Hammer velocity measurement system

Abstract

A system 100, for determining the velocity of a hammer 120 of a keyboard instrument, with a light transceiver 140 and processing circuitry 160. The light transceiver 140 being configured to transmit a light signal to a hammer 120 to measure a hammer velocity, receive a reflected light signal from the hammer 120 indicative of the velocity of the hammer 120 and send an electrical signal to the processing circuitry 160, where the electrical signal is based on the reflected light signal from the hammer 120. The processing circuitry 160 being configured to receive and process the electrical signal so that a time interval between the electrical signal passing through a first trigger point and a second trigger point and the velocity of the hammer 120 can be determined.

Claims

1. A method for determining a velocity of a hammer of a keyboard instrument, the method comprising: transmitting a light signal to a hammer; receiving a reflected light signal from the hammer indicative of a position of the hammer as the hammer moves between a rest position and a strike position; generating an electrical signal based on the reflected light signal received from the hammer; determining a time interval between the electrical signal passing through a first trigger point representative of a first hammer position and a second trigger point representative of a second hammer position; and determining a velocity of the hammer based on the time interval, wherein i) the first hammer position corresponds to a first hammer height above the rest position, or ii) the second hammer position corresponds to a second hammer height below the strike position, the second hammer height being in close proximity to the strike position.

2. The method of claim 1, wherein processing circuitry is configured to: receive and process the electrical signal; determine the time interval between the electrical signal passing through the first trigger point and the second trigger point; and determine the velocity of the hammer based on the time interval.

3. The method of claim 2, wherein the processing circuitry is configured to: store information related to a third trigger point; and determine a time at which the electrical signal passes through the third trigger point, wherein: the third trigger point is representative of a third hammer position at a third hammer height, and the third hammer height corresponds to a time at which a damper of the keyboard instrument is no longer in contact with a string associated with the hammer.

4. The method of claim 2, wherein a light transceiver is configured to transmit the light signal and receive the reflected light signal.

5. The method of claim 4, wherein the light transceiver and the processing circuitry together form a hammer module, wherein the keyboard instrument comprises several hammer modules arranged to form a group module, wherein each hammer module in the group module is physically interconnected to an adjacent hammer module.

6. The method of claim 5, wherein the group module is mounted on a printed circuit board, and the printed circuit board is configured to magnetically couple to a corresponding group of hammers.

7. The method of claim 6, wherein the corresponding group of hammers comprises a saddle magnetically attractive to the printed circuit board and configured to magnetically couple thereto.

8. The method of claim 7, wherein the saddle includes a pair of alignment members configured to engage with a corresponding pair of cut-outs on the printed circuit board when the printed circuit board is magnetically coupled to the saddle.

9. The method of claim 8, wherein the cut-outs and the alignment members are positioned such that a longitudinal axis of the light transceiver of each hammer module is aligned with a hammer axis of a corresponding hammer of the group when the alignment members are engaged with the cut-outs.

10. The method of claim 9, wherein the longitudinal axis of each light transceiver runs between a center of a light source and a center of a photo transistor to minimize cross-talk between neighboring hammer modules.

11. The method of claim 8, wherein the alignment members comprise heads of fasteners that affix the saddle to flanges of the group of hammers.

12. The method of claim 5, wherein light transceivers of adjacent hammer modules are configured to be positioned at different relative points along lengths of adjacent hammers corresponding to the adjacent hammer modules.

13. The method of claim 1, wherein the first hammer position and the second hammer position are separated by a distance of 3-7 mm.

14. The method of claim 13, wherein the distance between the first hammer position and the second hammer position is chosen such that a difference between a velocity of the hammer at the first hammer position and a velocity of the hammer at the second hammer position is minimized.

15. The method of claim 14, wherein the second hammer height is 0.1-1.0 mm below the strike position in which the hammer makes contact with a string associated with the hammer.

16. The method of claim 1, wherein the second hammer height is 0.1-1.0 mm below the strike position.

17. The method of claim 1, further comprising: setting the hammer to the first hammer height; storing the first trigger point on a first sample-and-hold device; setting the hammer to the second hammer height; and storing the second trigger point on a second sample-and-hold device.

18. The method of claim 17, wherein the first trigger point and the second trigger point are voltages supplied by a light transceiver that transmits the light signal and receives the reflected light signal.

19. The method of claim 17, further comprising: setting the hammer to a third hammer height; and storing a third trigger point on a third sample-and-hold device, wherein the third hammer height corresponds to a time at which a damper of the keyboard instrument is no longer in contact with a string associated with the hammer.

20. The method of claim 1, wherein the light signal is a visible light signal or an infra-red light signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram that shows a system for determining the velocity of a hammer of a keyboard instrument using two reference hammer heights.

(3) FIG. 2 is a schematic circuit diagram showing the system of FIG. 1.

(4) FIG. 3 is a schematic diagram that shows some of the circuitry of a group module.

(5) FIG. 4 is a perspective view of a magnetic attachment between a group module of FIG. 3 and a corresponding group of hammers of a keyboard instrument.

(6) FIG. 5 depicts a side view that shows the system of FIG. 1 installed in a keyboard instrument in one embodiment.

(7) FIG. 6 is a schematic diagram that shows the system of FIG. 1 with a third reference hammer height.

(8) FIG. 7 is a schematic diagram that shows a calibration arrangement 400 for the system of FIG. 1.

(9) FIG. 8 is a flowchart that shows a method of calibration using the calibration arrangement of FIG. 7.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(10) FIG. 1 shows a system 100 for determining a velocity of a hammer 120 of a keyboard instrument using two reference hammer heights H.sub.1 and H.sub.2. The system 100 has a light transceiver 140 and processing circuitry 160 and is attached to a keyboard instrument comprising a hammer 120. As the hammer 120 moves from a rest position, R.sub.p, (where the hammer is inactive) to a strike position S.sub.p (where the hammer strikes a string of the keyboard instrument) the hammer head 122 of the hammer 120 moves through a first hammer height, H.sub.1, and a second hammer height, H.sub.2. Meanwhile, the light transceiver 140 transmits a light signal to a hammer shank 124 of the hammer 120 to measure a hammer position.

(11) The light transceiver 140 receives a reflected light signal from the hammer shank 124 indicative of the position of the hammer 120. The light transceiver 140 sends an electrical signal 170, based on the reflected light signal from the hammer shank 124, to the processing circuitry 160. The processing circuitry 160 receives and processes the electrical signal 170 so that a time interval between the electrical signal 170 passing through a first trigger point representative of a first hammer position and a second trigger point representative of a second hammer position and the velocity of the hammer 120 can be determined. The electrical signal 170 is an analogue signal, although alternatively it could be an analogue current signal or digital signal.

(12) The light transceiver is made up of a light source 142 and a phototransistor 144. The light signal sent by the light source 142 of the light transceiver 140 is preferably a visible light signal or an infra-red light signal and hence the light source 142 may be a visible light source or an infra-red light source. The signal could be any other suitable electromagnetic signal.

(13) Using the velocity of the hammers of a keyboard instrument to record how the keyboard instrument was played, later gives a more accurate and precise reproduction when compared to using the motion of the keys of the keyboard instrument. This is because the relationship between the keys and the hammer is not straightforward and is in fact highly complex. Using the velocity of the keys of the keyboard instrument results in recordings that are very unmusical and do not accurately represent the original piece played on the keyboard instrument.

(14) The first trigger point is a voltage and represents the first hammer position at hammer height H.sub.1. The second trigger point is also a voltage and represents the second hammer position at the second hammer height H.sub.2. The trigger points may alternatively be or represent analogue current values or digital values. As shown in FIG. 1, hammer heights H.sub.1 and H.sub.2 represent first and second positions of the hammer head 122. The hammer head 122 will always travel from a rest position R.sub.p to a strike position S.sub.p when used in a keyboard instrument such as a grand piano and so associating the position of the hammer head 122 with the first and second trigger points allows the system 100 to be used in different keyboard instruments even though the length of the hammer shank, the length of the hammer head and the position of light transceiver may change between instruments (i.e. the uncertainties surrounding the configuration of different pianos is avoided) and even between hammers on the same instrument.

(15) Using the position of the hammer head 122 in combination with the first and second trigger points, as opposed to using the position of the hammer shank 124, also means that the recorded musical performance is not limited to being played back on keyboard instruments of the same make or type as the one used in the original performance. In fact the performance can be played back on any variation of the keyboard instrument.

(16) The first and second trigger points which electrically represent the first and second hammer heights are able to be changed during a calibration process, and optionally may also be at pre-set values which are set during the production of system 100. By having calibrated trigger points, allowing the trigger points and the hammer heights to be made bespoke not only for each different keyboard instrument but also for each hammer of the keyboard instrument, there is increased precision of the calculated hammer velocity, as each hammer is treated individually, which also increases the precision and the accuracy of any recordings made. The first and second trigger points are stored by the processing circuitry 160.

(17) In an alternative embodiment, the first and second trigger points may be other electrical values, such as current values.

(18) The first and second hammer heights, H.sub.1 and H.sub.2, are preferably separated by a distance of 5 mm. Although H.sub.1 and H.sub.2 may be separated by one of: 4 to 6 mm or 3 to 7 mm. The second hammer height, H.sub.2, is preferably 0.5 mm below the strike position, S.sub.p, of the hammer 120. Although, the second hammer height, H.sub.2, could be positioned at any point that is between 1 mm and 0.1 mm below the strike position, S.sub.p, of the hammer 120. An advantage of positioning the hammer heights, H.sub.1 and H.sub.2, so close to the strike position, S.sub.p, of the hammer 120 is that the hammer is at a terminal velocity and so the calculation required to determine the velocity from the time interval between the hammer head 122 passing through H.sub.1 and then H.sub.2 is less complex and more accurate than if the hammer heights were positioned in such a way so that the velocity of the hammer 120 was appreciably different at H.sub.1 compared with at H.sub.2. Positioning the hammer heights, H.sub.1 and H.sub.2, close together minimises the potential for differences in velocity to arise. Positioning hammer height that a distance of 0.5 mm below the string height helps to ensure the strike of the hammer does not interfere with the time measurement of the interval between the hammer passing between the first and second hammer positions represented by H.sub.1 and H.sub.2 respectively.

(19) A further advantage of using trigger points associated with different heights of the hammer 120 together with the system 100 is that the procedure is less invasive than those known in the art and allows the piano to retain its integrity by being functional even if the system 100 were to be removed.

(20) Using trigger points in combination with system 100 as opposed to fitting hammer flags to each hammer and using an optical sensor eliminates the need to remove each hammer from the keyboard instrument in order to machine a slit and a hole in each hammer in order to fit the flag. To re-fit the hammers to the keyboard instrument, after an addition of a flag, is a demanding task and aligning the hammers correctly is time consuming and tricky which may result in the hammers not being aligned properly and the keyboard instrument not playing in the correct way.

(21) An advantage of sending and receiving a light signal from the hammer shank 124 of the hammer 120 as opposed to the hammer head 122 of the hammer 120 is that the light transceiver 140 does not interfere with the movement and strike of the hammer on the string of the keyboard instrument whilst also determining an accurate hammer velocity for the hammer 120.

(22) FIG. 2 is a schematic circuit diagram showing the system 100 of FIG. 1. The processing circuitry 160 receives the electrical signal 170. Processing circuitry 160 includes first and second sample-and-hold devices 164a and 164b, first and second comparators 166a and 166b, a logic block 168 and a shift register 169A.

(23) The first sample-and-hold device 164a stores the voltage of the first trigger point. The second sample-and-hold device 164b stores the voltage of the second trigger point. The first and second comparators 166a and 166b are coupled to the first and second sample-and-hold devices 164a and 164b, respectively. Each comparator 166a and 166b receives the electrical signal 170 and compares the voltage of the received electrical signal 170 with the corresponding stored voltage of the corresponding sample-and-hold device 164a and 164b. The comparators 166 each send a signal to the logic block 168 which describes the status of the voltage of the electrical signal 170 in relation to the first and second trigger points. Logic block 168 generates a logic signal 770 calculated from the electrical signal 170 received from the light transceiver 140 and the first and second trigger points.

(24) The logic signal 770, shown in more detail in the call-out of FIG. 2, is representative of the time interval between the electrical signal 170 passing through the first trigger point and the second trigger point. If the logic block 168 receives a signal from the first comparator 166a, that signifies the voltage of the electrical signal 170 is the same as or greater than the first trigger point voltage, e.g. the comparator 166a sends a 1 signal, the logic block 168 produces a first pulse 770a where the leading edge of the first pulse 770a denotes the moment electrical signal 170 passes through the first trigger point and hence the moment the hammer 120 passes through H.sub.1. If the logic block 168 receives a signal from the second comparator 166b that the voltage of the electrical signal 170 is the same as or greater than the second trigger point voltage the logic block 168 produces a second pulse 770b wherein the leading edge denotes the moment electrical signal 170 passes through the second trigger point and hence, the moment the hammer 120 passes through H.sub.2. Thus, the logic signal 770 has a first pulse 770a representative of when the electrical signal 170 passes through the first trigger point, and a second pulse 770b representative of when the electrical signal 170 passes through the second trigger point.

(25) The first pulse 770a is shorter than the second pulse 770b and needs to be short enough so that the first pulse 770a can transition from logic 0 to logic 1 and back to logic 0 before the second pulse is produced. The second pulse 770b is long relative to the first pulse because the second pulse 770b is sustained by the logic block 168 until the electrical signal 170 passes back through the second trigger point and reaches the first trigger point again, as the hammer 120 moves downward after a strike. In other words, the falling edge of the second pulse 770b denotes the time at which the hammer 120 passes through H.sub.1 for the second time after the hammer 120 has impacted the string, measured by comparator 166b. An advantage of using two pulses on one logic signal is that there is one signal which contains all of the information, and as a result the shift register 169A only has to process one signal.

(26) Occasionally, once a hammer has hit a corresponding string the hammer may oscillate near the string. In prior art systems this may cause additional information to be generated, sometimes resulting in the piano recorder recording non-existent or extraneous strikes. To overcome the fluctuations of the hammer causing the piano recorder to record non-existent hammer strikes, logic block 168 ensures that once the leading edge of second pulse 770b has first occurred the second pulse 770b remains at logic high until the hammer passes back through hammer height H.sub.1, even if the hammer 120 oscillates further through H.sub.2. Any fluctuations of the hammer through hammer height H.sub.2 are ignored as extraneous strikes and filtered out, which results in a more accurate and useful file of data being stored in the central processing unit 180, and non-existent, or extraneous, hammer strikes are not recorded and hence replayed later. Also, with a clean leading edge of the second pulse, the central processing unit 180 is able to calculate hammer velocities much more quickly and efficiently (see the following paragraphs explaining that the hammer velocity is calculated from the time between the rising edge of the first pulse 770a of the logic signal 770, and the rising edge of the second pulse 770b of the logic signal 770). If the fluctuations of the hammer through H.sub.2 are recorded, as in existing systems, low velocity signals or extraneous strikes that do not represent a hammer strike would be present in the recording which may negatively affect the piano performance, especially when true notes are required from the same hammer shortly after an extraneous strike.

(27) The logic signal 770 is sent to the shift register 169A. The shift register 169A outputs a signal representative of the logic signal 770.

(28) The light transceiver 140 and the processing circuitry 160 together form a hammer module of the system 100. Several hammer modules of the system are arranged to form a group module. Each hammer module in a group module is physically interconnected to an adjacent hammer module in the group module.

(29) FIG. 3 is a schematic diagram showing some of the circuitry of a group module. The group module comprises five hammer modules and for simplicity only the logic blocks 168-1, 168-2, 168-3, 168-4 and 168-5 are shown of each hammer module. The shift registers 169A-1, 169A-2, 169A-3, 169A-4 and 169A-5 of adjacent hammer modules are arranged together to form a parallel-in serial-out shift register which is arranged to be clocked by signal line 775 and latched by signal line 175 from a central processing unit 180 to move the logic signal 770 for each hammer to the central processing unit 180.

(30) The latch signal on signal line 175 loads the values of the logic signals 770-1, 770-2, 770-3, 770-4 and 770-5 (parallel data) produced by the corresponding logic blocks 168-1, 168-2, 168-3, 168-4, and 168-5 into the corresponding shift registers 169A-1, 169A-2, 169A-3, 169A-4 and 169A-5 at a frequency of approximately 25.6 kHz. The value of each logic signal 770-1, 770-2, 770-3, 770-4 and 770-5 will be either a logic 0 or a 1. The shift registers 169A, in response to the clock signal on signal line 775, clock out each value that they hold in a leftward direction to the central processing unit 180 via downstream shift registers. The shift registers 169A are clocked at a frequency of 2.56 MHz.

(31) The central processing unit 180 populates a file of binary data for each hammer 120 that represents the logic signal 770. The central processing unit 180 is arranged to count the number of latch pulses between the leading edge of the first pulse 770a and the leading edge of the second pulse 770b for each hammer 120. The number of latch pulses represents the inverse hammer velocity (IHV). The central processing unit 180, determines the velocity of the hammer 120 by taking the reciprocal of the IHV. Alternatively, the central processing unit 180 may count the clock pulses of the shift registers instead of the latch pulses.

(32) Preferably, the shift register clock pulses are at 2.56 MHz however they may be in one of the following ranges 1 MHz to 4 MHz, 1.5 MHz to 3.5 MHz and 2 MHz to 3 MHz. The latch signal frequency will depend on the number of keys in the keyboard instrument, and needs to be lower than the clock frequency to allow the parallel-in serial-out shift register arrangement to transfer all the information to the CPU 180. For example, if there are 100 keys the latch signal 175 needs to be at least 100 times slower than the clock signal.

(33) The hammer modules 150 in FIG. 3 are in a group module comprising five hammer modules however, a group module optionally may comprise four or six hammer modules. The hammer modules are grouped in this way to match the conventional distribution of hammers in several groups in a keyboard instrument. The grouping of hammers, and thus modules, allows for the mechanical construction of the keyboard instrument and the easy installation of the system 100 into the keyboard instrument. The quantity of circuitry needed to couple each single module to the central processing unit 180 is reduced, as each group module of hammer modules 150 may use a single connection, thus decreasing the complexity of the system 100. Each group module is interconnectable with adjacent group modules to relay the latch, clock and data signals therethrough, ultimately from and to the CPU 180.

(34) FIG. 4 shows a perspective view of a magnetic attachment between a group of five hammers of a keyboard instrument and the group module 150 of FIG. 3. Each hammer 120 has a hammer flange 129. Each hammer flange 129 has a hole to receive a screw which acts to attach the hammer flange 129, and hence the hammer 120, to the piano. A saddle 200 is positioned between the group of hammers and the group module 150 which is mounted on a printed circuit board 190. The printed circuit board 190 has magnets that are magnetically coupleable to the saddle 200. The magnets may be neodymium magnets. The saddle 200 has two longitudinal raised parallel rails, 210 and 212, upon which the printed circuit board 190 magnetically attaches to and rests. The saddle 200 also has a pair of dowels at the end of the parallel rails, 210 and 212, which engage with corresponding cut-outs 192 on the printed circuit board 190 to help with alignment. Alternatively, screw heads may be used instead of dowels. The saddle 200 comprises either magnetic parts or is otherwise magnetically attractive to correspond to the magnets of the printed circuit board 190. Alternatively, the saddle 200 may comprise magnets or magnetic parts, and the printed circuit board 190 comprises magnetically attractive parts to correspond to the magnetic saddle 200.

(35) The saddle 200 is connected to the group of hammers using the screws of the first and the fifth hammer flanges of the group of hammers, whereby the first and the fifth hammers are located on either side of the group of hammers. The screws of the first and the fifth hammer flanges 129 are long enough to take into account the thickness of the saddle 200. Using the saddle 200 has the benefit of creating consistent attachment points for the printed circuit board 190 to a corresponding group of hammers, and also means the modules 150 are consistently positioned relative to modules associated with neighbouring groups of hammers. As the saddle 200 is attached re-using screws of the outer hammer flanges 129 associated with the outer hammers 120 of the group of hammers, no extra screws are needed to secure the saddle 200 to the hammer flanges 129. The use of magnets has the advantage of making the installation process easier, quicker and simpler. Furthermore, the need for specialised tools to attach the system 100 to the saddle 200 is eliminated. Additionally, as no additional screws are used to attach the printed circuit board 190 to the saddle 200 there is less potential for screws to be lost in the complex mechanisms of the keyboard instrument. A piano technician may also lift the printed circuit board temporarily out of the way and put it simply back on the dowels without the need for special tools or screws.

(36) Of course, on some keyboard instruments the group of hammers may comprise four or six hammers and corresponding groups of four or six modules 150 are provided. The screws of the two outer hammer flanges are used to secure the saddle 200. Optionally, the saddle 200 may be attached using the screws of any of the hammer flanges 129 associated with the group of hammers, depending on the saddle design.

(37) FIG. 4 also shows a hammer axis 126 of the hammer shank 124. The hammer axis 126 runs along the length of the hammer shank 124 between the pivot point and the hammer head 122. Each module of the group of modules, each light transceiver 140, has a longitudinal axis 128, shown in FIG. 4, running between the centre of the light source 142 and the centre of the photo transistor 144. The longitudinal axis 128 runs along the hammer axis 126 so that the longitudinal axis 128 and the hammer axis 126 align substantially with each other. This arrangement reduces any cross-talk between neighbouring modules on adjacent hammers. The cross-talk is also reduced due to the close proximity of the hammer shank 124 to the light transceiver 140, which causes the view of the photo transistor 144 of the light transceiver 140 to be blocked by the hammer shank 124 as the hammer is raised and so the phototransistor 144 is less likely to receive light from adjacent hammer shanks. The reduction of cross-talk means the electrical signal received by the photo transceiver 144 will be a more accurate indication of the position of the hammer 120 and the processing circuitry 160 will not receive an erroneous electrical signal which may cause timing to start or stop earlier or later than it should resulting in the velocity that is determined being inaccurate.

(38) Additionally or alternatively, neighbouring light transceivers on adjacent hammers may be coupled to different relative points on corresponding hammers. This arrangement reduces cross-talk because the light source 142 on a first hammer will not be in line with the photo transistor 144 on a second hammer, and so the photo transistor 144 of the second hammer is less likely to receive reflected light from the light source 142 of the first hammer because the light will be reflected from a point on the first hammer that is not in line with the photo transistor of the second hammer.

(39) FIG. 5 depicts a side view that shows the system 100 of FIG. 1 installed in a keyboard instrument according to an embodiment. FIG. 5 shows a downward force, represented by arrow 1000, hitting key 800. The movement of the key 800 downwards causes a damper lever cushion 740 to move upwards and exert a force on a damper lever 720. The damper lever 720 is raised up which in turn lifts a damper 700 so that a string 900 is free to vibrate. Simultaneously, the hammer 120 receives an upward force and pivots to move from a rest position towards a strike position on string 900. As the hammer 120 pivots the light transceiver 140 sends and receives a reflected light signal to and from the hammer shank 124. The saddle 200, as described, is positioned to magnetically attach the hammer flange 129 to the printed circuit board 190 upon which the system 100 is mounted.

(40) FIG. 6 is a schematic diagram that shows the system 100 of FIG. 1 with a third reference hammer height representative of a position of the damper 700 shown in FIG. 5. The hammer 120 passes through a third reference hammer height, H.sub.D, which represents the point at which the damper 700, associated with the hammer 120, is no longer in contact with a string 900 associated with the hammer 120. The processing circuitry 160 further comprises a damper shift register 169B. The damper shift register 169B outputs a signal representative of whether the damper 700 is in contact with the string 900. In more detail, the processing circuitry 160 receives and processes the electrical signal 170 from the light transceiver 140. A sample-and-hold device 164c stores the voltage of the third trigger point value, also referred to as a damper trigger point, that is representative of the hammer at a hammer position equal to the third hammer height, H.sub.D. A comparator 166c compares the electrical signal 170 to the damper trigger point value and sends a signal to the shift register 169B describing the status of the voltage of the electrical signal 170. If the voltage of the electrical signal 170 equals the damper trigger point the comparator 166c will send a 1 to the damper shift register 169B. The 1 signifies the time at which the damper associated with the hammer 120 has been lifted from the string of the keyboard instrument. A latch signal 175, at 25.6 kHz, will load the signal sent by the comparator onto the shift register 169B. The damper shift register 169B is coupled to adjacent damper shift registers of neighbouring hammer modules, in the same way as the shift registers 169A are coupled as shown in FIG. 3. The latch signal 175 and the clock signal 775 will also be applied to the damper shift registers to load and clock information about the position of the damper of each respective hammer. The damper shift registers will clock out the data they hold to the central processing unit 180 at a frequency of 2.56 MHz.

(41) The central processing unit 180 uses the data from the damper shift register 169B to determine the time at which a damper of each key of the keyboard instrument was lifted from each string associated with each key, respectively.

(42) Using both shift register 169A and damper shift register 169B the central processing unit 180 can compute the velocity of the hammers, the time of strike of the hammers and the duration of the note played. The shift registers 169A and 169B of each hammer combine to form parallel-in serial-out shift registers of 88 bits for 88 keys and hammers typically found on a grand piano.

(43) Using a third hammer position associated with a third reference hammer height and a damper trigger point provides a reliable way of identifying when a key of the keyboard instrument has been played or released without having to implement an additional system and install the additional system under the keyboard of the instrument. Furthermore, having the ability to detect when the damper has been lifted from a string associated with the hammer allows for the fine details and artistic flair of the performer to be accurately captured, for example if a performer allows the damper to rest back on the string for a brief moment before exerting force to raise the hammer again, the short moment in time that the damper rests on the string will be captured precisely. In more detail, the installation of system 100 will not result in the keys of the keyboard instrument needing to be machined by removing wood from the underside of the keys to make room for a separate key-detect system. Since wood is not being removed from the keyboard instrument, balancing weights do not have to be added to each key to compensate for the loss of wood, this makes the installation process more efficient and easier

(44) FIG. 7 is a schematic diagram that shows a calibration arrangement 400 for the system of FIG. 1. The system 100 is installed on a keyboard instrument, as in FIG. 5, and the calibration arrangement 400 is used to calibrate the system 100. The calibration arrangement comprises a calibration module 500 and a thickness gauge 410. The calibration module 500 is coupled to the processing circuitry 160 of at least one hammer 120 of the keyboard instrument.

(45) The hammer 120 is set to a first hammer height, H.sub.1, using a thickness gauge 410. In this instance, the thickness gauge 410 is preferably 5.5 mm thick. A first button 520a is activated on the calibration module 500. The calibration module 500 sends an instructing signal to the processing circuitry 160 to store the voltage supplied by the light transceiver 140 as the first trigger point.

(46) The hammer 120 can be set, using a thickness gauge 410, at a second hammer height H.sub.2, preferably the thickness gauge 410 is 0.5 mm thick. A second button 520b of the calibration module 500 can be activated so that the second voltage received by the processing circuitry 160 can be stored by the processing circuitry 160 as the second trigger point.

(47) In a modified embodiment, shown in FIG. 7, the hammer 120 can be set at a third hammer height, H.sub.D, using thickness gauge 410. The third hammer height, H.sub.D, is representative of the height at which the damper is lifted from the string. Conventionally, the height at which the damper is lifted from the string is always set at 50% of the distance between the rest position, Rp, of the hammer and the smile strike position, Sp, of the hammer. The distance between the rest and strike positions of the hammer 120 is usually 47 mm, thus, the height at which the damper is lifted from the string is 23.5 mm below the string. Consequently, a thickness gauge 410 that is 23.5 mm thick is used to calibrate the third hammer height, H.sub.D. At this point, a third button, 520c, of the calibration module 500 can be activated so that the voltage supplied by the light transceiver 140 is stored by the processing circuitry 160 as the third trigger point.

(48) This procedure is repeated for the remaining hammers of the keyboard instrument.

(49) The calibration process accounts for the reflective properties of the hammer shank 124 of each hammer and so no special reflective paints or labels are necessary, making the process more cost effective and the system 100 easier to install.

(50) Alternatively, the keyframe of the keyboard instrument may be removed from the keyboard instrument and set on a level surface together with a string height assembly jig, which puts an adjustable bar at precisely the height of the strings relative to the key-bed. The hammer assembly, the system 100 and the string height assembly jig may be manoeuvred so that the hammers can be manually raised to touch the artificial string line. The thickness gauge 410 may be inserted in between the hammer 120 and the artificial string line. In much the same way as described above, the hammer 120 may be set to a first hammer height, H.sub.1, using the thickness gauge 410. The first button 520a of the calibration module 500 connected to the processing circuitry 160 may then be pressed so that the voltage received by the processing circuitry 160 is stored as the first trigger point. This process can be repeated for each key of the keyboard instrument, and also for the second and third trigger points associated with second and third hammer positions that are represented by hammer heights H.sub.2 and H.sub.D, respectively.

(51) FIG. 7 also shows calibration circuitry. The calibration module 500 is coupled to the processing circuitry 160. The calibration buttons, 520a-c, are each connected to corresponding sample-and-hold devices, 164a-c. When the hammer 120 is set to hammer height H.sub.1, as shown in FIG. 7, the phototransistor 144 sends an electrical signal 170 representative of H.sub.1 to the sample-and-hold devices 164. Calibration button 520a is pressed which sends an output signal to sample-and-hold device 164a instructing sample-and-hold device 164a to store the voltage of the received electrical signal 170 as a first trigger point.

(52) When the hammer is set to hammer height H.sub.2 the phototransistor 144 sends an electrical signal 170 representative of H.sub.2 to the sample-and-hold devices 164. Calibration button 520b is pressed which sends an output signal to sample-and-hold device 164b instructing sample-and-hold device 164b to store the voltage of the received electrical signal 170 as a second trigger point.

(53) A third trigger point, the damper trigger point, representative of when the damper is lifted from the string, is stored by setting the hammer to height H.sub.D and pressing calibration button 520c so that the voltage of the electrical signal supplied to the processing circuitry 160 is stored as the damper trigger point.

(54) As shown in FIG. 7, it is the hammer head 122 of hammer 120 that comes into contact with the thickness gauge 410 to calibrate the trigger point values. Using the hammer head 122 to calibrate has the advantage of creating trigger point values that are less dependent on variables that may change between different keyboard instruments. Although, for example, the length of the hammer shank 124 and the position of the light transceiver 140 relative to the hammer shank 124 may change, the point of the hammer 120 (i.e. the hammer head 122) which reaches the hammer heights associated with the trigger points is consistent in all keyboard instruments. Thus, using the hammer head 122 position for calibration provides a reliable and accurate benchmark upon which to base associated trigger points. In this way, the velocity determined is an accurate representation of the original velocity of the hammer head 122 when the music was originally performed.

(55) FIG. 8 is a flowchart that shows a possible calibration method using the calibration arrangement 400 with a string-height assembly jig. At step 420, the keyframe of the musical piano is removed and set on a level surface along with a string height assembly jig which causes an adjustable bar to be set at precisely the height of the strings relative to the key-bed. The hammer action assembly with system 100 installed and the string height assembly jig are manoeuvred so the hammer can be manually raised to touch the adjustable bar (artificial string line).

(56) At step 422, the calibration module 500 is connected to the printed circuit board associated with a group of modules 150.

(57) At step 424, the thickness gauge 410 of 23.5 mm thickness is inserted below the artificial string. A hammer 120 associated with a module of the group of modules 150 is manually raised so that the hammer head 122 touches the thickness gauge 410.

(58) At step 426, the calibration button 520a is pressed and the voltage of signal 170 from the light transceiver 140 is stored in sample-and-hold device 164c.

(59) At step 428, the procedure of steps 424 and 426 is repeated for the remaining hammers associated with the group of modules 150.

(60) At step 430, a thickness gauge 410 of thickness 5.5 mm is inserted below the artificial string and a hammer 120 associated with the group of modules 150 is manually raised so that the hammer head 122 of the hammer 120 touches the thickness gauge 410.

(61) At step 432, calibration button 520a is pressed to store the voltage of the electrical signal 170 as the first trigger point.

(62) At step 434, the process of steps 430 and 432 are repeated for the remaining hammers associated with the group of modules 150.

(63) At step 436, a thickness gauge 410 of thickness 0.5 is inserted below the artificial string and a hammer 120 associated with the group of modules 150 is manually raised so that the hammer head 122 of hammer 120 touches the thickness gauge 410.

(64) At step 438, calibration button 520b is pressed to store the voltage of the electrical signal 170 as the second trigger point.

(65) At step 440, the process of steps 436 and 438 are repeated for each hammer 120 associated with the group of modules 150.

(66) At step 442, steps 424 to 440 are repeated for the remaining groups of modules of the keyboard instrument.

(67) At step 444, the key frame is fitted back into the keyboard instrument.

(68) When the first and second trigger points are being calibrated, the hammer head 122 is raised substantially above the third reference hammer height associated with the damper trigger point. This results in the comparator 166c associated with the damper trigger point signifying which hammer is currently being raised.

(69) The combined transmission/reception gain of the chosen devices exhibits very well-controlled thermal sensitivity, changing by less than 0.5% over a temperature range from 10 to 50 C. Any small effect that this may have on the measured IHV would tend to cancel out because the same opto device is used for both IHV trigger points.

(70) The system 100 and the calibration arrangement 400 and the calibration method allow the total original musical performance to be digitally captured by recording the following keyboard parameters: The detection of which key is pressed sufficiently to lift the damper off the string. The identity and velocity measurement of the hammer before it strikes the string. The instant in time the hammer strikes the string, defining the note-on event. The instant in time when the pianist releases the key; the damper is no longer lifted, so the sound is quenched, defining the note-off event.

(71) Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.