Abstract:
A cable connector configured to receive a sound signal and alter the tonality of the sound by switching among a plurality of capacitors. The cable connector comprises a switch coupled to a binary coded plurality of capacitors. The cable connector receives an input signal corresponding to a sound through a conductor, which is also coupled to the switch. The switch may be used to select one of a plurality of capacitances, affecting the tonality of the sound. A cable implementing the cable connector and a method for using the cable connector are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Application No. 61/584,678, entitled “Musical Instrument Interconnect Cable,” filed on Jan. 9, 2012, the entire contents of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to an instrument interconnect cable, and more particularly to an instrument interconnect cable wherein the user can adjust the cable&#39;s capacitance. 
         [0003]    Guitars and other stringed instruments are often amplified by attaching a passive magnetic pickup in close proximity to the vibrating metallic strings of the guitar and connecting this pickup to an amplifier and speaker using a cable. The vibrating strings change the magnetic flux within the core of the pickup. This flux change induces a voltage change in the outer coils of the pickup, thus completing the translation of mechanical vibration to electrical signal. This signal is transmitted through the cable to the amplifier. 
         [0004]    The cable connecting the pickup to the amplifier is typically between 5 and 30 feet to allow the musician adequate mobility while playing. The cable typically is terminated on each end with a standard ¼′ male connector. Both the guitar and amplifier will typically have the mating female ¼″ connector. 
         [0005]    Instrument cables are typically of the coaxial type, wherein the signal is surrounded by a 360-degree metallic wire shield. This type of cable protects the very low voltage signal coming from the instrument from radio frequency interference (RFI) or electro-magnetic fields (EMF). 
         [0006]    Some musicians have noticed that different brands of instrument cables at different lengths will cause a difference in tonality in an instrument&#39;s sound output. One cause for this variance in tonality is the variance in the overall capacitance of the cables being used. Capacitance in cables is caused by the insulating material having a dielectric quality that causes capacitive coupling between the signal wires and the ground, or shield, wires. Coaxial cables are typically given a capacitance per foot rating (pF/ft). This rating typically can be anywhere from 10 pF/ft to 50 pF/ft. By multiplying the pF/ft rating by the length of the cable, a person can calculate the overall capacitance of a particular length of a particular cable. The overall capacitance of a cable typically ranges from 300 pF to 1200 pF. Cables of different capacitances will have different tonal qualities when used with an instrument having passive magnetic pickups. 
         [0007]    With present cables, musicians are able to vary the capacitance only by using different cables of different lengths. This is inconvenient for several reasons. First, if a musician wants to produce the same tonality from his or her instrument, then he or she must use the same cable with the same length all the time, or the musician must try to find two or three cables of different lengths that have the same capacitance, exchanging one for the other whenever a cable of a different length is needed. Additionally, if a musician would like to take advantage of the different tonalities offered by cables having different capacitances, then he or she must undertake the inconvenient process of unplugging one cable and then plugging in another having a different capacitance to replace it. The current options available for addressing this issue do not offer a sufficient range of adjustment for altering the capacitance. 
         [0008]    It can readily be appreciated that there is a need for an instrument cable that avoids the problems described above. The present invention fulfills this need and provides further related advantages. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is embodied in a cable connector comprising a switch, a plurality of capacitors each coupled to the switch, and a conductor coupled to the switch. The capacitance of the connector can be changed by switching among the capacitors using the switch. The conductor is configured to receive an input signal corresponding to a sound, and the tonality of the sound is altered by changing the capacitance of the connector. 
         [0010]    In one embodiment, the cable connector connects to an instrument cable. 
         [0011]    The switch may be implemented in a variety of ways, and may comprise any of the following: a rotary binary coded switch, a plurality of individual switches, a plurality of transistors, or a plurality of buttons. 
         [0012]    In one embodiment, the conductor receives an input signal created by an instrument. The input signal may be created by a passive magnetic pickup on the instrument. 
         [0013]    In a particular embodiment, if there are “n” number of capacitors, the switch may be configured such that the capacitance of the connector can be changed to one of 2 n  possible capacitances by switching among the capacitors or combinations of capacitors using the switch. Alternatively, if there are “n” number of capacitors, the switch may be configured such that the capacitance of the connector can be changed to one of 2 n −1 possible capacitances by switching among the capacitors or combinations of capacitors using the switch. 
         [0014]    The present invention is also embodied in a cable comprising an input connector, a switch, and a plurality of capacitors each coupled to the switch. The cable has a capacitance that can be changed by switching among the capacitors using the switch. The input connector is configured to receive an input signal corresponding to a sound, and the tonality of the sound can be altered by changing the capacitance of the cable. 
         [0015]    In one embodiment, the cable receives an input signal created by an instrument. The input signal may be created by a passive magnetic pickup on the instrument. 
         [0016]    In a particular embodiment, if there are “n” number of capacitors, the switch may be configured such that the capacitance of the cable can be changed to one of 2 n  possible capacitances by switching among the capacitors or combinations of capacitors using the switch. Alternatively, if there are “n” number of capacitors, the switch may be configured such that the capacitance of the cable can be changed to one of 2 n −1 possible capacitances by switching among the capacitors or combinations of capacitors using the switch. 
         [0017]    The present invention is also embodied in a method for transmitting a sound signal, the method comprising selecting one of a plurality of capacitance options using a switch, receiving a signal corresponding to a sound having a tonality, and altering the tonality of the sound by applying a selected one of the plurality of capacitance options. 
         [0018]    In one embodiment, the received signal is created by an instrument. The signal may be created by a passive magnetic pickup on the instrument. 
         [0019]    In a particular embodiment, if there are “n” number of capacitors, the switch may be configured such that the selected capacitance can be changed to one of 2 n  possible capacitances by switching among the capacitors or combinations of capacitors using the switch. Alternatively, if there are “n” number of capacitors, the switch may be configured such that the selected capacitance can be changed to one of 2 n −1 possible capacitances by switching among the capacitors or combinations of capacitors using the switch. 
         [0020]    These and other features and advantages of the invention should become more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings. 
           [0022]      FIG. 1  is a perspective view of an instrument, an amplifier, and an instrument cable having adjustable capacitance, in accordance with an embodiment of the present invention. 
           [0023]      FIG. 2  is a circuit diagram representing an instrument, amplifier, and instrument cable, in accordance with an embodiment of the present invention. 
           [0024]      FIG. 3  is a circuit diagram showing a capacitance switching circuit for use with an instrument cable having adjustable capacitance, in accordance with an embodiment of the present invention. 
           [0025]      FIG. 4  is a response curve chart for a cable at different capacitances, in accordance with an embodiment of the present invention. 
           [0026]      FIG. 5A  is a side elevation view of a cable connector, in accordance with an embodiment of the present invention. 
           [0027]      FIG. 5B  is an internal view of the cable connector of  FIG. 5A . 
           [0028]      FIG. 6A  is a perspective view of an external capacitance switch for use with an instrument cable, in accordance with an embodiment of the present invention. 
           [0029]      FIG. 6B  is an internal view of the external capacitance switch of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    With reference to the drawings, and in particular to  FIG. 1  thereof, there is shown an instrument, an amplifier, and an instrument cable  10  in accordance with an embodiment of the present invention. One end of the instrument cable  10  is connected to the instrument  12 , in this case an electric guitar, and the other end of the instrument cable  10  is connected to the amplifier  14 . The instrument cable  10  is connected to the guitar  12  at a point removed from the playing area. Internal cables (not shown) connect the instrument cable  10  internally to a passive magnetic pickup  16  on the guitar  12 . When played, the vibrating strings on the guitar  12  induce voltage changes in the outer coils of the pickup  16 , thus completing the translation of a mechanical vibration to an electrical signal. This electrical signal is transmitted through the cable  10  to the amplifier  14 . 
         [0031]    In one embodiment, the instrument cable  10  is between 5 and 30 feet to allow the musician adequate mobility while playing. The cable is terminated on each end with a standard ¼″ male connector. Both the guitar  12  and the amplifier  14  have the mating female ¼″ connector. The instrument cable  10  is of the coaxial type, wherein the signal is surrounded by a 360-degree metallic wire shield. This type of cable protects the very low voltage signal coming from the instrument from radio frequency interference (RFI) or electro-magnetic fields (EMF). The instrument cable  10  includes a rotary switch  18  that can be used to adjust the capacitance of the cable so as to adjust the tonality of the sound produced. 
         [0032]    With reference to  FIG. 2 , there is shown a circuit diagram representing a guitar  12 , an amplifier  14 , and an instrument cable  10 , in accordance with an embodiment of the present invention. The guitar  12  includes a guitar pickup  16 , a “tone control”  53 , and a “volume control”  43 . The guitar pickup  16  is represented by a pickup resistance  20 , a pickup inductance  22 , a string voltage  24 , and a pickup capacitance  26 . The instrument cable  10  is represented by a cable capacitance  36  and an added capacitance  28 . Vibrations in the strings of the guitar cause the pickup  16  to register voltage changes at the string  24 . The voltage changes create an electrical sound signal that passes to and through the cable  10 . As the sound signal passes through the cable  10 , it is affected by the cable capacitance  36  and the added capacitance  28  on its way to the amplifier  14 . The cable capacitance  36  is not a discrete capacitor, but instead an inherent capacitance that is caused by the cable&#39;s insulating material having a dielectric quality, which causes capacitive coupling between the signal wires and the ground/shield wires, as described above. As such, traditional cables contain an inherent cable capacitance  36 , but do not have the “added capacitance”  28 , which is added in the present invention so as to give the user greater control over the sound produced. The guitar&#39;s tone control  53  also includes a variable capacitance, C-tone  27 . For the present invention, it is preferable for the tone control capacitance  27  to be set to its lowest possible capacitance, so that it has little to no effect on the produced sound. The cable  10  outputs a sound signal to the amplifier  14  at the output  40 . 
         [0033]    When the tone capacitance  27  is set to its lowest capacitance setting, as discussed above, the minimum capacitance of the entire system is essentially equal to the sum of the cable capacitance  36  and the pickup capacitance  26  (26+36). In a traditional instrument cable, the tonality created by the instrument cable depends mostly on the interaction of the pickup inductance  22  and this minimum capacitance. In the instrument cable of the present invention, this minimum capacitance is augmented by the added capacitance  28 . This then results in a “total capacitance” (26+36+28). A resonant frequency is created where the reactance of the total capacitance (26+36+28) and pickup inductance  22  are equivalent in magnitude. The resonant frequency of the 
         [0000]    circuit in  FIG. 2  is calculated by using the equation: 
         [0000]    
       
         
           
             
               
                 f 
                 r 
               
               = 
               
                 1 
                 
                   2 
                    
                   π 
                    
                   
                     LC 
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where L is the fixed pickup inductance  22  and C is the total capacitance (26+36+28), which is determined by adding the cable capacitance  36 , the pickup capacitance  26  and the added capacitance  28 . Changes to the resonant frequency affect the tonality of a sound by emphasizing or de-emphasizing certain frequencies within the sound signal. Generally, frequencies approaching the resonant frequency of a sound signal are heard more clearly, while those frequencies that are further away from the resonant frequency of a sound signal are more subtle or inaudible. 
         [0034]    The resonant frequency can be changed by changing the total capacitance (26+36+28), which is the sum of the cable capacitance  36 , pickup capacitance  26  and the added capacitance  28 . The cable capacitance  36  is a function of the cable&#39;s capacitance per foot rating and the cable&#39;s length. As such, the cable capacitance is essentially fixed for a given cable of a given length. In the present invention, by changing the added capacitance  28 , the total capacitance (26+36+28) can be changed, which yields a change in the resonant frequency of the sound signal, thereby changing the tonality of the sound produced. 
         [0035]    The added capacitance  28  is selected from a plurality of capacitances by using the variable capacitance circuit shown in  FIG. 3 . In  FIG. 3 , a rotary binary coded switch  52  is used to select the added capacitance  28 . When the instrument is played, a sound signal is received from the guitar pickup  16  at the input  44 . The sound signal is then passed through the cable, where the tonality of the sound signal is affected by the cable capacitance  36  and the added capacitance  28 . The capacitance-affected sound signal is then output to the amplifier  14  at the output  48 . The shields  46  and  50  provide grounding for the sound signal so as to prevent interference from outside sources. 
         [0036]    The added, and thus, total, capacitance can be changed using a suitable switching circuit, and may be accomplished using a rotary binary coded switch, a combination of individual switches, a combination of transistors, a combination of buttons, or another combination of elements that allows for varying the capacitance by adding individual capacitors or combinations of capacitors in parallel. In the embodiment shown in  FIG. 3 , the rotary binary coded switch  52  allows the user to adjust the added capacitance 28 in 100 pF increments from 0 pF to 1500 pF by selecting different combinations of the capacitances of the four capacitors C 1 , C 2 , C 3  and C 4 . For example, if the user wishes to have an added capacitance  28  of zero, then the switch  52  is set to the setting in which none of the capacitors are selected, and the added capacitance  28  acts as an open circuit having effectively zero capacitance. If the user wishes to have an added capacitance  28  of 100 pF, then the switch  52  is set to select only capacitor C 1 . If the user wishes to have an added capacitance  28  of 200 pF, then the switch  52  is set to select only capacitor C 2 . If the user wishes to have an added capacitance of 300 pF, then the switch is set to select both capacitors C 1  and C 2 . In the embodiment shown in  FIG. 3 , the switch  52  can have up to 16 different settings, each setting corresponding to a different combination of the capacitors C 1 -C 4 , allowing the user to adjust the added capacitance  28  in 100 pF increments from 0 pF to 1500 pF. In this embodiment, the four capacitance values C 1 -C 4  have been specifically selected (100 pF, 200 pF, 400 pF, and 800 pF) so that every 100 pF value from 0 pF to 1500 pF is possible. Being able to increase the capacitance in 100 pF increments allows for finer resolution in the tonal adjustment. This capacitance range was selected because, in certain applications, the ability to vary the capacitance from 0 pF to 1500 pF permits the most dramatic variation in tone. The different combinations and capacitance values are detailed in Table 1. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Capacitor Value Combinations 
               
             
          
           
               
                 Capacitors Selected 
                 Added Capacitance 
                 Rotary Switch Position 
               
               
                   
               
               
                 None 
                   0 pF 
                 0 
               
               
                 C1 
                  100 pF 
                 1 
               
               
                 C2 
                  200 pF 
                 2 
               
               
                 C1 + C2 
                  300 pF 
                 3 
               
               
                 C3 
                  400 pF 
                 4 
               
               
                 C1 + C3 
                  500 pF 
                 5 
               
               
                 C2 + C3 
                  600 pF 
                 6 
               
               
                 C1 + C2 + C3 
                  700 pF 
                 7 
               
               
                 C4 
                  800 pF 
                 8 
               
               
                 C1 + C4 
                  900 pF 
                 9 
               
               
                 C2 + C4 
                 1000 pF 
                 A 
               
               
                 C1 + C2 + C4 
                 1100 pF 
                 B 
               
               
                 C3 + C4 
                 1200 pF 
                 C 
               
               
                 C1 + C3 + C4 
                 1300 pF 
                 D 
               
               
                 C2 + C3 + C4 
                 1400 pF 
                 E 
               
               
                 C1 + C2 + C3 + C4 
                 1500 pF 
                 F 
               
               
                   
               
             
          
         
       
     
         [0037]    Although the embodiment of  FIG. 3  shows only four capacitors C 1 -C 4 , greater or fewer numbers of capacitors are possible. In one embodiment, for “n” total capacitors connected to the switch  52 , there are 2 n  possible capacitance values that may be selected by a user for the added capacitance  28 . In  FIG. 3 , there are 4 capacitors connected to the switch  52 , so there are 16 possible capacitance values. If the circuit had 5 different capacitors connected to the switch  52 , then there would be 32 possible capacitance values. If the circuit had only 3 different capacitors connected to the switch  52 , then there would be only 8 possible capacitance values. If there is not an option for a 0 pF added capacitance  28 , then there would be 2 n −1 possible capacitance values. 
         [0038]    In embodiments for which the added capacitance  28  can be set to zero, the minimum total capacitance is determined by cable capacitance  36  combined with the pickup capacitance (26+36), which is a result of the type and length of the cable being used and the pickup being used. In one embodiment, a lower capacitance cable of a shorter length is used because it places the range of adjustment in an area that offers a more musical range of tonal choices. One example of such a cable is the Belden cable 8255 standard coax cable. 
         [0039]    With reference to  FIG. 4 , there is shown a measurement chart showing response curves for different total capacitances (26+36+28). The resonant frequencies for the four curves are represented by the points  54 ,  56 ,  58  and  60 , and roll-off points are represented by the points  62 ,  64 ,  66  and  68 . The response curves shown in  FIG. 4  demonstrate that the amplitude of the resonant frequency is decreased and the frequency of the resonant frequency is increased as the total capacitance (26+36+28) is decreased, thereby causing a variation in tone. A higher total capacitance (26+36+28) yields a tonality in which a smaller range of lower frequencies is emphasized, while a lower total capacitance (26+36+28) yields a tonality in which a larger range of higher frequencies is highlighted. Additionally, the frequency at which the response curve begins to roll off also changes as a result of changes to the total capacitance (26+36+28). Generally, frequencies at which the amplitude is below the roll-off point will not be heard in the sound signal. For a given pickup inductance, as the total capacitance (26+36+28) decreases, the roll off point will increase, leading to a greater range of frequencies being heard in the sound signal. As the total capacitance (26+36+28) increases, the roll off point decreases and yields a smaller, more focused range of frequencies being heard. 
         [0040]    With reference to  FIGS. 5A and 5B , there is shown cable connector  70  containing a variable capacitance circuit, in accordance with an embodiment of the present invention. The added capacitance  28  is selected by using the rotary switch  18 . The cable connector  70  has a cable end portion  72 , which can be a ¼″ male connector. The cable end portion  72  is sized and shaped to plug into an instrument and receive an electrical sound signal. The sound signal passes from the cable end portion  72  to the main body of the cable connector  70 , where the sound signal is subjected to an adjustable capacitance that varies the tonality of the sound. The user can rotate the rotary switch  18  to select one of a plurality of possible capacitance values. In one embodiment, the rotary switch  18  has 16 setting options, allowing the user to select from 16 different capacitance values. The rotary switch may be rotated using a small screwdriver-like tool. 
         [0041]      FIG. 6A  depicts another embodiment of the present invention. In  FIG. 6A , the variable capacitance circuitry is housed in a box  80  that is separate from the instrument cable  10 .  FIG. 6B  is a view of the inside of the variable capacitance box  80  of  FIG. 6A . The male cable end portion  72  of the instrument cable  10  engages the box  80  at the female connector  82 . Four switches  84 ,  86 ,  88  and  90  allow the user to select the added capacitance  28 . Each of the four switches  84 ,  86 ,  88  and  90  connects or disconnects one of four capacitors  94 ,  96 ,  98  or  100 . Different combinations of the four switches  84 ,  86 ,  88  and  90  create different combinations of the four capacitors  94 ,  96 ,  98  and  100 , thus creating 16 different added capacitance values  28  for the user to select from. The output connector  92  allows the box  80  to be connected to an amplifier, which amplifies the sound signal from the instrument. 
         [0042]    Each of the four capacitors  94 ,  96 ,  98  and  100  is connected on one end to the ground/shield wire  102 , and on the other end to one of the four switches  84 ,  86 ,  88  or  90 . The input  82 , the output  92 , and the four switches  84 ,  86 ,  88  and  90  are connected by the wire  104 , which carries the sound signal. When all four switches  84 ,  86 ,  88  and  90  are turned off, none of the capacitors are connected to the sound signal in the wire  104 . In this configuration, the sound signal passes through the wire  104  with no capacitance added by the variable capacitance circuit. When any of the four switches  84 ,  86 ,  88  and  90  is turned on, the switches that are turned on connect their respective capacitors to the sound signal wire  104 , thereby adding those capacitances to the circuit. For example, turning on only switch  84  connects only capacitor  94 , and turning on switches  86  and  90  connects capacitors  96  and  100 . By using the different combinations of switches available, the user is able to select from 2 n  possible capacitance values for “n” different switches and capacitors. In  FIGS. 6A and 6B , there are 16 possible capacitance values that may be selected. 
         [0043]    Although the invention has been disclosed with reference only to the presently preferred embodiments, those of ordinary skill in the art will appreciate that various modifications can be made without departing from the invention. Accordingly, the invention is defined only by the following claims.