Patent Publication Number: US-7220913-B2

Title: Breakout box for digital guitar

Description:
This application claims benefit of each of the following noted applications, and the relationship of this application to each prior application is noted below:
     (1) this application claims benefit of co-pending provisional U.S. Patent Application Ser. No. 60/478,725, filed Jun. 13, 2003, entitled “Digital Guitar System and Method”; and   (2) this application claims benefit of co-pending provisional U.S. Patent Application Ser. No. 60/438,898, filed Jan. 9, 2003, entitled “Digital Guitar System”   

     All of the above referenced applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to guitars, guitar pickups, and guitar equipment. More particularly, this invention pertains to digital guitars, multi-signal guitar pickups, and digital guitar interface devices. The present invention is particularly focused on the digital guitar interface device, sometimes referred to herein as a breakout box, for allowing the digital guitar to interface with conventional analog equipment. 
     Guitars are well known in the art and include a wide variety of different types and designs. For example, the prior art includes various types of acoustic and electric guitars. These guitars are typically adapted to receive analog audio signals, such as analog microphone signals, and to output analog audio signals, such as analog string signals (analog audio signals generated by guitar pickups when guitar strings are strummed) and analog headphone signals. 
     The prior art includes monophonic guitars, i.e., guitars that output a single string signal when one or more of the guitar strings mounted on the guitar are strummed. The prior art also includes guitars that output a single string signal for each string mounted on a guitar. The latter type of guitar is generally referred to as a polyphonic guitar. 
     All of these guitars have a common disadvantage—they all receive and output analog audio signals. Analog audio signals are susceptible to various kinds of electrical and environmental noise that can degrade the quality of the analog audio signal. This is particularly true in environments where the analog audio signals are transmitted through cables exposed to electrical power cables or other cables that are also carrying analog audio signals. Regardless of the cause, degraded analog audio signals are undesirable because they are unpleasant to listen to and do not accurately reflect the audio output of the guitar. 
     Although conventional guitars, and the associated noise problems discussed above, have been around for years, no one appears to have addressed this problem in the prior art. Thus, there is a need for a guitar that can receive and output audio signals that are less susceptible to electrical and environmental noise. 
     SUMMARY OF THE INVENTION 
     As described in detail in this application, this problem can be solved by using a guitar that is capable of receiving and outputting digital audio signals rather then analog audio signals, i.e., a digital guitar. Digital audio signals are less susceptible to electrical and environmental noise because they can only take on discrete values and a system can be designed to ignore noise signal values that are not within a certain range of the discrete values. The benefits of digital signals with regard to noise resistance are well known in the art and will not be repeated here. It is sufficient to point out that digital signals have a discrete nature and it is that discreteness that provides the noise resistance. 
     The development of a digital guitar and the adoption of that guitar in the consumer marketplace, however, creates an additional series of problems. First, a guitar that receives and outputs digital audio signals is incompatible with conventional guitar equipment, such as amplifiers, effects boxes, and synthesizers. These devices are adapted to receive and output analog audio signals, not digital audio signals. They cannot process digital audio signals. 
     This incompatibility creates a serious problem with regard to the adoption of a digital guitar in the consumer marketplace. Many consumers have invested a substantial amount of money in conventional guitar equipment and are unlikely to purchase a digital guitar that is incompatible with the conventional guitar equipment that they already own—even if that guitar outputs audio signals that are less susceptible to noise. Thus, in addition to the need for a digital guitar, there is a need for a digital guitar that is compatible with conventional guitar equipment. 
     Second, many consumers may be unwilling to purchase a digital guitar because they are unwilling to give up their conventional analog guitar. For example, many consumers have used their conventional analog guitars for years and have become accustomed to the way those guitars look and feel. These consumers may be unwilling to begin using a digital guitar regardless of its benefits. While this problem might be overcome to some extent by fashioning the digital guitar to have an appearance similar to that of conventional analog guitars, this may not be sufficient for some consumers. 
     Furthermore, some consumers may be unwilling to replace their conventional analog guitar with a digital guitar because their guitar has significantly increased in value. Many conventional analog guitars have become very popular among consumers and, as a result, have increased in value. Consumers owning these types of guitars are very unlikely to sell these guitars in order to purchase a digital guitar or to use a digital guitar in place of their existing conventional analog guitar. Many of these consumers, however, still have a need for and would like to obtain the benefits provided by a digital guitar. As explained in detail in this application, one way to address this problem is to develop a method of modifying a conventional analog guitar so that it can receive and output digital audio signals. 
     In addition to the problems addressed above, the present invention is also directed to solving two problems common to conventional guitar pickups. The first relates to the fact that these pickups typically generate analog audio signals that contain noise signals and the second relates to the fact that these pickups typically generate mixed analog string signals. Although the prior art has addressed both of these problems in part, as explained below the prior art solutions are not suitable for some applications. 
     With regard to the first issue, the assignee of the present application has recognized that conventional guitar pickups, in addition to generating analog audio signals in response to guitar string vibrations, also pick up electrical or environmental noise and generate analog noise signals. Conventional guitar pickups cannot separate these noise signals from the desired analog audio signals and, as a result, mix the noise signals with the analog audio signals. The resulting output is an analog audio signal contaminated with noise. 
     The prior art has addressed this issue using, most notably, conventional humbucker guitar pickups. As is well known in the art, a monophonic humbucker guitar pickup generates two analog string signals when guitar strings are strummed, both of which include the same noise signal. The humbucker pickup is designed so that one of the analog string signals includes an analog string component that is inverted with respect to the analog string component in the second analog string signal. The noise signal has the same polarity in each signal. By subtracting the two analog string signals from one another, the noise signal can be cancelled out, leaving only the desired analog string signal. Polyphonic humbucker pickups operate in a similar manner. 
     While analog string signals generated by prior art humbucker guitar pickups can be used to cancel out the effects of noise, the pickups themselves can be complicated. Monophonic humbucker guitar pickups essentially require two monophonic guitar pickups arranged so that one of the pickups generates an inverted analog string signal. Polyphonic humbuckers operate in a similar manner and require two monophonic pickups for each string on a guitar. The requirement for duplicate pickups increases the complexity of these humbucker pickups and, in some cases, makes these pickups unsuitable for use. 
     The prior art does not appear to have addressed this limitation in a suitable manner and, accordingly, there is a need for a guitar pickup that does so. In other words, there is a need for a less complicated guitar pickup that generates a noise signal that can be used to cancel out the effects of noise in analog string signals generated by the pickup. 
     Moving to the second issue, the assignee of the present application has recognized that conventional guitar pickups generate mixed analog string signals that include horizontal and vertical string components. When a guitar string is strummed, it vibrates in an elliptical or oval-shaped pattern. This pattern can be broken down into movement in two different planes—the horizontal string plane, which is defined as the plane that passes through the guitar strings and is parallel to the upper surface or face of the guitar, and the vertical string plane, which is defined as the plane that is perpendicular to the horizontal string plane. When a guitar string vibrates, it moves in both of these planes. Conventional guitar pickups, in turn, generate an analog string signal based on this elliptical type vibration pattern, but cannot separate that signal into the appropriate horizontal and vertical string signal components. 
     The assignee has further recognized that, by separating these mixed analog string signals into their respective string component signals, new and different sounds, not currently available using conventional pickups, can be generated. The sound associated with a mixed analog string signal is different from the sounds associated with the horizontal and vertical string signal components of that mixed signal. In addition, the sounds associated with horizontal and vertical string vibrations are different from one another. This is true because guitar strings do not vibrate in the horizontal and vertical planes in the same manner. In many cases, vibrations of a guitar string in the horizontal plane are much greater than vibrations of the guitar string in the vertical plane. 
     This problem has been addressed, in part, by the assignee in U.S. Pat. No. 6,392,137, issued to Isvan on May 21, 2002 and assigned to the assignee, and entitled “Polyphonic Guitar Pickup For Sensing String Vibrations In Two Mutually Perpendicular Planes.” The &#39;137 patent is hereby incorporated by reference into this application. 
     The digital guitar system includes a digital guitar and a digital guitar interface device, and the method includes the steps necessary to convert a conventional analog guitar into a digital guitar. The digital guitar outputs digital audio signals, which are less susceptible to noise, and the interface device allows the digital guitar to be compatible with conventional analog guitar equipment by converting the digital audio signals into analog audio signals. 
     The digital guitar is adapted to generate a plurality of different types of analog audio signals, convert those audio signals into digital audio signals, format the digital audio signals according to a predetermined digital communication protocol, and to output the formatted signals. The digital guitar is also adapted to receive digital audio signals, convert those digital audio signals into analog audio signals, and to output the analog audio signals. The guitar is further adapted to receive external analog audio signals, such as microphone signals, convert those signals into digital audio signals, and to output the digital microphone signals. 
     To facilitate the above-referenced functions, the digital guitar includes a guitar pickup assembly, a digital guitar processing circuit, a guitar digital input/output assembly, a guitar analog input/output assembly, and a guitar control assembly. The guitar pickup assembly includes a novel multi-signal hexaphonic guitar pickup that is adapted to generate two or more mixed analog audio signals for each guitar string, and, is further adapted to generate an analog noise signal, which can be used to cancel out the effects of noise in the mixed analog audio signals. The mixed analog audio signals, in turn, can be processed to generate the horizontal and vertical string signal components associated with each vibrating guitar string. 
     The digital guitar interface device is adapted to receive a plurality of different types of digital audio signals, to convert those signals into analog audio signals, and to output the analog audio signals. The interface device is also adapted to receive digital control signals and to use those signals to control the outputs of the interface device. The interface device is still further adapted to receive external analog audio signals, convert those signals into digital signals, format the digital signals according to a predetermined digital communication protocol, and to output the formatted digital signals. 
     The interface device includes the following components: an interface device digital input/output assembly, an interface device analog input/output assembly, and an interface device processing circuit. These components work together to allow the interface device to perform its required functions. 
     The method includes the steps of removing a conventional guitar output assembly from a conventional analog guitar, inserting and mounting the digital guitar processing circuit inside the guitar, connecting the digital guitar processing circuit to the guitar pickup assembly mounted on the guitar and to a guitar digital input/output assembly, and replacing the conventional guitar output assembly with the guitar digital input/output assembly. 
     Accordingly, one object of the present invention is to provide a breakout box for use with a guitar that is capable of outputting digital signals, i.e., a digital guitar, so that the digital guitar can interface with traditional analog equipment. 
     Another object of the present invention is to provide an interface device processing circuit that is adapted to receive digital signals, convert those signals into analog signals, and to output the analog signals. 
     A third object is to provide a digital guitar that is compatible with conventional guitar equipment. 
     Another object is to provide a digital guitar operable to output analog signals. 
     Still another object of the present invention is to provide a digital guitar interface device capable of receiving digital signals and converting them into analog signals. 
     And another object of the present invention is to provide an digital guitar interface device capable of receiving a single digital string signal and converting that signal into a single analog string signal. 
     Yet another object is to provide a digital guitar interface device for use with a novel multi-signal guitar pickup, wherein the interface device receives a separate digital string signal for each string and the interface device generates an analog string signal for each string. 
     These and other objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the system of this invention showing a typical arrangement that interconnects instrument devices with various control devices. 
         FIG. 2  is a schematic diagram of an embodiment of the system of this invention showing a physical implementation and interconnection of devices in an on-stage performance audio environment. 
         FIG. 3  is a front perspective view of a music editing control device usable in the system of this invention. 
         FIG. 4  is a block diagram showing the digital guitar and interface device of the present invention. 
         FIG. 5  is a block diagram showing the various components included in the digital guitar. 
         FIG. 6  shows schematically a digital guitar with a breakout box for use with a traditional analog amplifier and speaker components. 
         FIG. 7  is perspective view of the novel multi-signal hexaphonic guitar pickup of the present invention. 
         FIG. 8  is a front view of one of the novel guitar string pickup subassemblies of the present invention. 
         FIG. 9  is a block diagram of the digital guitar processing circuit of the present invention. 
         FIG. 10  is a block diagram showing one embodiment of the mixing circuit included in the digital guitar processing circuit. 
         FIG. 11  is a block diagram showing a second embodiment of the mixing circuit included in the digital guitar processing circuit. 
         FIG. 12  is a block diagram showing one embodiment of the guitar digital communication circuit included in the digital guitar processing circuit. 
         FIG. 13  is a block diagram showing one embodiment of the analog and digital sections of the digital guitar processing circuit. 
         FIG. 14  is a block diagram showing the guitar control assembly of the present invention. 
         FIG. 15  illustrates schematically one embodiment of the digital guitar of the present invention. 
         FIG. 16  is a block diagram of the preamp section of the analog section of the digital guitar T2 board. 
         FIG. 17  is a block diagram of the digital section of the T2 board in the digital guitar. 
         FIG. 18  is a block diagram of one implementation of the I2S Engine and Sync portion of the T2 board using a field programmable gate array. 
         FIG. 19  is a block diagram showing the digital guitar interface device of the present invention. 
         FIG. 20  is a block diagram showing one embodiment of the interface device processing circuit. 
         FIGS. 21A and 21B  illustrate two alternative arrangements of the headphone and microphone connections on the digital guitar. 
         FIG. 21C  illustrates an alternative arrangement for the headphone, microphone, and MaGIC connections on the digital guitar. 
         FIGS. 22A and 22B  show two alternative arrangements for the breakout box. 
         FIG. 23  shows the details of the connections to the breakout box. 
         FIG. 24  illustrates schematically four alternative arrangements for connecting, equipment to the breakout box. 
         FIG. 25  is a schematic illustration of the analog section of the T2 module in the breakout box. 
         FIG. 26  is a schematic illustration of the digital section of the T2 module in the breakout box. 
         FIG. 27  is a cross-sectioned schematic view of the internal arrangement of the control knobs and the T2 board. 
         FIG. 28  is a block diagram of the passive legacy system and control section of the showing the volume and tone controls for the humbucker pickups on the digital guitar and the connection of these controls to the T2 board in the digital guitar. 
         FIGS. 29–36  are schematic drawings showing one embodiment of the preamplifier and mixing circuits of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Digital Guitar in an All Digital System 
     The digital guitar of the present invention will first be described in an all digital system. Later sections describe the digital guitar with a breakout box that allows for use of the digital guitar with legacy analog components. 
     The digital guitar is designed for use with a predetermined digital audio communication protocol. The following description refers to the use of a preferred protocol which is the MaGIC protocol developed by the assignee of the present invention, Gibson Guitar Corp. It will be understood, however, that the digital guitar as described herein could be used with any suitable protocol. 
     MaGIC, which stands for Media-accelerated Global Information Carrier, is an open architecture digital connection system developed by Gibson Guitar Corp, the assignee of the present application. The operation of the MaGIC system is described in detail in an engineering specification dated May 3, 2003 and entitled Media-accelerated Global Information Carrier, Engineering Specification, Revision 3.0c. The disclosure contained in that specification is hereby incorporated by reference into this application. The specification may be accessed at the following web address, http://MaGIC.gibson.com/specification.html. In addition, the MaGIC system is described in detail in U.S. Pat. No. 6,353,169, issued to Juszkiewicz et al. on Mar. 5, 2002 and entitled “Universal Audio Communications and Control System and Method.” The disclosure of the &#39;169 patent is also hereby incorporated by reference into this application. 
     Typical arrangements of the digital guitar and related audio and control hardware in a MaGIC system are shown in  FIGS. 1 and 2 . 
     Each of the instruments and the microphones are digital. In alternative embodiments, the microphones may be analog as well. Each of the amplifiers, preamplifiers and the soundboard are connected using the MaGIC data link. The stage has a hub  28  with a single cable (perhaps an optical fiber) running to the control board  22 . A gigabit MaGIC data link will allow over a hundred channels of sound with a 32 bit–192 kHz digital fidelity, and video on top of that. 
     As each instrument and amplifier are connected into a hub  28  on the stage via simple RJ-45 network connectors, they are immediately identified by the sound board  22  which is really a PC computer with a Universal Control Surface ( FIG. 3 ) giving the sound professional complete control of the room. Microphones are actually placed at critical areas throughout the room to audit sound during the performance. The relative levels of all instruments and microphones are stored on a RW CD ROM disc or other digital storage medium, as are all effects the band requires. These presets are worked on until they are optimized in studio rehearsals, and fine tuning corrections are recorded during every performance. 
     The guitar player puts on his headset  27 , which contains both a stereo (each ear) monitor and an unobtrusive microphone. In addition, each earpiece has an outward facing mike allowing sophisticated noise canceling and other sound processing. The player simply plugs this personal gear directly into his guitar  12  and the other players do the same with their respective instruments. The monitor mix is automated and fed from different channels per the presets on the CD-ROM at the board. The monitor sound level is of the artists choosing (guitar player is loud). 
     The guitar player has a small stand-mounted laptop  17  ( FIG. 2 ) that is MaGIC enabled. This allows sophisticated visual cues concerning his instrument, vocal effects and even lyrics. The laptop  17  connects to a pedal board  15  that is a relatively standard controller via a USB cable  16  to a connector on the laptop  17 . Another USB cable is run to the amplifier  13 , which is really as much of a specialized digital processor as it is a device to make loud music. This guitar  12  is plugged into this amplifier  13 , and then the amplifier  13  is plugged into the hub  28  using the MaGIC RJ-45 cables  11 . 
     The laptop  17  contains not only presets, but stores some of the proprietary sound effects programs that will be fed to the DSP in the amplifier, as well as some sound files that can be played back. Should the drummer not show up, the laptop could be used. 
     The guitar player strums his instrument once. The laptop  17  shows all six strings with instructions on how many turns of the tuner are required to bring the instrument in tune, plus a meter showing the degree of tone the strings have (i.e., do they need to be replaced). The DSP amplifier can adjust the guitar strings on the fly to tune, even though they are out of tune, or it can place the guitar into different tunings. This player, however, prefers the “rear” sound so he turns off the auto-tune function. 
     The best part of these new guitars is the additional nuance achieved by squeezing the neck and the touch surfaces that are not part of the older instruments. They give you the ability to do so much more musically. 
     The sound technician, for his part is already prepared. The room acoustics are present in the “board/PC”. The band&#39;s RW CD-ROM or other digital storage medium contains a program that takes this info and adjusts their entire equipment setup through out the evening. The technician just needs to put a limit on total sound pressure in the house, still and always a problem with bands, and he is done except for monitoring potential problems. 
     The complexity of sound and room acoustic modeling could not have been addressed using prior art manual audio consoles. Now, there is sophisticated panning and imaging in three dimensions. Phase and echo, constant compromises in the past, are corrected for digitally. The room can sound like a cathedral, opera house, or even a small club. 
     The new scheme of powered speakers  18  throughout is also valuable. Each speaker has a digital MaGIC input and a 48 VDC power input. These all terminate in a power hub  19  and a hub at the board  22 . In larger rooms, there are hubs throughout the room, minimizing cable needs. Each amplifier component is replaceable easily and each speaker is as well. The musician has the added components and can switch them out between sets if necessary. 
     The MaGIC system dispenses with the need for walls of rack effects and patch bays. All of the functionality of these prior art devices now resides in software plug-ins in either the board-PC or the attached DSP computer. Most musicians will bring these plug-ins with them, preferring total control over the performance environment. 
     The band can record their act. All the individual tracks will be stored on the board-PC system and downloaded to a DVD-ROM for future editing in the studio. 
     To set up the MaGIC system, the players put their gear on stage. They plug their instruments into their amplifiers, laptops, etc. These are, in turn, plugged into the MaGIC Hub. The band presets are loaded and cued to song  1 . The house system goes through a 30-second burst of adjustment soundtrack, and then the band can be introduced. 
     The keyboard business several years ago went to a workstation approach where the keyboard product became more than a controller (keys) with sounds. It became a digital control center with ability to control other electronic boxes via midi, a sequencer and included very sophisticated (editing) tools to sculpt the sounds in the box. It included a basic amount of reverb and other sound effects that had been external previously. 
     In the MaGIC system, the guitar amplifier can be a workstation for the guitar player, encompassing many effects that were previously external. In effect, the amplifier is actually become part of the player&#39;s control system, allowing control via the only appendage the player has that is not occupied playing, his foot. Additionally, a small stand mounted laptop will be right by the player where he can make more sophisticated control changes and visually see how his system is functioning. The view screen can even allow the lyrics and chord changes to be displayed in a set list. 
     The amplifier in the new MaGIC system will allow flexible real time control of other enhancements and integration into the computer and future studio world. 
     The amplifier can be separated into its constituent parts: 
     The preamplifier  1  (the controls, or the knobs); 
     The preamplifier  2  (the sound modifier); 
     The power stage (simple amplification); 
     The speakers (create the sound wave envelope). 
     The cabinet (esthetics and durability); 
     This is a lot of functionality when you look at the constituent components. The MaGIC system introduces a novel technology and a whole new way of looking at a musical instrument amplifier. Many designers and companies have already identified the constituents of the whole and marketed one of them as a single purpose product with modest success. But, just as a controller keyboard (one without the sounds) has not made a major market penetration, the single purpose constituent is not satisfying to the player. The MaGIC Workstation encompasses all of the constituents in an easy to use form. 
     As described above, the MaGIC Link uses currently available components, the Ethernet standard (the communications protocol), a commonly used RJ-45 connector and a new communications protocol utilizing Internet type formatting. This allows the system to send ten channels of digital musical sound over standard cables directly from the instrument for further processing and amplification. A new upgraded MIDI standard signal along with a music description language can also travel over this cable. This scheme allows for up to phantom instrument power as described over that same cable to power circuits in the instrument, including D/A conversion. In one embodiment, phantom power is supplied using the industry standard 802.3af “power over Ethernet” method. 
     The MaGIC circuit board is very small and uses custom application specific integrated circuits (ASIC) and surface mount technology. It will connect to standard pick-ups and CPA&#39;s in classic guitars and is particularly suited for new hexaphonic pick-ups that provide an individual transducer for every string. 
     The MaGIC Enabled Musical Instrument 
     The only noticeable hardware difference in MaGIC enabled traditional instruments will be the addition of a RJ-45 female connector, and a small stereo headphone out. Of course, this innovation makes a host of new possibilities possible in the design of new modern instruments. Older instruments will be able to access most of the new functionality by simply replacing the commonly used monophonic audio connector with a new RJ-45 connector and a tiny retrofit circuit board. Vintage values can be retained. 
     The original analog output will be available as always with no impact on sound, and the digital features need never be used. The MaGIC system will allow access to both the digital signal and the unadulterated analog signal. 
     Having eight digital channels available for output, six of these will be used by each string in a six-string instrument. Two channels will be available to be input directly into the instrument for further routing. In a typical set up, one input will be a microphone from the performer&#39;s headset and the other input is a monitor mix fed from the main board. The headphones would then be the stereo monitor adjusted to the musicians liking without impacting the sound of the room. 
     The physical connector will be a simple, inexpensive and highly reliable RJ-45 locking connector, and category  5  stranded 8-conductor cable. 
     A new hex pickup/transducer will send 6 independent signals to be processed. The transducer is located in the stop bar saddles on the guitar bridge. Alternatively, the classic analog signal can be converted post CPA to a digital signal from the classic original electromagnetic pick-ups. There are also two analog signal inputs that are immediately converted into a digital signal (A/D converter) and introduced into the MaGIC data stream. 
     This MaGIC ASIC and the MaGIC technology can be applied to virtually every instrument, not just guitars. 
     1. The Preamplifier  1  (the Controls, or the Knobs); 
     The Control Surface 
     The knobs or controls for the current generation of amplifiers are unusable in a performance setting, and practically in virtually every other setting. It is very difficult to adjust the control knobs in the presence of 110 dB of ambient sound level. Utilizing both the MaGIC and USB protocols, a communication link is available with all components of the performance/studio system. Any component can be anywhere without degrading the sound. The MaGIC standard includes a channel for high-speed control information using the MIDI format but with approximately one-hundred times the bandwidth. Thus, the MaGIC system is backward compatible with the current instruments utilizing MIDI (most keyboards and sound synthesizers). 
     The display and knobs will be a separate unit. In the MaGIC system, this is referred to as the physical control surface that will be plugged into either the Master Rack directly, or into a laptop computer via a USB connector. When using the laptop, it will function as the visual information screen showing various settings, parameters, etc. Software resident on the laptop will be the music editor allowing control over infinite parameters. 
     This laptop will be unobtrusive but highly functional and the settings can be displayed on this screen visible from a distance of 12 feet to a player with normal vision. It will have a USB connection. There will also be a pedal controller with a USB or MaGIC out to the Master Rack where processing shall take place. Because both MaGIC and USB have phantom power, both the Control Surface and the Foot Controller have power supplied via their connectors. Software drivers for major digital mixers and music editors will allow the controller function to be duplicated in virtually any environment. 
     The foot controller will have one continuous controller pedal, one two-dimensional continuous controller pedal, and eleven-foot switches clustered as above. 
     2. The Preamplifier  2  (the Sound Modifier); 
     The Master Rack Unit 
     The Master Rack unit is a computer taking the digital MaGIC unprocessed signals in and outputting the MaGIC processed digital signals out for distribution (routing). The Master Rack will be in a cabinet enclosure that will allow five-rack unit. The Global Amplification System will use two of these, and the other three will allow any rack-mounted units to be added. 
     The Master Rack enclosure is rugged with covers and replaceable Cordura TM gig bag covering. It will meet UPS size requirements and is extremely light. The three empty racks are on slide-in trays (which come with the unit) but will allow the effects devices to be removed easily, substituted and carried separately. The rack trays will make electrical contact with the motherboard unit, so that stereo input, stereo output, two-foot switch inputs, and digital input and output are available so that no connections are necessary once the effects device is docked. 
     The Master Rack enclosure has several unconventional features that will be highly useful for the performer/player. There are power outlets, four on each side that will allow for power to the three empty rack bays, plus others. The power outlets will allow wall plug power supplies (wall worts) both in terms of distance between outlets and allowing space for these unlikable supplies. The supplies are nested inside the enclosure (protected and unobtrusive) and will never have to be dealt with again. Loops will allow these supplies to be anchored in using simple tie wraps. 
     All rack units mount to a sliding plate on which they will rest. The effects devices can thus slide out and be replaced, similar to “hot swap” computer peripherals. A set of patch bay inputs and outputs is installed on the back plane, accessible via a hinged action from the backside of the Master Rack. The other side of the patch bay will be accessible from the top of the enclosure, which will be recessed and unobtrusive when not needed. All I/O to the integral Global Amplification System will be on the bay for flexible yet semi permanent set-ups. 
     The Global Amp rack units can also slide out for maintenance and replacement. One of the rack units is the. control computer for the MaGIC system, including a “hot swappable” hard disk, a “hot swappable” CD-RW unit, and the digital processing and signal routing and control circuits. The control unit takes the digital MaGIC signals in and out and 2 USB connectors, coupled to a general purpose processing section. The processor section processes multiple digital signals intensively on a real time basis and handles all the MaGIC control functions. 
     The rack unit uses an internal SCSI interface to communicate with outboard storage devices. This allows not only modification of the sound, but the ability to record and store musical signals for real time play back. The unit has a built in Echoplex™, plus the ability to store large programs to load from cheap hard media. Using the SCSI protocol allows the use of hard disks, ZIP drives, CD drives, etc. to minimize use of expensive RAM. 
     The other rack units include a power supply and other “high voltage” relays, etc. The power supply is preferably a switching supply that can be used throughout the world. The power outlets for the rack bays are connected to a transformer, which can be switched in or out to accommodate worldwide use even for these effects. 
     The Master Rack will nest on top of the Base Unit/Sub Woofer and will extend from the Base via microphone type locking extension rods. Thus, the unit can be raised to a level to be easily accessed and view by the performer/player. 
     A 48 VDC power bus will be provided. Modules stepping this down to common voltages for non-AC boxes will be available (i.e. 12 VDC, 9 VDC). This will eliminate ground loops and heavy wall plug power supplies. 
     3. The Power Stage (Simple Amplification); 
     The major effort in amplification of a signal deals with the power supply section, particularly when the amplification is at high levels. The MaGIC system devices use conventional switching power supplies to supply standard 48 VDC. This will address issues of certification in various countries, will allow the “amplifier” to work in any country around the world, reduce weight, insure safety and increase reliability and serviceability. 
     4. The Speakers (Sound Modifier, Create the Sound Envelope). 
     The speakers have both a digital MaGIC signal and 48 VDC power input. Optionally, the speaker can have a built in power supply and thus could take AC in. 
     The speaker cabinet can have a built in monitoring transducer that sends information back to the Master Rack via the MaGIC Link, allowing sophisticated feedback control algorithms. Thus, with adjustments digitally on the fly by the DSP amplifier, even poor speakers can be made to sound flat or contoured to suit personal taste. 
     Additionally, multi-speaker arrays can be used, where individual speakers are used per guitar string in a single cabinet, giving a more spacious sound. 
     5. The Cabinet (Esthetics and Durability); 
     By “packetizing” speaker cabinets, they can be made small and scalable. In other words, the can be stacked to get increased sound levels, or even better, distributed on stage, in the studio, or throughout the performance arena. Sophisticated panning and spatialization effects can be used even in live performance. The speakers can be UPS shippable, and plane worthy. 
     The Universal Control Surface 
     One embodiment of a universal control surface usable in the MaGIC system is shown in  FIG. 3 . 
     24 Slider Port Controls. 
     Each slider has LED&#39;s acting as VU meters (or reflecting other parameters) on the left of the slider. A single switch with an adjacent LED is at the bottom of the slider. Four rotary controls are at the top of each slider. Preferably, a full recording Jog Shuttle, recording type buttons, and “go to” buttons are included. 
     Standard control position templates can be printed or published that can be applied to the control surface for specific uses. 
     The control surface shown in  FIG. 3  does not represent a true mixing console. The controls are simply reduced to a digital representation of the position of knobs, etc., and are then sent to a computer via USB, MIDI or MaGIC where any real work takes place, such as mixing, editing, etc. The control surface can connect via USB to a remote PC. 
     Thus, a system. and method has been described that allows for the universal interconnection, communication and control of musical instruments and related audio components in the digital domain. 
     Digital Guitar in a Legacy System 
     The digital guitar  12  is also completely compatible with traditional analog equipment such as analog amplifiers, speakers, effects boxes etc. One route to use of the digital guitar  12  with analog equipment is to simply connect the traditional analog output from the guitar to the analog equipment. But it is also desirable to connect the digital output to the analog equipment in order to take advantage of the flexibility of manipulating the digital signals from the individual strings. This can be done via an interface device referred to herein as a digital guitar interface device, or breakout box,  102 . 
     Referring to  FIG. 4 , the digital guitar system  100  of the present invention includes the digital guitar  12 , discussed previously, and the digital guitar interface device  102 . The guitar  12  is connected to the interface device  102  using a MaGIC connection cable  104 . The guitar  12  is adapted to output a variety of different digital audio and control signals and the interface device  102  is adapted to convert the digital audio signals into analog audio signals and to use the digital control signals to control the analog outputs of the interface device  102 . The guitar  12  is also adapted to receive both external digital and analog audio signals. The external digital audio signals are received from the interface device  102  and the external analog audio signals are received from any one of a variety of external audio devices, such as a microphone. The interface device  102  is also adapted to receive external analog audio signals from any one of a variety of external audio devices. In this case, however, the external analog audio signal may be from a CD player or a monitor mixer. Regardless of the source, the interface device  102  converts these external audio signals into the external digital audio signals that are sent to the guitar  12 . 
     Referring to  FIGS. 5 and 6 , the digital guitar  12  (also referred to as the MaGIC guitar) includes a guitar body  106 , six (6) guitar strings  108  mounted on the guitar body  106 , a guitar pickup assembly  110 , a digital guitar processing circuit  112 , a guitar digital input/output assembly  114 , a guitar analog input/output assembly  116 , and a guitar control assembly  118 . The guitar pickup assembly  110  includes two humbucker guitar pickups  120  adapted to generate two (2) analog humbucker string signals. The guitar pickup assembly  110  also includes a novel multi-signal hexaphonic guitar pickup  122  adapted to generate two analog mixed string signals for each of the six guitar strings  108  mounted on the guitar  12  and an analog noise signal representative of noise in the analog mixed string signals. Each analog mixed string signal is a signal that includes an x-plane signal component (i.e., an analog string signal representative of horizontal string vibrations relative to the guitar body) and analog y-plane signal component (i.e., an analog string signal representative of vertical string vibrations relative to the guitar body). In addition, each pair of analog mixed string signals for a particular string includes inverted x-plane signal components. In other words, the analog mixed string signals in each pair include x-plane signal components that have inverted, or opposite, polarities. 
     The MaGIC guitar  12  is 100% backward compatible with all traditional gear. The signal path from the 2 humbucker pickups  120 , humbucker volume/tone control knobs  182  ( FIG. 14 ), pickup selector switch  178  ( FIG. 15 ), and ¼″ output  186  ( FIG. 15 ) is electrically identical to existing Gibson guitars. Physically, the traditional point-to-point wiring is replaced by a passive system inside the guitar digital processing circuit, or T2 module,  112  ( FIG. 15 ). 
     The guitar  12  can be operated in two different modes: traditional and MaGIC. The traditional output is available regardless of whether there is a MaGIC connection. 
     The guitar pickup assembly  110  may vary from application to application. For example, in some embodiments, the pickup assembly  110  may only include a single monophonic guitar pickup. In others, the pickup assembly  110  may only include a polyphonic guitar pickup or one of the novel multi-signal guitar pickups  122 . In short, any type of guitar pickup that generates one or more analog string signals can be used with the digital guitar  12  of the present invention. 
     As shown in  FIGS. 7–8 , the novel multi-signal hexaphonic guitar pickup  122  is a  13  coil electromagnetic array and includes six (6) string pickup subassemblies  124  (i.e., electrical transducers) and one (1) noise pickup subassembly  126  mounted on a bridge  128 . Each string pickup subassembly  124  includes a bobbin-shaped support structure  129 , a magnetic assembly  130  inside the support structure  129 , and a coil assembly  132  mounted on the support structure  129  so that the magnetic assembly passes through the coil assembly  132 . The bobbin-shaped support structure  129  in each string pickup subassembly  124  includes two support structure subassemblies  134  that have identical shapes. Each support structure subassembly  134  includes a flanged top  136 , a base  138 , and a core  140  between the flanged top  136  and the base  138 . Each core  140  includes a core opening  142  that is adapted to receive pole pieces  144  used with the magnetic assembly  130 . Each base  138  includes a base opening  146  that allows the pole pieces  144  of the magnetic assembly  130  to be easily inserted into the cores  140  of the support structure subassemblies  134  and a magnet  148  used with the magnetic assembly  130  to be inserted into the bases  138  and into contact with the pole pieces  144 . Each pole piece  144  is T-shaped and includes a flanged portion  150  on one end. Each coil assembly  132  includes two (2) coils  152 , which are wrapped around the cores  140  of the support structure subassemblies  134  so that they pass around the pole pieces  144  of the magnetic assembly  130  and are out of phase with one another. Each coil assembly  132  also includes a four (4) pin output assembly  154  connected to the two (2) coils and mounted on the support structure subassemblies  134 . 
     The hex pickup  122  is designed to have a 95 dB signal to noise ratio and 45 dB inter-string isolation built into the bridge. In addition, the bridge to body and string to body connections through the neck can be mechanically isolated. In certain applications, the use of the hex pickup  122  may require the addition of magnetic structure to the bridge of the guitar  12 . The guitar  12  also may include internal shielding between the digital and analog sections. 
     For clarity, the coils  152  are shown only partially covering the cores  140  in  FIG. 8 . In practice, the coils  152  would completely cover the cores  140  and include thousands of turns as is well known in the art. 
     Each string pickup subassembly  124  is adapted to be positioned adjacent to a guitar string  108  on the digital guitar  12  and to generate a predetermined number of analog string signals in the coils when that string is strummed. The magnet assembly  130  generates two parallel magnetic fields (not shown) that extend a predetermined distance outward from the magnet  148 , through the magnet pole pieces  144 , through the cores  140  in the support structure subassemblies  134 , and through the coils  152  wrapped around the cores  140 . The distance that the magnetic fields extend outward from the magnet  148  may vary from application to application. In general, however, they should extend outward far enough that one of the magnetically permeable guitar strings  108  may be positioned in the magnetic fields and can vary the magnetic fields by vibrating when it is strummed. When each string pickup assembly  124  is properly positioned on the digital guitar  12  adjacent to a guitar string  108 , the change in the magnetic fields caused by the vibrating guitar string generates mixed analog string signals in the coils  152 . 
     The coils  152  wrapped around one core  140  are adapted to be connected to the digital guitar processing circuit  112  so that the mixed analog string signals generated by these coils are out of phase with the mixed analog string signals generated by the coils  152  wrapped around the other core  140 . 
     The features of the string pickup subassembly  124  (also referred to simply as the novel audio transducer  124 ) may vary depending on a particular application. For example, in some embodiments, the audio transducer  124  includes only two coils  152  and is adapted to generate only two analog audio signals using these coils when a guitar string  108  is strummed. In other embodiments, the audio transducer  124  is adapted so that the coils  152  and magnet  148  are completely enclosed by the support structure  129 . In still other embodiments, the support structure  129  is manufactured using plastic, the wire used to form the coils  152  has a gauge of 58 according to the American Wire Gauge standard, the pole pieces  144  are steel, and the magnet  148  is neodymium boron and generates a magnetic field strength of approximately 50 oersted. In yet another series of embodiments, the coil assemblies  132  are adapted to output the mixed analog string signals differentially in order to improve the signal to noise ratio of the signals, i.e., each coil  152  has two ends and both ends are used to output the mixed analog string signal associated with that coil. 
     The noise pickup subassembly  126  includes one of the bobbin-shaped support structures subassemblies  134  and one of the coil assemblies  132  used with the string pickup subassemblies  124 . The noise pickup subassembly  126  does not include a magnetic assembly  130  like the string pickup subassemblies  124 . The noise pickup subassembly  126  receives electrical and environmental noise from the air surrounding the pickup, i.e., low frequency planar waves that create the well known “hum” associated with conventional guitar pickups, and generates a noise signal that can be used to cancel out this noise in the analog string signals generated by the string pickup subassemblies  124 . 
     Referring to  FIG. 9 , the digital guitar processing circuit  112  includes a guitar preamplifier circuit  156 , a guitar mixing circuit  158 , an guitar analog/digital converter circuit  160 , and a guitar digital communication circuit  162 . The preamplifier circuit  156  is adapted to amplify the analog string signals generated by the humbucker  120  and multi-signal hexaphonic guitar pickups  122  to increase perceived sound quality. The preamplifier circuit  156  is also adapted to amplify an analog microphone signal and an analog headphone signal, both of which will be discussed in more detail below. Schematics showing one embodiment of the preamplifier circuit  156  of the present invention are shown in  FIGS. 29–36 . 
     The guitar mixing circuit  158  is adapted to combine the two analog mixed string signals for each string to generate the analog x-plane and y-plane string signal components for each string, and then to combine the x-plane and y-plane string signal components to generate a single analog combined string signal for each guitar string. The mixing circuit  158  includes a summing circuit  164 , a subtracting circuit  166 , and a combining circuit  168 . The summing circuit  164  is adapted to generate an analog summed string signal for each string by summing the two analog mixed string signals for each string. The subtracting circuit  166  is adapted to generate an analog subtracted string signal for each string by subtracting the two analog mixed string signals for each string. The combining circuit  168  is adapted to combine the analog summed and subtracted string signals to generate the single analog combined string signal for each string. 
     The mixing circuit  158  may also optionally include a noise subtracting circuit  170  that is adapted to subtract the noise signal generated by the noise pickup subassembly  126  from the summed string signal before it is combined with the subtracted string signal. 
     Two different implementations of the guitar mixing circuit  158  are shown in  FIGS. 10 and 11 . In  FIG. 10 , the mixing circuit  158  is shown with differential coil signal outputs, while in  FIG. 11 , the mixing circuit  158  is shown with single coil signal outputs. The use of differential outputs improves the signal to noise ratio of the mixed analog string signals generated by the coils  152 , but either implementation may be used. 
     The guitar analog/digital converter circuit  160  converts one of the analog humbucker string signals (which is selected as indicated below), the analog microphone signal, and the analog combined string signals for each string into digital combined string signals. This produces six (6) digital combined string signals, one (1) digital humbucker string signal, and one (1) digital microphone signal. The analog/digital converter circuit  160  is further operable to convert a digital headphone signal (discussed in more detail below) into an analog headphone signal. 
     The digital communication circuit  162  is operable to format all of the digital string signals generated by the analog/digital converter circuit  160 , the digital microphone signal, and digital control signals, which will be discussed below, into a format that is compatible with the MaGIC digital communication protocol. Referring to  FIG. 12 , the digital communication circuit  162  includes a bi-directional audio interface  172 , a bi-directional control interface  174 , and an Ethernet interface  176 . The bi-directional audio interface  172  is adapted to send and receive digital audio signals, such as the digital string and microphone signals, and the bi-directional control interface  174  is adapted to send and receive digital control signals. The Ethernet interface  174  is adapted to allow the digital communication circuit  162  to interface with an Ethernet physical layer, which forms part of the MaGIC digital communication system. 
     One embodiment of the digital guitar processing circuit  112  is shown in  FIG. 13  (see also,  FIG. 16 , which shows a similar embodiment of the circuit  112 ). In this embodiment, the guitar preamplifier circuit  156  is separated into a preamp (labeled preamp x 13) for the  12  mixed analog string signals generated by the multi-signal pickup  122 , a preamp (labeled simply preamp) for the humbucker pickup string signals, or legacy system string signals, a preamp (again labeled simply preamp) for the microphone signal, and a headphone preamp  156  for amplifying the analog headphone signal output by the DAC portion of the guitar analog/digital converter circuit  160 . This embodiment also includes a potentiometer (Pot)  155 , which is used to control the headphone signal volume, and limiter circuit  157 , which is adapted to prevent any large analog audio signals generated by the multi-signal guitar pickup  122  from exceeding the design limits of the guitar analog/digital converter circuit  160 . The guitar digital communication circuit  162  is shown including a T2 chip or module, and an I2s Engine and sync, both of which are used to process and format the digital audio signals generated by the guitar analog/digital converter circuit  160 . Finally, the digital guitar processing circuit  112  is split into two sections: an analog section (or plane)  111  and a digital section  113 , with the guitar analog/digital converter circuit  160  separating the two sections. Both the analog and digital sections can be combined onto a single circuit board. 
     As shown in  FIG. 16 , the outputs of the coils are fed into  13  preamps with differential inputs. Once sufficient signal conditioning is performed, the outputs of each pair of coils are added and subtracted from one another. The inverse of the 13th coil is applied to the added pairs to negate hum and noise. Both axes are combined to provide all possible harmonic content for processing on future products. Note that while there are 13 transducers, only 6 digital channels are actually digitized for later processing. In alternative embodiments, the signals from each axis may not be combined and can be digitized separately. In this case, 12 digital channels would be available for later processing. 
     Referring back to  FIG. 5 , the guitar digital input/output assembly  114  is adapted to output the digital string, microphone, and control signals to and receive a pair of digital audio signals from the digital guitar interface device  102 . The guitar analog input/output assembly  116  is adapted to output one of the analog humbucker string signals selected using the guitar control assembly  118 . The guitar analog input/output assembly  116  is also adapted to receive the analog microphone signal and to output the analog headphone signal. In one embodiment, the guitar digital input/output assembly  114  is a RJ-45 output port and is a MaGIC compatible output connector. The RJ-45 output  130  is a single bi-directional MaGIC Out port that provides six channels of digitized hex pickup output, 1 channel of digitized humbucker output, 1 channel of digitized microphone output, and two channels of digitized monitor mix input. The guitar  12  supports 24-bit audio at 48 and 96 kHz sample rates. 
     Turning now to  FIG. 14 , the guitar control assembly  118  includes a guitar pickup selector  178 , a headphone volume control  180 , and two sets of humbucker guitar pickup volume and tone controls  182 . The guitar pickup selector  178  is adapted to allow a user to select one of the humbucker guitar pickups  120  to be output on the guitar analog input/output assembly  116  and the headphone volume control  180  is adapted to control the volume of the analog headphone signal output. The humbucker guitar pickup volume and tone controls  182  are adapted to control the volume and tone of the humbucker guitar pickup outputs. The tone and volume knobs  182  include dual stacked potentiometers so they can simultaneously regulate analog output and generate MaGIC control packets. Each potentiometer includes an 8 bit analog to digital converter (ADC) that is used to sample the position of its associated knob. The digital data obtained from each potentiometer is then relayed to the digital guitar interface device  102 , which is described in more detail below. This data may also be output to other digital devices as well. 
     One specific embodiment of the digital guitar  12  is shown in  FIG. 15 . In this embodiment, the guitar analog input/output assembly  116  has been split into two separate assemblies: a microphone/headphone assembly  184  and a ¼″ output assembly  186 . The microphone/headphone assembly  184  is adapted to receive the microphone audio signal and to output the headphone audio signal. The ¼″ output assembly  186  is adapted to output one of the humbucker pickup string signals. In this figure, the digital guitar processing circuit  112  is referred to as a T2 module and the guitar digital input/output assembly  114  is implemented using an RJ-45 output connector. The headphone volume control  180  and humbucker guitar pickup volume and tone controls  182  are not shown in  FIG. 15 . 
     In another specific embodiment, shown in  FIGS. 21A and 21B , the microphone/headphone (plate) assembly  184  includes a microphone input  230 , a headphone output  232 , and the headphone volume control  180 , which is included for safety reasons. Two alternative versions of the microphone/headphone assembly  184 ,  184 A and  184 B, are also shown in  FIGS. 21A and 21B . As shown, the assembly  184  may be in a side by side configuration or it may be in a stacked configuration. In addition, the assembly  184  may be located on the same panel as the RJ-45 output (digital input/output assembly  114 ) and the ¼″ output assembly  186  (see  FIG. 21C ), on the side of the guitar, on the top of the guitar, hidden in the guitar so that it can be flipped out with a soft spring, or located in the strap shaft. 
     When the RJ-45 output port  130  is connected to a MaGIC network, power is applied to the active and digital electronics of the guitar  12  and analog signals from the hex pickup  122 , the traditional ¼″ output  186 , and the microphone input  230  are all digitized and sent over the MaGIC connection cable  104 . Regardless of whether the guitar  12  is connected to a MaGIC network, the ¼″ output  186  operates in a conventional manner. 
       FIGS. 17 and 18  show one particular embodiment of the digital guitar processing circuit  112 , and more specifically, the digital section  113  of that circuit. As shown in  FIG. 17 , the digital section  113  includes a T2 chip  188 , an I2S Engine and Sync  190 , clocks  192 , magnetics  194 , boot ROM  196 , an analog to digital converter  198  to convert the analog control signals generated by the humbucker volume/tone controls  182  into digital control signals, a header  200  for the RJ-45 connector, and a power conditioning circuit  202 .  FIG. 18  shows one specific implementation where the I 2 S Engine and Sync  190  is implemented using a field programmable gate array (FPGA)  204 , a buffer  206 , a phase locked loop  208 , and a 16 bit counter  210 . As mentioned previously, a detailed discussion of the operation of these components can be found in the MaGIC engineering specification and the &#39;169 patent. In brief, however, it is sufficient to note that these components are responsible for formatting and outputting the digital audio and control signals generated by the digital guitar processing circuit  112 . It also should be noted that the functions performed by these components may be implemented using other types of logic circuits as well. 
     The T2 module  112  is a single MaGIC OUT port device, and is therefore by definition always a sync slave device. It is powered by 802.3af over Ethernet power to ensure MaGIC compliance and supplies 8 output channels and accepts 2 input channels in I 2 S format audio. It includes a unique programmable MaGIC address and can store programmable parameters for different applications and manufacturers. 
     To ensure that the digital guitar is compatible with existing guitar equipment, the present invention includes the digital guitar interface device  102  (also referred to as the legacy box  102 ), which is adapted to convert digital audio signals output by the digital guitar into analog audio signals that are compatible with various types of conventional guitar equipment. In other words, it is a simple converter box that can be used to connect MaGIC compatible devices to traditional analog devices. It includes a single circuit board, which is a T2 module that is a variation of the T2 module (or digital guitar processing circuit)  112  used in the MaGIC guitar  12 . 
     Looking at  FIG. 19 and 22A , the digital guitar interface device  102  includes a housing  212 , an interface device digital input/output assembly  214 , an interface device analog input/output assembly  216 , and an interface device processing circuit  218 . The housing  212  includes indicator lights that indicate when power is applied to the interface device and when audio signals are present on the inputs and outputs of the interface device. The housing  212  also provides support for the various input and output assemblies. Power is supplied to the breakout box  114  using a “line lump” style switching power supply and enters the unit using a DC style plug  215 . The plug should be smaller than a standard AC adaptor to avoid under-powering the unit by connecting other Original Equipment Manufacturer (OEM) AC adaptors. The power supplied is greater than or equal to 48 Volts DC and greater than or equal to 0.40 Amps. An alternative embodiment of the digital guitar interface device  102  is shown in  FIG. 22B . 
     The interface device digital input/output assembly  214  is adapted to receive digital combined string, microphone, and control signals from, and output a pair of digital audio signals from an external audio device, such as a CD player, to the digital guitar  12 . The interface device analog input/output assembly  216  is adapted to output six (6) analog combined string signals, one of the analog humbucker string signals selected using the guitar control assembly  118 , and an analog microphone signal. The interface device analog input/output assembly  214  is also adapted to receive a pair of analog audio signals from the external audio device, i.e., the CD player, and the interface device processing circuit  218  is adapted to convert these analog signals into the pair of digital audio signals that are sent to the digital guitar  12 . 
     Moving to  FIG. 20 , the interface device processing circuit  218  is similar to the digital guitar processing circuit  112  and is adapted to convert received digital signals into analog signals and to convert received analog signals into digital signals. The interface device processing circuit  218  includes an interface device digital communication circuit  220 , an interface device analog/digital converter circuit  222 , an interface device preamplifier circuit  224 , an interface device filtering circuit  226 , and an interface device multiplexer circuit  228 . 
     The interface device digital communication circuit  220  is operable to receive the digital combined string and microphone signals generated by the digital guitar and to pass those signals to the interface device analog/digital converter circuit  222  for conversion into analog signals. The communication circuit  220  also receives the digital control signals output by the digital guitar, but does not pass those signals to the converter circuit  222  for conversion into analog signals. Instead, the communication circuit  220  uses those control signals to control the analog outputs of the interface device  102 . As was the case with the guitar digital communication circuit  162 , the digital communication circuit  220  in the interface device includes a bidirectional audio interface  172 , a bi-directional control interface  174 , and an Ethernet interface  176  (see  FIG. 12 ). For convenience, both the circuits have been shown in a single figure. In practice, however, these circuits would be physically located in two different devices, i.e., the digital guitar  12  and the interface device  102 . As before, the bidirectional audio interface  172  is adapted to send and receive digital audio signals, such as the digital combined string and microphone signals, and the bidirectional control interface  174  is adapted to send and receive digital control signals. The Ethernet interface  176  is adapted to allow the digital communication circuit to interface with an Ethernet physical layer, which forms part of the MaGIC digital communication system discussed previously. 
     The interface device analog/digital converter circuit  222  converts the digital humbucker string signal, the digital microphone signal, and the digital combined string signals for each string into analog string signals. This produces six (6) analog combined string signals, one (1) analog humbucker string signal, and one (1) analog microphone signal. The analog/digital converter circuit  222  is further operable to convert the analog external audio signals into the digital external audio signals that are sent to the digital guitar  12 . 
     The interface device preamplifier circuit  224  is adapted to amplify the analog combined string, humbucker string, and microphone signals generated by the interface device analog/digital converter circuit  222 . The preamplifier circuit  224  is also adapted to amplify the analog external device audio signals prior to their conversion into digital signals by the interface device analog/digital converter device  222 . The interface device filtering circuit  226  is adapted to filter out undesirable frequencies in the analog combined string, humbucker string, and microphone signals that may be generated during the digital to analog conversion process prior to their output. The interface device multiplexer  228  is adapted to output each of the combined analog string signals individually, combined into a single analog 6-string combined signal, and combined into a single analog 3-string combined signal, which includes the lower three (3) string signals. 
     Turning now to  FIG. 23 , there are 10 ¼″ tip-ring-sleeve (TRS) connectors on one side of the breakout box  102 . Eight of these connectors,  234 ,  236 ,  238 ,  240 ,  242 ,  244 ,  246 , and  248  are outputs, and two are inputs,  250  and  252 . There is also an RJ-45 input connector  216  ( FIG. 22A ) that can be used to connect the breakout box  102  to a MaGIC compatible device. In alterative embodiments, when the breakout box  102  is powered, it illuminates its top panel to indicate that power is on. When the unit is connected to a MaGIC output port, there is feedback to the user that a positive MaGIC link has been established. 
     Classic output, or humbucker output,  246  and microphone output  248  are always independent outputs from the humbuckers  120  and the microphone on the guitar  12 , respectively. In other words, the classic output  246  is simply the output of one of the humbuckers  120  (as determined by the pickup selector switch  178 ) that has been converted into a digital signal, passed over the MaGIC data link, and then converted back into an analog signal. The microphone output  248  is processed in a similar manner. The hex pickup outputs,  234 – 244 , operate in a different manner. When a single ¼″ connector is connected to the # 1 (Sum) output  234 , all 6 strings are filtered, summed, and output out of the # 1  output  234 . When output  234  and the # 2 ( 3 – 6 ) output  236  are connected to ¼″ connectors, the sum of all 6 strings will come out of output  234  and the sum of the lowest 3 strings will come out of output  236 . In either mode, outputs  240 ,  242 , and  244 , i.e., outputs  4 ,  5 , and  6 , respectively, output discretely their respective strings. When a ¼″ connector is connected to output # 3 ,  238 , the outputs are discrete from each string, i.e., filtered but not summed.  FIG. 24  shows four different possible output configurations for the breakout box  102 . 
     All filtering referenced above takes place in the analog domain (although digital filtering may be used as well). This filtering is required because the sound captured by the hex pickup  122  is the raw string stimulus in both the X and Y-axis. While this provides flat and complete sound content, the sound is unlike traditional electric guitar sounds. 
     Also, since the purpose of the breakout box  102  is to interface into legacy amplification devices, the tone is shaped to provide a pleasing tone that is more pure than standard humbucker pickups. The user of the breakout box  102  can choose to output the standard humbucker, the summed hex, individual strings, or combinations of signals to provide the tone desired. 
     If none of the breakout box  102  outputs are connected to a ¼″ connector, the summed output is looped back up the MaGIC cable  104  to the headphone output  232  on the guitar  12 . The user of the breakout box  102  can choose to plug a CD player into the inputs,  250  and  252 , on the breakout box  102  and play along in the headphone mix. 
     The breakout box  102  also includes the following programmed MaGIC components: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                 Control 
                   
                   
                 Default 
               
               
                 Name 
                 Type 
                 Type 
                 Address 
                 Value 
                 Links 
               
               
                   
               
             
            
               
                 Master 
                 Target 
                 Scale 
                 To be 
                 8-bit value 
                 To be 
               
               
                 Volume 
                   
                   
                 determined 
                 between 
                 determined 
               
               
                   
                   
                   
                   
                 0–255 
               
               
                   
               
            
           
         
       
     
       FIGS. 25 and 26  show one particular embodiment of the interface device processing circuit  218  (or T2 module) discussed previously. The processing circuit  218  includes an analog section  254  and a digital section  256 . As shown in  FIG. 25 , the analog section  254  includes the interface device analog/digital converter circuit  222 , which is a CODEC chip in  FIG. 25  that includes a two channel analog to digital converter and an 8 channel digital to analog converter, a series of output amplifiers  258 , a series of output filters  226  (i.e., interface device filtering circuit  226 ), the multiplexer circuit  228 , and two input amplifiers  260 . The output amplifiers  258  and input amplifiers  260  collectively form the interface device preamplifier circuit  224 . The inputs of the CODEC  222  are connected to the outputs of the input amplifiers  260 . The outputs of the CODEC  222  are connected to the output amplifiers  258  and the outputs of the output amplifiers  258  are connected to the output filters  226 . Multiplexing control is provided by normalization switched on the TRS ¼″ inputs and outputs. In one embodiment, the CODEC chip is an AK4529 chip. 
     The digital section  256  includes an I 2 s Engine and Sync  260 , clocks  262 , a power conditioning circuit  264 , an 802.3af power controller  266 , a T2 chip  268 , boot ROM  270 , a transformer  272 , and the RJ-45 input port  216 , all connected as shown in  FIG. 26 . These components are operable to communicate with the digital guitar  12  and to transmit and receive digital audio and control data from the digital guitar  12 . The operation of these components is described in the MaGIC Engineering Specification and Patent referenced above and will not be repeated here. 
     Power is provided by the 48 Volt power supply and is regulated down to +12 Volts DC, +5 Volts DC, +3.3 Volts DC, +2.5 Volts DC, −12 Volts DC, and +48 Volt DC compliant with the 802.3af Power over Ethernet specification. 
     Referring back to  FIGS. 14 and 15  (see also  FIG. 28 ), traditional signals pass from the pickups  120  into a T2 chip located on the T2 module  112  in the guitar  12 , from the pickups  120  to the volume/tone knobs  182 , out to the pickup selector switch  178 , back to the knobs  182  and filter caps (not shown), and then to the traditional ¼″ output jack  186 . The hex pickup  122  outputs all coils directly to the T2 module  112  in differential pairs ( FIG. 16 ). 
     Referring to  FIG. 28 , one embodiment of the passive control system for the traditional electric guitar components is shown with the T2 module  112 . This board is responsible for taking raw data from a data AID sampling knob position and translating it into MaGIC control data. This board can be expanded to add other control elements as necessary. While different boards may be required for different guitars, the control in each must define and present a common interface to the digital board containing the MaGIC chip, which translates the serial data into MaGIC control information. 
     The T2 board (i.e., module)  112  is an ‘A’ port device. It is always a sync slave. It is powered by 802.3af Power over Ethernet. The T2 module  112  supplies 2 channels out and 8 channels in of audio, bit-banged in I 2 S format. It takes raw data from a data AID sampling knob position and translates it to MaGIC control data. In one embodiment, the T2 module  112  is a single board, but may be separated into multiple boards if necessary. One embodiment of the physical subassembly in the digital guitar is shown in  FIG. 27 . 
     In one embodiment, the T2 module  112  includes 2 AK5384 chips, which are analog to digital converters for audio with 4 channels each, an analog to digital M62334, 4 channel multiplexer (mux) chip from Mitsubishi connected to the guitar knobs, and an AK4380 digital to analog chip for the headphone output. 
     The guitar  12  includes the following programmed MaGIC components: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                 Control 
                   
                   
                 Default 
               
               
                 Name 
                 Type 
                 Type 
                 Address 
                 Value 
                 Links 
               
               
                   
               
             
            
               
                 Guitar 
                 Source 
                 Scale 
                 To be 
                 8-bit value 
                 To be 
               
               
                 knob 1 
                   
                   
                 determined 
                 between 0–255 
                 determined 
               
               
                 Guitar 
                 Source 
                 Scale 
                 To be 
                 8-bit value 
                 To be 
               
               
                 knob 2 
                   
                   
                 determined 
                 between 0–255 
                 determined 
               
               
                 Guitar 
                 Source 
                 Scale 
                 To be 
                 8-bit value 
                 To be 
               
               
                 knob 3 
                   
                   
                 determined 
                 between 0–255 
                 determined 
               
               
                 Guitar 
                 Source 
                 Scale 
                 To be 
                 8-bit value 
                 To be 
               
               
                 knob 4 
                   
                   
                 determined 
                 between 0–255 
                 determined 
               
               
                 Guitar 
                 Source 
                 Toggle 
                 To be 
                 0 or 1 
                 To be 
               
               
                 switch 1 
                   
                   
                 determined 
                   
                 determined 
               
               
                 Guitar 
                 Source 
                 Toggle 
                 To be 
                 0 or 1 
                 To be 
               
               
                 switch 2 
                   
                   
                 determined 
                   
                 determined 
               
               
                 Guitar 
                 Source 
                 Toggle 
                 To be 
                 0 or 1 
                 To be 
               
               
                 switch 3 
                   
                   
                 determined 
                   
                 determined 
               
               
                   
               
            
           
         
       
     
     The MaGIC component addresses, device classes, and default control links can be determined and assigned as necessary. 
     For increased reliability, robust Neutrik EtherCon series connectors can be used. Both the male cable carriers and female receptacles in this series contain robust die cast shell with a secure latching feature. These devices are pre-assembled RJ-45 plugs. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 T2 Module connectors 
                 # of pins minimum 
               
               
                   
                   
               
             
            
               
                   
                 Humbucker pickups 
                  3 
               
               
                   
                 Hex Pickups 
                 27 
               
               
                   
                 Selector switch 
                  4 
               
               
                   
                 To RJ-45 
                  9 
               
               
                   
                 To I/O plate 
                  4(more if we want LEDs) 
               
               
                   
                 To ¼″ jack 
                  2 
               
               
                   
                   
               
            
           
         
       
     
     Existing hard-sleeved network cables are not robust enough to sustain the repeated twisting, turning, and mechanical stress commonly experienced in live audio environments. As a result, custom soft-sleeved cables that are reliable enough to sustain repeated mechanical stress and can provide adequate shielding against nearby high voltage/current cables are strongly recommended. Also, all environments except permanent installations should use stranded instead of solid wire cables to further increase reliability under mechanical stress. 
     The present invention also includes a retrofit method that can be used to convert conventional analog guitar into a digital guitar. The method includes the steps (in any order) of removing a conventional analog output assembly from a conventional analog guitar, inserting and mounting the digital guitar processing circuit  112  inside the conventional analog guitar, connecting the digital guitar processing circuit  112  to a guitar pickup assembly  110  mounted on the conventional analog guitar and a digital input/output assembly  114 , and mounting the digital input/output assembly  114  on the conventional analog guitar. 
     Alternatively, the retrofit method can leave the existing analog output assembly in place, and add the new features by inserting and mounting the digital guitar processing circuit  112  inside the conventional analog guitar, connecting the digital guitar processing circuit  112  to a guitar pickup assembly  110  mounted on the conventional analog guitar and a digital input/output assembly  114 , and mounting the digital input/output assembly  114  on the conventional analog guitar. 
     Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for the purposes of the present disclosure, numerous changes in the construction and steps thereof may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the appended claims.