Patent Publication Number: US-6703552-B2

Title: Continuous music keyboard

Description:
RELATED APPLICATIONS 
     The present application claims priority to provisional application No. 60/294,038, filed on May 29, 2001. 
    
    
     BACKGROUND 
     The present invention, the Continuous Music Keyboard, can track the left-to-right and front-to-back position, and the pressure, of each of 10 fingers simultaneously touching its control surface. Unlike a traditional music keyboard, the Continuous Music Keyboard has no discrete keys; it has a single continuous polyphonic control surface. Any pitch and any tuning may be played by properly placing fingers on the control surface. Finger movements produce smooth glissandi, crescendi, and vibrato. The Continuous Music Keyboard also tracks front-to-back position of each finger, providing another dimension of continuous control for the performer. Its output can be used to control any synthesis technique. 
     Modern electronic music keyboards allow the performer to use key velocity and aftertouch to control sound synthesis. Some keyboards provide a polyphonic aftertouch, which allows the performer continuous control over each individual note in a chord (as in Buchla&#39;s invention U.S. Pat. No. 4,558,623, December 1985). These capabilities are extended by certain experimental keyboards, such as Moog&#39;s clavier (R. Moog, “A Multiply Touch-Sensitive Clavier for Computer Music,”  Proc.  1982  Int. Computer Music Conf. , Int. Computer Music Assoc., San Francisco, pp. 155-159, 1982). Moog&#39;s clavier measures not only pressure aftertouch, but also other parameters including the exact horizontal and vertical location of each finger on its keyboard key. Suzuki invented a variable resistor strip for music keyboards (U.S. Pat. No. 3,626,350, February 1970). Asher invented a touch strip for position and pressure (U.S. Pat. No. 5,008,497, Apr. 1991). Chapman invented a pressure transducer for musical instrument control (U.S. Pat. No. 5,079,536, January 1992). All of these inventions result in keyboards divided into a plurality of keys; in contrast, the Continuous Music Keyboard does not have discrete keys, but rather consists of one continuous polyphonic control surface. 
     Snell proposed a keyboard with the standard layout, but with the black keys sloping down at the rear to a flat plane where pitch would be continuous, as on a ribbon controller (J. M. Snell, “Sensors for Playing Computer Music with Expression,”  Proc.  1983  Int. Computer Music Conf. , Int. Computer Music Assoc., San Francisco, pp. 113-126, 1983). Keislar proposed the use of a planar controller for implementing a microtonal keyboard, in which spaces between constant-pitch “keys” could optionally be used for continuous pitch (D. Keislar, “History and Principles of Microtonal Keyboards,”  Computer Music J. , vol. 11, no. 1, pp. 18-28, 1987). Fortuin presented a planar controller, built at STEIM and the Institute of Sonology, used as a two-dimensional microtonal keyboard (H. Fortuin, “The Clavette: A Generalized Microtonal MIDI Keyboard Controller,”  Proc.  1995  Int. Computer Music Conf. , Int. Computer Music Assoc., San Francisco, p. 223, 1995). Translucent overlays are placed on the controller to change the keyboard layout, allowing different sorts of scales with discrete pitches. Van Duyne invented a microtonal keyboard based on key clusters (U.S. Pat. No. 4,972,752, November 1990). Starr invented a fingerboard for guitar-shaped musical instruments (U.S. Pat. No. 5,398,585, Mar. 1995). In contrast to all these devices that have a plurality of keys or switches, the Continuous Music Keyboard allows the performer to play in any microtonal tuning using one uniform continuous polyphonic control surface. 
     Johnstone invented a device that optically tracks finger positions on a glass surface (E. Johnstone, “The Rolky: A Poly-Touch Controller for Electronic Music,”  Proc.  1985  Int. Computer Music Conf. , Int. Computer Music Assoc., San Francisco, pp. 291-295, 1985). In contrast, the Continuous Music Keyboard uses magnetic sensing to track fingers on a cloth-covered control surface. 
     Deutsch and Deutsch invented the Portamento Keyboard, which allows polyphonic sliding portamento (U.S. Pat. No. 4,341,141, July 1982). This device is based on an array of keyswitches to track the finger positions. In contrast, the Continuous Music Keyboard uses magnetic sensing to track the fingers, and the Continuous Music Keyboard tracks the front-to-back position of each finger. 
     Eventoff invented a pressure-sensitive digitizer pad (U.S. Pat. No. 4,810,992, March 1989). This can detect exact position and pressure of a force applied at any one point on the control surface. In contrast, the Continuous Music Keyboard tracks many fingers simultaneously pressing on the control surface. 
     TacTex corporation distributes a multiply-touch sensitive touch pad utilizing optical fiber pressure sensing technology (U.S. Pat. No. 5,917,180, June 1999, Reimer and Danisch). This pad is used as an electronic music controller, but it has a much smaller touch surface than a traditional music keyboard. In contrast, the Continuous Music Keyboard is the size of a traditional keyboard, and utilizes magnetic, not optic, sensing. 
     The Continuous Music Keyboard is my alternative to traditional MIDI keyboards. I previously invented other continuous devices (L. Haken, E. Tellman, and P. Wolfe, “An Indiscrete Music Keyboard,”  Computer Music J. , vol. 22, no. 1, pp. 30-48, 1998). The present invention differs in many essential ways from my previous inventions. My previous inventions (1) lacked pitch and amplitude detection accuracy, (2) produced pitch aberrations when tracking perfectly smooth glissandi, (3) could not track fast finger movements, (4) could not track short staccato notes, (5) could not withstand normal use because internal parts wore out. The present invention corrects these problems with new mechanical arrangement and new algorithms. 
     SUMMARY 
     The present invention, the Continuous Music Keyboard, is my alternative to a traditional MIDI keyboard. It is a new music performance device that allows the performer more continuous control than that offered by a traditional MIDI keyboard. It resembles a traditional keyboard in that it is approximately the same size and is played with ten fingers. Like keyboards supporting MIDI&#39;s polyphonic aftertouch, it continually measures each finger&#39;s pressure. It also resembles a fretless string instrument in that it has no discrete pitches; any pitch and any tuning may be played, and smooth glissandi are easily produced. 
     The Continuous Music Keyboard tracks an X, Y, Z position for each finger pressing on its control surface. The output of the Continuous Music Keyboard can be used to control any synthesis technique. Because of its continuous three-dimensional nature, the output of the fingerboard works especially well with sound morphing and cross-synthesis. 
     The X (side-to-side) position of each finger provides continuous pitch control for a note. In the most common configuration of the Continuous Music Keyboard, one inch in the X direction corresponds to a pitch range of 160 cents, and one octave is approximately the same size as an octave on a traditional piano keyboard. The performer must place fingers accurately to play in any particular tuning and can slide or rock fingers for glissando and vibrato. 
     The Z (pressure) position of each finger provides dynamic control. The performer produces tremolo by changing the amount of finger pressure. An experienced performer may simultaneously play a crescendo and decrescendo on different notes. 
     The Y (front-to-back) position of each finger provides timbral control for each note. By sliding fingers in the Y direction while notes are sounding, the performer can create timbral glides. 
     Depending upon the timbres generated by the sound synthesizer used with the Continuous Music Keyboard, the Y position can have a variety of effects. One possibility is to configure a sound synthesizer so that the Y position on the Continuous Music Keyboard corresponds to the bowing position on a string instrument, where bowing near the fingerboard produces a mellower sound and bowing near the bridge produces a brighter sound. Another possibility is to select source timbres so that Y position morphs between timbres of different acoustic instruments. The performer can bring out certain notes in a chord not only by playing them more loudly, as on a piano, but also by playing them with a different timbral quality. 
     The Continuous Music Keyboard comprises a flat control surface substantially the same size as a conventional music keyboard. Under the control surface is an array of thin rods that are mounted to a chassis. Springs are mounted near the ends of each rod. The rod is machined with a hole to accept the spring. This ensures that the springs are not overcompressed, even under excessive finger pressure. The rods are held in place with regularly-spaced in-line pins, utilizing a pair of pins near each rod, one pin between the rod and its neighbor and the other extending through a hole in the rod. The pins between the rods are subsequently referred to as “between rods posts.” The pins extending through a hold in the rod are subsequently referred to as “through rod posts.” 
     The apparatus may also include cover material for the rods, which is mounted on a bracket that can be easily removed for replacement. This material may comprise synthetic velvet. The continous music keyboard playing surface may also display a pattern based on the black and white key ordering of a piano as a pitch reference for the performer. 
     When a finger presses down on the control surface, one or more rods are displaced vertically (in the Z-plane). Which rods are displaced depends on the left-to-right position (X value) of the finger. The vertical (Z-plane) displacement of each end of each rod depends on the front-to-back position (Y value) and pressure (Z value) of the finger. 
     The displacement of each end of each rod is measured through the use of magnets and Hall-Effect sensors. Magnets are mounted at each end of each rod and Hall-Effect sensors are mounted on the chassis. When the end of the rod is displaced vertically, the mounted magnet is displaced in kind. The displacement of the magnet is measured by a Hall-Effect sensor. In a presently preferred embodiment, the sensors are mounted on the chassis such that the plane of the face of each sensor is in parallel with the line between the poles of a corresponding magnet. These values may then be collected and analyzed by a software package. 
     In the presently preferred embodiments. the software is operable to track the left-to-right, front-to-back, and pressure of each of 10 fingers simultaneously pressing on the surface. The software can then convert the finger position and pressure data into pitch, volume and timbre information, which can be communicated to standard electronic musical instruments. In a presently preferred embodiment, the pressure and left-to-right position is determined by the maximum point of a vertical parabola drawn through a peak rod value and its two neighboring rod values (a rod value is proportional to the total measured pressure exerted on a rod). The front-to-back position is computed from the ratio of two end sums taken to a fractional power, where an end sum is the sum of a service of a service of sensor values corresponding to magnets proximate to an end of the playing surface. The software in the presently preferred embodiments also includes predictive position analysis based on previous finger position and motion direction and speed. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG.  1 —A performer playing the Continuous Music Keyboard. The position, pressure, and movement of the performer&#39;s fingers are tracked on the control surface. 
     FIG.  2 —A top view of a small-size Continuous Music Keyboard. 
     FIG.  3 —A top view of a full-size Continuous Music Keyboard. 
     FIG.  4 —Configuration of rods, magnets, springs, and sensors in the control surface according to a preferred embodiment of the present invention. 
     FIG.  5 —Top and side view of a single rod according to a preferred embodiment of the present invention. 
     FIG.  6 —A flow chart of software for controlling the control surface according to a preferred embodiment of the present invention. 
     FIG.  7 —A graphical representation of the calculation of a parabola according to a preferred embodiment of the present invention. 
     FIG.  8 —A block diagram of a system for controller a control surface according to a preferred embodiment of the present invention. 
     FIG.  9 —A flowchart for software for generating left-to-right (X value) and depth (Z value) coordinates according to a preferred embodiment of the present invention. 
     FIG.  10 —A flow chart for software for generating front-to-back (Y value) coordinates according to a preferred embodiment of the present invention. 
     FIG.  11 —A flow chart for software for evaluating received and predicted coordinate values according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     FIG. 1 shows a performer playing the Continuous Music Keyboard. The Continuous Music Keyboard  1  has approximately the same dimensions as a traditional keyboard. The performer presses down on the control surface  2 . The Continuous Music Keyboard tracks the right-to-left and front-to-back position and movement of each of the fingers pressing on the control surface. The finger position and pressure information can be used to control a sound synthesizer in a variety of ways. Most commonly, the right-to-left position is used to control the pitch of notes, the pressure is used to control the dynamics (loudness), and the front-to-back position is used to control some other timbral aspect of the sound (such as brightness). The pattern  3  on the frame of the device is based on the black and white key ordering on a traditional piano keyboard; it serves as a pitch reference for the performer. 
     FIG.  2  and FIG. 3 show two sizes of the Continuous Music Keyboard. In FIG. 2, the control surface  12  provides a 4600-cent pitch range (nearly four octaves) when the right-to-left finger positions are interpreted as pitch with standard music keyboard pitch spacing. The frame  11  is approximately the same size as a 46-key standard electronic music keyboard. The pattern drawn on the frame  13  serves as a pitch reference; the pattern repeats nearly four times, corresponding to the nearly four-octave range assuming standard music keyboard pitch spacing. 
     In FIG. 3, the control surface  22  provides a 9430-cent pitch range (nearly eight octaves) when the right-to-left finger positions are interpreted as pitch with standard music keyboard pitch spacing. The frame  21  is approximately the same size as a large (concert grand) music keyboard. The pattern drawn on the frame  23  serves as a pitch reference; the pattern repeats nearly eight times, corresponding to the nearly eight-octave range assuming standard music keyboard pitch spacing. 
     FIG. 4 shows internal mechanics of the Continuous Music Keyboard. The control surface is covered with a synthetic velvet cloth  33 . The performer&#39;s fingers press down on this cloth. An array of thin rods  31  is under the control surface. These rods are narrower than a finger&#39;s width. Magnets  32  are attached to both ends of each rod, and corresponding Hall-Effect sensors  34  are mounted to the chassis. The rods are suspended on springs  35  and move up and down on metal posts. 
     The top view of ends of rods  36  shows the arrangement of magnets  37  and posts. The posts are in two groups; between rods posts  38  and through rod posts  39 . The through rod posts  39  each have a spring around them, not visible in this view. The rods and the mounting hardware are symmetric; both ends of the rods have this same physical arrangement. 
     The end-on view of a rod  36  shows the between rods posts  38  at either side of the rod, and the through rod post  39 . A spring  47  is mounted around each through rod post  39 . The rod  36  is manufactured to accommodate the spring; when the rod  36  is fully depressed, the spring completely fits in the rod&#39;s tapered hole  48 . The magnet  49  is seen end-on in this view. 
     FIG. 5 is a top view  51  and a side view  52  of a single rod. The rod is machined aluminum, with two mounting holes for magnets  53  at each end, four indents  54  for the posts between neighboring rods, and two holes  55  for the posts through the rod. The holes  55  are wider at on the bottom of the rod  56  than on the top, so that the spring can fit into the rod when the rod is fully depressed. This provides protection for the spring if the performer applies excessive finger pressure to the rod. 
     FIG. 6 is a flow chart representation of the software associated with the Continuous Music Keyboard. The software uses sensor values to identify the left-to-right and front-to-back position, and pressure, of each finger on the control surface; it encodes this position and pressure information to control standard music synthesizers. 
     The software tracks each finger as the fingers move on the control surface. In act  80 , the sensor value from the Continuous Music Keyboard are inputted. In a preferred embodiment, a full scan of the sensor values occurs every four milliseconds. Next, in act  81  the values inputted are normalized to account for differences in range and magnitude of individual sensors. After the sensor values are normalized, peak values are identified and formulated in a list in act  82 . The process repeats for all the peaks in the list in act  83 . For each peak, the software t computes  84  the right-to-left position (X value), the front-to-back position (Y value), and the pressure (Z value) corresponding to the peak. Details of act  84  are further described with reference to FIGS. 7,  9 , and  10  below. In act  85 , the XYZ value is then compared to the predicted XYZ value of all the fingers that were found in the previous scan of the sensors. The predicted XYZ is based on the previous position and trajectory of each finger. Details of act  85  are further described with reference to FIG.  11 . If the new XYZ value does not correspond to any predicted value, a new finger started pressing on the control surface is indicated in act  86 . If the new XYZ value corresponds to one of the predicted values, this indicates a new XYZ for that finger. The finger position is updated, and a new projected value is computed for use in the next scan in act  87 . 
     After all the peaks are processed in acts  83 - 87 , fingers that had no new XYZ values corresponding to predicted values are eliminated in act  88 . These are fingers that were lifted from the control surface during this scan. The XYZ for each finger is then encoded for the synthesizer in act  89 . Most commonly the right-to-left position is encoded as pitch information, but it could be encoded to control some other aspect of sound synthesis. Most commonly the pressure encoded as dynamic (volume) information, but it could be used to control some other aspect of synthesis. Most commonly the front-to-back is encoded as some timbre control (such as filter cutoff, or morphing control). Finally all the data is sent to the synthesizer as a high-speed MIDI stream in act  90 . Then the scanning cycle repeats with a new scan of the sensor values in act  80 . 
     FIG. 7 shows how the Continuous Music Keyboard can find right-to-left positions that are much more accurate than the width of a rod. Assume the center rod (rod  3 ) in FIG. 7 is a peak found in act  82  of FIG. 6; the discussion that follows describes details of computations in  84  of FIG.  6 . First, a rod value for the center rod (rod  3  in FIG. 7) and the two neighboring rods (rods  2  and  4  in FIG. 7) is computed. The rod value is the sum of both normalized values from the sensors at each end of the rod. Next, a vertical parabola is drawn through the three rod values ( 2 ,  3 , and  4  in FIG.  7 ). The minimum point of this parabola corresponds to the finger pressure and right-to-left position. As shown in FIG. 7, the vertical location of the minimum point corresponds to the figure pressure on the control surface and the horizontal location corresponds to the right-to-left position. This method can detect slight variations in finger position, to the left  71 , straight on  72 , or to the right  73  of the center rod. 
     This present method of drawing a parabola through rod values computes a more accurate finger pressure than the previously published method of direct summation of normalized sensor values of all sensors on rods  2 ,  3 , and  4 . Also, the present method of drawing a single parabola through rod values provides a more accurate right-to-left estimate at low finger pressures than previously published methods. It is less susceptible to the interacting magnetic forces of neighboring magnets than the previously published method of drawing parabolas through the normalized sensor values at one end of the rods. 
     As shown in FIG. 8, the continuous music keyboard system  100  may comprise a continuous music keyboard playing surface  110  coupled with a controller  120 . The controller  120  operates using the software described in FIG.  6 . One skilled in the art would appreciate that there are numerous different methods in which the software may be implemented on a hardware device. In one embodiment of the controller  120 , several software modules may be designed to perform specific tasks. As used herein, the controller  120  refers to any assembly of electronics that may analyze generated sensor values. In a preferred embodiment, a sensor value retrieval module  122  may scan the sensor values from the playing surface  110 . These retrieved values may then be normalized through a normalization module  124 . Next, Peak XYZ Value Module  126  may calculate the peak XYZ value from the received the normalized values. The Peak XYZ Value Module  126  may also communicate with a Predictive Value Module  130 , which can be used to predict where a next finger position is likely to occur. This information may be used to determine if a new finger has been placed on the playing surface, or if is simply a movement of a finger that has already pressing down on the playing surface. These values assessed by the Peak XYZ Value Module  126  may be sent to an electronic music data output module  128  which may transmit data to a synthesizer. As one skilled in the art would appreciate, the functions of the controller  120  may be accomplished through the use of a different number and arrangement of software modules. 
     FIG. 9 graphically depicts an exemplary method of determining the Left-To-Right (X Value) Position and Depth (Z Value) of a depression on a control surface, which was also disclosed above. In act  200 , normalized sensor values are received. Next, the sum of the normalized sensor values from each end of the rod is computed for each depressed rod in act  202 . Next, a vertical parabola is fitted using the computed rod values as data points in act  204 . The minimum point of the vertical parabola is then assessed in act  206 . The vertical component of the parabola corresponds to the Z Value; the horizontal component corresponds to the X Value; the horizontal component corresponds to the X Value. The corresponding Left-To-Right (X value) and Depth (Z Value) Positions are then outputted in act  208 . 
     FIG. 10 graphically depicts an exemplary method of determining the Front-To-Back (Y Value) Position of a depression on the control surface, which was also disclosed above. In act  220 , normalized sensor values are received. Next, in act  222 , the sum of normalized sensor values at the same end of neighboring rods is computed for a first side of the depressed rods. As noted in FIG. 7, this typically comprises three rods. However, normalized sensor for more or less rods may be utilized. This process is repeated in act  224  for the second side of the depressed rods. In act  226 , the ratio of the first end sum computed in act  222  to the second end sum computed in act  224  is calculated. A corresponding Front-To-Back (Y Value) Position is then outputted in act  228 . 
     The evaluation of whether an X,Y,Z coordinate corresponds to a finger that is already down, depicted in FIG. 6 as act  85 , is further graphically depicted in FIG.  11 . In act  240 , a computed XYZ value is received. Next, the three-dimensional derivative is computed in act  242 . Here, the trajectory, including the speed and direction of a finger at the previous XYZ value is calculated. From this trajectory, a predicted XYZ value is generated in act  244 . This predicted XYZ value is then compared with the actual XYZ in act  246 . The comparison of where the finger is predicted to be located with the actual XYZ value is then used to determine if the received XYZ value is a new finger position in act  248 .