Loudness adjustment of audio signals in vehicles

Abstract

Method (400) for adjusting the loudness of an audio signal (211) in a vehicle (100), the method (400) comprising: - determining (401) a rate of change (222) of a vehicle speed (221) (100); and / or - the setting of a volume control of a system for playing back the audio signal (211); - recursively determining a loudness factor based on the audio signal in order to adapt the loudness factor to the audio signal; wherein the adaptability of the loudness factor to the audio signal depends on a time constant used for the recursive determination of the loudness factor; - changing (402) the adaptability of the loudness factor by changing the time constant as a function of the rate of change (222); and - adjusting (403) the loudness of the audio signal (211) using the loudness factor.

Description

[0001] The invention relates to a method and a corresponding device for adjusting the loudness of audio signals in vehicles.

[0002] Vehicles, such as road vehicles, typically include audio playback systems. At high speeds, a high level of background noise is typically generated inside the vehicle. This can lead to situations where, when playing audio signals with alternating passages of relatively high and relatively low loudness (e.g., in classical music), the passages of relatively low loudness are masked by the background noise, or the audio playback volume must be adjusted to hear the passages of relatively low loudness.

[0003] Active Gain Control (AGC) or a compressor can be used to equalize the loudness of audio signals (e.g., music and / or speech). This typically reduces the dynamic range of the audio signal. Furthermore, these measures can cause unpleasantly audible loudness fluctuations.

[0004] This document addresses the technical challenge of reproducing audio signals with relatively large loudness fluctuations in an artifact-free and consistently audible manner.

[0005] The problem is solved by the independent claims. Advantageous embodiments are described, among other things, in the dependent claims.

[0006] According to one aspect, a method for adjusting the loudness of an audio signal in a vehicle (especially a road vehicle) is described. The method involves determining the rate of change of one or more state variables. The rate of change can include the rate of change of the vehicle's speed (i.e., the degree of acceleration or deceleration). Alternatively or additionally, the rate of change can include the rate of change of the setting of a volume control in a system for playing the audio signal in the vehicle. Alternatively or additionally, the rate of change can include the rate of change of the loudness of the audio signal. The latter can ensure artifact-free playback, particularly at transitions between different pieces of music.

[0007] The method further involves changing the adaptability (e.g., a factor or a time constant α) of a loudness factor g(t) as a function of the rate of change. The loudness factor g(t) depends on the audio signal x(t). For example, the loudness factor g(t) can be determined recursively based on the audio signal x(t) and adapted to it. The adaptability of the loudness factor g(t) to the audio signal x(t) can depend on a time constant α, which is used for the recursive determination of the loudness factor g(t).

[0008] In particular, the adaptability of the loudness factor can be increased if the rate of change of a state variable increases. Alternatively or additionally, the adaptability of the loudness factor can be reduced if the rate of change of a state variable decreases.

[0009] The loudness factor g(t) can depend on a target loudness K for the audio signal. Furthermore, the loudness factor g(t) can depend on an amplitude of the audio signal, on an indication of an energy E(t) of the audio signal, and / or on a root mean square of the amplitudes of the audio signal.

[0010] The method further includes adjusting the loudness of the audio signal using the loudness factor. Specifically, the audio signal can be multiplied by the loudness factor to adjust its loudness. By varying the loudness factor's adaptability based on the rate of change of one or more state variables (especially a state of the vehicle), artifact-free playback of the audio signal can be ensured even at different loudness levels.

[0011] The loudness factor's adaptability can be adjusted depending on a combination of the change rates of a variety of state variables (e.g., various vehicle states). This further improves artifact-free audio signal reproduction. Furthermore, the loudness factor can be limited by an upper and / or lower limit depending on a vehicle state (e.g., vehicle speed) and / or the setting of the audio system's volume control. Such limits further enhance the audio signal reproduction quality.

[0012] The method can further include adjusting the dynamics of the audio signal using a compressor curve. The dynamic adjustment can be performed before the loudness is adjusted using a loudness factor. The compressor curve can depend on a vehicle condition. In particular, the compressor curve can depend on an indicator of the vehicle's driving condition and / or an indicator of a vehicle occupant's playback preference. The indicator of the vehicle's driving condition can include the vehicle's speed. The indicator of the vehicle occupant's playback preference can include the setting of the audio playback system's volume control.

[0013] Thus, the vehicle's condition can be taken into account when selecting the compressor's operating curve. Furthermore, the rate of change of the vehicle's condition can be considered in an AGC unit to adjust the AGC unit's adaptability. This combination allows for particularly advantageous artifact-free playback of audio signals with high loudness fluctuations.

[0014] According to another aspect, a control unit for a system for playing back an audio signal in a vehicle is described. The control unit is configured to determine the rate of change of one or more state variables. The rate of change can include, in particular, the rate of change of the vehicle's speed, the rate of change of the loudness of the audio signal, and / or the rate of change of the volume control setting of the audio signal playback system. The control unit is further configured to adjust the adaptability of an Active Gain Control (AGC) unit to the audio signal being played back, depending on the rate of change. Additionally, the control unit is configured to cause the loudness of the audio signal to be adjusted by the AGC unit.

[0015] According to another aspect, a vehicle (e.g. a passenger car, a truck or a motorcycle) is described which includes the control unit described in this document.

[0016] According to another aspect, a software (SW) program is described. The SW program can be set up to run on a processor (e.g., on a vehicle's control unit) and thereby execute the procedure described in this document.

[0017] Another aspect describes a storage medium. This storage medium can include a software program configured to run on a processor and thereby execute the procedure described in this document.

[0018] It should be noted that the methods, devices, and systems described in this document can be used both alone and in combination with other methods, devices, and systems described in this document. Furthermore, any aspect of the methods, devices, and systems described in this document can be combined with one another in a variety of ways. In particular, the features of the claims can be combined with one another in a variety of ways.

[0019] The invention will now be described in more detail using exemplary embodiments.

[0020] Fig. 1. Exemplary components of a vehicle;

[0021] Fig. 2. An example of signal processing of an audio signal;

[0022] Fig. 3 exemplary compressor curves; and

[0023] Fig. 4 A flowchart of an exemplary procedure for adjusting the loudness of an audio signal in a vehicle.

[0024] As stated at the outset, this document deals with the artifact-free playback of audio signals in a vehicle. The audio signal should be reproduced in such a way that both low-loudness and high-loudness passages can be perceived by a vehicle occupant. Furthermore, the greatest possible dynamic range of the audio signal should be maintained. The loudness of an audio signal typically depends on the sample values ​​of the audio signal (especially the amplitude of the sample values). Conversely, the playback volume of the audio signal depends on the settings of the volume control of the vehicle's playback system.

[0025] Fig. Figure 1 shows exemplary components of a vehicle 100 In particular, it shows Fig. 1 a control unit 101 (e.g. as part of the vehicle's infotainment system) 100 ), which is set up to transmit an audio signal through one or more loudspeakers 104 of the vehicle 100 to reproduce. The control unit 101 It is further configured to adjust the audio signal depending on one or more parameters. Via a vehicle sensor 102 Vehicle data regarding the vehicle's driving condition can be accessed 100 The vehicle data can be provided as a parameter. This data can include the vehicle's speed and / or its rate of change (e.g., acceleration or deceleration). 100 include. Via an input unit 103 Playback data regarding the playback preference of the vehicle occupant can be stored. 100 provided as parameters. In other words, via the input unit 103can provide data regarding the status of a playback system or infotainment system of the vehicle. 100 be recorded. Exemplary data regarding the condition of the vehicle's playback system. 100 This may include a volume control setting and / or a rate of change of the volume control setting.

[0026] The control unit 101 It can be set up to adjust an audio signal depending on one or more parameters. Fig. Figure 2 shows an example of signal processing of an audio signal. 211 through the control unit 101 The audio signal 211 can be used, for example, in a compressor 201 be adjusted. The compressor 201 is set up, the dynamics of the audio signal 211 to change. In particular, the compressor can 201 be set up to block the audio signal above a certain level or threshold. 211to change by the compressor 201 the level is reduced by a fixed ratio. The compressor 201 It can be given an additional gain factor to compensate for the level lost through compression. Through the compressor 201 This allows the loudness of passages with low loudness to be increased. In particular, this can be achieved using a compressor. 201 the dynamics of the audio signal 211 will be reduced.

[0027] Fig. Figure 3 shows exemplary compressor curves 301 , 302 of the compressor 201 For the course 301 The amplitude corresponds to 311 of the input audio signal 211 the amplitude 312 of the output audio signal 212 of the compressor 201 In other words, when using the compressor curve 301 This takes place in the compressor 201 no compression of the audio signal's dynamic range 211On the other hand, the compressor process 302 relatively high amplitudes 311 of the input audio signal 211 reduced, thus compressing the dynamics of the audio signal. 211 This has been done.

[0028] The control unit 101 It can be set up to control the compressor flow 301 , 302 depending on one or more parameters 221 , 231 to adjust. In particular, the compressor curve can be adjusted. 301 , 302 of the compressor 201 depending on the driving speed 221 of the vehicle 100 and / or depending on the setting 231 the volume control of the vehicle's playback system 100 The driving speed can be adjusted. 221 This is an exemplary indicator of the extent of the background noise in the vehicle. 100 The attitude 231The volume control setting is an exemplary indicator of the playback preferences of a vehicle occupant. 100 .

[0029] The degree of compression can be increased (i.e., a compressor curve can be used). 302 (with relatively high compression) if the index 221 The level of background noise indicates a relatively high level of interference. In particular, the degree of compression can increase with increasing driving speed. 221 be increased or decrease with decreasing driving speed 221 can be reduced. On the other hand, the degree of compression can be reduced if the indication 231 for the playback preferences of the vehicle occupant 100 indicates that the occupant prefers the full dynamic range of the audio signal. 211 perceives this. This is, for example, due to a relatively high attitude. 231 the volume control is displayed.

[0030] The signal processing of the control unit 101 can also include an Active Gain Control (AGC) unit 202 include the AGC unit. 202 It can be set up to receive the audio signal 212 to modify it so that (averaged over a period of time) the same loudness (e.g., loudness K) is present at every point in time t. The AGC unit 202 It can be parameterized, for example, in terms of potency and speed of action.

[0031] The AGC unit 202 can the compressor 201 be downstream, so that the input signal 212 the AGC unit 202 the compressor's output signal 201 corresponds to, or is derived from, the output signal of the compressor. 201 can be derived. The AGC unit 202 is set up, the audio signal 212 to amplify or attenuate in order to adjust the loudness of the audio signal 212 to adjust. In particular, the AGC unit can 202the output audio signal y(t) 213 the AGC unit 202 at time t, the input audio signal x(t) is calculated using the following formula. 212 the AGC unit 202 determine: y(t) = g(t)x(t), where g(t) is an adaptive loudness factor of the AGC unit 202 The loudness factor g(t) can be determined based on the input audio signal x(t). 212 can be determined, e.g., by the following recursive formula: g(t) = αg(t – 1) + (1 – α) K E(t) where K corresponds to a desired average loudness or target loudness level and where E(t) is the root mean square (RMS) energy of the input audio signal x(t) 212 at time t. The energy E(t) can be determined using a moving average function. The factor α ∊ {0, ..., 1} corresponds to a time constant of the AGC unit. 212 , and expresses an adaptability of the AGC unit 202The factor α, or the time constant of the AGC unit, is... 202 can depend on the driving speed 221 (as an indication of the level of background noise) and / or from the setting 231 of the volume control (as an indication of the playback preferences of the vehicle occupant) 100 ) be dependent.

[0032] Choosing a small factor α results in rapid loudness adjustment (i.e., the AGC unit). 202 or the loudness factor g(t) exhibit a high adaptability) with the disadvantage that the dynamics of the audio signal 212 It may be completely eliminated. Choosing a large factor α results in slow loudness adjustment (i.e., the AGC unit). 202 or the loudness factor g(t) exhibits low adaptability) with the disadvantage that in the event of a sudden change in the loudness of the audio signal 212(e.g., during a transition from one piece of music to the next), the change in loudness of the audio signal 212 It is only detected with a delay, and such a transition is disturbingly audible.

[0033] This document describes measures to address the aforementioned disadvantages of the AGC unit. 202 These can be reduced and possibly avoided. In particular, it is proposed to increase the adaptation speed or adaptability of the AGC unit. 202 (e.g., a smoothing time and / or an attack / release time and / or the factor α) to depend on one or more parameters, thereby determining the speed of changes or the adaptation rate of the vehicle state, user preferences and / or the audio signal. 211 , 212 is displayed. An indicator of the speed of changes in the vehicle's condition is the degree of acceleration / deceleration. 222 of the vehicle100 One indicator of the speed at which user preferences change is the extent / speed of this change. 232 The change in the volume control setting. An indication of the speed of changes in the audio signal. 211 , 212 is a measure / speed 214 the change in loudness of the audio signal 211 , 212 .

[0034] By choosing such a speed of adaptation or adaptability of the AGC unit 202 It can be achieved that the short-term dynamics of the audio signal 211 , 212 largely preserved and that short-term changes in playback conditions (such as adjusted volume, changed driving speed, and / or a change in the music signal due to a track change) can be quickly taken into account.

[0035] The adaptation rate or adaptability of the AGC unit202 (e.g. the factor α) can depend on the magnitude of the acceleration 222 (i.e., dν(t) / dt) of the vehicle 100 be made dependent, where ν(t) is the driving speed 221 of the vehicle 100 This corresponds to the higher the acceleration. 222 of the vehicle 100 the faster the AGC unit can 202 Adjusting the gain factor g(t) (i.e., the smaller the factor α), the faster the loudness can be adjusted. This allows for speed-dependent trailing effects of the AGC unit. 202 This can be avoided. Furthermore, effects caused by a speed-dependent compressor setting can be prevented. 201 These occurrences can be balanced out.

[0036] Alternatively or additionally, the adjustment rate or adaptability (e.g., the factor α) of the AGC unit can be used. 202 of speed or velocity 232the change in volume of the vehicle's occupant 100 become dependent. The faster the vehicle's occupant... 100 The more you turn the volume control of the playback system, the faster the AGC unit can operate. 202 Adjusting the gain factor g(t) (i.e., the smaller the factor α), the faster the loudness can be adjusted. This eliminates loudness-dependent trailing effects of the AGC unit. 202 This avoids effects caused by the compressor's volume-dependent setting. 201 These occurrences can be balanced out.

[0037] Alternatively or additionally, the adaptation rate or adaptability of the AGC unit can be used. 202 (e.g. the factor α) of the change 214 the loudness (e.g., the RMS level) of the audio signal 211 , 212 become dependent. The more dependent the loudness of an audio signal becomes, the more pronounced the effect. 211 ,212 The more changes, the faster the AGC unit can operate. 202 Adjusting the gain factor g(t) (i.e., the smaller the factor α), allows for faster loudness adjustment. This is achieved through appropriate parameterization of the RMS smoothing of the AGC unit. 202 This can prevent short-term loudness peaks or loudness spikes in the audio signal. 211 , 212 These changes can be detected as loudness variations. Furthermore, effects caused by a changing loudness of the audio signal can be detected. 211 , 212 These events can be avoided. For example, the audio signal 211 This includes a piece of music whose loudness increases and then remains at the increased loudness level, without adjusting the AGC parameters (e.g., the factor α) depending on the rate of change. 214 the loudness of the audio signal 211 would the adapted piece of music 213The sound level initially increases in volume and then slowly (according to α) returns to the target loudness level (according to K). This is achieved by adjusting the AGC parameters depending on the rate of change. 214 The loudness remains the adapted musical pieces. 213 even during the loudness transition at the desired target level. Another advantage of adjusting the AGC parameters depending on the rate of change. 214 The loudness issue is that loudness jumps or a delayed and / or too slow adjustment of loudness can be avoided when switching tracks between music pieces.

[0038] The various pieces of evidence 222 , 232 , 214 Regarding the changes of state, in a combination unit 203 can be combined with each other. For example, based on the different pieces of evidence, 222 , 232 , 214(e.g. by multiplication) a common coefficient of change Δ can be determined (e.g. ΔE {0, ..., 1}), which can be used to determine the time constant (e.g. the factor α) or the adaptability of the AGC unit. 202 to change.

[0039] Fig. Figure 4 shows a flowchart of an example procedure. 400 to adjust the loudness of an audio signal 211 in a vehicle 100 The procedure 400 includes determining 401 of a rate of change 222 , 232 a condition (in particular a condition of the vehicle) 100 The condition of the vehicle 100 This could include, for example, the vehicle's driving condition. 100 (e.g. a driving speed) 222 of the vehicle 100 ) and / or a state of a vehicle's playback system 100 (e.g., a setting) 232(of the playback system's volume control). Alternatively or additionally, the state can be a state of the audio signal. 211 (e.g., the loudness of the audio signal) 211 ) include.

[0040] The procedure 400 further includes changing 402 an adaptability (e.g. a time constant) of a loudness factor g(t) or an AGC unit 202 depending on the rate of change 222 , 232 . where the loudness factor g(t) of the AGC unit is 202 from the audio signal 211 dependent. In other words, the loudness factor g(t) is determined based on the audio signal. 211 determined. Furthermore, the procedure includes the adjustment. 403 the loudness of the audio signal 211 using the loudness factor, e.g. by multiplying a sample value x(t) of the audio signal 211 with the loudness factor g(t).

[0041] The adaptability of the loudness factor g(t) or the AGC unit 202 depending on the condition of the vehicle 100 be limited. In particular, limit values ​​of the loudness factor g(t) can depend on a state of the vehicle. 100 depend. In other words, the loudness factor can depend on the condition of the vehicle. 100 have an upper limit and / or a lower limit. For example, the loudness factor g(t) can be limited to a first maximum value if the driving speed 221 greater than or equal to a predefined maximum speed. Alternatively or additionally, the loudness factor g(t) can be limited to a second maximum value if a volume control of the system for playing back the audio signal is used. 211a volume setting that is greater than or equal to a predefined maximum setting. Furthermore, the loudness factor g(t) can, in this case, be limited downwards to a second minimum value. This allows the quality of the audio signal playback to be adjusted. 211 will be further improved.

[0042] The dependency of the AGC unit 202 from the acceleration 222 , from the change in volume 232 and / or from the change in loudness 214 of the audio signal 211 enables an effective combination of an AGC unit 202 and from a compressor 201 Furthermore, this allows for improved parameterization of the AGC unit. 202 and the compressor 201 This is made possible by the dynamic adjustment of the timing factors (e.g., factor α) of the AGC unit. 202 Is it possible to adjust the loudness of the audio signal? 211It allows for rapid adaptation to changing circumstances, balancing quiet and loud pieces of music without affecting the short-term dynamics of a piece or causing unpleasant distortion. This also prevents delayed adjustments to the volume of a piece after a change has occurred.

[0043] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed methods, devices, and systems.

Claims

[1] Procedure ( 400 ) to adjust the loudness of an audio signal ( 211 ) in a vehicle ( 100 ), wherein the procedure ( 400 ) includes, - Determine ( 401 ) of a rate of change ( 222 ) a driving speed ( 221 ) of the vehicle ( 100 ); - Change ( 402 ) an adaptability of a loudness factor depending on the rate of change ( 222 ); where the loudness factor depends on the audio signal ( 211 is dependent; and - Adjust ( 403 ) the loudness of the audio signal ( 211 ) using the loudness factor. [2] Procedure ( 400 ) to adjust the loudness of an audio signal ( 211 ) in a vehicle ( 100 ), wherein the procedure ( 400 ) includes, - Determine ( 401 ) of a rate of change ( 232) the setting of a volume control of a system for playing back the audio signal ( 211 ); - Change ( 402 ) an adaptability of a loudness factor depending on the rate of change ( 232 ); where the loudness factor depends on the audio signal ( 211 is dependent; and - Adjust ( 403 ) the loudness of the audio signal ( 211 ) using the loudness factor. [3] Procedure ( 400 ) to adjust the loudness of an audio signal ( 211 ) in a vehicle ( 100 ), wherein the procedure ( 400 ) includes, - Determine ( 401 ) of a rate of change ( 214 ) the loudness of the audio signal ( 211 ); - Change ( 402 ) an adaptability of a loudness factor depending on the rate of change ( 214 ); where the loudness factor depends on the audio signal ( 211 is dependent; and - Adjust ( 403 ) the loudness of the audio signal ( 211 ) using the loudness factor. [4] Procedure ( 400 ) according to one of the preceding claims, wherein the adaptability of the loudness factor depends on a time constant for recursive determination of the loudness factor. [5] Procedure ( 400 ) according to one of the preceding claims, wherein the loudness factor depends on – a target loudness K for the audio signal ( 211 ); – an amplitude ( 311 , 312 ) of the audio signal ( 211 ); – an indication of an energy E(t) of the audio signal ( 211 ); and / or – a square mean of the audio signal ( 211 ). [6] Procedure ( 400 ) according to one of the preceding claims, wherein – the adaptability of the loudness factor is increased when the rate of change (222 , 232 , 214 ) increased; and / or – the adaptability of the loudness factor is reduced when the rate of change ( 222 , 232 , 214 ) reduced. [7] Procedure ( 400 ) according to one of the preceding claims, wherein the adaptability of the loudness factor depends on a combination of the rates of change ( 222 , 232 , 214 ) is changed by a multitude of state variables. [8] Procedure ( 400 ) according to one of the preceding claims, wherein the loudness factor depends on a state of the vehicle ( 100 ) and / or a setting of the volume control of a system for playing back the audio signal ( 211 ) has an upper limit and / or a lower limit. [9] Procedure ( 400 ) according to one of the preceding claims, further comprising, adjusting the dynamics of the audio signal (211 ) by means of a compressor curve ( 301 , 302 ); where the compressor curve ( 301 , 302 ) from an indication of the vehicle's driving condition ( 100 ) and / or an indication of a playback preference of an occupant of the vehicle ( 100 depends. [10] Procedure ( 400 ) according to claim 9, wherein – the indicator of the vehicle's driving condition ( 100 ) a driving speed ( 221 ) of the vehicle ( 100 ) includes; and / or – the indicator of the playback preference of the vehicle occupant ( 100 ) an attitude ( 231 ) of a volume control of a system for playing back the audio signal ( 211 ) includes. [11] Control unit ( 101 ) for a system for playing back an audio signal ( 211 ) in a vehicle ( 100 ), wherein the control unit ( 101 ) is set up, – a rate of change ( 222 , 232 , 214 ) to determine; where the rate of change ( 222 , 232 , 214 ) a rate of change ( 222 ) a driving speed ( 221 ) of the vehicle ( 100 ), a rate of change ( 214 ) the loudness of the audio signal ( 211 ) and / or a rate of change ( 232 ) the setting of a volume control of a system for playing back the audio signal ( 211 ) includes; – an adaptability of an Active Gain Control, or AGC, unit ( 202 ) to the audio signal to be played back ( 211 ) depending on the rate of change ( 222 , 232 , 214 ) to change; and – to cause the loudness of the audio signal ( 211 ) from the AGC unit ( 202 ) is adjusted.

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