Abstract:
A system and method of improving the efficiency in the power consumption of an audio system. In essence, the technique is to adjust the power delivered from the power supply to the analog section, such as the power amplifier, in response to the volume level indicated by the volume control module and/or in response to the detected characteristic of the input audio signal. Thus, in this manner, the analog section is operated in a manner that is related to the level of the signal it is processing. Additionally, the system and method also relate to a technique of adjusting the dynamic ranges of the digital signal and the analog signal to improve the overall dynamic range of the system without needing to consume additional power.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present disclosure relates generally to audio systems, and more specifically, to a system and method of reducing power consumption in an audio system by adjusting the power supplied to an audio power amplifier based on the volume level indicated by a volume control module and/or the envelope of the input audio signal. 
         [0003]    2. Background 
         [0004]    The output of a typical audio system consists of a digital section followed by an analog section. For example, the digital section may include a digital signal processor (DSP) adapted to receive an input digital audio signal, and apply some predetermined signal processing upon the input digital signal. The output of the digital section is coupled to the input of the analog section. The analog section may include a digital-to-analog converter (DAC) adapted to convert the digital audio signal received from the digital section into an analog audio signal. The analog section may also include a power amplifier (PA), such as a class A, A/B, D, E or G power amplifier, adapted to increase the power level of the analog audio signal to sufficiently drive a speaker. This is explained in more detail with reference to the following example. 
         [0005]      FIG. 1A  illustrates a block diagram of an exemplary conventional audio system  100 . In this example, the audio system  100  is configured to generate a stereo output. 
         [0006]    The left channel section of the stereo output includes a DSP  102 -L adapted to receive a left-channel N-bit input audio digital signal and perform some predetermined signal processing upon the signal, a DAC  104 -L adapted to convert the digital audio signal received from the DSP  102 -L into an analog audio signal, and a power amplifier (PA)  106 -L adapted to increase the power level of the analog audio signal to sufficiently drive a left-channel speaker  108 -L. The right-channel section of the stereo output includes a DSP  102 -R, a DAC  104 -R, and a power amplifier (PA)  106 -R, and may be configured similar to the left-channel section, except that it acts upon a right-channel N-bit input digital audio signal to generate an analog audio signal with sufficient power to drive a right-channel speaker  108 -R. 
         [0007]    Generally, the power supply for the digital section is configured differently than the power supply for the analog section. For example, the power supply for the digital section may produce a relatively low supply voltage of approximately 1.2 Volts. Whereas, the power supply for the analog section may produce a higher supply voltage of approximately 3.3 Volts. Both supply voltages are generally fixed. The analog power supply is typically configured to provide power to the analog section such that the analog section can support the maximum audio signal amplitude. However, the analog signal amplitude is usually not at its maximum amplitude. Accordingly, this results in inefficiency in the power used by the audio system  100 . This is explained in more detail with reference to the following example. 
         [0008]      FIG. 1B  illustrates a block diagram of the left-channel of the conventional audio system  100 , as discussed above. Additionally, in this diagram, a power supply  110  for supplying power to the digital section, DSP  102 -L, is shown. Also, a power supply  112  for supplying power to the analog section, DAC  104 -L and power amplifier (PA)  106 -L, is shown. As discussed above, the power supply  112  is configured to provide sufficient power to the DAC  104 -L and power amplifier  106 -L such that these devices can handle the maximum audio signal amplitude. Further, the bias currents for these devices are typically chosen for worst case scenario. 
         [0009]    This results in inefficiency in the power consumed by the audio system  100  if the analog section is supporting an audio signal with an amplitude less than the maximum supported amplitude. For instance, this is true if the volume control of the audio system  100  is set to lower than the maximum volume. Additionally, since many audio content, such as music, have moments of high and low signal amplitude, the efficiency of the power consumed by the audio system  100  is lower at low audio signal amplitude. 
       SUMMARY 
       [0010]    An aspect of the disclosure relates to a technique of improving the efficiency in the power consumption of an audio system. In essence, the technique is to adjust the power delivered from the power supply to the analog section, such as a power amplifier, in response to the volume level indicated by a volume control module and/or in response to the detected characteristic of the input audio signal. Thus, in this manner, the analog section is operated in accordance with the level of the signal it is processing. Additionally, the system and method also relate to a technique of adjusting the dynamic ranges of the digital signal and the analog signal to improve the overall dynamic range of the system without needing to consume additional power. 
         [0011]    For instance, at relatively high audio signal levels, the power delivered to the analog section is relatively high. At relatively low audio signal levels, the power delivered to the analog section is relatively low. This improves the power consumption efficiency over that of a system that always delivers power to the analog section per the maximum signal level, regardless of the actual signal level being handled by the analog section. 
         [0012]    In one exemplary embodiment, an audio system comprises an audio amplifier adapted to amplify a first analog audio signal to generate a second analog audio signal; 
         [0013]    a power supply adapted to supply power to the audio amplifier; a volume control module adapted to generate a signal indicating a volume level related to the second analog audio signal; and a control module adapted to control an amount of power delivered by the power supply to the audio amplifier in response to the volume level signal. 
         [0014]    In another exemplary embodiment, an audio system comprises an audio amplifier adapted to amplify a first analog audio signal to generate a second analog audio signal; a power supply adapted to supply power to the audio amplifier; a detection module adapted to generate a signal related to a characteristic of the first analog audio signal; and a control module adapted to control an amount of power delivered by the power supply to the audio amplifier in response to the characteristic indicating signal. 
         [0015]    In yet another exemplary embodiment, an audio system comprises an audio amplifier adapted to amplify a first analog audio signal to generate a second analog audio signal; a power supply adapted to supply power to the audio amplifier; a volume control module adapted to generate a signal indicating a volume level related to the second analog audio signal; a detection module adapted to generate a signal related to a characteristic of the first analog audio signal; and a control module adapted to control an amount of power delivered by the power supply to the audio amplifier in response to the volume level and characteristic indicating signals. 
         [0016]    Continuing, in another exemplary embodiment, an audio system comprises a digital companding module adapted to receive a first digital audio signal, and generate a second digital audio signal being a product of the first digital audio signal and a digital gain parameter G D ; a digital-to-analog (DAC) converter adapted to generate a first analog audio signal derived from the second digital audio signal; an analog companding module adapted to receive the first analog audio signal, and generate a second analog audio signal being a product of the first analog audio signal and an analog gain parameter G A ; and a controller adapted to adjust the digital gain parameter G D  and the analog gain parameter G A  in response to a characteristic of the first digital audio signal. 
         [0017]    Other aspects, advantages and novel features of the present disclosure will become apparent from the following detailed description of the disclosure when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  illustrates a block diagram of an exemplary conventional audio system. 
           [0019]      FIG. 1B  illustrates a block diagram of the left-channel of the conventional audio system. 
           [0020]      FIG. 2  illustrates a block diagram of an exemplary audio system in accordance with an aspect of the disclosure. 
           [0021]      FIG. 3  illustrates a block diagram of another exemplary audio system in accordance with another aspect of the disclosure. 
           [0022]      FIG. 4  illustrates a block diagram of yet another exemplary audio system in accordance with another aspect of the disclosure. 
           [0023]      FIG. 5  illustrates a block diagram of still another audio system in accordance with another aspect of the disclosure. 
           [0024]      FIG. 6  illustrates a block diagram of still another audio system in accordance with another aspect of the disclosure. 
           [0025]      FIG. 7  illustrates a diagram of an exemplary noise model of the an audio system in accordance with another embodiment of the invention. 
           [0026]      FIG. 8  illustrates a block diagram of still another audio system in accordance with another aspect of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 2  illustrates a block diagram of an exemplary audio system  200  in accordance with an aspect of the disclosure. In this example, only the left-channel section of the audio system  200  is shown for illustrative purposes. It shall be understood that the concepts described herein are applicable to a right-channel section of the audio system  200 , or to any or other audio channel that may be present in an audio system. For example, the concepts described herein are applicable to mono, stereo, surround sound, and other types of audio systems. 
         [0028]    In particular, the audio system  200  comprises a digital section including, for example, a digital signal processor (DSP)  202 -L. It shall be understood that the digital section may include other or different components. The audio system  200  also comprises an analog section, including a digital-to-analog converter (DAC)  204 -L and a power amplifier (PA)  206 -L. The power amplifier (PA) may be configured as an A, A/B, D, E, G or other class amplifier. As with the digital section, it shall be understood that the analog section may include other or different components. 
         [0029]    If the digital section power supply  210  supplies a Vdd voltage to the DSP  202 -L that is different than the Vdd voltage supplied to the DAC  204 -L by the analog section power supply  212 , a DC level shift  203 -L may be provided between the DSP  202 -L and DAC  204 -L to provide the appropriate DC level shift. Similarly, if the analog section power supply  212  supplies a Vdd voltage to the DAC  204 -L that is different than the Vdd voltage that it supplies to the power amplifier (PA)  206 -L, a DC level shift or block  205 -L may be provided between the DAC  204 -L and the power amplifier (PA)  206 -L to provide the appropriate DC level shift or block. 
         [0030]    In this example, the DSP  202 -L receives an input N-bit digital audio signal, and performs one or more predetermined processes upon the input signal. The DAC  204 -L converts the digital audio signal received from the DSP  202 -L into an analog audio signal. The power amplifier (PA)  206 -L amplifies the analog audio signal, in accordance with an indicated volume level as discussed in more detail below, to a sufficient level to drive an L-channel speaker  208 -L. 
         [0031]    The audio system  200  further comprises a power supply  210  for supplying power to the digital section (e.g., the DSP  202 -L). Additionally, the audio system  200  comprises a power supply  212  for supplying power to the analog section (e.g., DAC  204 -L and power amplifier (PA)  206 -L). The power supply  212  may deliver direct current (DC) power to the analog section. Alternatively, or in addition to, the power supply  212  may deliver power to the analog section via non-DC techniques, such as by pulse width modulation (PWM) or pulse frequency modulation (PFM). As discussed above, the power supply  212  may supply power differently to the DAC  204 -L than it does to the power amplifier (PA)  206 -L. In such a case, the control module  214  may instruct the power supply  212  to generate PWM power when the indicated volume level is above a predetermined threshold, and to generate PFM power when the indicated volume level is below the predetermined threshold. 
         [0032]    The audio system  200  further includes a power supply control module  214  to control the amount of power delivered to the analog section by the power supply  212  in response to a volume control module  216 . In order to improve the efficiency in the power consumption of the audio system  200 , the power supply control module  214  controls the power supply  212  so that the power delivered to the analog section is related to the current volume level indicated by the volume control module  216 . The relationship between the power supplied to the analog section and the current volume level could be substantially linear or non-linear. 
         [0033]    As an example, if the current volume level indicated by the volume control module  216  is at the maximum volume level, the power supply control module  214  may control the power supply  212  to supply a voltage of approximately 3.3 Volts to the analog section. If the user lowers the volume to 50% of the maximum volume level as indicated by the volume control module  216 , the power supply control module  214  controls the power supply  212  to supply a voltage of approximately 2.2 Volts to the analog section. 
         [0034]    As another example, if the current volume level indicated by the volume control module  216  is at the maximum volume level, the power supply control module  214  may control the power supply  212  to supply a PWM signal having an 85% duty cycle to the analog section. If the user lowers the volume to 50% of the maximum volume level as indicated by the volume control module  216 , the power supply control module  214  controls the power supply  212  to supply a PWM signal having a 55% duty cycle to the analog section. 
         [0035]    As yet another example, if the current volume level indicated by the volume control module  216  is at the maximum volume level, the power supply control module  214  may control the power supply  212  to supply a PFM signal with a frequency of 300 MHz to the analog section. If the user lowers the volume to 50% of the maximum volume level as indicated by the volume control module  216 , the power supply control module  214  controls the power supply  212  to supply a PFM signal with a frequency of 255 MHz to the analog section. 
         [0036]      FIG. 3  illustrates a block diagram of another exemplary audio system  300  in accordance with another aspect of the disclosure. In the prior example, the power supply control module controls the power supply for the analog section in response to the volume level indicated by the volume control module  216 . In this example, a power supply control module controls the power supply for the analog section in response to the detected envelope of the input audio signal. This improves the power consumption efficiency of the audio system  300  in response to the dynamics of the input audio signal. 
         [0037]    As with the prior example, only the left-channel section of the audio system  300  is shown for illustrative purposes. It shall be understood that the concepts described herein are applicable to a right-channel section of the audio system  300 , or to any or other audio channel that may be present in an audio system. As previously discussed, the concepts described herein are applicable to mono, stereo, surround sound, and other types of audio systems. 
         [0038]    In particular, the audio system  300  comprises a digital section including a digital signal processor (DSP)  302 -L for performing particular audio processing upon an input N-bit digital audio signal, as discussed in more detail below. The audio system  300  further comprises an analog section including a digital-to-analog (DAC) converter  304 -L to convert the digital audio signal received from the DSP  302 -L into an analog audio signal, and a power amplifier (PA) to increase the amplitude of the analog audio signal, in response to a power supply control module that is responsive to the envelope of the input digital audio signal, to sufficiently drive an L-channel speaker  308 -L. 
         [0039]    The audio system  300  further comprises a power supply  310  for supplying power to the digital section, such as the DSP  302 -L. Additionally, the audio system  300  comprises a power supply  312  to supply power to the analog section, such as the DAC  304 -L and power amplifier (PA)  306 -L. As with the prior example, the power supply  312  may deliver direct current (DC) power to the analog section. Alternatively, or in addition to, the power supply  312  may deliver power to the analog section via non-DC techniques, such as by pulse width modulation (PWM) or pulse frequency modulation (PFM). As previously discussed, the power supply  312  may supply power differently to the DAC  304 -L than it does to the power amplifier (PA)  306 -L. In such a case, the control module  314  may instruct the power supply  312  to generate PWM power when the level indicated by the envelope signal is above a predetermined threshold, and to generate PFM power when the level indicated by the envelope signal is below the predetermined threshold. 
         [0040]    If the digital section power supply  310  supplies a Vdd voltage to the DSP  302 -L that is different than the Vdd voltage supplied to the DAC  304 -L by the analog section power supply  312 , a DC level shift  303 -L may be provided between the DSP  302 -L and DAC  304 -L to provide the appropriate DC level shift. Similarly, if the analog section power supply  312  supplies a Vdd voltage to the DAC  304 -L that is different than the Vdd voltage that it supplies to the power amplifier (PA)  306 -L, a DC level shift or block  305 -L may be provided between the DAC  304 -L and the power amplifier (PA)  306 -L to provide the appropriate DC level shift or block. 
         [0041]    The audio system  300  further includes a power supply control module  314  to control the amount of power delivered to the analog section by the power supply  312  in response to the detected envelope of the input digital audio signal. More specifically, the DSP  302 -L comprises an audio processing module  302 -L- 1  adapted to perform a specified processing to the input N-bit digital audio signal. The DSP  302 -L further comprises an envelope detection module  302 -L- 3  adapted to generate a signal related to the current envelope of the input digital audio signal. The power supply control module  314  then controls the power supply  312  in response to the signal generated by the envelope detection module  302 -L- 3 . The DSP  302 -L further comprises a delay module  302 -L- 2  in order to compensate for the processing delay of the envelope detection module  302 -L- 3 . The delay  302 -L- 2  ensures that the power delivered to the analog section timely corresponds to the envelope of the audio signal being processed by the analog section. 
         [0042]    The envelope detection module  302 -L- 3  may detect the envelope of the input digital audio signal by buffering or storing k samples of the input digital audio signal. In one embodiment, the envelope detection module  302 -L- 3  determines the peak value of the k samples, and generates an envelope signal indicative of the peak value. In this manner, the power supply  312  is configured to supply power to handle the peak value. In another embodiment, the envelope detection module  302 -L- 3  performs an integration of the k-samples to determine an “average” amplitude level for the k-samples, and generates an envelope signal indicative of the “average” amplitude level of the k-samples. In this manner, some compromise in signal quality is afforded for lower power consumption. In yet another embodiment, the envelope detection module  302 -L- 3  determines a root mean square (RMS) value of the k-samples, and generates an envelope signal indicative of the RMS value of the k-samples. Similarly, with this embodiment, some compromise in signal quality is afforded for lower power consumption. 
         [0043]    The power supply control module  314  may control the power supply  312  in response to the envelope-indicative signal generated by the envelope detection module  302 -L- 3 . It shall be understood that the envelope detection module  302 -L- 3  may perform other algorithms to generate a signal related to the envelope of the input digital audio signal. 
         [0044]    In order to improve the efficiency in the power consumption of the audio system  300 , the power supply control module  314  controls the power supply  312  so that the power delivered to the analog section is related to the detected envelope of the input digital audio signal as indicated by the envelope detection module  302 -L- 3 . The relationship between the power supplied to the analog section and the current envelope of the input digital audio signal could be substantially linear or non-linear. 
         [0045]    Additionally, by the envelope detection module  302 -L- 3  knowing the k-samples of the input digital audio signal, the power supply control module  314  has pre-knowledge of whether the input signal is making a rapid transition from high to low, or low to high. In this way, the power supply control module  314  may control the power supply  312 , such as in a slow manner, to avoid clicks and pops distortion from creeping into the output audio signal of the system  300 . In some cases, for example that use a class D power amplifier (PA), the power supply rejection may be relatively poor. By having advance knowledge of the k-samples of the input digital audio signal, the power supply control module  314  may be configured to limit the rate of changing the power supplied by the power supply  312  to be lower than the human audible range (e.g., ≦10 Hz), so as to prevent distortion of the output audio signal. 
         [0046]      FIG. 4  illustrates a block diagram of yet another exemplary audio system  400  in accordance with another aspect of the disclosure. The audio system  400  is basically a combination of the previously-discussed audio systems  200  and  300 . Thus, the audio system  400  includes a power supply control module  414  that controls the power delivered to the analog section by the power supply  312  in response to the volume level indicated by the volume control module  216  and the detected envelope of the input digital audio signal as indicated by the envelope detection module  302 -L- 3 . 
         [0047]      FIG. 5  illustrates a block diagram of still another audio system  500  in accordance with another aspect of the disclosure. As discussed in more detail below, the audio system  500  is configured to generate an output analog audio signal in a power efficient manner. The audio system  500  comprises a digital audio section  510 , an analog audio section  530 , a digital signal power detector  540 , an adaptive power supply  550  that may be configured, for example, as a switch mode power supply (SMPS), and a digital audio source  560  for generating an input digital audio signal. 
         [0048]    The digital section  510 , in turn, may comprise a first up-sampling interpolation module  512 , a finite impulse response (FIR) filter  514 , a second up-sampling interpolation module  516 , and a digital delta-sigma modulator  518 . The first up-sampling interpolation module  512  receives the input digital audio signal from the digital audio source  560 , and produces a digital audio signal with a higher sampling rate. As an example, the input digital audio signal may have a sampling rate of 8 kHz to 48 kHz. The first up-sampling interpolation module  512  then uses an interpolation algorithm to generate a digital audio signal with a sampling rate eight (8) times higher (e.g., 64 kHz to 384 kHz). The FIR filter  514  receives the output of the first up-sampling interpolation module  512  and uses an oscillator signal with a frequency eight (8) times the sampling rate of the input digital audio signal to filter out image and other unwanted signals. 
         [0049]    The second up-sampling interpolation module  516  receives the output signal from the FIR filter  516 , and produces a digital audio signal with a higher sampling rate. As an example, the output digital audio signal from the FIR filter  514  may have a sampling, rate of 64 kHz to 384 kHz. The second up-sampling interpolation module  516  then uses an interpolation algorithm to generate a digital audio signal with a sampling rate 32 times higher (e.g., 2.048 MHz to 12.288 MHz). The digital delta-sigma modulator  518  performs an algorithm on the output digital audio signal from the second up-sampling interpolation module  516  to reduce the number of bits to quantify the digital audio signal generated by the digital section  510 . It shall be understood that the digital section  510  may be configured in other manners. The digital section  510  described herein is merely one example. 
         [0050]    The analog section  530 , in turn, may comprise a digital-to-analog (DAC)  532  to convert the output digital audio signal from the digital section  510  into an analog audio signal. Additionally, the analog section  530  may further comprise a power amplifier (PA)  536  to increase the power of the analog audio signal form the DAC  532  to a sufficient level to drive a speaker. It shall be understood that the analog section  530  may be configured in other manners. The analog section  530  described herein is merely one example. 
         [0051]    The digital signal power detector  540 , in turn, receives the input digital audio signal from the digital audio source  560 , and generates a signal indicative of the approximate power level of the input digital audio signal. The adaptive power supply  550  supplies power to the analog section  530  on the basis of the power-indicating signal generated by the digital signal power detector  540 . In this configuration, the adaptive power supply  550  may supply power to the analog section in a power efficient manner. For example, when the power level of the input digital audio signal is relatively low as indicated by the signal generated by the digital signal power detector  540 , the adaptive power supply  550  supplies relatively low power to the analog section  530 . On the other hand, when the power level of the input digital audio signal is relatively high as indicated by the signal generated by the digital signal power detector  540 , the adaptive power supply  550  supplies relatively high power to the analog section  530 . 
         [0052]      FIG. 6  illustrates a block diagram of still another audio system  600  in accordance with another aspect of the disclosure. As discussed in more detail below, the audio system  600  increases the dynamic range of the input signal in a power efficient manner. In particular, the audio system  600  comprises a digital audio section  610 , a DC level shift  620 , an analog audio section  630 , a dynamic range controller  640 , and a digital audio source  660 . 
         [0053]    The digital section  610  may be configured similarly to the digital section  510  of the previous embodiment, and may include a first up-sampling interpolation module  612 , an FIR filter  614 , a second up-sampling interpolation module  616 , and a digital delta-sigma modulator  618 . Additionally, the digital section  610  comprises a digital companding module  611  to adjust the dynamic range of an input digital audio signal received from the digital audio source  660  in response to a control signal received from the dynamic range controller  640 . 
         [0054]    The analog section  630  may be configured similarly to the analog section  530  of the previous embodiment, and may include a DAC  632  and a power amplifier (PA)  636 . Additionally, the analog section  630  includes an analog companding module  634  to adjust the dynamic range of the analog audio signal generated by the DAC  632  in response to a control signal received from the dynamic range controller  640 . The DC level shift  620  may provide the appropriate DC level shifting if the digital and analog sections  610  and  620  are supplied with different Vdd voltages. 
         [0055]    The dynamic range controller  640  is configured to receive the input digital audio signal from the digital audio source  660 , determine the power of the input digital audio signal, and generate dynamic range control signals for the digital companding module  611  and the analog companding module  634  based on the detected power of the input digital audio signal. In particular, the dynamic range controller  640  may be configured to generate control signals such that the gain G D  of the digital companding module  611  multiplied by the gain G A  of the analog companding module  634  is substantially unity (e.g., G D ×G A =1). Additionally, the dynamic range controller  640  may be configured to adjust the gain G D  of the digital companding module  611  inversely with the detected power of the input digital audio signal. The minimum gain for the digital companding module  611  may be set to zero (0) dB. With this configuration, the audio system  600  is able to increase its dynamic range without increasing its power consumption, as explained in more detail with reference to the following example. 
         [0056]      FIG. 7  illustrates a diagram of an exemplary noise model of the audio system  600 . In the diagram, the variable Vin represents the input digital audio signal of the audio system  600 , and the variable Vout represents the output analog audio signal of the audio system  600 . Additionally, the variable Vnq represents the digital quantization noise of the input digital audio signal, the variable Vnlpf represents the noise due to the DAC  632 , and Vnpa represents the noise due to the power amplifier  636 . As discussed above, the gains of the digital companding module  611  and the analog companding module  634  are represented as G D  and G A , respectively. 
         [0057]    The total noise power at the output of the audio system  600  may be represented by the following equation: 
         [0000]        Vn   2 =( Vnq*G   D   *G   A ) 2 +( Vnlpf*G   A ) 2   +Vnpa   2    Eq. 1 
         [0000]    As previously discussed, the dynamic range controller  640  controls the respective gains G D  and G A  of the digital and analog companding modules  611  and  634  such that their product is substantially unity. This may be represented as follows: 
         [0000]        G   D   *G   A =1   Eq. 2 
         [0000]    Substituting Eq. 2 into Eq. 1, the total noise power at the output of the audio system  600  may be represented as: 
         [0000]        Vn   2   =Vnq   2 +( Vnlpf*G   A ) 2   +Vnpa   2    Eq. 3 
         [0000]    Generally, among the various devices of the audio system  600 , the dominant noise source is typically from the DAC+SCLPF (i.e., Vnlpf). 
         [0058]    When the power of the input digital audio signal is relatively small, the dynamic range controller  640  increases the gain G D  of the digital companding module  611  (i.e., G D &gt;&gt;1). At the same time, the dynamic range controller  640  decreases the gain GA of the analog companding module  634 , such that the product of the gains G D  and G A  is substantially equal to unity (i.e., G A =1/G D &lt;&lt;1). Because the gain G A  of the analog companding module  634  is relatively small, the noise Vnlpf from the DAC  632  is greatly attenuated because the component (Vnlpf*G A ) 2  of the total output noise is relatively small. Thus, in this scenario, the total output noise can be approximated as follows: 
         [0000]      Vn 2 ≈Vnq 2 +Vnpa 2    Eq. 4 
         [0000]    Thus, at relatively low power level of the input digital input signal, the total output noise of the audio system  600  is significantly reduced. At relatively high power level of the input digital audio signal, the noise becomes less a factor due to the high audio signal levels. Thus, the audio system  600  provides a relatively large dynamic range without increasing its power consumption to achieve this end. 
         [0059]      FIG. 8  illustrates a block diagram of another exemplary audio system  800  in accordance with another aspect of the disclosure. Any of the embodiments described herein may be combined into a single audio system. For example, the embodiments that relate to controlling the amount of power delivered to the analog section in response to the volume control and/or a characteristic of the input audio signal as described with reference to  FIGS. 2-5  may be combined with the audio companding embodiment described with reference to  FIGS. 6-7 . As an example, the audio system  800  comprises the audio system  600  that includes the audio compacting technique previously discussed, as well as the adaptive power supply  550  for controlling the amount of power delivered to the audio section (e.g., the DAC  632  and the PA  636 ) in response to the dynamic range controller  640 . The dynamic range controller  640 , in turn, controls the adaptive power supply  550  in response to a characteristic of the input signal audio signal from the digital audio source  660 . 
         [0060]    In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
         [0061]    While the invention has been described in connection with various aspects, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.