Patent Publication Number: US-2006013415-A1

Title: Voice activation and transmission system

Description:
FIELD OF THE INVENTION  
      The invention relates generally to the field of voice-activated transmission (“VOX”) systems, and more particularly to an improved method and system for ensuring reliability of complete transmission and for noise cancellation in connection with VOX systems.  
     BACKGROUND OF THE INVENTION  
      One form of transmission of voice in wireless communications is to have voice-activated transmission (“VOX”) where a radio transmitter opens when a human voice is recognized. These types of systems have been in use for some time. Generally, voice activation is achieved using circuitry design, such as is disclosed in U.S. Pat. No. 5,457,769 which is incorporated herein by reference.  
      VOX systems are designed such that the system will not transmit unless a human voice is detected. However, a problem that is common to these systems is the latency of the transmission. There is a lag time between the start time of human speech into the VOX system, and the start time of transmission once the system has identified human voice. This lag time causes the beginning of the human speech to be lost, which may have adverse effects. For instance, the adage is described as follows; the user speaks into the VOX system saying “Don&#39;t shoot” while the hearer, because of the delay in the starting of transmission, only hears “Shoot.” 
      A number of patents have attempted to deal with the problem of loss of data in voice-activated systems. For instance, U.S. Pat. No. 6,385,304 to Hunt et al. (“the &#39;304 patent”) and U.S. Pat. No. 5,155,760 to Johnson et al. (“the &#39;760 patent”) disclose a system and method for speech-responsive voice messaging. Both the &#39;304 patent and the &#39;760 patent disclose the use of a buffer for holding audio data to compensate for time delays in, for instance, determining whether logging is to begin. However, both of these references are directed at a voice messaging and retrieval system, not a VOX system. A VOX system presents different problems and parameters than do voice messaging systems. For instance, a VOX system is generally portable, the voice activation circuitry many times being located in the voice input device, such as a microphone or other portable device. In addition, the VOX system is a system that not only receives an input, but generates an output according to selected criteria to be transmitted to for instance, a transducer. This requires that that the voice activation circuitry be designed to integrate with the output devices. These are integration problems that neither the system taught in the &#39;304 patent nor the &#39;760 patent face because they utilize voice-activation after receiving a pre-processed and transmitted signal, whereas in a VOX system, the voice-activation is preformed first, then the signal is processed and/or converted for transmission.  
      The systems taught in the &#39;304 patent and the &#39;760 patent also don&#39;t deal with the problem of transmission delay because they are only directed at recording, not transmission. A VOX system is designed to transmit a detected human voice. Therefore, if the voice was recorded and then played back as disclosed in the &#39;304 patent and the &#39;760 patent, the individual speaking into the input device, typically a microphone, would hear his time-delayed voice making it very difficult for him to speak.  
      Another problem associated with VOX systems is power consumption and sparking. It is highly undesirable to have a portable system that has high power consumption as the portable power supply will be quickly exhausted and become correspondingly large and heavy. In addition, in certain applications, such as in classified hazardous locations or accidents zones, systems that generate any sparking cannot safely be utilized because of highly flammable substances that may be in the area.  
      Both the &#39;304 patent and the &#39;760 patent are non-portable systems and as such neither are concerned with providing very low power consumption to limit the size of a portable power supply and/or supply extended use between recharging. In addition, neither the &#39;304 patent nor the &#39;760 patent identify sparking as a problem or provide systems that effectively eliminate sparking for use in for instance, a hazardous location.  
      Still another problem facing VOX systems is ambient noise, especially in hostile acoustic environments such as, for instance, in a manufacturing facility or at an airport. In these extremely noisy conditions, it is difficult for VOX systems to operate properly. For example, it is undesirable for the VOX system to pickup and transmit ambient noise along with the human speech content.  
      Automatic Noise Reduction (“ANR”) technology has been in existence for a number of years, particularly in connection with protecting workers from very high ambient noise levels, such as on the tarmac at an airport. Currently, noise cancellation is primarily accomplished by means of mechanical, analog means involving the microphone elements and other parts of the microphone. These techniques however have had limited success.  
      In attempting to deal with cancellation of ambient noise, U.S. Pat. No. 5,046,103 to Warnaka et al. (“the &#39;103 patent”) discloses a speech source that is exposed to ambient noise. To counter the ambient noise, a reference microphone is also exposed to the same ambient noise and both signals are fed into an acoustical signal controller to attenuate the noise component present in the voice signal. However, the &#39;103 patent is not directed to VOX systems and is limited to the use with analog signals. Generally it is easier to manipulate digital signals than analog signals. In addition, analog circuitry typically requires more space which is undesirable in portable systems. Still further, the system taught in the &#39;103 patent cannot be used in a hazardous location where sparking of the electronics may cause an explosion.  
      U.S. Pat. No. 6,483,923 to Marash (“the &#39;923 patent”) discloses another system for reducing interference in a signal utilizing adaptive filters to generate canceling signals that approximate interference present in the received signal. The &#39;923 patent further teaches converting the analog signals to a digital format. However, the &#39;923 patent is not directed toward a VOX system for transmission but is adapted for use with an array of sensors utilized in connection with a recording system. (Col. 1, lines 17-20). A VOX system however, presents a different set of problems as compared to only recording systems as previously discussed. In addition, the large stationary sensor array disclosed in the &#39;923 patent is not adapted for use with portable systems. In addition, the system taught in the &#39;923 patent is not usable in hazardous locations because of sparking caused by the electronic circuitry.  
      U.S. Pat. No. 6,278,786 to McIntosh (“the &#39;786 patent”) discloses still another noise cancellation system. The system is adapted for use with an earcup. A microphone is mounted in an earcup for transducing acoustic pressure within the earcup to a corresponding error signal which is converted into a noise cancellation signal. Again, the system taught in the &#39;786 patent is not directed toward a VOX system and does not have to integrate with transmitting circuitry. In addition, the &#39;786 patent fails to teach the use of voice activation to control a storage device or for processing of the received signals to generate a transmission signal. Still further, the &#39;786 patent fails to teach a very low power consumption by the electronic circuitry, which is highly advantageous in portable systems. In addition, the &#39;786 patent also fails to teach a system that reduces or effectively eliminates sparking such that it may be utilized in hazardous locations.  
      In view of the forgoing, a voice-activated transmission system is desired that limits or entirely eliminates any loss of speech to be transmitted.  
      It is further desired to provide a voice-activated transmission system that limits or effectively eliminates any time-delay associated with voice transmission.  
      It is still further desired to provide a voice-activated transmission system that limits or effectively eliminates ambient noise from the transmitted voice signal.  
      It is yet further desired to provide a portable voice-activated transmission system that limits loss of speech to be transmitted and limits ambient noise from the transmitted voice signal that is relatively light-weight and small in size.  
      It is still further desired to provide a voice-activated transmission system that uses very little power.  
      It is yet further desired to provide a portable voice-activated transmission system that may be safely used in a hazardous location where flammable vapors may be present in the area.  
      It is still further desired to provide a portable voice-activated transmission system that effectively eliminates any sparking.  
     SUMMARY OF THE INVENTION  
      Accordingly, a VOX system has been provided integrating a store and forward integrated circuit. The storage function of the circuit would ensure that none of the speech picked up by the input device would be lost while the system determines if human speech is detected. In addition, the system utilized digital signal processing to provide superior noise cancellation. The use of digital circuitry for manipulation of the voice signal further reduces power consumption.  
      With the use of both an input device for receiving a voice input and a reference device for receiving a reference input corresponding to ambient noise. The VOX system can then utilize the reference input to cancel out ambient noise contained in the voice input. However, because both the voice input and the reference input are converted to digital signals, more effective noise cancellation is achieved as opposed to traditional analog systems. In addition, with the use of digital signal processing the lag time between voice identification and transmission is not discernable by the human ear, typically in the range of one nano-second.  
      The result is a VOX system that will effectively transmit all of the speech picked up by the input device without any discernable delay in transmission, while at the same time providing superior noise reduction characteristics in a light-weight, portable package.  
      The digital signal format the VOX system uses to manipulate the voice signal also reduces the power consumption of the system. This allows the power supply to be smaller and lighter weight and allows the system to operate for longer periods of time between recharging. The circuit design still further reduces or effectively eliminates sparking, which is necessary for use in hazardous locations.  
      The term “data” as used herein means any indicia, signals, marks, domains, symbols, symbol sets, representations, and any other physical form or forms representing information, whether permanent or temporary, whether visible, audible, acoustic, electric, magnetic, electromagnetic, or otherwise manifested. The term “data” as used to represent particular information in one physical form shall be deemed to encompass any and all representations of the same particular information in a different physical form or forms.  
      The term “storage” as used herein means data storage devices, apparatus, programs, circuits, systems, subsystems, or other elements whether implemented in hardware, software, or both, and whether used to process data in analog or digital form, into which data may be entered, and from which data may be obtained, as desired. Storage can be primary and/or secondary and can store data in electromagnetic, magnetic, optical, magneto-optical chemical and/or holographic forms.  
      The term “processor” as used herein means data processing devices, apparatus, programs, circuits, systems, and subsystems, whether implemented in hardware, software, or both, and whether used to process data in analog or digital form. The processor can operate on data in electromagnetic, magnetic, optical, magneto-optical chemical and/or holographic forms.  
      The terms “communicate”, “communicating” and “communications” as used herein include both conveying data from a source to a destination, as well as delivering data to a communications medium, system or link to be conveyed to a destination. The term “communication” as used herein means the act of communicating or the data communicated, as appropriate.  
      The terms “coupling”, “coupled”, “coupled to”, and “coupled with” as used herein each mean a relationship between or among two or more devices, apparatus, files, programs, media, components, networks, systems, subsystems, and/or means, constituting any one or more of (a) a connection, whether direct or through one or more other devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means, (b) a communications relationship, whether direct or through one or more other devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means, or (c) a functional relationship in which the operation of any one or more of the relevant devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means depends, in whole or in part, on the operation of any one or more others thereof.  
      The term “network” as used herein means the communications linkage used to join two or more units, such as systems, networks, links, nodes, equipment, circuits, and devices and includes without limitation networks of all kinds, including coupling amongst components of a system, both intra-networks and inter-networks and including, but not limited to, the Internet, and is not limited to any particular such network.  
      The term “hazardous location” as used herein means any physical area within which any sparking or elevated temperature may cause an explosion or ignite a substance within that area that may be in the air such as, for instance but not limited to, any classified hazardous location (i.e. a refueling location, paint spray area, manufacturing facility, etc.), an accident location (i.e. fuel or flammable substance spill), or even a clean-up site.  
      In one advantageous embodiment a voice-activated transmission system is provided comprising, an audio input device for receiving an audio input, and a reference audio input device for receiving a reference audio input. The system further comprises a signal processor coupled to the audio input device and the reference audio input device, to store the audio input and the reference audio input when the audio input exceeds a threshold level, and to analyze the audio input for the presence of speech. The signal processor is further provided for generating an audio signal corresponding to the audio input and the reference audio input when speech is detected. The system still further comprises a transmitter coupled to the signal processor for transmitting the audio signal.  
      In another advantageous embodiment a voice-activated transmission system is provided comprising, an audio input device for receiving an audio input, and a reference audio input device for receiving a reference audio input. The system further comprises a signal analyzer coupled to the audio input device to determine if the audio input exceeds a threshold level and a storage device coupled to the audio input device and the reference audio input device to store the audio input and the reference audio input when the audio input exceeds a threshold level. The system still further comprises an activation device coupled to the storage device and for analyzing the audio input for the presence of speech, a signal processing device coupled to the activation device, for processing both the audio input and the reference audio input to generate an audio signal corresponding to both the audio input and the reference audio input when speech is detected by the activation device, and a transmitter coupled to the signal processing device for transmitting the audio signal.  
      In still another advantageous embodiment a method for voice-activated transmission is provided comprising the steps of, receiving an audio input, receiving a reference audio input, and determining whether the audio input exceeds a threshold level. The method further comprises the steps of, storing the audio input and the reference audio input when the audio input exceeds a threshold level, and determining whether the audio input comprises speech. The method still further comprises the steps of, processing the audio input and the reference audio input to generate an audio signal corresponding to both the audio input and the reference audio input, and transmitting the audio signal.  
      In yet another advantageous embodiment a method for voice-activated transmission is provided comprising the steps of, receiving an audio input, receiving a reference audio input, and storing the audio input and the reference audio input when the audio input exceeds a threshold level. The method further comprises the steps of, analyzing the audio input for the presence of speech, and converting the audio input and the reference audio input to digital signals when speech is detected. The method still further comprises the steps of, processing the audio input and the reference audio input to generate a audio signal corresponding to both the audio input and the reference audio input when speech is detected, and transmitting the audio signal to a transducer.  
      In still another advantageous embodiment a portable voice-activated audio transmission system is provided comprising, a first microphone for receiving an a first analog input signal representative of a voice input, and a second microphone for receiving a second analog input signal representative of an ambient noise input. The system further comprises a signal analyzer coupled to both the first and second microphones to analyze the first input signal for the presence of speech when an amplitude of the first input signal exceeds a threshold level. The system still further comprises a signal processor for converting both the first and second analog input signals to first and second digital signals respectively, and for processing the first and second digital signals to generate an output signal corresponding to both first and second digital signals, when speech is detected by the signal analyzer, and a transmitter coupled to the signal processor for transmitting the output signal.  
      The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram illustrating an advantageous embodiment of the present invention.  
       FIG. 2  is a block diagram according to  FIG. 1  illustrating the signal processor in greater detail.  
       FIG. 3  is a block diagram according to  FIG. 2  illustrating the audio input conditioning device in greater detail.  
       FIG. 4  is a block diagram according to  FIG. 2  illustrating the activation/storage device in greater detail.  
       FIG. 5  is a block diagram according to  FIG. 2  illustrating the signal processing device in greater detail.  
       FIG. 6  is a flow diagram illustrating an advantageous embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates one advantageous embodiment of VOX transmission system  100 . As illustrated, VOX transmission system  100  includes reference audio input device  102  and audio input device  104 , which may comprise for instance in one advantageous embodiment, microphones for picking up audio signals. Audio input device  104  is provided to pick up audio input  108 , which may comprise speech. In addition, reference audio input device  102  is provided to pick up reference audio input  106 , which may comprise ambient noise. In practice, audio input device  104  would advantageously be located near the source of audio input  108 . If audio input device  104  is a microphone designed to pick up human speech, then the microphone would be located in close proximity to the user&#39;s mouth. Alternatively, reference audio input device  102  would be located apart from audio input device  104  so as not to pick up audio input  108 . Rather, the purpose of reference audio input device  102  is to pick up ambient noise in the environment that may also be picked up by audio input device  104  in addition to audio input  108 . Therefore, while audio input device  104  is advantageously picking up audio input  108 , it is also disadvantageously picking up reference audio input  106  that comprise ambient noise. Alternatively, reference audio input device  102  is only picking up reference audio input  106 . This is advantageous because in this manner, the audio input  108  can be distinguished from the reference audio input  106 .  
      Ambient noise can be a major problem in harsh acoustical environments such as, manufacturing facilities, airport, construction sites, or any other environment where high levels of ambient noise are generated. These high ambient noise levels can interfere with the proper functioning of VOX equipment.  
      It is contemplated that both reference audio input device  102  and audio input device  104  may comprise any number of audio pick up devices, such as microphones. These audio pick up devices may be, for instance, hand-held units, boom-mounted units, or even mounted to a headset worn by a user. In addition, these audio pick up devices may be either hard wired and/or wireless systems. In one advantageous embodiment, both reference audio input device  102  and audio input device  104  comprise portable, miniature wireless microphones located in a headset worn by a user.  
      Reference audio input device  102  generates a reference audio input signal  103  which corresponds to reference audio input  106 . Alternatively, audio input device  104  generates an audio input signal  105  that corresponds to a combination of both audio input  108  and reference audio input  106 . Since reference audio input  106  corresponds to ambient noise in the environment, it is advantageous to remove this component from audio input signal  105 .  
      Both reference audio input device  102  and audio input device  104  are coupled to signal processor  110  such that both reference audio input signal  103  and audio input signal  105  may be transmitted to signal processor  110 . It is contemplated that reference audio input device  102  and audio input device  104  may be coupled to signal processor  110  by for instance, either a hardwired system and/or by wireless transmission. The data picked up by the input devices may be communicated by means of: electromagnetic energy, direct current (DC) energy, and the like.  
      Signal processor  110  monitors audio input signal  105  to determine if the signal strength is above a threshold level. If so, signal processor  110  will process both reference audio input signal  103  and audio input signal  105  to generate output signal  107 . To generate output signal  107 , signal processor  110  utilizes reference audio input signal  103  as a canceling signal to remove any like components from audio input signal  105 . The result is that output signal  107  will only comprise the components of audio input  108 , with all components of reference audio input  108  removed therefrom. This method provides superior noise cancellation for audio input  108  resulting in a signal free from ambient noise.  
      Output signal  107  is then sent to transmitter  150  which may comprise any suitable signal transmitter appropriate for the application. Transmitter  150  is coupled to transducer  160  via network connection  155 . While  FIG. 1  illustrates the use of network connection  155 , it is contemplated that any connection means, local or networked may be utilized to transmit output signal  107  as desired. Network connection  155  may furthermore be or include for instance, but not limited to, any one or more of a WAP (Wireless Application Protocol) link, a GPRS (General Packet Radio Service) link, a GSM (Global System for Mobile Communication) link, or other wired or wireless, digital or analog interfaces or connections.  
      In addition, while output signal  107  is illustrated as being transmitted to transducer  160 , it is still further contemplated that output signal may further be distributed as desired. For instance, rather than only terminating at transducer  160 , output signal  107  may optionally be coupled to a dissemination link  165 , which may be or include a Personal Area Network (PAN), a Family Area Network (FAN), a cable modem connection, an analog modem connection such as a V.90 or other protocol connection, an Integrated Service Digital Network (ISDN) or Digital Subscriber Line (DSL) connection, a BlueTooth wireless link, a WAP (Wireless Application Protocol) link, a Symbian™ link, a GPRS (General Packet Radio Service) link, a GSM (Global System for Mobile Communication) link, a CDMA (Code Division Multiple Access) or TDMA (Time Division Multiple Access) link such as a cellular phone channel, a GPS (Global Positioning System) link, CDPD (cellular digital packet data), a RIM (Research in Motion, Limited) duplex paging type device, an IEEE 802.11-based radio frequency link, or other wired or wireless links.  
      It should be noted that VOX transmission system  100  is provided as an extremely low power consumption portable system. The circuit design of VOX transmission system  100  is further provided to suppress essentially any sparking or heating that may be generated by traditional electronic circuitry. As such VOX transmission system  100  does not require a large power supply and further may safely be utilized in hazardous locations. The effective elimination of sparking in VOX transmission system  100  is achieved in part by through use of spark-suppression techniques in the system. It should further be noted that the minimal power consumption of the portable equipment also has a tendency to reduce sparking of the system.  
       FIG. 2  is a block diagram according to  FIG. 1  illustrating one advantageous embodiment of signal processor  110  in greater detail. Signal processor  110  is divided into three parts: audio input conditioning device  120 , activation/storage device  130 , and signal processing device  140 .  
      Audio input conditioning device  120  is coupled to both audio input device  104  and reference audio input device  102  in a manner previously described in connection with  FIG. 1 . Audio input conditioning device  120  receives and measures audio input signal  105  to determine if it is above a threshold level. If audio input signal  105  is not above the threshold level, audio input conditioning device  120  will not forward audio input signal  105  or reference audio input signal  103  to activation/storage device  130 . If however, audio input signal  105  is measured to be above the threshold level, audio input conditioning device  120  will forward both audio input signal  105  and reference audio input signal  103  to activation/storage device  130 . In addition, in one advantageous embodiment, audio input conditioning device  120  will condition both audio input signal  105  and reference audio input signal  103  prior to forwarding them to activation/storage device  130 .  
      Upon receipt, activation/storage device  130  begins storing received audio input signal  105  and reference audio input signal  103 . Activation/storage device  130  further analyzes audio input signal  105  for the presence of speech components. If speech components are detected, activation/storage device  130  transmits both stored reference audio input signal  103  and audio input signal  105  to signal processing device  140  for processing. Signal processing device then processes both reference audio input signal  103  and audio input signal  105  to generate output signal  107  in a manner previously described in connection with  FIG. 1 . Output signal  107  may then be sent to transmitter  150  for transmission as desired.  
       FIG. 3  is block diagram according to  FIG. 2  illustrating one advantageous embodiment of audio input conditioning device  120  in greater detail. Audio input conditioning device  120  is generally divided into three parts: audio input level analyzer  122 , band-pass filter  124 , and amplifier  126 .  
      Audio input level analyzer  122  is provided to analyze audio input signal  105  to determine if it exceeds a threshold level. In this manner, VOX transmission system  100  will not initiate a transmission sequence unless a minimum signal level is present at audio input device  104 . Once a minimum signal level has been detected by audio input level analyzer  122 , audio input signal  105  and reference audio input signal  103  are passed to band-pass filter  124 . Band-pass filter  124  is typically selected to pass frequencies in the range in which human speech resides. Therefore, if audio input device  104  and reference audio input device  102  picking up robust ambient noise signals, any frequency component not within the range of human speech is removed. Any frequency components within the range of human speech are then transmitted to amplifier  126 . Amplifier  126  is provided to increase the signal amplitude of audio input signal  105  and reference audio input signal  103  prior to them being sent to activation/storage device  150 . Amplifier  126  may comprise any suitable amplifying device including, for instance but not limited to one or more, an operational amplifier(s) (op-amp), a transistor(s), a discrete circuit(s), an integrated circuit(s), a computer program(s), hardware, software, firmware, or any other selected means to amplify the signal amplitude to a desired level. Filtered and amplified audio input signal  105  and reference audio input signal  103  are then passed to activation/storage device  150 .  
       FIG. 4  is block diagram according to  FIG. 2  illustrating one advantageous embodiment of activation/storage device  130  in greater detail. Activation/storage device  130  is generally divided into two parts: voice activation device  132 , and storage  134 .  
      Storage  132  is coupled to audio input conditioning device  120  to receive audio input signal  105  and reference audio input signal  103 . Storage  132  is selected to operate such that upon receipt of audio input signal  105 , storage  132  will begin storing both audio input signal  105  and reference audio input signal  103 . Storage  132  will then forward audio input signal  105  and reference audio input signal  103  to voice activation device  134  for analysis.  
      Upon receipt of both audio input signal  105  and reference audio input signal  103 , voice activation device  134  analyzes audio input signal  105  for the present of human speech. As previously mentioned, typically voice activation is achieved using circuitry design, such as is disclosed in U.S. Pat. No. 5,457,769 which is incorporated herein by reference. Once voice activation device  134  positively identifies the presence of human speech in audio input signal  105 , both audio input signal  105  and reference audio input signal  103  are forwarded to signal processing device  140 .  
       FIG. 5  is block diagram according to  FIG. 2  illustrating one advantageous embodiment of signal processing device  140  in greater detail. Signal processing device  140  is generally divided into three parts: analog-to-digital converter  142 , signal inverter  144 , and adder  146 .  
      Both audio input signal  105  and reference audio input signal  103  are received by analog-to-digital converter  142 . Analog-to-digital converter  142  then converts both audio input signal  105  and reference audio input signal  103  from analog signals to digital signals. Reference audio input signal  103  is further sent to signal inverter  144  that inverts it and sends it to adder  146 . Alternatively, audio input signal  105  is sent from analog-to-digital converter  142  to adder  146 , bypassing inverter  144 . Adder  146  combines both audio input signal  105  and inverted reference audio input signal  103  to generate output signal  107 . This combination has the effect of canceling out the noise component still present in audio input signal  105  to provide superior noise cancellation. Output signal  107  is then sent to transmitter  150  for transmission as described in connection with  FIG. 1 .  
       FIG. 6  is a flow chart illustrating the process steps of VOX transmission system  200  according to one advantageous embodiment. A first step is initiation of VOX system  205 .  
      Once initiated, VOX transmission system  200  will monitor for reference audio input signal and audio input signal  210 . The monitoring and receipt of both reference audio input signal  103  and audio input signal  105  may be completed as previously described in connection with  FIG. 1 . If an audio input signal  103  is received, the next step is to determine if audio input signal  105  exceeds a threshold value  215 . Typically this threshold value is a measure of signal strength or signal amplitude. The threshold value may be any selected value appropriate for the application. If audio input signal  103  does not exceed the threshold value, VOX transmission system  200  returns to monitoring for reference audio input signal and audio input signal  210 . If however, audio input signal  103  does exceed the threshold value VOX transmission system  200  proceeds to condition audio input signal and reference audio input signal  220 . The signal conditioning preformed during this step may comprise all or any portion of the signal conditioning previously described in connection with  FIGS. 2 and 3 .  
      After audio input signal  103  and audio input signal  105  have been conditioned, VOX transmission system  200  proceeds to store reference audio input signal and audio input signal  225 . This provides the distinct advantage of eliminating any potential loss of speech prior to VOX transmission system  200  transmitting an output signal as described in connection with  FIGS. 2-4 .  
      VOX transmission system  200  next determines if audio input signal comprises speech  230 . There are a number of methods that may be utilized for voice recognition and as previously mentioned, typically voice activation is achieved using specific circuitry design, alternatively, computers utilizing software programs, hardware or firmware may effectively be utilized. If VOX transmission system  200  determines that audio input signal  105  does not comprise speech, VOX transmission system  200  returns to monitoring for reference audio input signal and audio input signal  210 . If however, VOX transmission system  200  determines that audio input signal  103  does comprise speech, VOX transmission system  200  proceeds to convert reference audio input signal and audio input signal to digital signals  235 .  
      VOX transmission system  200  further proceeds to invert reference audio input signal  240  and then add inverted reference audio input signal to audio input signal to generate an output signal  245 . As these steps have already been described in connection with  FIGS. 2 and 5 , they will not be re-described here. Finally, VOX transmission system  200  proceeds to transmit output signal to transducer  250 .  
      It should be noted that, while various functions and methods have been described and presented in a sequence of steps, the sequence has been provided merely as an illustration of one advantageous embodiment, and that it is not necessary to perform these functions in the specific order illustrated. It is further contemplated that any of these steps may be moved and/or combined relative to any of the other steps. In addition, it is still further contemplated that it may be advantageous, depending upon the application, to utilize all or any portion of the functions described herein.  
      It should further be noted that VOX transmission system  200  is provided as a fully portable system with very low power consumption thereby requiring a small and lightweight power source. VOX transmission system  200  is further designed such that effectively no sparking is generated and as such is safe to utilize in a hazardous location.  
      Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.