Abstract:
An electromagnetic field pickup ( 10 ) for a musical instrument including an electromagnetic signal generator ( 12 ), an electromagnetic field transducer ( 18 ), a mixer ( 28 ), the electromagnetic signal generator ( 12 ), the electromagnetic field transducer ( 18 ) and the mixer ( 28 ) are respectively connected in series, the electromagnetic signal generator ( 12 ) is also connected directly to the mixer ( 28 ), so constructed and arranged that when power is supplied to the electromagnetic field pickup ( 10 ) an audio electrical signal of substantially same pitch, intonation and sustain as a vibrating element ( 22 ) of the instrument is generated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation of U.S. patent application Ser. No. 12/396,711 filed Mar. 3, 2009, which claims benefit of priority to U.S. patent application Ser. No. 61/038,567, filed on Mar. 21, 2008 now expired and Australia patent application serial number 2008901054, filed on Mar. 4, 2008; the contents of each are herein incorporated by reference. 
    
    
     BACKGROUND OF INVENTION 
     1. Technical Field 
     The present invention has application to the field of music and to the sub fields of electrical musical tone generation using transducers and electromagnetic fields and with particular application to stringed and percussion instruments. 
     2. Background Art 
     Since Thomas Edison first used a vibrating thorn to cut a sound track in a revolving wax cylinder producing a very rough and poor quality sound by contemporary standards, many scientists, inventors and experimenters have striven for perfect reproduction and recording of sound and music, using devices referred to as “pickups” to detect and attempt to reproduce sound produced by musical instruments. 
     The imperfections and limitations of current electrical pickups have generated a vast multitude of variations and combinations of pickup types with a sole goal of achieving perfect electrical reproduction of sound. 
     The reproduced sound from many musical instruments relies upon a pickup conversion process to convert mechanical musical vibrations into an electrical signal that can be amplified and recorded. 
     Types of conventional pickups include: 
     
         
         a) a magnetic pickup which includes an inductive coil surrounding a permanent magnet; 
         b) a piezoelectric pickup which includes vibration sensitive crystalline material; 
         c) an acoustic pickup which includes a microphone with a vibration sensitive diaphragm; 
         d) an optical pickup which includes a light source and a phototransistor detector; 
         e) and combinations of above types of pickups.
 
General problems with background art:
 
         a) conventional pickup systems rely on intermediary mediums to transfer a primary mechanical musical vibration to a pickup&#39;s electrical signal generating components; 
         b) the conventional pickup can load a primary mechanical musical vibrating element and distort true pitch and intonation of the element and reduce sustain and limit amplitude and frequency response of a resulting electrical signal.
 
Specific problems with background art including:
 
         a) magnetic pickup needs steel strings to vibrate in a magnetic field with a large inductive coil to pick up audio frequency vibrations consequently loading a vibrating string and reducing a resulting frequency response; 
         b) a piezoelectric pickup needs a vibrating component including at least one of a bridge and a soundboard, often leading to a poor low frequency response; 
         c) an acoustic microphone relies upon variations in air pressure to transfer a musical vibration and is subject to an external noise and frequency response limitation; 
         d) an optical pickup requires a light source and detector to be above and below each of an instrument&#39;s strings without affecting operation of an instrument, the optical pickup is receptive to displacement of a string&#39;s shadow in one dimension only, and accordingly, information pertaining to sound received by an optical pickup is limited as a string vibrates in three dimensions, as a result sound reproduction is limited in quality and physical requirements limit the optical pickup&#39;s application to a bridge area of the instrument. 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     To substantially solve the general problems and the specific problems as recited above. 
     Technical Solution 
     Transmitting a radiated electromagnetic field (a first electromagnetic field) to a vibrating element of a musical instrument, receiving a re-radiated and modulated electromagnetic field (a second electromagnetic field) from the vibrating element, subtracting a first electromagnetic signal used to produce the first electromagnetic field from a second electromagnetic signal derived from the second electromagnetic field to produce a difference signal (audio signal), where the difference signal will precisely replicate vibration of the vibrating element with respect to pitch, sustain and intonation of vibration and where the reradiated and modulated electromagnetic signal is subject to “Doppler” frequency shift modulation caused by the vibrating element. 
     The solution is a direct conversion process without any intermediary medium, which will provide an accurate and true electrical reproduction of sound emitted by the vibrating element of the instrument. 
     Advantageous Effects 
     Advantageous effects include: 
     
         
         a) accurate reproduction of a full frequency range of sound emitted by of an instrument; 
         b) preservation of relative amplitude and duration of each frequency; 
         c) use of conventional electrical components in combination resulting in reduced development and manufacturing costs; 
         d) enhancement of quality of a recording and reproduction of music from an instrument; 
         e) simplification of pickup construction resulting in increased flexibility and improvement in the instrument&#39;s aesthetic appearance; 
         f) reduced size allowing greater application flexibility and easier retro fitting to the instrument; 
         g) low power consumption allowing internal battery operation; 
         h) can be used with a non-metallic vibrating element if high electromagnetic frequencies are used; 
         i) electromagnetic signal frequency alignment is completely automatic; 
         j) increasing scope of creativity for an artist using the instrument; 
         k) faithfully reproduces true pitch, intonation and superior sustain of the instrument; 
         l) close proximity of the pickup to a vibrating element of the instrument does not affect the vibrating element including when the vibrating element is a string; 
         j) the pickup exhibits greater sensitivity than a conventional pickup and so can operate at a greater distance from the vibrating element.
 
In a first aspect of invention, an electromagnetic field pickup for a musical instrument comprising:
 
         a) an electromagnetic signal generator; 
         b) an electromagnetic field transducer; 
         c) a mixer; 
         the electromagnetic signal generator, the electromagnetic field transducer and the mixer are respectively connected in series; 
         the electromagnetic signal generator is also connected directly to the mixer; 
         so constructed and arranged that when power is supplied to the electromagnetic field pickup an audio electrical signal of substantially same pitch, intonation and sustain as a sound vibration from a vibrating element of the musical instrument is generated. 
       
    
     Another feature of the first aspect of invention includes, a filter connected to the mixer. 
     Another feature of the first aspect of invention includes, an audio amplifier connected to the filter. 
     Another feature of the first aspect of invention includes where the mixer is a mixer diode biased to operate in a linear region of the mixer diode&#39;s range of operation. 
     Another feature of the first aspect of invention includes where the electromagnetic field transducer includes an array of dielectric chip antennas. 
     Another feature of the first aspect of invention includes where the dielectric chip antennas are oriented with respect to the vibrating element so that a radiated field produced by the dielectric chip antennas has a same polarization as the vibrating element. 
     Another feature of the first aspect of invention can include where the electromagnetic field transducer is a waveguide antenna having at least one slot. 
     Another feature of the first aspect of invention can include where alignment of the waveguide antenna with respect to a string of the vibrating element is such as to place the slot substantially at right angle to the string and to place the string substantially over a centre of the slot so that a radiated field emitted from the slot has a same polarization as the string. 
     In a second aspect of invention, a method for generating a musical frequency audio electrical signal comprising a step of:
     subtracting a first electromagnetic signal from a second electromagnetic signal to produce a difference signal;   the first electromagnetic signal and the second electromagnetic signal are of substantially same frequency;   the first electromagnetic signal is modulated by vibration of a vibrating element of a musical instrument to produce the second electromagnetic signal;   the difference signal is the musical frequency audio electrical signal of substantially same pitch, intonation and sustain as a sound vibration of the vibrating element of the musical instrument.
 
Another feature of the second aspect of invention includes steps of:
   a) transmitting a first electromagnetic field towards the vibrating element;   b) receiving a second electromagnetic field from the vibrating element;   the first electromagnetic field is derived from the first electromagnetic signal;   the second electromagnetic field is derived by re-radiation and modulation of the first electromagnetic field;   the second electromagnetic signal is derived from the second electromagnetic field.   

     Another feature of the second aspect of invention includes a step of filtering out additional signals generated with the difference signal. 
     Another feature of the second aspect of invention includes, where transmitting the first electromagnetic field comprises transmitting a radio frequency field. 
     Another feature of the second aspect of invention can include, where transmitting the first electromagnetic field comprises transmitting a microwave frequency field. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  discloses a best mode of invention for use with an electric guitar. 
         FIG. 2  discloses an isotropic view of a best mode of invention. 
         FIG. 3  An isotropic view of a mode of invention for use with a steel stringed electric guitar and for use with a nylon stringed acoustic guitar. 
     
    
    
     DETAILED DESCRIPTION 
     Best Mode 
     Definitions and Terms 
     “Detection”, also called demodulation, is a process of re-creating original modulating frequencies (intelligence) from frequencies which are present in a composite signal”, extracted and adapted from Basic Electronics, Prepared by Bureau of Naval Personnel, Dover, first published 1973, at p 232. 
     Consistent with the definition of “detection” as recited above, a term “mixer” can further comprise filtration. 
     Modulation—“Radio—in radio transmission, the process whereby the frequency, amplitude, or some other property of a carrier wave (signal-carrying wave) is made to increase or decrease instantaneously in response to variations in the characteristics of the signal being transmitted”—Chambers Concise Dictionary &amp; Thesaurus, Chambers Harrap Publishers, Edinburgh, 2001. 
     A transducer is “A device that converts one form of energy into another. Electronic transducers either convert electric energy to another form of energy or convert non electric to electric energy”, Microsoft Computer Dictionary, Fifth Edition, Microsoft Press 2002. Accordingly, term “transducer” can refer to a single integrated device for purpose of reception and transmission of electromagnetic energy. Similarly, a transducer can include a device having a separate component for transmission of electromagnetic energy and a separate component for reception of the electromagnetic energy. 
     Term Doppler effect (shift) is defined to mean “the change in wavelength observed when the distance between a source of waves and the observer is changing, eg the sound change perceived as an aircraft or vehicle passes by (19c: named after the Austrian physicist Christian Doppler)” Chambers Compact Dictionary, Chambers Harrap Publishers, Edinburgh, 2005. Accordingly, term “Doppler effect” (“Doppler shift”) includes a reference to an effect that is common to all electromagnetic wave phenomena and is produced when an object moves relative to a source of the electromagnetic wave, resulting in a Doppler shifted electromagnetic wave that will exhibit a change in frequency and wavelength that is related to frequency of movement of the object. 
     Term “electromagnetic field”, as used in specification can include any electromagnetic wave radiation that can reliably produce a Doppler frequency shifted electromagnetic signal for use with a musical instrument. The term “electromagnetic field” includes, any ultrasonic, radio frequency, microwave, infrared, visible spectrum, and ultra violet electromagnetic wave radiation. 
     Term “electromagnetic signal” can include a reference to a process of generation of the signal. 
     Accordingly, when a musical instrument&#39;s vibrating element oscillates in an electromagnetic field, the vibrating element causes Doppler shifting in frequency of the electromagnetic field that is related to frequency of vibration of the vibrating element. 
     Power supplies below are not illustrated and the power supplies, with associated filtration of input power is assumed inherent. 
       FIG. 1  discloses a best mode of invention, in general form, for use with a steel string electric guitar. 
     An electromagnetic signal generator  12  produces a first electromagnetic signal  14  at 2.4 GHz, the first electromagnetic signal  14  is sent to electromagnetic field transducer  18  and a second electromagnetic signal  16  is sent to mixer  28 . 
     The electromagnetic field transducer  18  includes an array of 2.4 GHz dielectric chip antennas  42  as best seen in  FIG. 2 . The electromagnetic field transducer  18  radiates a first electromagnetic field  20  towards an instrument&#39;s vibrating element  22  illustrated as strings in  FIG. 1 . 
     The strings are vibrating at an audio frequency so as to cause a Doppler frequency shift in the first electromagnetic field  20 . After Doppler shifting the first electromagnetic field  20  is re-radiated and modulated and represented as the second electromagnetic field  24 . The second electromagnetic field  24  is reflected back towards the electromagnetic field transducer  18 . 
     The electromagnetic field transducer  18  receives the second electromagnetic field  24  and a third electromagnetic signal  26  is then sent to the mixer  28 . The mixer  28  is a linear mixer. The third electromagnetic signal  26  contains effects of Doppler shifting contained in the second electromagnetic field  24 . 
     The mixer  28  mixes the third electromagnetic signal  26  and the second electromagnetic signal  16  to produce a fourth electromagnetic signal  30 . The fourth electromagnetic signal  30  also includes effects of Doppler shifting contained in the second electromagnetic field  24 . 
     Components of the fourth electromagnetic signal  30  include the second electromagnetic signal  16 , the third electromagnetic signal  26 , a summation signal and a difference signal (the difference signal is later filtered out and represented as a fifth electromagnetic signal  34 ). The summation signal is an addition of the second electromagnetic signal  16  and the third electromagnetic signal  26 . The difference signal is a subtraction between the second electromagnetic signal  16  and the third electromagnetic signal  26 . The fourth electromagnetic signal  30  is sent to a filter  32 . 
     The filter  32  removes all electromagnetic signals except for the difference signal represented as the fifth electromagnetic signal  34 . The fifth electromagnetic signal  34  is in an audio frequency signal and can be referred to as an audio signal, which has same frequency of vibration as the strings represented as the vibrating element  22 . The fifth electromagnetic signal  34  is then sent to audio amplifier  36 . 
     The audio amplifier  36  amplifies and processes the fifth electromagnetic signal  34  to produce an additional audio frequency signal represented as a sixth electromagnetic signal  38 . The sixth electromagnetic signal  38  is then sent to output connection  40 . Output connection  40  can interface and connect with an external device. The external device can include a main amplification unit. In another mode, the external device can include recording equipment. 
     The electromagnetic field pickup is an active device and can be powered by an external DC supply. The pickup can also be powered by an internal battery supply. 
       FIG. 2  is an isotropic view of a best mode of invention. An electromagnetic field pickup  10  includes an electromagnetic field transducer  18 ; the electromagnetic field transducer  18  includes an array of radiating 2.4 GHz dielectric chip antennas  42 . Alignment of the dielectric chip antennas  42  is such that the first electromagnetic field  20  seen in  FIG. 1  is in a same polarization as the vibrating element  22 . 
     Mode for Invention 
       FIG. 3  is an isotropic view of a 24 GHz mode of invention for nylon stringed acoustic guitars and steel stringed electric guitars. General, mode of operation of embodiment illustrated in  FIG. 3  is as illustrated and described in relation to  FIG. 1  and  FIG. 2 . 
     The electromagnetic field transducer  18  (depicted generally in  FIG. 1 ) takes a specific form of a six-slot waveguide antenna in  FIG. 3 . The electromagnetic signal generator  12  (seen in  FIG. 1 ) is mounted in a first chamber  46  at a distal portion of the six-slot waveguide antenna and powered through connection  44 . The electromagnetic signal generator  12  located in the first chamber  46  in  FIG. 3  is a Gunn device electromagnetic signal generator. 
     The mixer  28  seen in  FIG. 1  is located in a second chamber  50  at a proximal portion of the six-slot waveguide antenna. The first chamber  46  is continuous with the second chamber  50 . The mixer  28  in  FIG. 3  is a mixer diode. The mixer diode is biased to operate in a linear part of the mixer diode&#39;s range of operation by a DC bias voltage fed to, connection  52 . 
     The electromagnetic field transducer  18 , seen in  FIG. 3  as the 6-slot waveguide antenna, radiates a first electromagnetic field  20  from each of slots  48  in the 6-slot waveguide antenna towards an instrument&#39;s vibrating element  22 , shown in  FIG. 3  as a set of strings. The 6-slot waveguide antenna also receives a second electromagnetic field  24  from the strings (as best seen in  FIG. 1 ). 
     Alignment of each of the slots  48  in the 6-slot waveguide antenna is such that the strings are substantially at right angles to each of the slots and each of the strings rests over a centre of one of the slots. Generation of the difference signal  34  referred to in  FIG. 1  occurs in  FIG. 3  using same processes described in relation to  FIG. 1 . 
     The difference signal  34  is an audio signal. The difference signal  34  has a frequency that is substantially same frequency of vibration of the strings and is outputted via a dc blocking capacitor from the connection  52 . 
     At 24 GHz the electromagnetic field pickup  10  is very sensitive to vibrations of both metallic and non-metallic strings and vibrating surfaces. There is also sensitivity to hand movements, an effect that could be used creatively by an artist to add to music played on the instrument. 
     Industrial Applicability 
     In use, modes of invention can be applied to stringed instruments including guitars, violins and harps. Modes of invention can also be applied to percussion instruments including drums. Further, modes of invention can be applied to wind instruments. Modes of invention can be used with instruments having strings constructed from materials including nylon and steel. 
     Modes of invention applied to non-metallic vibrating musical surfaces are best seen to use frequencies above 10 GHz (Gigahertz). Modes of invention for metallic surfaces used with frequencies above 10 GHz can exhibit hand distortions caused by hand movement. The distortions can be removed by lowering the frequencies. The distortions can also be used to provide additional artistic effect. 
     Modes of invention applied to metallic only vibrating musical surfaces are seen to operate best using radio frequency signals between 1 and 10 GHz. 
     Additional modes of invention can be contemplated in use. The mixer  28  can be implemented in various embodiments including a diode, a transistor and an integrated circuit provided that the mixer  28  is capable of satisfying essential feature of invention of mixing a first electromagnetic signal (unmodulated) and a second electromagnetic signal (modulated) so as to generate a difference signal (audio signal) where the first electromagnetic signal and the second electromagnetic signal are of substantially same frequency. 
     In practical use of electromagnetic signals, mixing of the first electromagnetic signal (unmodulated) and the second electromagnetic signal (modulated) of substantially same frequency, respectively associated with a first electromagnetic field and a second electromagnetic field, has been discouraged because of potential phase differences leading to presence of a low frequency beat. In case of musical instruments, short distances between a pickup and a vibrating element mean that the low frequency beat is unlikely to represent a problem in generation of the resultant difference signal (audio signal). Substantial absence of the low frequency beat, over short distances, means that mixing of the first electromagnetic signal (unmodulated) and the second electromagnetic signal (modulated) of substantially same frequency is of practical utility when applied to musical instruments. 
     Further, in use, audio amplification is not critical to operation of invention in all embodiments. In various uses it is envisaged that amplification level of the difference signal (audio signal) can be sufficient for direct entry into an external device. 
     Further, modes of invention, in use, are seen in  FIG. 2  and  FIG. 3 . 
     In use,  FIG. 2  shows the electromagnetic field pickup  10  using an array of radiating 2.4 GHz dielectric chip antennas  42 .  FIG. 2  shows position of the 2.4 GHz dielectric chip antennas  42  in relation to the vibrating element  22  illustrated as strings in  FIG. 2 . 
     Further, in use,  FIG. 3  shows the electromagnetic field pickup  10  using a 6-slot waveguide antenna as the electromagnetic field transducer  18 .  FIG. 3  also shows position of the 6-slot waveguide antenna in relation to the vibrating element  22  illustrated as strings in  FIG. 3 .