Patent Publication Number: US-2007104337-A1

Title: Apparatus and method for automatic volume synchronization of a digital audio device with an analog audio source

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates generally to systems and, more particularly, to audio systems in which an audio source device provides a signal to a digital speaker system.  
      2. Background of the Invention  
      Many commercial audio sources (e.g., home stereo receivers) can, in addition to audio signals with a volume control, provide digital audio output signals that may be used to provide digitalized version of the audio signal. The digitized audio signal lacks the information to provide volume control.  
      The problem arises for implementing devices such as digital speakers that would utilize the digital audio output signals because such a device would require a separate volume control, the volume control not automatically synchronized with the volume setting of the audio source device itself. An example of the dilemma is the Bluetooth or IEE 802.11 wireless LAN wireless rear speakers for a surround sound audio system. Such speakers could be implemented using the digital audio output signal from a consumer receiver, but separate volume control on the speakers would be inconvenient for the end user.  
      A need has therefore been felt for apparatus and an associated method having the feature of providing an improved audio source. It would be another feature of the apparatus and associated method to provide an improved digital signal from and audio source. It would be yet another feature of the apparatus and associated method to provide for control of the volume of the digital signal produced by an audio source. It would be a still further feature of the apparatus and associated method to provide a digital signal having a volume related to the volume of an associated analog signal.  
     SUMMARY OF THE INVENTION  
      The foregoing and other features are accomplished, according the present invention, by providing apparatus monitoring the analog signals that are generated by an audio source. The volume of the audio from speakers will be determined by the amplitude of the analog signals which vary with the volume control at the receiver end. The amplitude of the audio analog signals and peak is detected then digitized. The analog signal volume amplitude determines the amplitude of the digitized signals thereby relating the digitized signal audio volume to the analog signal audio volume.  
      Other features and advantages of present invention will be more clearly understood upon reading of the following description and the accompanying drawings and the claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of apparatus for controlling the volume of an audio digital signal produced by an analog source device according to the present invention.  
       FIG. 2  is a block diagram of apparatus for controlling the volume of an audio digital signal with specific reference to the Bluetooth technology or IEEE 802.11 wireless LAN technology according to the present invention. 
    
    
     1. DETAILED DESCRIPTION OF THE FIGURES  
      Referring to  FIG. 1 , the apparatus for controlling the volume of an audio digital signal generated by an audio source  10  is shown. The audio source  10  provides (L-out and R-out) analog audio signals to two speakers  11 A and  11 B. A summing unit  12  is coupled to the conductors carrying the two analog audio analog signals to speakers  11 A and  11 B. The output signal from the summing unit  12  is applied to peak detector  13 . The output signal of peak detector  13  is applied to integrator  14 . The output signal of the integrator  14  is applied to analog to digital converter  15 . A transport stream interface unit  16  receives a stream of digital output signals from the audio source  10  and a digital volume control signal from the analog to digital converter  15 . The signal from the analog to digital converter  15  is used to control the volume of the digital audio signal.  
      Referring to  FIG. 2 , a block diagram of the apparatus to control a digital audio signal with specific reference to Bluetooth or IEEE 802.11 wireless LAN technology is shown. A consumer audio receiver applies analog audio L_OUT signals to speaker  21 A and analog audio R_OUT signals to speaker  21 B. The conductors carrying the L_OUT and the R_OUT signals are each coupled to input terminals of a summing unit  22 . The output signal of the summing unit  22  is applied to a peak detector  23 . The output signal of the peak detector  23  is coupled to an input terminal of integrator  24 . The output terminal of integrator  24  is coupled to an input terminal of analog to digital logic  25 . The output signal of the analog to digital converter  25  is applied to the Bluetooth or IEEE 802.11 transport stream generation logic  27 . The Bluetooth or IEEE 802.11 transport stream generation logic  27  also receives the SPDIF_OUT signal from the consumer audio receiver  20 . The output signal from the Bluetooth or IEEE 802.11 transport stream generation unit  27  is applied to the RF transmitter. The output signal from the RF transmitter  28  is the over the air transmission to the wireless digital speaker.  
     2. OPERATION OF THE PREFERRED EMBODIMENT  
      The operation of the present invention can be understood as follows. The analog output signal of the audio source is processed by the summing network; the peak detector and the integrator provide a value that is related to the average amplitude of the signal in the two channels of the audio source output. The analog to digital device then periodically digitizes this average amplitude. The digitized value can be used in two ways. In the first method, the digitized amplitude signals are incorporated in the transported signal. The incorporated signals can then be analyzed by the apparatus receiving the signals and the volume of the output audio signal derived from the transported signal adjusted to be consistent with analog audio signals. Another technique for controlling the volume of the digitized audio signals is to use the amplitude derived from the analog audio signals to determine the strength of the transported digital signal, the changes in the amplitude of the transported signal being used to determine the volume of the digital audio signals resulting from the transported signals.  
      While the invention has been described with respect to the embodiments set forth above, the invention is not necessarily limited to these embodiments. Accordingly, other embodiments, variations, and improvements not described herein are not necessarily excluded from the scope of the invention, the scope of the invention being defined by the following claims.