Method for adjusting the volume of audio signals of different volumes and audio control device for carrying out the method

Abstract

Method for adjusting the volume of audio signals (8) of different volumes, in particular of stored music files from different audio sources (2, 3, 4), which are reproduced successively as a sound sequence, comprising the steps - Specification of a target volume for all audio signals to be played back one after the other (8), - Determining the volume of an audio signal (8) in a first phase (19) of its reproduction, - applying dynamic compression to the audio signal (8) during this first phase (19), - after completion of the determination of the volume during the first phase (19), increasing or decreasing the volume to adapt to the target volume during a second phase (21), and - Termination of the application of dynamic compression to the audio signal (8) during the transition from the first phase (19) to the second phase (21).

Description

The invention relates to a method for adjusting the volume of audio signals of different volume, in particular of stored music files of different origin, which are reproduced one after the other as a sound sequence, and to an audio control device for carrying out the method.It is known that music files from arbitrary sources are merged and played on music players such as computers or MP3 players. The only prerequisite is that the player know the coding such as "mp3", "ogg" or "wav" and is thus able to play the music file. Music file is also understood to mean video files with audio content. The files are then coded differently, but the problems are the same.Even the titles or pages of a single CD may have different loudness.It is known from DE 10 2010 003 306 A1 to store control information for each audio signal and to call it when playing it repeatedly and to perform the playback accordingly as in the last playback.DE 102 32 645 A1 relates to a circuit arrangement for reducing the dynamic range of audio signals. The audio signal is transformed into the frequency range, the spectrum obtained is processed and the processed spectrum is transformed back.DE 10 2009 026 589 A1 discloses a method for setting the running intensity of one or more sound sources in a motor vehicle as a function of its operating state.The problem here is that the circuit arrangement requires complex signal processing and, in particular, a continuous back-and-forth transformation of the audio signal from the time domain into the frequency domain is necessary.On the basis of this, the object of the present invention is to specify an improved method for volume adaptation of audio signals of different volume and a correspondingly improved audio control device for volume adaptation of audio signals of different volume.This object is achieved by a method having the features of claim 1 and by an audio control device having the features of claim 10. Advantageous further developments are evident from the dependent claims.The essence of the invention is considered to be that the audio signal is dynamically compressed in a first phase, i.e. that the dynamic range of the audio signal is reduced. One phase is a time segment. This prevents the volume from being exceeded without previous measurements. In this phase, the volume of the audio signal is then determined in order to compare it with the target volume. This comparison results in leaving, raising or lowering the volume.Volume is understood to mean the loudness, i.e. the volume perceived by humans. In contrast, the sound level or sound pressure level is known as the measured variable. The volume is of course also dependent on the sound pressure level, but not exclusively. This leads to two audio signals with the same sound pressure level being perceived to be differently loud.The volume is not directly measurable as a psychoacoustic variable, but rather is derived from measurable variables.Once the comparison of the instantaneous volume of the audio signal with the target volume has been completed, the volume is adjusted on the basis of the comparison result and the dynamic compression is ended. The second phase of the method is then present.The advantage of this method for adjusting the volume is that the volume is adjusted only at the beginning of an audio signal and no continuous signal transformation is necessary.Preferably, the method according to Zwicker, also called Zwicker loudness calculation, can be used for determining the loudness. In this case, in addition to the sound pressure level, the spectral composition and other factors are also taken into account.An intermediate phase is particularly advantageously provided between the first phase and the second phase, in which intermediate phase the dynamic compression is reduced and the volume is adapted. The dynamic compression is thus not switched off and the volume is adapted in a single step, but rather either in a plurality of steps or particularly preferably continuously and thus continuously. The duration of the intermediate phase can be permanently predefined in this case. In an advantageous embodiment, the duration of the intermediate phase depends on the distance of the instantaneous volume from the target volume. In addition, the duration of the intermediate phase may depend on the influence of the dynamic compression on the audio signal. If the comparison of the instantaneous volume with the target volume reveals that the audio signal is very strongly dynamically compressed and a comparatively strong adaptation is necessary, then, overall, more time is necessary for this than in the case of minor deviations.Advantageously, the reduction of the dynamic compression and the adaptation of the volume takes place non-linearly, i.e. initially a stronger adaptation takes place than towards the end of the intermediate phase. Thus, the volume can be changed more in the areas in which a change is less noticeable, i.e. the perceived volume change over time is perceived as a constant change.In order to achieve the best possible adaptation even in the first phase, it is preferably provided that the dynamic compression and the volume are each set via a predefined value and the predefined value is predefined as a function of the audio source. The audio source can be regarded as devices which output audio signals, i.e. signals perceptible with the ear. These are in particular CD players, radios, DVD players, MP3 players, etc. This can also be a navigation device.Each of the audio sources outputs an audio signal to the devices further using the signal, such as a compressor or other amplifier or loudspeaker with a different basic volume. As is known, the volume must often be corrected on a television when a movie is played back via a DVD player instead of via a receiver. A first adaptation of the volume and the dynamic compression is thus effected in that they are set as a function of the audio source. By this first adjustment already at the very beginning of the first phase, the possible difference between the volume of the first and the second phase can be reduced.A further object is to determine the time of the change of an audio signal. If the control device which carries out the method can query corresponding signals, in this case no audio signals, the changeover time can be established via these status signals. For example, it is known to provide the individual audio signals on CDs, in this case, songs or other signal units such as a sketch or the recording of a bird's voice, with metadata, so that the CD player "knows" when an audio signal ends and thus a new audio signal starts in the sequence. If the control device can access such information in the form of signals, the change from one audio signal to the next can be reliably detected.Otherwise, it is preferably provided that the change from one audio signal to the next is determined on the basis of a predefined signal sequence. In particular, it indicates a change if a digital "0" occurs as the signal sequence for at least a few milliseconds. This normally occurs only between two audio signals or when the audio source is changed, but not within one audio signal.In addition, it can be provided that the volume is also analyzed during or after the second phase, i.e. determined and compared with the reference volume. It is possible that the volume determined in the first phase, which is carried out only on the basis of a short sequence, is not representative of the entire audio signal. The repeated check of the volume ensures that no incorrect setting of the volume has been carried out.Furthermore, it can be provided that the volume is adapted as a function of the volume of the environment, in particular by the target volume being defined as a function of the environment volume. The environment is the area surrounding the listener of the audio signal. In a motor vehicle, the ambient volume may depend on where the motor vehicle is moving. For example, with increasing travel speed, without other influences, a greater ambient volume results. It is therefore not absolutely necessary to record the ambient volume using a microphone or the like. The ambient volume can also be determined on the basis of operating data of a motor vehicle.The target volume is a volume resulting from an audio signal having been adjusted in volume by a listener by an input means such as a rotary knob. This volume, once selected, is stored as a target volume, either as a numerical value or as a pollable position of a rotary knob. The following audio signals are then adjusted in volume to the thus selected and defined target volume. In order to determine the target volume, the volume can thus be determined and stored after the input means has been actuated.The aforementioned methods can be implemented in a control device as software or else as (hard-wired) hardware.In addition, the invention also relates to an audio control device for processing audio signals according to claim 10, which is characterized by a determination unit for determining a volume of an audio signal, a memory for storing a target volume, a comparison unit for comparing the determined volume with the stored target volume, and an adaptation device for adapting the volume of the audio signal.Further advantageous embodiments of the audio control device correspond to corresponding embodiments of the method according to the invention. In order to avoid unnecessary repetitions, reference is thus made to the corresponding method features and the advantages thereof. In this case, a method step is implemented as a corresponding "unit". If, for example, it is provided according to the method that the dynamic compression is set via a predefined value and the predefined value is predefined as a function of the audio source, then the audio control device has a predefined unit for setting a predefined value as a function of the audio source, wherein the dynamic compression can be set via the predefined value. In general, values in the audio control device can be set and used if they are set and changed according to the method.The invention is explained in more detail below with reference to exemplary embodiments in the drawing figures. The following are shown: FIG. 1 shows an audio system, FIG. 2 shows signal paths during the reproduction of an audio signal, FIG. 3 shows an audio signal in a first embodiment, FIG. 4 shows an audio signal in a second embodiment, FIG. 5 shows an audio signal in a third embodiment, FIG. 6 shows an audio signal in a fourth embodiment, and FIG. 7 shows an audio signal in a fifth embodiment.FIG. 1 shows an audio system 1 with a CD player 2, an MP3 player 3 and a radio 4 as audio sources, wherein a USB connection 5 is also provided, with which a USB stick storing MP3 can be connected. The controller 6 controls the reproduction of the audio signals from the CD player 2, the MP3 player 3 or the radio 4. A coherent unit, for example a track on a CD, is considered as the audio signal. An audio signal is composed of a plurality of sub-elements such as bytes. A plurality of audio signals are reproduced in succession as a sound sequence. Audio signals are not only pieces of music, they can also be voice presentations, individual chapters of a hearing book or announcements of a navigation system.The control device 6 comprises a determination unit 7 for determining the volume of an audio signal 8, a memory 9 for storing a target volume, a comparison unit 10 for comparing the determined volume with the stored target volume, and an output unit 11 for outputting control signals.The audio system 1 further comprises a compressor 12, an amplifier 13 and at least one loudspeaker 14.The audio system 1 can have further components, these are not shown, as long as they are not relevant for the present application.Fig. 2 shows the signal paths during the first phase of the reproduction of an audio signal. The compressor 12 is adjusted depending on the audio source. Depending on whether the audio signal 8 originates from the CD player 2, the MP3 player 3 or the radio 4, the dynamic range of the audio signal 8 is limited differently. This setting is made via the control device 6, which has a unit for interrogating the audio source. The incoming audio signal 8 is accordingly output from the compressor 12 as a dynamic range-limited audio signal 15.At the same time, the determination signal 16 is supplied to the determination unit 7. A mono signal can be the audio signal 8, and a stereo signal is used to mix the audio signal 8 by a mixer 17 to form the determination signal 16. The mixer 17 mixes the audio signal 8 so that the volume of the detection signal 16 comes as close as possible to the volume of the audio signal output at the loudspeakers, which a listener feels due to the loudspeaker positions.In the first phase, the volume of the determination signal 16 is determined with the aid of the Zwicker loudness calculation and compared at the comparison unit with a target volume stored in the memory 9.As a result of the comparison, there may be left, increase or decrease in volume. In the following intermediate phase, the dynamic compression is continuously reduced and the volume is adapted depending on the comparison result, i.e. converted into the target volume. The intermediate phase thus begins with the presence of the comparison result or with the adaptation of the volume, wherein the adaptation is immediately started with the presence of the comparison result.Thereafter, the audio signal 15 can be subjected to further processing steps in order to be supplied to the loudspeaker 14 as the outgoing audio signal 18.FIG. 3 shows an audio signal 8 without dynamic compression in a first phase 19, an intermediate phase 20 and a second phase 21, Lines 22 and 23 indicate the desired limits of the dynamic range, which are predefined via the target volume. The audio signal 8 is too loud, i.e. its volume is above the target volume and the amplitude therefore exceeds the lines 22 and 23.FIG. 4 shows the audio signal 18 which corresponds to the audio signal 8 with dynamic compression in the first phase 19. The audio signal 18 could also exceed the lines 22 and 23 slightly than in FIG. 3, however, since the dynamic compression in the first phase 19 is intended to reduce the volume of the audio signal 18 to such an extent that the target volume is not exceeded.In the intermediate phase 20, the volume of the audio signal 18 approaches the target volume continuously, wherein the dynamic compression is likewise continuously reduced.In the second phase 21, the target volume is reached, the dynamic compression is ended, and the amplitudes of the audio signal 18 touch the boundaries 22 and 23 tangentially.FIGS. 5 and 6 show audio signals 8 and 18, analogous to FIGS. 3 and 4, wherein the volume of audio signal 8 is lower than the target volume. Accordingly, the volume of the audio signal 18 is continuously increased in the intermediate phase 20.FIG. 7 finally shows an audio signal 8, the volume of which changes in the second phase 21, namely increases. While in the first half an increase in the volume is still necessary in order to achieve the target volume, in the second half a reduction is required. It is therefore provided that in the second phase 21, at least one further analysis of the volume of the audio signal 8 or of the ascertainment signal 16 derived therefrom takes place and, in the event of a deviation from the target volume, a dynamic compression of the audio signal 8 is carried out.LIST OF REFERENCE CHARACTERS1 Audio system 2 CD player 3 MP3 player 4 Radio 5 USB connection 6 Control device 7 Detection unit 8 Audio signal 9 Memory 10 Comparison unit 11 Output unit 12 Compressor 13 Amplifier 14 Loudspeaker 15 Audio signal 16 Detection signal 17 Mixer 18 Audio signal 19 First phase 20 Intermediate phase 21 Second phase 22 Line 23 Line

Claims

Method for volume adaptation of audio signals (8) of different volume, in particular of stored music files from different audio sources (2, 3, 4) which are reproduced successively as a sound sequence, comprising the steps - presetting a target volume for all audio signals (8) to be reproduced successively, - determining the volume of an audio signal (8) in a first phase (19) of its reproduction, - applying dynamic compression to the audio signal (8) during this first phase (19), - after completion of the determination of the volume during the first phase (19), raising or lowering the volume for adaptation to the target volume during a second phase (21), and - ending the application of dynamic compression to the audio signal (8) during the transition from the first phase (19) to the second phase (21).Method according to claim 1, wherein an intermediate phase (20) is provided between the first phase (19) and the second phase (21), in which intermediate phase the dynamic compression is reduced and the volume is adjusted.Method according to claim 2, wherein the reduction of the dynamic compression and the adjustment of the volume are carried out continuously.Method according to one of the preceding claims, wherein at least one further determination of the volume takes place during or after the second phase (21) and a dynamic compression of the audio signal (8) is carried out in the event of a deviation from the target volume.Method according to one of Claims 2 to 4, wherein the target volume is predefined as a function of the volume of the environment.Method according to one of the preceding claims, wherein the volume is determined by the method according to Zwicker.Method according to one of the preceding claims, wherein the audio signal (8) from the supply is mixed in a mixer (17) to determine the volume.Method according to one of the preceding claims, wherein the dynamic compression is set via a predefined value and the predefined value is predefined as a function of the audio source (2, 3, 4).Method according to claim 8, wherein a radio (4) and / or a CD player (2) and / or an MP3 player (3) and / or a DVD player are used as audio source.Audio control device (6) for processing audio signals (8), wherein the audio control device (6) comprises a determination unit (7) for determining the volume of an audio signal (8), a memory (9) for storing a target volume, a comparison unit (10) for comparing the determined volume with the stored target volume, an output unit (11) for outputting control signals and a compressor (12), wherein the compressor (12) is controllable as a function of the control signals output with the output unit (11), wherein the audio control device (6) is configured to carry out a method according to one of the preceding claims.Audio control device according to claim 10, wherein the audio control device (6) comprises a mixer (17) for mixing an audio signal (8).

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