Abstract:
An automatic audio level control device for adjusting the audio level of an appliance in response to changes in ambient sound levels. A microprocessor ( 16 ) monitors the ambient sound produced by an audio appliance using a microphone ( 10 ) to determine average low and high audio thresholds. When the ambient sound level is outside the threshold range, the microprocessor transmits volume control signals using infrared emitter ( 20 ) to the audio appliance to sustain a user-defined average audio level.

Description:
FIELD OF INVENTION 
     This invention relates to an automatic adaptive audio volume control device and in particular to an electronic circuit for remote automatic volume adjustment of an audio appliance. 
     BACKGROUND OF INVENTION 
     Radio and television receivers often produce disagreeable changes in the average audio volume level when a user changes channels or when a broadcaster inserts advertising segments. Program transitions to advertising or from speech to music frequently produce a greater average volume level that exceeds the desired volume level. 
     The user can compensate for such audio variances through the bothersome task of manually adjusting the volume during each channel or program transition. 
     Various systems have been created to automatically adapt average volume levels in audio appliances. Radio receivers in motor vehicles have been designed to adapt volume levels based on external ambient sound, typically road noise, which varies with vehicle speed. Similar systems have been incorporated into television receivers to maintain an average audio volume level by adapting to changes in the received audio signal. 
     While automatic audio level control systems are available on some audio appliances, the user is typically required to purchase a completely new appliance to gain this feature. U.S. Pat. No. 5,363,147 to Joseph et al. (1994) and U.S. Pat. No. 5,444,783 to Na (1995) disclose circuits that, when incorporated into television receivers, provide automatic audio level control. 
     An external device providing automatic audio level control for television receivers has been proposed in U.S. Pat. No. 5,631,714 to Saadoun (1997). This solution requires access to input and output paths for both the audio and video signals of a television receiver to operate. The numerous connectors and cables for these signals further increase the cost of production of this device. 
     All previous solutions for automatic audio level control are either built into an appliance or, if external, are specific to an appliance and thus do not have the flexibility to operate with various audio appliances in a convenient manner. 
     OBJECTS AND ADVANTAGES 
     Accordingly, several objects and advantages of the present invention are: 
     (a) to provide a system to automatically sustain a user-defined average audio volume level of an appliance during channel changes and program transitions in audio level; 
     (b) to provide a system that determines the user-defined average audio volume level by acoustically monitoring the ambient sound level produced by an audio appliance; 
     (c) to provide adaptive control of an appliance audio level by responding to changes in the ambient sound level produced by the audio appliance; 
     (d) to operate with an audio appliance that utilizes a wireless remote control interface to change the appliance audio volume level; and 
     (e) to provide a low cost device that is simple to use and that requires no electrical connections to be installed to the audio appliance; 
     Further objects and advantages of the invention will become apparent from a consideration of the drawings and ensuing description. 
    
    
     DRAWING FIGURES 
     FIG. 1 is a block diagram showing the key elements of a system of the invention for automatically sustaining a user-defined average audio volume level for an audio appliance. 
     FIG. 1A is a block diagram showing functional units within a typical microprocessor. 
     FIG. 2 is a flowchart diagram outlining the software control system of the invention. 
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 Reference Numerals in Drawings 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Microphone 
                 12 
                 Amplifier 
               
               
                 14 
                 Digital-to-Analog Converter 
                 16 
                 Microprocessor 
               
               
                 18 
                 Switch Bank 
                 20 
                 Infrared Emitter 
               
               
                 22 
                 Resistor 
                 40 
                 CPU 
               
               
                 42 
                 ROM 
                 44 
                 Set of Input Ports 
               
               
                 46 
                 RAM 
                 48 
                 Timer 
               
               
                 50 
                 Set of Output Ports 
                 100-130 
                 Flowchart Labels 
               
               
                   
               
             
          
         
       
     
     SUMMARY 
     In accordance with the present invention an automatic audio level control device comprises a microprocessor that monitors the ambient sound produced by an audio appliance using a microphone to continuously determine average low and high audio thresholds. When the ambient sound level is outside the threshold range, the microprocessor transmits remote volume control signals using an infrared emitter to the audio appliance to sustain an average audio level. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a microphone  10  produces an analog electrical signal that is proportional to the magnitude of the ambient sound. The output signal from microphone  10  is fed through an amplifier  12 , which increases the magnitude of the signal from microphone  10 . 
     The output of amplifier  12  is connected to the input of an analog-to-digital converter  14 . The output of analog-to-digital converter  14  is a digital value having a magnitude that is proportional to the ambient sound sensed by microphone  10 . 
     The output of analog-to-digital converter  14  is connected to a first input port of a microprocessor  16 . A switch bank  18  is connected to a second input port of microprocessor  16 . A first output port of microprocessor  16  is connected to the cathode of an infrared emitter  20 . A second output port of microprocessor  16  is connected to power inputs of microphone  10 , amplifier  12 , and analog-to-digital converter  14 . The anode of infrared emitter  20  is connected to system voltage VCC through a resistor  22 , which limits the current to infrared emitter  20 . 
     FIG. 1A shows the functional units within microprocessor  16 . A CPU  40  is connected through a common bus to a RAM  46 , a ROM  44 , a timer  48 , a set of input ports  44 , and a set of output ports  50 . 
     Operation 
     The logical flow of FIG. 2 shows the sequence of operation of a control program performing audio level control using the circuit shown in FIG.  1 . 
     Referring to FIG. 2, the control program begins at step  100  when system power is first applied. Program variables are initialized in step  102 . 
     In step  104 , the timer in the microprocessor is initialized. This timer is used to control the frequency of execution of program steps for measuring ambient sound levels. These measurements are required infrequently (typically less than 20 times per second). Thus, power savings are achieved by placing the microprocessor into a low-power idle state when the control program is not required to operate. 
     In step  106 , a digital sample from the microphone is recorded. Further power savings are achieved by applying power to the microphone, amplifier, and digital to analog converter only during this program step. 
     The digital sample is copied to a buffer in step  108 . A low-pass filter algorithm is performed on this buffer by step  110  to calculate the ambient sound level. 
     In steps  112  and  114 , low and high audio threshold levels are determined. An average ambient sound level is first computed by averaging the ambient sound level over a fixed period of time. The threshold levels are then calculated from the averages of measured low-level and high-level ambient sound. A low-level measurement is one that is less the average ambient sound level. All other measurements are considered high-level. 
     In step  116 , the switch bank is read. The settings of the switch bank represent an appliance manufacturer number that the user has configured. This value is used to look-up appliance codes for volume-up and volume-down commands in step  118 . The use of such appliance codes is well known in the prior art for devices such as universal infrared remote controls. 
     If the ambient sound level is less than the computed low threshold level in step  120 , control is passed to step  128 , which transmits an appliance volume-up command via the infrared emitter. Program execution then continues at step  106 . 
     Otherwise, in step  122 , if the ambient sound level is greater than the computed high threshold level, control is passed to step  130 , which transmits an appliance volume-down command via the infrared emitter. Program execution then continues at step  106 . 
     Step  124  is executed if the ambient sound level lies between the low and high threshold levels. Here the microprocessor is placed into a power-saving idle mode. Control is passed to step  126 , which waits for the system timer to expire. When the timer expiration occurs, program execution continues at step  106 . 
     Conclusions, Ramifications, and Scope 
     Accordingly, the automatic sound level control device of the invention maintains a user-defined average audio sound level of an appliance. In addition, it functions with audio appliances that utilize wireless remote control, requires no electrical connections to the appliance, and is simple to operate. 
     The invention may be practiced in many ways other than as specifically described herein. For example, another possible embodiment could substitute the low-pass filtering of program step  110  with a simple external analog filter. Another hardware substitution could utilize a microprocessor that includes a built-in analog-to-digital converter rather than the external converter shown in FIG. 1. A final alternative embodiment is the combination of the invention with a universal remote control device to gain economy by sharing common hardware and software resources. 
     Thus, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents.