Abstract:
A device and method for controlling reproduction of an audio signal is provided, wherein the device is operated by means of an energy storage device. The method comprises the steps of deactivating a normal mode and activating an energy saving mode. Power consumption from the energy storage device for reproduction of the audio signal is reduced in the energy saving mode when compared to the normal mode. The method comprises reducing in the energy saving mode, a bass frequency component of a frequency spectrum of the audio signal and outputting the audio signal with reduced bass frequency component. The method further comprises ascertaining a charge state of the energy storage device and controlling the reduction in the bass frequency component based on a decrease in the charge state of the energy storage device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of EP Application No. 11008245.0-1233, entitled “Device and Method for Reproducing an Audio Signal,” filed on Oct. 12, 2011, the disclosure of which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to a device and a method for reproducing an audio signal. 
     BACKGROUND 
     EP1024577(A1) provides a power system that is known to include secondary batteries and a charging circuit. Another circuit is shown in U.S. Pat. No. 5,771,471 that provides a charge regulator for a radio telephone. U.S. Publication No. 2002/0044637 A1 provides a power circuit that is capable of improving use efficiency of a chemical cell. 
     SUMMARY 
     According to one aspect, an improvement to a device is described through a device with the features of independent claim  1 . Advantageous developments are the subject matter of dependent claims, and are contained in the description. 
     Accordingly, a device is provided for reproducing an audio signal. The device may have a first interface for connection to an energy storage device. The energy storage device may comprise a battery, a fuel cell, or a rechargeable battery. The first interface may have connections for energy supply and/or signal connections. 
     The device may have a second interface for connection to a loudspeaker. The second interface may be a preamplifier output and/or a final amplifier output for outputting the audio signal. The loudspeaker may be connected to the second interface by means of a cable. It is possible for the loudspeaker to be connected to the second interface through an amplifier, such, for example, as a subwoofer. 
     The device may have an amplifier, which may be connected to the second interface and may be configured to amplify the audio signal. The amplifier may be a preamplifier or a power amplifier. The amplifier of the device may be connectable to the energy storage device for operation. 
     The device may have a control device, which may be connected to the first interface and to the amplifier. The control device may have a computing unit, such as for example a microcontroller, a signal processor, and/or a CPU for executing a control program, wherein the control program may provide control functions of the control device. 
     The control device may be configured to operate in a normal mode and in an energy saving mode. In the energy saving mode, a power consumption of electrical energy from the energy storage device is reduced for reproduction of the audio signal when compared to the audio signal while in the normal mode. 
     In the energy saving mode, the control device may be configured to reduce a bass frequency component of a frequency spectrum of the audio signal and to output the audio signal through the second interface with the reduced bass frequency component. 
     The control device may be configured to determine a charge state of the energy storage device. The energy storage device may transmit a digital or analog charge state signal to the control device such that a charge state is determined. 
     The control device may be configured to control the reduction in the bass frequency component based on a decrease of the charge state of the energy storage device. The control device may be configured to reduce the bass frequency component by means of a function when there is a decrease in the charge state. The bass frequency component may be reduced proportionately or by means of a Look Up Table (LUT). 
     According to one aspect, an improvement to a method is described through a method with the features of an independent claim. Advantageous developments are contained in the description. 
     Accordingly, a method is provided for controlling a reproduction of an audio signal. The audio signal may be reproduced by a device that is operated by means of an energy storage device. 
     In the method, a normal mode may be deactivated and an energy saving mode may be activated. In the energy saving mode, power consumption from the energy storage device may be reduced while the audio signal is being reproduced when compared to the normal mode. 
     In the energy saving mode, a bass frequency component of a frequency spectrum of the audio signal may be reduced and the audio signal may be output with the reduced bass frequency component. 
     A charge state of the energy storage device may be determined during the energy saving mode. 
     The reduction in the bass frequency component may be controlled based on a decrease in the charge state of the energy storage device. 
     The developments described below relate to the device as well as to the method for reproducing an audio signal. 
     According to one embodiment, the control device may be connectable to a database with stored audio files. Metadata associated with the audio files may be stored in the database. The metadata may be ID3 tags and other data as applicable. 
     An energy value for each audio file may be stored as an item of the metadata. The energy value may be based on the bass frequency component of a frequency spectrum of the applicable audio file. The energy value may be determined using a transformation in the frequency range and stored. 
     The control device may be configured to determine an energy threshold based on the charge state of the energy storage device. In one embodiment, the control device may be configured to evaluate at least one additional input quantity for determining the energy threshold. The additional input quantity may depend on other electrical devices such as an electric motor or a solar cell that affects the charge state of the energy storage device. A distance to destination or a remaining travel time of an electric vehicle may be used for determining the energy threshold. 
     To control the bass frequency component, the control device may be configured to determine an audio file to be output based on the energy threshold and on the associated energy value of the audio file from the database. The control device may be further configured to output the audio file as the audio signal. 
     According to one embodiment, the control device may be configured to use a digital or analog filter for filtering the audio signal to be output in order to reduce the bass frequency component. Such a filter may be an analog or digital high-pass filter or band-pass filter. The filtering by the filter may be combined with the above-described selection using the energy threshold. 
     In one embodiment, the control device may be configured to determine a threshold frequency of the filter based on the charge state of the energy storage device. The threshold frequency of the filter may be increased for low frequencies of the audio signal as the charge state decreases. 
     In one embodiment, the control device may be configured to determine a current position and a route to a destination with a distance to destination. The distance to the destination preferably may be determined by a Global Positioning System (GPS). The distance between the current position and the destination may be determined via the GPS. The charge state needed for this range may be determined on the basis of the distance. For example, a difference may be ascertained between the current charge state and the necessary charge state for reaching the destination. As such, the reduction in the bass frequency component may be controlled by means of the ascertained difference. Therefore, the control device may be configured to control the reduction in the bass frequency component based on the current charge state and the distance to the destination. 
     In one embodiment, the control device may be configured to activate the energy saving mode via an input through an input unit. 
     The variant embodiments described above are advantageous, both individually and in combination. All embodiments may be combined with one another. Some possible combinations are explained in the description of the drawings. However, these combinations of the variant embodiments introduced herein are not exhaustive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram that depicts curves of equal loudness; 
         FIG. 2  is a schematic block diagram; 
         FIG. 3  is a schematic diagram from an exemplary embodiment; 
         FIG. 4  is another schematic diagram for another exemplary embodiment; 
         FIG. 5  is a schematic representation of a device for reproducing an audio signal; 
         FIG. 5 a    is a schematic embodiment of a control device; 
         FIG. 5 b    is another schematic embodiment of another control device; and 
         FIG. 6  is a schematic embodiment of an input unit. 
     
    
    
     DETAILED DESCRIPTION 
     Shown schematically in  FIG. 1  is a diagram with curves of equal loudness pursuant to ISO standard 226(2003).  FIG. 1  is a graph illustrating a loudness level (e.g., with phon as a unit of measure) as a function of frequency.  FIG. 1  illustrates that the perceived loudness is strongly frequency-dependent. The frequency dependence is in turn sound-pressure-dependent, which indicates that different frequency dependencies exist for different levels. For this reason, a frequency spectrum X(f SA ) of the sound is to be determined if statements are to be made about the perception of a sound event. In addition, a sound event that extends over multiple frequency groups (overtones) and time behavior of such a sound event also have an effect on the perception of loudness. The perceived loudness can be quantified as a function of frequency. For example, it is known to use an A-filter for evaluation such that the frequency filter used in each case can be appended to the dB value (dB=decibels) in parentheses, as for example 20 dB(A). The curves have regions est. that are extrapolated by calculation. 
     The curves with equal perceived loudness level (e.g. 20 phon) represented in  FIG. 1  illustrates that the sound pressure dB with a bass frequency component B, also called bass portion B, rises sharply with a decreasing frequency below approximately 200 Hz. In order to reproduce a sound event in the bass frequency component “B”, a significantly higher sound pressure dB may be generated when compared to a frequency of 1 kHz. Thus, when a sound event is reproduced with a loud speaker, higher electrical power is needed to generate the high sound pressure dB of the bass portion B. If, for example, a sound event with a bandwidth of 20 Hz to 2 kHz is to be reproduced with a perceived loudness level of 20 phon, then a sound pressure of approximately 20 dB is to be generated for the frequency of 2 kHz. In contrast, a sound pressure of 90 dB is to be generated for the frequency of 20 Hz. Consequently, more electrical power must be applied for the bass portion B in the low-frequency range in order to produce the same perception of loudness in the human ear as at mid-range or high audio frequencies. 
     Furthermore, the required electrical power depends on an efficiency and/or a directional characteristic of the loudspeaker. For example, tweeters may have a higher efficiency than woofers. The higher the frequency, the more the sound is directed and the power theoretically increases at the listening point. The lower the frequency becomes, the more omnidirectional the sound becomes, requiring more power for the same sound pressure at the listening point. Furthermore, the radiated power may decrease when the wavelength of the frequency is smaller than a membrane radius. Moreover, the acoustical space may influence the sound pressure in a frequency-dependent manner. For example, a pressure chamber effect occurs in a motor vehicle. When all physical effects that act are taken into account, the majority of the electrical power is required for the bass portion B at the same perceived loudness. 
       FIG. 2  schematically shows a device  1  for reproducing an audio signal, “S A ”. The device  1  may be an infotainment system of a motor vehicle or a portable player for the audio signal S A . The device  1  may have a first interface  101  for connection to a rechargeable battery  2  as an electrical storage device. The device  1  also may have a second interface  102  for connection to a loudspeaker  3 . For example, the loudspeaker  3  may be connected directly to a connection of the second interface  2  via cables. It is also possible to connect the loudspeaker  3  to the second interface  102  through a subwoofer amplifier (not shown). The device  1  may have an amplifier  110  that may be connected to the second interface  102  and may be configured to amplify the audio signal S A . For operation, the amplifier  110  may be connected to the rechargeable battery  2  through the first interface  101 . In addition, the device  1  may have a control device  120 , which may be connected to the first interface  101  and to the amplifier  110 . 
     One embodiment is explained in detail with reference to the diagram in  FIG. 3 . A charge state “C” of the rechargeable battery  2  is shown at respective charge states (e.g., 20%, 30%, 40%, 50% and 100% charge). In one embodiment, a charge state C of 50% or greater may be associated with a normal mode “M N ” and a charge state C of 50% or less may be associated with an energy saving mode “M S ” in connection to the device  1 . Also shown by way of example, is a frequency spectrum X(f SA ) of the audio signal S A  with respect to the frequency f. The control device  120  may be configured to reduce a power consumption from the rechargeable battery  2  while reproducing the audio signal S A  when the device  1  is in the energy saving mode M S  when compared to the device  1  operating in the normal mode M N . In one embodiment, the bass portion B of the audio signal S A  may be reduced in the energy saving mode M S  by the audio signal S A  being high-pass filtered. In  FIG. 3 , the frequency response of the filtering is shown for different threshold frequencies f G1 , f G2 , f G3 , f G4 . The audio signal S A  may be output with the reduced bass portion B after the high-pass filtering. 
     The control device  120  may be configured to determine the charge state C. For example, an electrical quantity of the rechargeable battery  2 , such as the rechargeable battery voltage or its behavior over time, may be measured by the control device  122  for this purpose. The control device  120  may be configured to control the reduction in the bass portion B based on a decrease in the charge state C of the rechargeable battery  2 . From  FIG. 3 , the reduction in the bass portion B may be accomplished by filtering. In one embodiment, the control device  120  may perform the digital and/or analog high-pass filtering. In one embodiment, the control device  120  may include a controllable filter function. In one embodiment, the high pass filter may be activated or deactivated as a function of the charge state C. For instance, the high-pass filter may be deactivated at a charge state C above 50%. 
     From  FIG. 3 , the high-pass filtering may be controlled by the control device  120  in that a cut-off frequency f G1 , f G2 , f G3 , f G4  of the high-pass filtering is altered. The high-pass filtering may be deactivated in the normal mode M N  at a charge state C above 50%. A first cut-off frequency value f G1  may be associated with a charge state C between 40% and 50%. A second cut-off frequency value f G2  may be associated with a charge state C between 30% and 40%. A third cut-off frequency value f G3  may be associated with a charge state C between 20% and 30%. A fourth cut-off frequency value f G4 , for example, 200 Hz may be associated with a charge state C below 20%. The cut-off frequencies f G1 , f G2 , f G3 , f G4  may be controlled as a function of the charge state C by means of a step function. Alternatively, a proportional dependency may be provided. It is also possible to deactivate a subwoofer amplifier in energy saving mode M S . In addition to the charge state C, additional input quantities may be analyzed for controlling the reduction. This will be explained in more detail in connection with  FIG. 5 . 
     The control device  120  may have a connection to a database  130  (see  FIG. 5, 130 ) for which will be used to explain the graph of  FIG. 4 . The database  130  may have audio files A 1 , A 2 , A 3  and metadata associated with each audio file A 1 , A 2 , A 3 . In this configuration, an energy value E may be included in the metadata.  FIG. 4  illustrates one frequency spectrum X(f A1 ), X(f A2 ), X(f A3 ) for each audio file A 1 , A 2 , A 3  and an associated energy value E stored in the database  130 . Thus, the energy value associated with the first data file A 1  is E=10, the energy value associated with the second audio file A 2  is E=1, and the energy value associated with the third audio file A 3  is E=4. The applicable energy value E may be determined on the basis of a power “P” in the bass portion B of the spectrum X(f A1 ), X(f A2 ), X(f A3 ). For example, the power P may be acquired as the average over an entire length of the audio file A 1 , A 2 , A 3 . 
     In  FIG. 5 , a device  1  for reproducing the audio signal S A  is explained in detail. The device  1  may include the control unit  120 , which may be connected through the first interface  101  to the rechargeable battery  2  (e.g. “Accu”). In addition, the device  1  may include the amplifier  110  (e.g. “AMP”), which may be connected to the loudspeaker  3  through the second interface  102 . The amplifier  110  may comprise multiple amplifier units, and may be supplied with a current “I Audio ” from the rechargeable battery  2 . A subwoofer amplifier unit may be additionally activated and deactivated by means of a control signal “SubOff”. The amplifier  110  may be configured to output the amplified audio signal S A  to the loudspeaker  3 . 
     The device  1  includes the control unit  120  for outputting the audio signal S A  to the amplifier  110 . The control device  120  may be configured to operate in the normal mode M N  and in the energy saving mode M S . The control device  120  may be configured to generate control signals associated with the normal mode M N  and the energy saving mode M S . The activation and deactivation of normal mode M N  and energy saving mode M S  may be accomplished by means of input signals, such as an input by a user by means of an input unit  4  and/or receipt of a monitoring signal of the energy storage device  2 , such as an output voltage of a rechargeable battery, and/or receipt of a position-dependent signal from a navigation unit, such as a distance to a destination of a route. The energy saving mode M S  may be activated and deactivated based on the input signals, where power consumption from the energy storage device  2  while reproducing the audio signal SA is reduced (i.e., the control device  120  operates in the energy savings mode M S ). 
     Music played in an electric motor vehicle may be manipulated as a function of the charge state C of the rechargeable lithium-ion battery in such a manner that low-power titles can be played as needed or the music played can be altered of high-power low frequencies by filtering. In this way, the energy saved in the rechargeable battery  2  by the device  1  may benefit the range of the motor vehicle. In addition, a loudness adjustment may also take place. 
     Music systems in electric motor vehicles consume electrical energy. If the energy is to be used for the range of the electric vehicle, the option exists of manually turning off the music system entirely. However, if vehicle occupants do not wish to forego the enjoyment of music altogether, the energy that is available is to be distributed intelligently. When the rechargeable battery has a low charge, only low power music  1  may be outputted at the loud speaker  3 . The low-power music may be obtained by categorizing the music pieces and/or by filtering out high-power portions of the frequency spectrum. This may have a direct effect on the acoustic power and, at the same time, on electrical power consumption. 
     Electrical power consumption of a music system in an electric vehicle depends largely on the playing loudness and the frequency spectrum X(f SA ) of the audio signal S A  that is output. The acoustic power emitted through the loudspeaker  3  is directly related to the electrical power. Since the range of an electric vehicle depends on the charge state C of the rechargeable battery  2 , the range is increased when the music system, as an energy consumer, conserves current I Audio  for amplification of the audio signal S A  to be output. 
     The control unit  120  may be connectable to multiple audio signal sources  130 ,  140 . A database  130  (e.g., one of the audio signal sources) is connected through an interface or a network and may permit the selection and output of an audio file as the audio signal S A . A receiving device “RX”  140  may be designed for audio reception, in particular via radio. The receiving device  140  may have a UHF receiver or a DAB receiver or the like. 
       FIG. 5 a    illustrates one embodiment of the control device  120  with an analysis unit  121  and a digital and/or analog filter  125 . Electrical energy may be taken from the audio signal S A  by means of filtering by the filter  125  when a filtering operation is performed. The filter  125  may have a high-pass filter or a band-pass filter, which acts on the audio signal S A . The audio signal S A  is provided from any desired source, such as the receiving device  140 , a CD player or an MP3 player. In reference to  FIG. 5 a   , a cut-off frequency f G  of the filter  125  may be adjusted as a function of a charge state C of the rechargeable battery  2  and/or of a remaining travel time/distance determined by the navigation unit  5 . 
     In one exemplary embodiment, the analysis unit  121  may be configured to analyze the signal S INP  from the input unit  4  and/or the signal S Accu  from the rechargeable battery  2  and/or the signal S GPS  from the navigation unit  5 . The signal S INP from the input unit  4  may be generated from input entered by the user on a touch screen. The signal S Accu  from the rechargeable battery  2  may be generated based on a voltage or a current budget of the rechargeable battery  2  and may depend upon the charge state C of the rechargeable battery  2 . The signal S GPS  from the navigation unit  5  may be determined as a function of, e.g., a remaining travel time or a distance to be traveled that has been determined by the navigation unit  5 . 
     Using the input signals S INP , S Accu , S GPS  the analysis unit  121  may generate a signal M N /M S  for controlling an activation or deactivation of a normal mode M N  and an energy saving mode M S . Furthermore, the analysis unit  121  may transmit a control signal C fG  to adjust the cut-off frequency f G  of the filter  125 . The filter  125  filters the bass portion B out of the input signal S DB  (from the database  130 ) or out of the input signal S RX  (from the receiving unit  140 ). The control may take place in accordance with the diagram for the exemplary embodiment in  FIG. 3  by means of a LUT (Look Up Table). The lower the charge state C of the rechargeable battery  2  is, the higher the cut-off frequency f G  may be set, since low frequencies in a bass portion B of the spectrum X(f SA ) consume more electrical energy. In addition, a provision is made for the amplifier and the loudspeaker to be switched off for low frequencies on the basis of the energy saving mode M S  and/or the threshold frequency f G  (see  FIG. 5 ). It may be acoustically advantageous for the cut-off frequency f G  of the filter  125  to be modified slowly over time. For example, this may be performed by means of a timer and/or as a function of the change state C over time of the rechargeable battery  2 . 
     It is possible to select from among low-power music titles (see  FIG. 5 b   ). For example, the control unit  120  may have an analysis unit  122  and a selection unit  126 . The energy content of each music title in the database  130  may be determined and an associated energy value E may be stored in the database  130  with metadata for the applicable music piece. For example, the energy content may be categorized from 1 to 10 by means of a scale of the energy values. For example, an energy value, E=1 is indicative of very low power with a small bass portion B. This music title can be played when the rechargeable battery  2  is in critically low charge states C. An energy value, E=10 is indicative of a very high power with a large bass portion B. This music title is not played in critical charge states C. 
     If the user is listening to content from his/her MP3 database  130 , audio files A 1 , A 2 , A 3  of titles in the database  130  may be selectively permitted based on a function of the charge state C of the rechargeable battery  2  and based on, when applicable, a function of the remaining travel time/distance (see  FIG. 5 b   ). The determination regarding permissibility may be made on the basis of an energy threshold th E . For example, all audio files A 1 , A 2 , A 3  from the database  130  that have an energy value E lower than the energy threshold th E  may be queried by means of a signal query Q(E). The threshold may be th E =5, so that only the second audio file A 2  and the third audio file A 3  may be read out (see,  FIG. 4 ). The audio files A(Q) dependent on the query Q(E) that are output may be looped through the control unit  120 , additionally optionally filtered, and may be output as audio signal S A  with reduced bass portion B. Embodiments in  FIG. 5 a    and  FIG. 5 b    may be combined with one another in the control unit  120  as deemed in order to achieve optional results. 
       FIG. 6  depicts the input unit  4  as a touch screen. The touch screen  4  included with a graphical user interface with various fields (or widgets). A first icon  41  may permit the activation or selection of only low power music pieces, in which their corresponding energy value E is below the energy threshold th E  (see  FIG. 2 ). A second icon  42  may enable the filter  125  to reduce the bass portion B (see  FIG. 5A ). In addition, a consumption indicator  43  may be shown on a widget on the touch screen, which symbolizes energy consumption in the form of a bar graph, for example. It is likewise possible for the consumption indicator  43  to act as an input function (e.g., a third selectable menu option), so that the user may specify the associated energy consumption directly by selecting the consumption indication  43  at a certain location. 
     In addition to the above-mentioned possibilities for reducing energy consumption it is recognized that the embodiment herein may reduce the loudness of the entire frequency spectrum X(f SA ) of the audio signal S A  in order to further reduce power consumption. An upper loudness threshold may be lowered when the charge state C of the rechargeable battery  2  drops. The threshold loudness may be reduced proportionately to the charge state C. If the energy situation is very critical, audio reproduction may also be eliminated entirely, so that only predetermined audio content such as radio traffic reports, news, telephone, and navigational announcements may be output as audio signal S A . The measures for reducing energy consumption may be combined with one another in any desired way. The energy consumption may be calculated as a function of the filter setting and/or the energy value E, and may be fed to a central energy management system or the range information in an electric vehicle. 
     This application is not restricted to the embodiments shown in the Figures. For example, it is possible to provide for the reduction of energy consumption for a mobile, portable device, such that the user may adjust the consumption through the entry of, for instance, predefined consumption levels. The remaining play time for audio files is then displayed to the user. In especially advantageous manner, the functionality of the device  1  from  FIG. 5  can be used for an electric vehicle. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  device 
           101 ,  102  interface 
           110 , AMP amplifier 
           120  control unit 
           121 ,  122  analysis unit 
           125  filter 
           126  selection unit 
           130 , DB database 
           140 , RX receiver 
           2 , Accu energy storage device, rechargeable battery 
           3  loudspeaker 
           4 , Inp input unit, touch screen 
           41 ,  42  input element, widget 
           43  display element 
           5 , GPS unit for position determination, navigation unit 
         A 1 , A 2 , A 3  audio file 
         B bass frequency component, bass portion 
         C charge state 
         E energy value 
         est calculated curve 
         f frequency 
         f G1 , f G2 , f G3 , f G4  threshold frequency 
         I Audio  current 
         M N  normal mode 
         M S  energy saving mode 
         P Power 
         S A  audio signal 
         S INP , S Accu , S GPS , S RX , S SB , C fG , Signal 
         Q(E), A(Q) 
         SubOff control signal 
         th E  energy threshold 
         X(f SA ), X(f A1 ), X(f A2 ), X(f A3 ) frequency response, spectrum