Patent Publication Number: US-8542849-B2

Title: Apparatus, method, and manufacture for connectable gain-sharing automixers

Description:
FIELD OF THE INVENTION 
     The invention is related to sound control systems, and in particular, to an apparatus, method, and manufacture for gain-sharing automixing of audio signals that allow the addition of more automixer inputs to the automixer by simply connecting one or more distributed gain-sharing automixers. 
     BACKGROUND OF THE INVENTION 
     An automixer is typically designed to balance multiple sound sources, usually microphones, based on the level of each source, attenuating inactive inputs. Automixers are typically used to mix panel discussions on television shows and at conferences and seminars. They can also be used to mix actors&#39; wireless microphones in theater productions and musicals. They may be used in audio systems in churches, schools, hotels, convention centers, and the like. They are frequently employed in commercial sound systems such as in courtrooms and city council chambers where it is not expected that a live sound operator will be present to mix the microphones. When automixers are used in live sound reinforcement, they work to maintain a steady limit on the overall signal level of the microphones. If a public address system is set up so that one microphone will not feed back, then, in general, multiple microphones will not feed back if they are automixed. 
     Further, various gain-sharing strategies have been developed in which the signal level in a particular channel is compared with the sum of all the channels to compute a gain-sharing factor. The channel with the highest level input receives highest gain which is a proportional fraction of the total gain available. Additionally, gain-sharing strategies have been developed in which a proportional, multichannel gain-sharing audio circuit has a gain control in the computing leg so that additional weight may be accorded the channel so that the channel is allocated greater gain in proportion to the total amount of signal available to all of the channels combined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  illustrates a block diagram of an embodiment of an automixer; 
         FIG. 2  shows a block diagram of an embodiment of the automixer of  FIG. 1 ; 
         FIG. 3  illustrates a block diagram of an embodiment of a system that includes automixers that are embodiments of the automixer of  FIG. 1  or  FIG. 2 ; and 
         FIG. 4  shows a block diagram of an embodiment of a system that includes an embodiment of the automixer of  FIG. 1  or  FIG. 2 , arranged in accordance with aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
     Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” includes plural reference, and the meaning of “in” includes “in” and “on.” The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Similarly, the phrase “in some embodiments,” as used herein, when used multiple times, does not necessarily refer to the same embodiments, although it may. As used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based, in part, on”, “based, at least in part, on”, or “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. The term “coupled” means at least either a direct electrical connection between the items connected, or an indirect connection through one or more passive or active intermediary devices. The term “signal” means at least one current, voltage, charge, temperature, data, audio, or other signal. 
     Briefly stated, the invention is related to a device for audio mixing that includes a cascade input port and a first cascade input component that includes a first cascade input level detector component that detects an audio level of an upstream sum audio signal. The first cascade input port also includes an attenuator component that attenuates the first upstream mix audio signal by a gain corresponding to difference between the upstream sum audio signal value and a detected audio level of an input sum audio signal. The device also includes a summer component where the signals summed include at least the first upstream sum audio signal. The device also includes an input sum level detector component that detects the audio level of the input sum audio signal. The device also includes a mixer component that is configured to provide a mix output signal by summing, where the signals summed include at least the first attenuated upstream mix signal. 
     The automixer may accordingly act as a distributed gain-sharing automixer that enables the addition of more automixer inputs to an automixer by simply connecting one or more distributed gain-sharing automixers. This allows for distributing the inputs, outputs, and processing of a single, gain-sharing, automatic microphone mix across a number of different physical automixers. A variety of devices in accordance with embodiments of the invention may have various input, output, and processing capabilities that may be connected together to produce an automatic mix of the microphone inputs on all interconnected products, and the devices may be used to build audio systems of various sizes (inputs, outputs, processing) that include gain-sharing automatic microphone mixing. 
       FIG. 1  illustrates a block diagram of an embodiment of automixer  100 , which may include cascade input port  101 , cascade input component  111 , input summer component  120 , and mixer component  130 . Cascade input component  111  includes cascade input level detector component  151 , attenuator component  161 , and cascade gain computation component  171 . Input summer component  120  includes summer component  121  and input sum level detector component  150 . Mixer component  130  includes summer component  122 . 
     Cascade input port  101  is configured to receive a first upstream sum audio signal Upstream-sum and a first upstream mix audio signal Upstream-mix. These signals, when present, are generated from another automixer, which may be substantially similar to automixer  100  of  FIG. 1  or automixer  200  of  FIG. 2 . 
       FIG. 1  illustrates one cascade input for automixer  100 . Automixer  100  has at least two inputs, which may include two or more cascade inputs, two or more microphone inputs, or at least one cascade input and at least one microphone input.  FIG. 1  shows only a single cascade input, because the additional input(s) may be either at least one additional cascade input, at least one microphone input, or both.  FIG. 2  shows an automixer with any number of microphone inputs and any number of cascade inputs.  FIG. 1  shows a simple embodiment with only one cascade input actually shown in the figure, with further inputs unspecified. Accordingly, automixer  100  may have one cascade input, and one or more additional inputs (cascade, microphone, or both). Alternatively, other embodiments of automixer  100  may have two or more microphone inputs, and no cascade inputs (but having a cascade output). For examples, Automixer A, B, and C of  FIG. 3  are embodiments of automixer  100  that each have multiple microphone inputs, no cascade inputs, and each have a cascade output. 
     Input level detector component  151  is configured to provide a detected value (shown as “Level of Upstream-sum” in  FIG. 1 ) corresponding to an audio level of Upstream-sum. Cascade gain computation component  171  is configured to provide a first cascade gain value, GainCI 1 , corresponding to a difference between the value of the detected audio level of signal Upstream-sum (“Level of Upstream-sum”) and an input sum level value (shown in  FIG. 1  as “Level of Sum of All Inputs”). Attenuator component  161  is configured to provide a first attenuated upstream mix signal AUM 1  by attenuating first upstream mix audio signal Upstream-mix based on first cascade gain value GainCI 1 . 
     Summer component  121  is configured to provide an input sum audio signal (shown as “Sum of All Inputs” in  FIG. 1 ) by summing together each signal provided as an input to the summer component, where at least first upstream sum audio signal Upstream-sum is provided as an input to the summer component. Input sum level detector component  150  is configured to provide the input sum level value (“Level of Sum of All Inputs”) corresponding to an audio level of the input sum audio signal. Mixer component  130  is configured to provide mix output signal Mix Output by summing together each signal provided as an input to the mixer component, where at least first attenuated upstream mix signal AUM 1  is provided as an input to the mixer component. 
       FIG. 2  shows a block diagram of an embodiment of automixer  200 , which may be employed as an embodiment of automixer  100  of  FIG. 1 . Automixer  200  is similar to automixer  100  of  FIG. 1 , but it includes n microphone inputs and m cascade inputs, where n and m are both integers, n is greater than or equal to zero, m is greater than or equal to zero, and the sum of n+m is greater than or equal to 2. 
     Each cascade input component (e.g.,  211 ) operates in a substantially similar manner as discussed above with regard to cascade input component  111  of  FIG. 1 , with each separate cascade input component receiving a separate Upstream-sum signal, receiving a separate Upstream-mix signal, and providing a different attenuated Upstream-mix signal (AUM 1 -AUMm). 
     Microphone input  281  is configured to receive microphone input audio signal Microphone Input. A microphone audio input is any audio signal input to automixer  200  that is not the output of an upstream automixer and for which gain-sharing is to be performed. Typically the input is from a microphone, but the invention is not so limited, and as stated the “microphone” input may be an audio input that is not the output of an upstream automixer for which gain-sharing is to be performed. First microphone input level detector component  252  is configured to provide a detected value (shown as “Level of Microphone Input” in  FIG. 2 ) corresponding to an audio level of Microphone Input. First microphone gain computation component  272  is configured to provide a first microphone gain value (GainM 1 ) corresponding to a difference between Level of Microphone Input and Level of Sum of All Inputs. First microphone attenuation component  262  is configured to provide first attenuated microphone input signal AMI 1  by attenuating Microphone Input based on GainM 1 . 
     Each of the n microphone inputs is configured to operate in a substantially similar manner as discussed above with regard to microphone input  281 , with each separate microphone input receiving a separate microphone input audio signal, and providing a separate attenuated microphone input signal (AMI 1 -AMIn). 
     Input summer component  221  is configured to provide the input sum audio signal (“Sum of All Inputs”) by summing together each of the n Microphone Input signals and each of the m Upstream-sum signals. Mixer component  230  is configured to provide signal Mix Output by summing together each of the m attenuated upstream signals AUM 1 -AUMm and each of the n attenuated microphone input signals MI 1 -MIn. The cascade output signal Cascade Output includes two audio signals: Mix Output and the input sum audio signal. The cascade output signal may be routed to the cascade input of another automixer  200 . 
     In some embodiments, each of the level detector components (e.g.,  250 ,  251 , and  252 ) is configured to monitor an audio signal and continually provide a value representing the level of the monitored audio signal in dB. In some embodiments, the root mean square (gins) value of the audio level is detected over a continuous rolling time window on the order of about 20 ms and a corresponding value is provided as the level of the monitored audio signal in dB. In other embodiments, other mathematical relationships and/or other time periods may be employed. The units of the audio level are not relevant—if signal Upstream-sum is an analog signal having a voltage that is proportional to the corresponding acoustical pressure of the sound produced if the audio signal were used to drive a speaker, then input level detector component  151  detects voltage (e.g., rms voltage); if signal Upstream-sum is a digital signal, input level detector component  151  detects the digital value (e.g., the rms of the digital value) representing the audio level. In some embodiments, each gain computation component (e.g.  271  and  272 ) provides a value representing the difference in dB between the outputs of two level detector components. 
     In some embodiments of automixer  200 , microphone input audio signals are acquired via microphone preamplifiers and analog to digital converters, before entering a 32-bit, floating-point, digital signal processor (DSP). In some embodiments, the cascade input audio signals enter via a stereo digital audio input port encoded as a stream of uncompressed, 32-bit, audio samples represented as floating-point values. In some embodiments, each of the level detector components, gain computation components, attenuation components, and summer components are implemented in the floating-point DSP. In some embodiments, the audio signals of the cascade output are output from automixer  200  via a stereo digital audio output port, encoded as a stream of uncompressed, 32-bit, audio samples represented as floating-point values. 
     In some embodiments of automixer  200 , the uncompressed digital audio of the cascade output and cascade input are encoded as streams of uncompressed, two&#39;s complement, 24-bit, fixed-point values, encoded using the Audio Engineering Society 3 (AES3) standard for digital audio input-output interfacing. This implementation allows the designer to leverage the built-in features of the floating-point DSP that expects data entering over synchronous serial audio ports to be represented as two&#39;s complement, 24-bit, fixed point values. 
     In some embodiments, some or all the components of automixer  200  (e.g., level detector components, gain computation components, attenuation components, and summer components) may be implemented using analog electronics instead of a DSP. For example, summing components as well as the gain computation components can be implemented by a summing amplifier such as an op amp summing circuit, or the like; and/or the attenuator components may be implemented with a voltage controlled amplifier, and/or the like. For example, in one embodiment, attenuation component  261  of  FIG. 2  may be implemented by a voltage controlled amplifier that is arranged to receive signal Upstream-sum at an input of the voltage controlled amplifier, to receive GainCI 1  at a gain input of the voltage-controlled amplifier, and to provide the signal AUM 1  at the output of the voltage controlled amplifier 
     Various embodiments of automixer  200  may be entirely encoded in a digital signal processor, and/or encoded as processor executable code stored in processor-executable memory together with one or more processors arranged to execute the software, may be all analog components, or may be some combination of hardware components and software components stored in memory to be executed by one or more processors in automixer  200 . Processor-readable code may be encoded on a processor readable medium for performing the actions of automixer  200  when executed by one or more processors. 
     Automixer  200  enables the addition of more automixer inputs by simply connecting one or more automixers  200 . Each distributed automixer  200  accepts audio inputs, such as microphone inputs, cascade inputs from the cascade outputs of other distributed automixers  200 , and/or the like. The group of distributed automixers accepts audio inputs, such as microphone inputs, and mixes together the audio from those inputs via a gain-sharing algorithm. Using a gain-sharing automatic mixing algorithm provides several benefits. First, the algorithm produces a mix that has a constant gain from all inputs to the output. When the gain of the system is constant, an operator can create a public address system in which the acoustic gain is constant, and equal to the Needed Acoustic Gain (NAG). In such a system, the Feedback Stability Margin (FSM) may be maximized, and remains constant regardless of the number of microphones. Also, in a system where background noise is detected evenly by all microphones, a gain-sharing algorithm produces a constant level of background noise at the mix output regardless of the number of microphones or their input signal levels. In other words, the gain-sharing algorithm produces no gating, pumping, or breathing effects in the reinforced background noise of the public address system. A gain-sharing algorithm also reduces the comb filtering effect produced by two or more microphones detecting the same acoustic signal. Using automixer  200  for distributing a gain-sharing automix across multiple devices, the gain-sharing algorithm and all of its benefits are preserved even though the mixing and inputs are shared among various physical devices. 
     Automixer  200  enables a method for distributing a gain-sharing automatic mix across a variety of series connected devices by sending the resulting automatic mix (mix(n−1)) and the sum of all inputs (sum(n−1)) from one mixer (mixer(n−1)) to the next mixer in the series (mixer(n)) where sum(n−1) is summed with all other inputs of mixer(n) to create a new sum(n). Mixer(n) then attenuates the signal mix(n−1) by the relative difference in dB between sum(n) and sum(n−1), before mixing it with the other mixer(n) inputs which have been attenuated by the difference in dB between their levels and the level of sum(n), producing the new output mix(n). Mix(n) and sum(n) may be sent to mixer(n+1) and so on. The result is a gain-sharing automatic mix(n) at the output of any mixer(n) that includes all inputs from mixer( 0 ) to mixer(n). 
     Distributing the inputs and processing of automixer  200  allows the series combination of an arbitrary number of gain-sharing automixers that each produce a gain-sharing automix at each automixer&#39;s output of all inputs up to and including that automixer&#39;s. For example, in a system with three automixers  200  connected in series, audio flows from Mixer 1  to Mixer 2  to Mixer 3 . Connecting three automixers  200  in series may be accomplished by connecting the cascade output of Mixer 1  to the cascade input of Mixer 2 , and connecting the cascade output of Mixer 2  to the cascade input of Mixer 3 . Mixer 1 &#39;s output is a gain-sharing mix of its inputs. Mixer 2 &#39;s output is a gain-sharing mix of the inputs on Mixer 1  and Mixer 2 . Mixer 3 &#39;s output is a gain-sharing mix of the inputs on Mixer 1 , Mixer 2 , and Mixer 3 . The processing required in any one automixer  200  does not change with the addition of more automixers  200  in the series chain. Also, in some embodiments, the series interconnect between each automixer consists of two audio channels regardless of the number of automixers in the chain. Further, there is no master/slave relationship between automixers  200 . Further, the gain computation for each microphone input does not require each microphone input to know the level in dB of the sum of all inputs on all automixers, and accordingly there is no need for a signal that flows back up the series chain from the last device representing the level of the sum of all inputs, and standard methods of stereo interconnect may be used for interconnecting the automixers  200  in the system. 
     Some embodiments of automixer  200  contain more than one cascade input. As automixers  200  are interconnected in topologies other than a simple daisy-chain, it remains true that the output of any automixer  200  is a gain-sharing automix of all mixer microphone inputs and upstream microphone inputs. The cascade input and cascade outputs are used to distribute the gain-sharing automixes across multiple devices in each topology. The Mix Output of any automixer in the system is a gain-sharing automix of all the mixer input and upstream inputs that is independent of downstream inputs. Virtually any topology of devices may be used—however a ring topology should not be employed—the cascade output of one automixer  200  may be used as the cascade input of any other automixer  200  unless that automixer  200  is already upstream, i.e., audio signals from that automixer  200  are already included as part of the gain-sharing mix of the automixer  200 . 
     Various embodiments of automixer  200  may be employed as a variety of devices with gain-sharing automatic mixing capability that may be combined to create larger systems. Further, the processing capability of each product may be designed without concern for the number or type of distributed automixers  200 . The various automixers  200  can use simple, low-cost, off-the-shelf solutions for stereo digital audio distribution to implement the series automixer interconnect between products. Further, use of automixers  200  simplifies the installation of interconnected products because the installer does not need to specify a master device. 
     The output of a system of distributed automixers  200  is the same result as if all of the inputs were provided to a single automixer  200 , as illustrated by the following examples. 
     If a four input automixer has all four inputs driven with non-coherent 10 dBu signals, the sum of all these inputs has an rms level of 16 dBu. According to the gain-sharing equation, each input must be attenuated by the difference in dB between its level and the level of the sum (6 dB). Accordingly, each input is attenuated by 6 dB, and then they are mixed together to produce the output of the automixer. 
     If the same inputs were provided to two distributed automixers  200  connected together, with two 10 dBu inputs to each automixer  200 , the upstream mixer sums the two microphone inputs and its unused cascade input, resulting in an Upstream-sum signal with an rms level of 13 dBu. Each microphone input is attenuated by 3 dB and the resulting mix is present at the automixer&#39;s output. Signals Upstream-sum and Upstream-mix are sent to the downstream automixer via standard stereo audio interconnect. The downstream automixer sums its two microphone inputs and its cascade input&#39;s Upstream-sum signal to produce a sum of all inputs with an rms level equal to 16 dBu. Each microphone input is attenuated by 6 dB, and signal Upstream-mix is attenuated by 3 dB. The three attenuated signals are mixed together to create the downstream automixer&#39;s output. The output mix of the downstream automixer includes all four inputs, each attenuated by 6 dB as required by the gain-sharing algorithm. The upstream microphone inputs were attenuated by 3 dB in the upstream automixer and 3 dB at the cascade input to the downstream automixer, while the downstream microphone inputs were attenuated by 6 dB in the downstream automixer. Further, the output of the upstream automixer is an accurate gain-sharing mix of its two inputs that is unaffected by downstream inputs. Also, as previously discussed, there is no need for an interconnect or user controls required to send the level of the sum of all inputs back up stream, which enables the use of standard stereo audio interconnect to connect the cascade output of the upstream automixer to the cascade input of the downstream automixer. 
     In some embodiments, microphone inputs within a single system may be partitioned into groups that may be combined or separated into different gain-sharing mixes. In such a system, several automixers  200  with microphone and/or cascade inputs may be used to collect inputs from the system. The cascade outputs of these automixers may be routed to the inputs of one or more downstream automixers  200  that have only cascade inputs. The inputs of upstream automixers  200  may be combined into gain-sharing mixes at the output of the downstream automixers  200  in different configurations by muting signals Upstream-sum and Upstream-mix signals at the cascade input to the downstream automixer. One example of such a system is illustrated in  FIG. 3  below. 
       FIG. 3  illustrates a block diagram of an embodiment of system  305 , which includes automixers A-F and mute switches  399 , where each of the automixers A-F may be an embodiment of automixer  100  of  FIG. 1  or automixer  200  of  FIG. 2 . 
     As shown, Automixer A is used for receiving microphone inputs  1 - 4 , Automixer B is used for receiving microphone inputs  5 - 7 , and automixer C is used for receiving microphone inputs  8  and  9 . The cascade outputs of Automixers A-C are coupled via mute switches to the cascade inputs of Automixers D-F to selectively provide different automatic mixes of the microphone, including the possibility of achieving an automatic mix of all of the microphone inputs. 
       FIG. 4  shows a block diagram of an embodiment of system  406 . System  406  includes two or more automixers  400 , which may each be an embodiment of automixer  100  of  FIG. 1  or automixer  200  of  FIG. 2 , as well as various peripheral components. The peripheral components may include wired microphones  490 , MP3 player  492 , DVD player  493 , wireless receive  494 , wireless microphone  495 , and/or the like. As shown, in some embodiments, a variety of audio sources may be used, with gain-sharing performed for microphone inputs, including wired microphones  490  and wireless microphones  495 , which may be connected by wireless receivers in some embodiments. The mix output of any of the automixers  400  may be provided to a speaker, such as powered speaker  491 , for outputting the mixed audio signal from the speaker. 
     The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.