US3553337A

US3553337A - Circuit arrangement for imitating the touch of musical instruments with percussion

Info

Publication number: US3553337A
Application number: US719832A
Authority: US
Inventors: Popko Reinder Dijksterhuis; Casper Antonius Henric Mulkens
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1967-04-08
Filing date: 1968-04-05
Publication date: 1971-01-05
Anticipated expiration: 1988-01-05
Also published as: BE713405A; NL150929B; ES352482A1; DE1622884A1; AT290269B; IE31863B1; NL6705025A; GB1162449A; DE1622884B2; CH485289A; SE353173B; JPS4814253B1; US3544695A; IE31863L; FR1562394A

Abstract

A circuit for controlling the amplitude of an audio oscillator in an electronic musical instrument in response to the intensity with which a key is depressed. A voltage produced by a coil in response to the movement of a magnet attached to the key charges and output capacitor through a resistor and a diode. A reverse bias of a predetermined level impressed on the diode insures that the time during which a charging voltage is impressed on the capacitor is approximately equal for all levels of voltage produced by the coil.

Description

United States Patent 11113,553,337

[7 2] Inventors Popko Reinder Dijksterhuis. deceased, [50] Field of Search 84/ l .01 late of Bilthoven, 1.13, 1.26, 1.27; 307/246, 256, 259 Casper Antonius l-lenricus Mulkens, Administrator, Eindhoven, Netherlands [5 6] References Clted [21] Appl. No. 719.832 UNITED STATES PATENTS 1 Filed P 1968 2,841,043 7/1958 Schreiber 84/1. 1 3

[ 1 Patented 5, 0 3,239,693 3/1966 Janning 307/259 [73] Assignee U. S. Philips Corporation 3,248,470 4/1966 Markowitz et al. 84/1. 13X New York, 3,336,484 8/1967 Ovshinsky 307/256X a corporation of Delaware. by mesne assignment Primary Examiner-Herman Karl Saalbach [32] Priority Apr. 8, 1967 Assistant Examiner-T. Vezeau [3 3] Netherlands AttorneyFrank R. Trifari [54] CIRCUIT ARRANGEMENT FOR IMITATING THE TOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION 5 Claims, 6 Drawing Figs.

[52] U.S. Cl 84/1.l3, 84/1.26 [51] Int. Cl GlOh 1/02 ABSTRACT: A circuit for controlling the amplitude of an audio oscillator in an electronic musical instrument in response to the intensity with which a key is depressed. A voltage produced .by a coil in response to the movement of a magnet attached to the key charges and output capacitor through a resistor and a diode. A reverse bias of a predetermined level impressed on the diode insures that the time during which a charging voltage is impressed on the capacitor is approximately equal for all levels of voltage produced by the coil.

PATENTED JAN 5 I97! SHEET 1 BF 2 INVENTOR. POPKO REINDER DlJKSTERHUlS,DEC-EASED, BY CASPER ANTONIUS HENRICUS MULKENS,ADM!NISTRATOR AGE I PATENTED JAN 5197! SHEET 2 BF 2 FEES INVENTOR. POPKO REINDER DIJKSTERHUIS, DECEASED, BY CASPER ANTONIUS HENRICUS MULKENS,ADMINISTRATOR AG NT produces a voltage having a value which depends upon the intensity of thetouch, which voltage then decreases again to zero. V

In such an instrument, it is desirable that the buildup time of the tone for various. intensities of touch should be as constant as possible or atleast should not exceed a given value with a soft touch, sincethe character of theinstrument is then lost.

For example, with a'pia no, the builduptime never exceeds milliseconds; The term buildup time is to be understood'to mean the time in which the tonerises from zero to its-maximum amplitude. lri the known instrument, this is the time in which the capacitor is charged by a current of a coil in which,

i when an associated key'is touched, an e.m.f. is produced by a magnetconnected to this key. v Since the-initial and final positions of this magnet are always the same, the flux variation db 2is constant and the voltage produced is in inverse proportion to the duration 1 of the touch and hence in direct proportion to the intensity of the touch. However, it is desirable for this buildup time to be constant or at least to vary to a smaller extent than the duration of the touch.

According tothe invention, this is achieved by biasing'the 'rectifying'element'so that only part of the touching pulse is Withthe sofiest touch, which is the touch producing sound vibrations which are just audible, the bias voltage has a considerably greater influence than with the strongest touch,

since the amplitude of the voltagepulses produced by the touch is proportional to the rate at which the magnetic field in the coil is varied, while the bias voltage remains constant.

.Thus, the part of the voltage pulse produced which ispassed by the rectifier has a duration equalto only part of the half period of this voltage pulse, whereas with'thestrongest touch substantially the whole voltage pulsev is passed and hence has a duration of substantially-a half period.

With a piano, for example, the ratio between the minimum intensity of touch, i.e. the intensity of touch with which the hammer just reaches the string, and the maximum intensity of touch is in practice approximately 1 100. This ratio cor- .responds to a ratio between the touching times of approximately l0 l and'between the amplitudes of the string of approximately l 10 so that the desired ratio between the capacitor voltages is also approximately 1 10.

In a preferred embodiment of a-musical instrument according to the invention, the bias voltage exceeds half the peak value of the voltage pulse produced with the softest touch. In this case, the ratio between the buildup times is at least 1.5

' times and with a triangular voltage.- pulse, which is usual in practice, even 2 times more favorable than without the application of a bias voltage.

It will be appreciated that this bias voltage can be produced in any known manner, while in certain cases the threshold voltage of the rectifying element may advantageously be used. Alternatively, the rectifying element may be biased by means of the series-combination of a direct voltage source and a resistance which is connected in parallel with the rectifying element, or the direct voltage may be connected in series with the whole charging circuit.

When according to a further embodiment a resistance is connected in the circuit in series with the rectifying element, it is achieved that with the softest touch, the capacitor is charged in a time t, which occupies a smaller part of the duration 1', of the smallest touching pulseyth'at is the time t of the duration 1, of the largest touching pulse with the strongest touch, so that the ratio between the buildup times of the tone corresponding to t, and t becomes even more favorable. The

resistance is then chosen to be high with respect to the resistance of the diode.

Thus, it is also achieved that the ratio between the capacitor to the invention, the rectifying element is connected in series with a member the resistance of which increases with increasing current in the starting-current range of the said rectifying element.

This is advantageous in those cases in which the resistance in the circuit is low with respect to the resistance of the diode and in which moreover the rectifying element is operative only in its starting-current range with a soft touch. The step described above ensures that the resistance in the circuit remains more constant so that the phase shift between the chargingcurrents of the capacitor-and the pulsatory voltage remains small.

As far as the ratio between the capacitor voltages, which had become unduly large owing to the application of the bias voltage, has not yet or not sufficiently been reduced to the correct value by the step described above, this may be effected in another embodiment ofa musical instrument according to the invention by connecting a biased overflow diode in parallel with the coil.

The invention will now be described with reference to the following FIGS. of which:

FIG. 1 tion;

touch;

FIG. 3 shows a circuit arrangement including a member the resistance of which increases with increasing current;

FIG. 4 shows in a graph the effect of this step;

, FIG. 5 shows a circuit arrangement including an overflow diode; and

FIG. 6 shows the voltage variation V of the coil as a function of the intensity of touch.

FIG. 1 illustrates that a magnet 2 coupled with a key 1 varies the magnetic field in the inductance L when the key is depressed. The voltage induced in the inductance L charges a capacitor C through a resistor R- and a diode D serving as rectifying element. The diode D is biased with a voltage E supplied by a battery B.

FIG, 2 illustrates the variation of the capacitor voltage as a function of time with two different intensities of touch. The soft touch is associated with the induced voltage E The half sine E has a duration 1' Without the application of a bias voltage, thecapacitor voltage would vary in accordance with the line V It thus appears that the buildup time t, slightly exceeds h 1 It is assumed that the resistance in the circuit is only low with respect to the impedance of the capacitor for this frequency. With a touch which is three times stronger than the softest touch and the associated voltage pulse of which is denoted by E the voltage across the capacitor becomes V, As is apparent from the FIG., the ratio between the times 1', and 7 is substantially equal to that between the times t, and t When according to the invention the diode D is biased with a voltage E which preferably exceeds half the peak value of E and in the case of the pulse in the form of a half sine shown 0.7 times this value, the duration r, of the voltage pulse IE is reduced to 1' and the duration 7 of the voltage pulse E, to 1 In case the voltage pulse is triangular, a bias voltage of 0.5 results in a reduction of the buildup time by 0.5. It will be appreciated that the reduction of these times is larger as the voltage pulse produced is smaller with respect to the bias voltage E. The buildup times t;, and t, of the voltages V,,' and V across the capacitor also decrease, bjut t3 to a larger extent than t,,, so that the ratio between the buildup times, which without the application of a bias voltage was approximately equal to 3 shows a circuit arrangement according to the inven- FIG. 2 shows the variation of thecapacitor voltage and'of Q the e.m.f. produced in the coil with different intensities of is now only 1.5 or smaller. However, due to this step, the ratio between V and V has become larger than 3, which may be undesirable. This disadvantage can be mitigated by connecting a resistor in series with therectifying element. At higher frequencies and hence with stronger touches, the phase'shift between the capacitor voltage and the voltage pulse induced in the coil will then increase, while with strong touches the capacitor voltage V will be low with respect to the voltages induced, so that the ratios between'these voltages more closely approximate the ratios between the intensities of touch. Moreover, with a stronger touch, the buildup time t of .the new. capacitor voltage V thus exceeds whilethe buildup ytime I, of the capacitor voltage V,," associated withthe soft touch hardly varies with a suitable proportioning of the resistor R and the capacitor C, so that the ratio between the bui]- I dup times t, and I is even further reduced.

If the peak value of the voltage E induced with the softest touch exceeds the bias voltage E by such a small amount that fect is compensated for by connecting in series with the diode a member X (cf. FIG. 3) the resistance of whichincreases with increasing current in the starting-current range of the diode D so that the overall resistanceof the circuit varies less strongly. Such a member may. comprise a resistorhaving a positive temperature coefficient, a tunnel diode of which the part having a vnegative resistance is .used, a. diode the current of which 4' remains constant in a wide voltage range, and so on. The result is shown by the dotted line in FIG. 4.

For the sake of clarity, F IGS. 2 and 4 show only the case in which the intensity of touch varies only by a factor 3', but it will be appreciated that what has been said as to a touch thrice stronger than the softest touch applies to an even greater extent to a touch intensity ratio of l l0.

The intensity of touch is here always correlated to the rate at which the magnet is pushed into the coil; the amplitude of the voltage pulse is then directly proportional thereto.

. As is apparent from FIGS. 2 and 4, the output voltage ratio exceeds 1 3.

This may be compensated for by providing an overflow diode biased with the voltage E, (cf. FIG. 5). The effect of this diode is shown in FIG. 6, in which the voltage V is plotted on the ordinate and the intensity of touch B on the abscissa. V, in-

dicates the variation of the voltage across the coil. This variation is linear. Due to the application of the bias voltage 8, the

capacitor voltage is reduced by thisval ueat. an ,inher ity of touch sothat at a ratio between the intensities, example, I

' Like inthe known instrument,"thecapacitorvoltageis'sup plied to a controlmember which"passes,tlie-oscillationscnly .when'the capacitor is in the chargedstate,

3, the. ratio between the: .c'apacit now become I': 7, as appears from ievariation to the capaciof which decreases withincreas ratio and hence the dynamic range rsfbrdtigh bac rect value, as shown by the curve Orv... A

The bias voltage of thezchargin'g ode D and the bias voltage'ofthe overflow rode by E The capacitor may also compris'e a s'ei ies-combination "of two capacitors-and a resistor;may.be onnected in parallel with one of them. Moreover,=the capacitor-maybe connected in parallel with a discharge circuit whichensures that the tone v willdecay correctly.

Iclaim: .T I l. A control circuit providinganoscillator in an electronic musical instrument-with am output voltage having an-amr plitude corresponding to theavelocitywithwhich movably .mounted key is depressed, comprising a magnet, a coil, means for providing relative motion between said .coil and said mag;

net in response to movement ofsaid key, whereby a voltage is Q induced in said coil corresponding to the velocity of said ltey i a capacitor, a diode, means for connecting said capacitor-a said diode'in series, circuit means for connecting said series. connected diode and capacitor across said coil, whereby said .capacitor is charged in response to the voltage acrossfsaidcoil,

andmeans for biasing the diode with a voltage less than the lowest peak voltage produced in the coil as a result of the softest touch on the key.

2. An electronic musical instrument as claimed in claim 1, wherein the bias voltage exceedshalf the peak value of the voltagepulse produced with the softest touch.

r 3. An electronic musical instrument as claimed in claim 1 further comprising a resistor-connected inseries with the

Claims

1. A control circuit providing an oscillator in an electronic musical instrument with an output voltage having an amplitude corresponding to the velocity with which movably mounted key is depressed, comprising a magnet, a coil, means for providing relative motion between said coil and said magnet in response to movement of said key, whereby a voltage is induced in said coil corresponding to the velocity of said key, a capacitor, a diode, means for connecting said capacitor and said diode in series, circuit means for connecting said series connected diode and capacitor across said coil, whereby said capacitor is charged in response to the voltage across said coil, and means for biasing the diode with a voltage less than the lowest peak voltage produced in the coil as a result of the softest touch on the key.

2. An electronic musical instrument as claimed in claim 1, wherein the bias voltage exceeds half the peak value of the voltage pulse produced with the softest touch.

3. An electronic musical instrument as claimed in claim 1 further comprising a resistor connected in series with the rectifying element.

4. An electronic musical instrument as claimed in claim 1, further comprising a member connected in series with the rectifying element, wherein the member has an increasing resistance in response to increasing current in the starting-current range of the rectifying element.

5. An electronic musical instrument as claimed in claim 4 further comprising a biased overflow diode connected in parallel with the coil.