SYSTEMS AND METHODS FOR CREATING DIGITAL NOTE INFORMATION FOR A METAL-STRINGED MUSICAL INSTRUMENT

Abstract

Systems and methods for a digital instrument are described, for example to simulate or be used in conjunction with a stringed instrument. A sensor system detects the deflection of one or more strings of the digital instrument, produces a measurement of the detected deflection, correlates the measurement to a musical note, and produces at least a portion of digital output based upon the musical note.

Claims

1. A method for capturing notes played on a stringed instrument, the method comprising: detecting deflection of a string at a first location when a user of the stringed instrument presses on the string in a second location remote from the first location; in response to detecting deflection of the string, producing a measurement of the detected deflection; and in response to producing the measurement, correlating the measurement to a. note to produce at least a portion of a digital output.

2. A system for capturing notes played on a stringed instrument, the system comprising: at least one inductive coil positioned under at least one string at a first longitudinal position along the length of the at least one string; a digital circuit communicatively coupled to the plurality of inductive coils to receive signals indicating displacement of the at least one string and to produce measurements of the displacement; and a microprocessor communicatively coupled to the digital circuit and configured to receive the measurements and correlate them to musical notes.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0017] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0018] FIG. 1 illustrates a musical instrument according to one embodiment.

[0019] FIG. 2A and 2B illustrate a fret board and strings of a musical instrument according to one embodiment.

[0020] FIG. 3 illustrates a musical instrument according to one embodiment.

[0021] FIG. 4 illustrates a block diagram according to one embodiment.

[0022] FIG. 5A, 5B, and 5C illustrate a metal string and inductive sensor according to one embodiment.

[0023] FIG. 6 illustrates an example inductive circuit schematic.

[0024] FIG. 7 illustrates a block diagram of a circuit according to one embodiment.

[0025] FIG. 8 illustrates a block diagram of a circuit according to one embodiment.

[0026] FIG. 9 illustrates a method for creating digital note information to one embodiment.

DETAILED DESCRIPTION

[0027] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, electrical changes, etc. may be made without departing from the scope of the present invention.

[0028] Various systems and methods for a digital guitar are described herein. The digital guitar may appear and play nearly identically to a standard guitar. However, the digital guitar may provide a digital output rather than a standard analog output provided by an electric guitar or by an acoustic guitar using an embedded pickup in the sound box.

[0029] Unlike previous attempts at creating a digital guitar, certain embodiments allow for the generation of a digital signal representative of the notes being played without noticeable latency that results from frequency analysis of the standard analog output signal. The digital guitar described herein may allow for the determination of where each string is being fretted based on detecting the locations of the musician's fingers. The digital guitar may also determine what expression nuances are modifying notes being played. According to some aspects of the disclosure, the digital guitar may detect which strings are being played and a volume associated with each string. The digital guitar may combine information about which strings are being played with information about which strings are being fretted to generate a digital output.

[0030] In certain embodiments, a digital interface for guitars may be used with, for example, educational or game-related software or systems. With certain systems and methods described herein, it is possible for an external program to determine the finger positions prior to actually plucking the string and for the player to see right away if the correct note has been played. This may be advantageous in learning applications or remote learning, where the proper chord position can he read before it is actually strummed.

[0031] In some embodiments, a digital guitar allows for the relatively inexpensive construction of an instrument that may be played in a similar manner to an existing instrument, while allowing nearly infinite variations. More advantages and novel aspects will be described below with reference to the drawings.

[0032] FIG. 1 shows a musical instrument 100. The instrument 100 is an electric guitar in the embodiment shown, but aspects of the disclosure are applicable to other instruments as well. For example, the instrument 100 could alternatively comprise an acoustic guitar, a cello, a violin, or some other musical instrument.

[0033] The example instrument 100 comprises a body portion 101, a neck portion 102, metal strings 103, an optical pickup array 104, and inductive coil to digital system. One end of the neck 102 is connected to the body portion 101 and an opposite end of the neck 102 has a headstock portion 107.

[0034] In FIG. 1, the fret area of the neck 102 of an electric guitar or bass consists of metal fret bars, across which some number of metal strings 103 pass over at a near 90-degree angle. In conventional analog instruments, the player presses a finger down behind the metal fret, which shortens the effective length of the string, thus increasing its frequency when the string is then plucked. As shown in FIG. 1, the neck of the instrument has a slight forward angle to it to avoid “fret buzz”. Fret buzz occurs when this forward angle is insufficient for the string to clear subsequent frets once a fret position has been selected. The strings rotate around when picked, and it can be seen that there is a certain amount of clearance needed above each fret so that the string will not contact undesirable fret positions. So, by definition, electric guitars and basses have strings that proceed down the fret area at a slight angle,

[0035] FIG. 2A and 2B shows the neck of a guitar including the fretboard and strings 210 and 220, FIG. 2A without the strings pressed down and FIG. 2B showing at least one string being pressed down by a finger. The string has a small amount of downward movement along its length when a string is pressed down behind a fret. The amount of this movement depends on which fret position is being pressed down, This downward movement increases progressively as the finger is moved down the neck area from one position to the next.

[0036] FIG. 3 shows a guitar 300 and that each metal string of the instrument passes over an inductive coil (the resonant coils 301 in the Figure) and an optical array 302. A conventional guitar pickup also consists of an inductive coil, but in a conventional pickup, a voltage is generated by the string moving across the magnetic field, as in the action of an electrical generator. A conventional guitar pickup is unsuited for picking up small vertical movements. In contrast, the inductive method used consists of a tuned circuit.

[0037] FIG. 4 shows a block diagram of an example system 400. The example system comprises a microprocessor 401, an optical string pick detector system 402 (also discussed and illustrated as optical pickup array 104), a Bluetooth wireless output device 403, an audio sound generator 404, a USB and MIDI interface 405, a inductance-to-digital converter (LDC) Processor 406, and inductive coils 407 (also discussed and illustrated as coils 301). FIG. 3 depicts an example location for the inductive coils 407 at 301.

[0038] In some examples, there is an inductive coil for each string of the musical instrument. In some examples, there are multiple inductive coils for each string of the musical instrument.

[0039] FIG. 5A-5C shows the deflection of a string based on different fingering positions on a fretboard. In an example, FIG. 5A shows a default position of a string with no corresponding fingering position 510. In an example, FIG. 5B shows a first string deflection at a first fingering position 520. In an example, FIG. 5C shows a second string deflection at a second fingering position 530.

[0040] FIG. 6 shows an example inductive circuit 600 comprising a conductive target 610, an inductive pickup 620, and a distance 630 between the two. The conductive target 610 includes an eddy current passing through a resistance and an inductor. The inductive pickup 620 includes an inductor and provides an AC signal source corresponding to the eddy current of the conductive target.

[0041] FIG. 7 shows an example circuit block diagram 700 for an LDC. In an example the input AC signal can be the AC signal source from FIG. 6. The LDC includes resonant circuit drivers, multiplexors, an internal oscillator, and an I2C interface for converting an analogue signal to a digital representation of the analogue signal frequency.

[0042] FIG. 8 shows an example circuit block diagram 800 for an LDC. In an example the input AC signal can be the AC signal source from FIG. 6. The LDC includes resonant circuit drivers, multiplexors, an internal oscillator, and an I2C interface for converting an analogue signal to a digital representation of the analogue signal frequency.

[0043] FIG. 9 shows an example method for creating digital note information 900. As shown, detecting deflection of a string at a first location when a user of the stringed instrument presses on the string in a second location remote from the first location occurs at operation 902. In response to detecting deflection of the string, producing a measurement of the detected deflection occurs at operation 904. In response to producing the measurement, correlating the measurement to a note to produce at least a portion of a digital output at operation 906.

Inductive Sensing of String Position

[0044] The fret area of an electric guitar or bass consists of metal fret bars, across which some number of metal strings pass over at a near 90-degree angle. In conventional analog instruments, the player presses a finger down behind the metal fret, which shortens the effective length of the string, thus increasing its frequency when the string is then plucked. As shown in FIG. 1, the neck of the instrument has a slight forward angle to it to avoid “fret buzz”. Fret buzz occurs when this forward angle is insufficient for the string to clear subsequent frets once a fret position has been selected. The strings rotate around when picked, and it can be seen that there is a certain amount of clearance needed above each fret so that the string will not contact undesirable fret positions. So, by definition, electric guitars and basses have strings that proceed down the fret area at a slight angle.

[0045] Because of this angle, the string has a small amount of downward movement along its length when a string is pressed down behind a fret. The amount of this movement depends on which fret position is being pressed down. This downward movement increases progressively as the finger is moved down the neck area from one position to the next (FIG. 2).

[0046] In some examples, if the amount of this movement could be accurately measured, it can be seen that it is possible to calculate what fret position has been pressed. This method would then serve to provide a no-latency method of determining what the intended pitch will be once the string is plucked. Since the position is known prior to plucking the string, the digital note code can be produced immediately upon release of the string, thus eliminating the sources of latency in prior methods. The difficulty involves devising a method to measure sub-millimeter movements of the metal string accurately. A mechanism capable of such sub-millimeter measurements is called an inductance-to-digital converter, or LDC. An LDC is essentially an inductive coil that is capable of detecting changes in distance of a metallic object located near the LDC. In an example, one such device is a multi-channel 28-bit inductance to digital converter for inductive sensing from Texas Instruments, such as LDC 1612 or LDC1614. In other examples, other LDC circuits can be used.

[0047] In an example, the amount of resolution in these devices is sufficient to measure the slight movement of a metal string when pressed down on in the fret area of a guitar or bass instrument that has metal strings. This is shown in FIG. 5. The prototype uses one inductive coil under each string. More or less coils might also be used depending upon resolution and measurement range. Thus, the problem of predetermining the fretted position that has been pressed down by a player can be solved in a novel way that does not require the custom manufacture of the neck of a fretted instrument.

[0048] As illustrated in FIGS. 5A-5C, different figuring positions produce a different downward deflection of the string. For example, FIG. 5A illustrates a default position of a particular string (no deflection from a user figuring a note on the fret board). Next, FIG. 5B illustrates a first deflection associated with a first figuring position along the fret board. Finally, FIG. 5C illustrates a second deflection associated with a second figuring position along the fret hoard. LDCs positioned properly under each string allows for measurement of the different deflection distances, which can then be correlated to different notes (or at least figuring positions along the fretboard).

Calibration Method

[0049] Because there can be a wide variation in the angle of the strings from one guitar or bass to another, it is desirable to have a calibration method so that a retrofit can be done on existing instruments. in an example, a calibration method can be used to account for these differences.

[0050] In an example, one method that can be used with the an inductive sensing method is that during initial setup, a player can fret specific positions, and the system will then “learn” and store the appropriate values in internal memory. String deflections associated with each learning position will be stored and associated with various notes or cords (multiple strings) to adjust for individual instrument variations.

Correlation With String Plucking

[0051] Guitars and basses produce notes through a combination of a fret selection with one hand, and a string pluck with the other. In an example, a digital system uses the correlation of these two actions. In the MIDI digital music standard, the velocity (volume) of the note needs to be transmitted at the same time as the pitch information. This can be a source of latency in a digital system because the amplitude of the vibrating string is not available immediately, but instead takes some time to analyze using typical technologies. Since a digital system does not require the string to produce a sound or be tuned, it can be advantageous to determine the volume of the string while also muting the string. Accordingly a system has been designed that measures the displacement of the string prior to the plucking of it. In an example, this system involves an optical pickup array, such as optical pickup array 104, detecting and measuring string defection. The volume of the note will be proportional to the amount of stretching that is done prior to its release. in the system described, an optical method is employed to achieve the goal of volume and pluck detection. The optical pickup array 104, can include a series of LEDs is positioned over the strings in such a way that the shadow of the strings falls on an array of photoreceptors. The optical pickup array 302 of FIG. 3 shows that the LEDs are mounted under a shield that protects stray light from affecting the photoreceptors, and preferably use infrared transmission to avoid ambient lighting issues. When the string is stretched in either direction during a pick event, the shadow of the string will move across the surfaces of the photodetector array that is shown in FIG. 3. In some examples, the LEDs are mounted adjacent to the photoreceptors, and instead of sensing a shadow the photoreceptors are sensing the peak reflected light from the strings.

[0052] In some examples, the analog signal that is produced can be read through an A/D converter in a microprocessor. Software that runs on this microprocessor can then execute an algorithm that can determine when the shadow (or peak reflection) of the string has reversed direction. At that point, the distance that the string has traversed from its rest position is used to generate a velocity code along with the pitch code.

[0053] As previously described, the pitch detection system can use an up and down movement of the string to detect a pitch selection on the fretboard. However, a signal will be output from the magnetic coils when a string is moved from side to side, as happens during string picking. In an example, software can be used to separate the pitch selection event from the picking event, as they often occur at different times, but there are activities such as “string bend” that create some challenges for the analysis software. If a pick is not perfectly perpendicular to the fret board the pick can also create slight upward and downward movements of the string, obscuring the information about string height used to determine the fretted position.

[0054] In an example, output from both the pick sensors and the pitch sensor can be examined and the analysis software can more readily distinguish the picking and fretting events. The pick sensor array can also see the shadow (or reflection) of the string being enlarged as the string is pressed down. This assists in the matter of detecting string bending after a note is plucked, thus providing an important expression parameter that would be difficult to detect using either system alone.

Description of an Example Complete System

[0055] As shown in the example of FIG. 3, each metal string of the instrument passes over an inductive coil (the resonant coils in the Figure), coils 301. A conventional guitar pickup also consists of an inductive coil, but in a conventional pickup, a voltage is generated by the string moving across the magnetic field, as in the action of an electrical generator. A conventional guitar pickup is unsuited for picking up small vertical movements. In contrast, the inductive method used consists of a tuned circuit, such as the circuits illustrated in FIGS. 7-9.

[0056] A block diagram of an example system is shown in FIG. 4, The effects of the very small up and down movement of conductive material (guitar string) are processed by a dedicated integrated circuit and digital information regarding its position is output to a microprocessor. The software running on this microprocessor analyzes the data coming from the inductive sensors and correlates this with the string plucking information. When the string is released, a calculated MIDI note code that includes volume and pitch information is output via a MIDI or USB port. Wireless operation is possible through the use of a Bluetooth transmitter. The microprocessor also manages this transmitter and can cause it to output BLE MIDI in a format that has now been standardized so that the instrument can be directly used with software programs used to edit and produce music.

[0057] An example internal method of generating sound can he included in the system. In this case, the digital information can be used to create notes with a wide variety of sounds. An external system is not required to create the sounds when this is included. The advantage of the internal system is that the very low latency aspect of the system can be used to capture a wider range and type of expression information. The combination of the pitch, pick, and sound generating system enables the capture of accurate expression information. In addition, it provides the ability to capture new forms of musical expression that are not at all possible with higher-latency digital music systems.

[0058] in an example, the parameters of the sound system can be controlled via the wireless interface using software running on external devices. Firmware updates to change or add features may also be done through this interface.