudspeakers activated by additional front and rear channels for providing a front-rear sound directivity. All loudspeakers are shared by all car users. For balancing the sound level between front and rear channels a dedicated fader is necessary. For the front/rear fader functionality only gain is changed on the front/rear channels.
However, a full loudspeaker setup also including front and rear loudspeakers is not available in some cars due to cost or space imitation reasons. This is in particular the case with some roadsters or sports cars.
Accordingly there is a need to provide a method and a car audio system of the above referenced kind by which the aforementioned problem is overcome. In particular, the left/right sound directivity together with the front/rear sound directivity should be achieved only by left/right loudspeakers activated only by the left/right channels.

SUMMARY

The present disclosure provides a method with the features of claim 1 and a car audio system with the features of claim 10. Embodiments of the method and of the car audio system are given in the subclaims, the description and the drawings.
In one aspect, the present disclosure is directed at a method for operating a car audio system comprising a loudspeaker setup connected to control means for reproducing audio information, with said loudspeaker setup comprising a left loudspeaker arrangement and a right loudspeaker arrangement activated by said control means via a left channel and a right channel, respectively. A fader function as to a rear/front audio directivity for the car occupants via only the left channel and right channel is generated by forming spectral subbands of the audio information by FIR filtering with fixed delay and adjustable by parameters such as gain, delays, edge frequencies in the subbands and/or the like, and/or by shaping the sound of the reproduced audio information by FIR filtering on the basis of Head Related Transfer Functions (HRTFs).
Due to this solution not only the left/right sound directivity but also the front/rear sound directivity is achieved by the left/right loudspeaker arrangements activated by the two left/right channels. Consequently, additional front/rear loudspeakers activated by additional front/rear channels can be dispensed with. The respective front/rear sound directivity is already achieved by the front/rear loudspeaker setups activated by the left/right channels. Hence, a front/rear sound directivity can also be realized in cars where a full loudspeaker setup including separate front/rear loudspeakers cannot be realized due to cost or space imitation reasons. In signal processing, a finite impulse response (FIR) filter is a filter whose impulse response is of finite duration, because it settles to zero in finite time. The impulse response of an Nth order discrete-time FIR filter lasts exactly N+1 samples before it then settles to zero. FIR filters can be discrete-time or continuous-time filters, and digital or analog.
A head-related transfer function (HRTF) is a response that characterizes how an ear receives a sound from a point in space. As sound strikes the listener, the size and shape of the head, ears, ear channel, density of the head, size and shape of nasal and oral cavities, all transform the sound and effect how it is perceived, boosting some frequencies and attenuating others. The HRTF responses of the human ear with varying location of the sound source are measured and collected in publicly available databases which can be used for the sound shaping by FIR filtering.
The method may comprise one or more of the following features:
Said step of generating said fader function may comprise the activation of more than one loudspeaker by each of the two channels, and/or the activation of at least two loudspeakers of different frequency characteristics. The step of associating at least one tweeter loudspeaker and at least one midrange loudspeaker with each of the two channels, with the generation of said fader function by the formation of adjustable spectral subbands optionally comprising changing the frequency spectrum of a respective channel in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel. The step of associating dedicated loudspeakers for the driver and at least one passenger with each of the two channels, with a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger optionally being associated with each of the two channels. The step of generating a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions comprises the use of average ear characteristics, optionally using average ear characteristics according to the KEMAR model. The step of activating a subwoofer of each of the loudspeaker arrangements by the respective channel. Optionally with said subwoofers not being affected by at least one of a respective change of the frequency spectrum and a respective sound shaping and are used only for a delay compensation.
The generation of said fader function may comprise the activation of more than one loudspeaker by each of the two channels. The generation of said fader function may comprise the activation of at least two loudspeakers of different frequency characteristics. The difference in the frequency characteristics in the loudspeakers connected to one channel is essential in particular in connection with the generation of said fader function by the formation of spectral subbands, since the respective space-frequency diversity of the loudspeaker setups can be exploited.
For example, at least one tweeter loudspeaker and at least one midrange loudspeaker may be associated with each of the two channels.
The generation of said fader function by the formation of adjustable spectral subbands may comprise changing the frequency spectrum of a respective channel in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel.
Dedicated loudspeakers for the driver and passenger and at least one passenger may be associated with each of the two channels.
In the latter case, a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger may be associated with each of the two channels.
According to an embodiment of the method, the generation of a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions comprises the use of average ear characteristics, in particular average ear characteristics according to the KEMAR model.
The KEMAR database comprises average Head Related Transfer Functions (HRTFs) for a torso of a typical anatomy.
According to an embodiment of the method each of the loudspeaker arrangements may comprise a subwoofer which is activated by the respective channel.
Said subwoofers may not be affected by a respective change of the frequency spectrum and/or a respective sound shaping and are used only for a delay compensation.
In another aspect, the present disclosure is directed at a car audio system comprising a loudspeaker setup connected to control means for reproducing audio information, with said loudspeaker setup comprising a left loudspeaker arrangement and a right loudspeaker arrangement activated by said control means via a left channel and a right channel. The control means are laid out for generating a fader function as to a rear/front audio directivity for the car occupants via only the left channel and right channel by forming spectral subbands of the audio information by FIR filtering with fixed delay and adjustable by parameters such as gain, delays, edge frequencies in the subbands and/or the like, and/or by shaping the sound of the reproduced audio information by FIR filtering on the basis of Head Related Transfer Functions.
The generation of the fader function by forming spectral subbands of the audio information, i.e. by source shaping, changes the spectrum on a common channel to balance sound energy especially between midrange and tweeter loudspeakers. The generation of the fader function by shaping the sound of the reproduced audio information by FIR filtering on the basis of Head Related Transfer Functions, i.e. by ear shaping, changes the spectrum to mimic move of the source relative to the ear. The source shaping results in a clear objective impression of a moving sound source. The ear shaping exploits characteristics of the human ear, which is highly individual. It causes the subjective impression of sound source moving.
Embodiments of the car audio systems are given in the subclaims.
The car audio systems may be configured to carry out the method described herein and may further comprise one or more of the following features:
One or more loudspeakers may be configured to be activated by said fader function by each of the two channels. Optionally at least two loudspeakers of different frequency characteristics may be configured to be activated by said fader function by each of the two channels. At least one tweeter loudspeaker and at least one midrange loudspeaker may be associated with each of the two channels. The generation of said fader function by the formation of adjustable spectral subbands may comprise changing the frequency spectrum of a respective channel in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel. Dedicated loudspeakers for the driver and at least one passenger may be associated with each of the two channels, optionally with a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger being able to be associated with each of the two channels. The generation of a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions may comprise the use of average ear characteristics, optionally average ear characteristics according to the KEMAR model. Each of the loudspeaker arrangements may comprise a subwoofer which is activated by the respective channel. Said subwoofers may not be affected by a respective change of at least one of the frequency spectrum and a respective sound shaping and are used only for a delay compensation.

DRAWINGS

Exemplary embodiments and functions of the present disclosure are described herein in conjunction with the following drawings, in which:

Fig. 1: depicts a conventional full loudspeaker setup for realizing the left/right audio directivity as well as the front/rear directivity,
Fig. 2: depicts a generic loudspeaker setup comprising at least two loudspeakers of different frequency characteristics associated with a respective channel,
Fig. 3: depicts an exemplary loudspeaker setup with dedicated loudspeakers for the driver and a passenger connected to each of the two channels,
Fig. 4: depicts exemplary spectral subbands created by FIR filters implemented for the front/rear sound directivity in connection with the loudspeaker setup as show in Fig. 3,
Fig. 5: depicts exemplary responses of the respective speakers of the loudspeaker setup as shown in Fig. 3 due to the spectral subbands as shown in Fig. 4,
Fig. 6: depicts the left/right channel frequency response variation for a virtual fader as shown in Fig. 3,
Fig. 7: depicts an exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for forming spectral subbands for the loudspeaker setup according to Fig. 3,
Fig. 8: depicts an exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for forming spectral subbands for the generic left/right audio channel setup as shown in Fig. 2,
Fig. 9: depicts a generic loudspeaker setup for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs) comprising at least one left loudspeaker and at least one right loudspeaker associated with the left channel and the right channel, respectively,
Fig. 10: depicts exemplary HRTF FIR responses used for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs), and
Fig. 11: depicts an exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs).

DETAILED DESCRIPTION

In Fig. 1 a typical conventional full loudspeaker setup for realizing a left/right audio directivity as well as the front/rear directivity is shown.
All loudspeakers of this conventional full loudspeaker setup are shared by all car users. Independent channels are provided for rear/front and left/right loudspeakers, i.e. a left channel and a right channel for the left/right audio directivity and separate front/rear channels for the front/rear audio directivity are necessary. Thus, a separate fader must be realized by balancing the sound level between the separate front and rear channels. With this typical conventional full loudspeaker setup only gain is changed on front/rear channels for realizing the front/rear fader functionality.
Such a conventional full loudspeaker setup is, however, not available in some cars due to cost or space limitation reasons.
Exemplary embodiments of a car audio system 10 are shown in Figs. 2 to 12.
A respective car audio system 10 comprises a loudspeaker setup 12 connected to control means for reproducing audio information, with said loudspeaker setup 12 comprising a left loudspeaker arrangement 12_L and a right loudspeaker arrangement 12_R activated by said control means via a left channel 14_L and a right channel 14_R, respectively (cf. in particular Figs. 2, 3 and 8).
The control means of a respective car audio system 10 are laid out for generating a fader function as to a rear/front audio directivity for the car occupants via only the left channel 14_L and right channel 14_R by forming spectral subbands of the audio information by FIR filtering with fixed delay and adjustable by parameters such as gain, delays, edge frequencies in the subbands and/or the like (cf. for example Figs. 2 to 7), and/or by shaping the sound of the reproduced audio information by FIR filtering on the basis of Head Related Transfer Functions (cf. for example Figs. 8 to 12).
The generation of a fader function may comprise the activation of more than one loudspeaker by each of the two channels 14_L, 14_R, in particular at least two loudspeakers of different frequency characteristics (cf. for example Fig. 2 to 7). The difference in the frequency characteristics in the loudspeakers connected two one channel is essential in particular in connection with the generation of said fader function by the formation of spectral subbands, since the respective space-frequency diversity of the loudspeaker setups can be exploited. For example, at least one tweeter loudspeaker and at least one midrange loudspeaker may be associated with each of the two channels 14_L, 14_R.
The generation of said fader function by the formation of adjustable spectral subbands may comprise changing the frequency spectrum of a respective channel 14_L, 14_R in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel 14_L, 14_R.
Dedicated loudspeakers for the driver and at least one passenger may be associated with each of the two channels 14_L, 14_R. In this case, e.g., a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger may, e.g., be associated with each of the two channels 14_L, 14_R.
The generation of a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions (HRTFs) may comprise the use of average ear characteristics, in particular average ear characteristics according to the KEMAR model (cf. for example Fig. 11).
Each of the loudspeaker arrangements 12_L, 12_R may comprise a subwoofer which is activated by the respective channel 14_L, 14_R (cf., e.g., Fig. 2). In this case, the subwoofers are not affected by a respective change or variation of the frequency spectrum and/or a respective sound shaping and used only for a delay compensation.
Fig. 2 shows a generic loudspeaker setup 12 comprising at least two loudspeakers of different frequency characteristics associated with a respective channel 14_L, 14_R. Each of the left loudspeaker arrangement 12_L and the right loudspeaker arrangement 12_R connected to the left channel 14_L and right channel 14_R, respectively, comprises a tweeter loudspeaker on the front side of the car, a midrange loudspeaker and a subwoofer on the rear side. In this case, the difference in the frequency characteristics of the loudspeakers connected to a respective channel is used for creating space-frequency sound diversity. The front/rear sound directivity on the basis of the left/right channel setup is achieved by exploiting space-frequency diversity of the loudspeaker setup 12. As the speaker responses are different and partially overlapping, special subband channels corresponding to individual loudspeakers are created which can be operated like physical channels.
Fig. 3 depicts an exemplary loudspeaker setup 12 comprising at least two loudspeakers of different frequency characteristics associated with a respective channel 14_L,14_R. Dedicated speakers for the driver and a passenger are provided on the two channels 14_L and 14_R. In particular, the loudspeaker setup 12 comprises nine loudspeakers including four front/tweeter loudspeakers 16, four midrange loudspeakers 18 and a subwoofer 20. Two of the four front/tweeter loudspeakers 16, namely the front/tweeter loudspeakers 16₁ and 16₂, and two of the four midrange loudspeakers 18, namely the midrange loudspeakers 18₁ and 18₂, may, e.g., be provided for the driver, whereas the other two front/tweeter loudspeakers 16₃ and 16₄ and the other two midrange loudspeakers 18₃ and 18₄ may, e.g. be provided for the passenger. The front/tweeter loudspeaker 16₁ and the midrange loudspeakers 18₁ provided for the driver and the front/tweeter loudspeaker 16₃ and the midrange loudspeaker 18₃ provided for the passenger may be connected to the left channel 14L. The front/tweeter loudspeaker 16₂ and the midrange loudspeakers 18₂ provided for the driver and the front/tweeter loudspeaker 16₄ and the midrange loudspeaker 18₄ provided for the passenger may be connected to the right channel 14R. A subwoofer 20 may be connected to both channels 14_L, 14_R. The front/tweeter loudspeakers 16 and the midrange loudspeakers 18 may have partially overlapping frequency responses.
Using the implementation of subbands aligned with frequency characteristics of the loudspeakers the effect of front/rear directivity is achieved by adjusting gains and thus balancing the sound energy between loudspeakers. For example, joint characteristics as shown in Fig. 6 are applied in the virtual fader implementation according to Fig. 3. In Fig. 6, the left/right channel frequency response variation for a virtual fader according to Fig. 3 is shown.
Whereas in Fig. 4 exemplary spectral subbands created by FIR filters implemented for the front/rear sound directivity in connection with the loudspeaker setup as shown in Fig. 3 are depicted, Fig. 5 shows exemplary responses of the respective speakers of the loudspeaker setup as shown Fig. 3 due to the spectral subbands A, B as shown in Fig. 4.
An exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for forming spectral subbands for the loudspeaker setup according to Fig. 3 is shown in Fig. 7.
Fig. 8 shows an exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for forming spectral subbands for the generic left/right audio channel setup as shown in Fig. 2.
Fig. 9 depicts a generic loudspeaker setup 12 for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs) comprising at least one left loudspeaker and at least one right loudspeaker associated with the left channel 14_L and the right channel 14_R, respectively. In this basic configuration there can be only two loudspeakers, namely one loudspeaker of the left loudspeaker arrangement 12_L connected to the left channel 14_L and another loudspeaker of the right loudspeaker arrangement 12_R connected to the right channel 14_R. In this case, the front/rear sound directivity on the basic loudspeaker setup is achieved by the implementation of Head Related Transfer Functions (HRTFs). The physics of frequency selective sound perception depending on sound source location is described in the book "The Auditory System and Human Sound-Location Behavior" by John van Opstal.
According to this disclosure anatomical features of the human pinna act as a direction-dependent acoustic aperture. Acoustic waves from a particular direction reach the ear channel directly and via reflections at the rims of the cavities, said reflections having different path lengths.
Fig. 10 depicts exemplary HRTF FIR responses used for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs). The perceived effect depends on how closely the HRTFs set match the characteristic of one's ear. A KEMAR database may give average HRTFs for a torso of a typical anatomy. For example, KEMAR ear2 in azimuth range ±50° and elevation -20° may be used.
Fig. 11 shows an exemplary structure of the sound processing of a digital signal processor (DSP) of the control means for the sound shaping by FIR filtering on the basis of Head Related Transfer Functions (HRTFs).
According to the present disclosure, HRTF FIR is varying with fader setting. Neutral fader setting affects only delay. The subwoofer channel is not affected, only delay is compensated.

Reference numeral list

10: car audio system
12: loudspeaker setup
12_L: left loudspeaker arrangement
12_R: right loudspeaker arrangement
14_L: left channel
14_R: right channel
16: front/tweeter loudspeaker
18: midrange loudspeaker
20: subwoofer

A: subband
B: subband

Claims

Method for operating a car audio system (10) comprising a loudspeaker setup (12) connected to control means for reproducing audio information, said loudspeaker setup (12) comprising a left loudspeaker arrangement (12_L) and a right loudspeaker arrangement (12_R) activated by said control means via a left channel (14_L) and a right channel (14_R), respectively, wherein for generating a fader function as to a rear/front audio directivity for the car occupants via only the left channel (14_L) and right channel (14_R) spectral subbands of the audio information are formed by FIR filtering with fixed delay and adjustable by parameters such as gain, delays, edge frequencies in the subbands and/or the like, and/or the sound of the reproduced audio information is shaped by FIR filtering on the basis of Head Related Transfer Functions.
Method according to claim 1, wherein the generation of said fader function comprises the activation of more than one loudspeaker by each of the two channels (14_L, 14_R), optionally at least two loudspeakers of different frequency characteristics.
Method according to claim 2, wherein at least one tweeter loudspeaker and at least one midrange loudspeaker is associated with each of the two channels (14_L, 14_R).
Method according to claim 3, wherein the generation of said fader function by the formation of adjustable spectral subbands comprises changing the frequency spectrum of a respective channel (14_L, 14_R) in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel (14_L, 14_R).
Method according to anyone of the preceding claims, wherein dedicated loudspeakers for the driver and at least one passenger are associated with each of the two channels (14_L, 14_R), wherein a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger are optionally associated with each of the two channels (14_L, 14_R).
Method according to anyone of the preceding claims, wherein the generation of a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions comprises the use of average ear characteristics, optionally average ear characteristics according to the KEMAR model.
Method according to anyone of the preceding claims, wherein each of the loudspeaker arrangements (12_L, 12_R) comprises a subwoofer which is activated by the respective channel (14_L, 14_R).
Method according to claim 8, wherein said subwoofers are not affected by a respective change of the frequency spectrum and/or a respective sound shaping and are used only for a delay compensation.
Car audio system (10), in particular for carrying out the method according to anyone of the preceding claims, comprising a loudspeaker setup (12) connected to control means for reproducing audio information, said loudspeaker setup (12) comprising a left loudspeaker arrangement (12_L) and a right loudspeaker arrangement (12_R) activated by said control means via a left channel (14_L) and a right channel (14_R), respectively, wherein said control means are laid out for generating a fader function as to a rear/front audio directivity for the car occupants via only the left channel (14_L) and right channel (14_R) by forming spectral subbands of the audio information by FIR filtering with fixed delay and adjustable by parameters such as gain, delays, edge frequencies in the subbands and/or the like, and/or by shaping the sound of the reproduced audio information by FIR filtering on the basis of Head Related Transfer Functions.
Car audio system according to claim 9, wherein the generation of said fader function comprises the activation of more than one loudspeaker by each of the two channels (14_L, 14_R), optionally at least two loudspeakers of different frequency characteristics.
Car audio system according to claim 10, wherein at least one tweeter loudspeaker and at least one midrange loudspeaker is associated with each of the two channels (14_L, 14_R).
Car audio system according to claim 11, wherein the generation of said fader function by the formation of adjustable spectral subbands comprises changing the frequency spectrum of a respective channel (14_L, 14_R) in order to balance the sound energy between the at least one tweeter loudspeaker and the at least one midrange loudspeaker associated with a respective channel (14_L, 14_R).
Car audio system according to anyone of the preceding claims 9 - 12, wherein dedicated loudspeakers for the driver and at least one passenger are associated with each of the two channels (14_L, 14_R), wherein optionally a tweeter loudspeaker and a midrange loudspeaker for the driver and a tweeter loudspeaker and a midrange loudspeaker for the at least one passenger is associated with each of the two channels (14_L, 14_R).
Car audio system according to anyone of the preceding claims 9 - 13, wherein the generation of a fader function by shaping the sound of the reproduced audio information by Head Related Transfer Functions comprises the use of average ear characteristics, optionally average ear characteristics according to the KEMAR model.
Car audio system according to anyone of the preceding claims 9 - 14, wherein each of the loudspeaker arrangements (12_L, 12_R) comprises a subwoofer which is activated by the respective channel (14_L, 14_R), wherein said subwoofers are optionally not affected by a respective change of the frequency spectrum and/or a respective sound shaping and are used only for a delay compensation.