US3509265A

US3509265A - Signal-selecting system for keyboard type electronic musical instrument

Info

Publication number: US3509265A
Application number: US727846A
Authority: US
Inventors: Masao Tsukamoto; Masahiko Tsunoo; Takatsugu Nakajima
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1968-05-09
Filing date: 1968-05-09
Publication date: 1970-04-28
Anticipated expiration: 1987-04-28

Description

April 23, 1970 MAsAOTsuKAMoTo ETAL 3,509,265 SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE C ELECTRONIC MUSICAL INSTRUMENT Filed May 9, 1968 9 Sheets-Sheet l TONE 5 FORMANTS INVENTORS MASAO TSUKAMOTO MASAHIKO TSU NOO TAKATSUGU NAKAJ [MA ATTORNEYS p ,1970 MASAOTSUKAMOTO ETAL I 3,509,265 SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE I ELECTRONIC MUSICAL INSTRUMENT Filed May 9, 1968 9 Sheets- Sheet 2 1 THE SELECTED-TONE SIGNALS OF THE COMMON OUTPUT CONDUCTOR 5o I I I I I I I I (b) TI-IE DIFFERENTIATED SIGNALS OF THE DIFFERENTIATING CIRCUITSI I I I I I I w I I {5 3 I BI-I62 i I 1 I I THE RULSE-TRAIN SIGNALS OF THE WAvE SHAPING CIRCuIT82 I I I I II I {5 I I E5 I A I I v I I THE DIVIDED SIGNALS OF THE FREQUENCY DIvIDER 83 I I I I I I v I I I I I I 'EI I'I /ZIS I I I I I I I J I (Z)I THE DIVIDED SIGNALS OF THE FREQUENCY DIvIDER 84 i I I I l I I I l LII- I I MS I I 4I3 I O I I I I al I I I I I E I I I I II t2 7 ts It4 THE TIME WHEN THE TIME WHEN I THE TIME WHEN T] H THE SELEC ING THE SELECTING- THE SELECTING" ALL IgEgIg/I T H KEYSWITCH KEY SWITCHES 4 ISCLGSED. FROMZS T023 AREoPENED.

INVENTORS MASAO TSUKAMOTO MASAI-IIKO TSUNOO TAKATSUGU NAKAJIMA ATTORNEYS April 28, 1970

MASAO TSUKAMOTO ETAL

3, 5

' SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT v 9 Sheets-Sheet 3 Filed May 9, 1968 INVENTORS MASAO TSUKAMOTO MASAHIKO TSUNOO TAKATSUGU NAKAJIMA ATTORNEYS April 28, 1970 MASAO TSU K AMOTO ETAL 1 I SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT Filed May 9, 1968 9 Sheets- Sheet 4.

TO TONE FORMING MEANS l5 5% u. m Mia? m T l m m I -11 g INVENTORS o: I MASAO TSUKAMOTO i $3f MASAHIKO TSUNOO r TAKATSUGU NAKAJ lMA ATTORNEYS A rll 28, 1970 MASAO TSUKAMOTO ET AL 3,509,265

, SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT Filed May 9, 1968 9 Sheets-Sheet 5 INVENTORS MASAO TSUKAMOTO TAKATSUGU NAKAJIMA ATTORNEYS April 28, 1970 MASAO TSUKAMOTO ETAL 3,509,265

. SIGNAL-SELECTING SYSTEMFOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT 9 Sheets-Sheet 6 Filed May.9, 1968,

INVENTORS MASAO TSUKAMOTO MASAHIKO TSUNOO FIGIO ATTORNEYS April 28, 1970 MASAO TSUKAMOTO ETAL 3,509,265

SIGNAIr-SELECTING SYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL- INSTRUMENT 9 Sheets-Sheet 7 Filed May 9, 1968 INVENTORS MASAO TSUKAMOTO MASAHIKO TSUNOO TAKATSUGU NAKAJIMA ATTORNEYS Apt-H 28,1970 MASAO TSUKAMOTO ETAL 3,509,265 I SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT Filed may 9. 1968 9 Sheets-Sheet 8 W {3| r q m w 1w wi l E :z L4 mm W lii L B E F INVENTORS MASAO TSUKAMOTO MASAHIKO TSUNOO TAKATSUGU NAKAJIMA ATTORNEYS 9 Sheets-Sheet 9 I I f I lllll lillllll MAsAo 'fsuKmm-o ETAL 'ELECTRON IC MUSICAL INSTRUMENT SIGNAL-SELECTING SYSTEM FOR KEYBOARD TYRE +uww4 ww w April 28, 1970- Filed May 9, 1:56a-

INVENTORS MASAO TSUKAMOTO MASAHIKO TSUNOO TAKATSUGU NAKAJIMA ATTORNEYS United States Patent 3 509 265 SIGNAL-SELECTINGEYSTEM FOR KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENT Masao Tsukamoto, Masahiko Tsunoo, and Takatsugu 1 US. Cl. 841.17 29 Claims ABSTRACT OF THE DISCLOSURE A signal-selecting system for a keyboard type electronic musical instrument. The system has a plurality of tone generators which generate tone signals at frequencies corresponding to notes of a musical scale, a plurality of switching devices which have input and output terminals, and a plurality of selecting-keyswitches. The keyswitches are activated by the keys of the keyboard and have one side coupled to said switching devices and the other side coupled to a common output conductor. A plurality of tone signal coupling means are coupled between said tone generators and said input terminals, and an output system is connected to said common output conductor. A bias system isprovided which produces a plurality of bias potentials which are fed to said switching devices. Said bias potentials are arranged in the order of magnitude of the potential in sequence in relation both to the order of frequencies of said tone generators and the order of notes of keys corresponding to selecting-keyswitches. The tone signals passing to said output terminals from said input terminals are switched on or off when said selecting keyswitches are closed or opened.

FIELD OF THE INVENTION This invention relates generally to a keyboard type electronic musical instrument and more particularly to-a novel signal-selecting system which is capable of selecting the tone signal having the highest frequency from among tone signals produced by keys which are depressed simultaneously or capable of selecting the tone signal having the lowest frequency from among'tone signals produced by keys which are depressed. simultaneously. i

DESCRIPTION OF THE PRIOR ART- A conventional keyboard ty-pe electronic musical instrument is provided with a conventional signal-selecting system comprising many transfer type keyswitches, each 3,509,265 Patented Apr. 28, 1970 "ice of a further transfer type keyswitch and so on. In addition, an output system comprising a frequency dividing means and a tone forming means is coupled to the movable-contact of the transfer type keyswitch corresponding to the lowest frequency tone generator and the lowest note key of the keyboard. The output of said output system is coupled to an amplifying means which in turn is coupled to an electro-acoustic translating means. Therefore, the conventional signal-selecting system is, of course, capable of selecting the lowest frequency tone signal corresponding to the lowest note key from among keys depressed simultaneously.

Said conventional signal-selecting system, however, is apt to have frequent break-downs due to poor contacts being made by the transfer type keyswitches, because a tone signal which is higher in frequency than the lowest frequency tone signal is coupled to the output system through a series connection consisting of many transfer type keyswitches having many contact points.

comprised of a make-contact and a movable-contact and a break-contact and a movable-contact, respectively.

Therefore, only a small number of transfer type keyswitches can be connected in series in a conventional signal-selecting system from the standpoint of reliability. In the conventional signal-selecting system, the more transfer type keyswitches, the lower the reliability.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide an improved and reliable signal-selecting system for a keyboard type electronic musical instrument.

Another object of the present invention is to provide a reliable signal-selecting system which employs a plurality of keyswitches which are easily available.

A further object of the present invention is to provide a signal-selecting system comprising a plurality of keyswitches of the make-contact type.

A further object of the present invention is to provide a signal-selecting system comprising a plurality of key-switches of the bus-bar type.

A. further object ofthe present invention is to provide a signal-selecting system capable of selecting the tone signal having the highest frequency from among the tone signals produced by the keys which are simultaneously depressed.

A further object of the present invention is to provide a signal-selecting system capable of selecting the tone signal having the lowest frequency from among the tone signals produced by the keys which are simultaneously depressed.

A further object of the present invention is to provide a signal-selecting system having an output system which is capable of dividing a selected-tone signal by means of a frequency dividing means and providing tone signals of octavely related to said selected-tone signal.

A further object of the present invention is to provide a signal-selecting system having an output system which comprises a foot pedal capable of controlling the output of said signal-selecting system.

A still further object of the present invention is to provide an improved keyboard type electronic musical instrument comprising a signal-selecting system.

These objectives are achieved by employing a signalselecting system according to the present invention comprising a plurality of tone generators which generate tone signals having frequencies corresponding to the notes of the musical scale, a plurality of switching devices comprising input terminals and output terminals, and a plurality of selecting-keyswitches which are coupled to said switching devices and to the corresponding keys, said selecting-keyswitches being further connected to a common output conductor which is connected through a shunt resistor to a reference potential. Said signal-selecting system further comprises a plurality of tone signal coupling means which are coupled between said tone generators and said input terminals, an output system connected to said common output conductor, and a bias system which produces a plurality of bias potentials to be fed to said switching devices.

Said bias potentials are arranged in order of potential in relation to both the order of frequencies of said tone generators and the order of notes of the keys corresponding to the respective selecting-keyswitches.

Said tone signals passing to said output terminals from said input terminals are switched on or off depending on whether said selecting-keyswitches are closed or opened.

The signal-selecting system of the present invention can only switch on the one switching device corresponding to the bias potential having the highest absolute value from among the bias potentials corresponding to the selecting-keyswitches which are simultaneously closed by depressing the keys. Said signal-selecting system can provide said common output conductor with a common potential which corresponds to said highest bias potential and switch off the other switching devices corresponding to bias potentials other than said highest bias potential by means of said common potential.

Said switching devices can comprise any voltage or current controlled switching devices such as solid state or vacuum tube diodes, solid state or vacuum tube triodes, transistors, thyristors or field effect transistors.

The bias potentials can be arranged in sequential order ranging from a high value to a low value or from a low value to a high value in relation to the order of both the tone generators and the notes of the keys extending from high frequency to low frequency or from low frequency to high frequency, respectively.

Therefore, said signal-selecting system can select the tone signal having the highest frequency from among the tone signals produced by the plurality of keys depressed simultaneously, in accordance with the arrangement of bias potentials.

BRIEF DESCRIPTION OF THE DRAWINGS These 'and other objects and particularities of the present invention will be made clear from the following detailed description of the invention considered together with the accompanying drawings wherein:

FIG. 1 is a schematic, circuit diagram of an embodiment of the signal-selecting system of the present invention;

FIG. 2 is a diagram showing voltage waveforms taken at various points in the signal-selecting system of the present invention;

FIG. 3 is a schematic circuit diagram of another embodiment of the signal-selecting system of the present invention;

FIG. 4 is a schematic circuit diagram of the differentiating circuit, the wave shaping circuit and frequency dividers employed in an embodiment of the signal-selecting system of the present invention;

FIGS. 5, 6 and 7 are schematic diagrams of various embodiments of the foot-switching means employed in the signal-selecting system of the present invention;

FIG. 8 is a schematic, circuit diagram of a further embodiment of the signal-selecting system of the present invention;

FIG. 9 is a perspective view showing an electronic musical instrument which is provided with the signalselecting system of the present invention;

FIG. 10 is a schematic circuit diagram of the embodiment of the electronic musical instrument shown in FIG. 9;

FIG. 11 is a schematic circuit diagram of another embodiment of the electronic musical instrumentsimilar to that of FIG. 9;

FIGS. 12, 13 and 14 show examples of musical notes which can be played on the electronic musical instrument of FIG. 10; and

FIG. 15 shows an example of musical notes which can be played on the electronic musical instrument of FIG. 11.

PREFERRED EMBODIMENTS Referring to FIG. 1 showing an embodiment of a signalselecting system,

tone generators

26, 27, 28, 29 and 30' generate tone signals having frequencies f f f f and f respectively, which correspond to the notes of a musical scale and which are arranged in order for their frequencies, for p f1 f2 f3 f4 f5- Switching devices are provided which are one-part devices, for example,

diodes

31, 32, 33, 34 and 35 which have anodes and cathodes. The anodes are connected to

input terminals

1, 2, 3, 4 and 5 which are capable of also serving as bias terminals and the cathodes are connected to

output terminals

6, 7, 8, 9, and 10 which are capable of also serving as control terminals.

Diodes

31, 32, 33, 34 and 35 are switched to the on position by a forward bias between said

input terminals

1, 2, 3, 4 and 5 and said

output terminals

6, 7, 8, 9 and 10- thus allowing tone signals having frequencies f f f f and f 'to pass from said

input terminals

1, 2, 3, 4 and 5 to said

output terminals

6, 7, 8, 9 and 10, respectively, and they are switched to the oif position by a reverse bias between said input terminals and said output terminals thus preventing said tone signals from passing from said input terminals to sad output terminals respectively.

Tone signal coupling means are coupled between said

tone generators

26, 27, 28, 29 and 30 and said

input terminals

1, 2, 3, 4 and 5, respectively. Any type of tone signal coupling means can be used.

Tone signal coupling means of the RC-coupled type comprise separating-

resistors

36, 37, 38, 39 and 40, source-

resistors

61, 62, 63, 64 and 65 and coupling-

capacitors

101, 102, 103, 104, and 105, respectively, source-

resistors

61, 62, 63, 64 and 65 and coupling-

capacitors

101, 102, 103, 104 and being connected, respectively, in series. The series connected elements are connected between said

tone generators

26, 27, 28, 29 and 30 and said

input terminals

1, 2, 3, 4 and 5, respectively, and feed the tone signals of frequencies f f f f and i from said

tone generators

26, 27, 28, 29, and 30 to said

input terminals

1, 2, 3, 4 and 5, respectively.

Selecting-

keyswitches

21, 22, 23, 24 and 25 are normally in an opened position and are closed by depressing the keys on the instrument keyboard corresponding to the notes of the musical scale and are coupled between said

output terminals

6, 7, 8, 9 and 10 and a common output conductor 50, respectively. Therefore, selecting-

keyswitches

21, 22, 23, 24 and 25 are of a bus-bar type. Said common output conductor 50 is connected to a parallel circuit comprised of a shunt-resistor 59 and a shunt capacitor 20 which in turn is connected to a reference potential 60.

An output system 12 is also connected to said common output conductor 50.

The output system 12 comprises a pulse generating means 13, a frequency dividing means 14, a tone forming means 15 and a foot-switching means 87. The pulse generating means 13 is connected directly to the common output conductor 50 and comprises a differentiating circuit 81 and a wave shaping circuit 82 connected to the output of the differentiating circuit 81.

The differentiating circuit 81 comprises a capacitor 90 which is connected between the input terminal and the output terminal of the differentiating circuit and a resistor 91 which is connected between the output termin'al and the reference potential. The differentiating circuit 81 removes D.C.- current and supplies a differentiatedsignal to the output terminal, Which is the junction of the capacitor 90 and resistor 91.

The wave shaping circuit 82 converts said differentiated-signal into a pulse-train-signal.

A frequency dividing means 14 is coupled to the output of the pulse generating means 13 and comprises, for example, two

frequency dividers

83 and 84.

Frequency dividers

83 and 84 successively divide the frequencies of input signals having frequencies of f and /2f by a factor of, for example, two, and produce a divided-signal having a frequency of A,, respectively. A single frequency divider or a number of frequency dividers greater than two can be utilized for the frequency dividing means 14.

The tone forming means 15 has three

tone formlng circuits

92, 93 and 94 which are connected to the Wave shaping circuit 82 and to the

frequency dividers

83 and 84, respectively. The tone forming means 15 is capable of changing the tone colors of the pulse-train-signal and of the two divided signals by means of

tone forming circuits

92, 93 and 94 and of producing tone-formed signals, respectively. A tone selecting means 86 is coupled to the tone forming means 85 and is capable of selecting tone-formed-signals by means of tone-selecting

switches

95, 96 and 97. A foot-switching means 87 is connected to the tone forming means 15 and is capable of allowing tone-formed signals to synchronously pass to an amplifying means 88 in accordance with the depression of a foot-pedal 98. i The amplifiying means 88 amplifies the output signals of the output system 12. An electro-acoustic translatlng means, for example a loud-speaker 89, is connected to said amplifier 88 and translates the output signals of said amplifier 88 into sounds.

A bias system is provided and is comprised of

biasresistors

51, 52, 53, 54, '55, 56 and 57 connected iIlSEIlCS and has a terminal 11 connected directly to the reference potential 60 and another terminal 49 connected to a power source 58 which in turn is connected to the reference potential 60. V

The bias system provides bias potentials V V V V V V V V and V at

terminals

41, 42, 43, 44, 45, 46, 47, 48, and 49, respectively.

Terminals

41, 42, 43, 44 and 45 are connected to separating-

resistors

36, 37, 38, 39 and 40 which in turn are connected to input

terminals

1, 2, 3, 4 and 5, respectlvely, so that bias potentials V V V V V fed therethrough arre arranged in descending order of potential, for example O V V V V V in relation to both the order of the frequencies of the

tone generators

26, 27, 28, 29 and 30 and the order of the notes of the keys corresponding to the selecting-

keyswitches

21, 22, 23, 24 and 25, respectively.

Terminals

43, 46, 47, 48 and.49 are connected to reverse-bias-

resistors

66, 67, 68, 69 and 70 which in turn are connected to

output terminals

6, 7, 8, 9 and 10, respectively, so that bias potentials V V V7, V and V fed therethrough are arranged in such a y that 1 3, V2 V6: 3 '1, 4 V and V 9- Therefore,

diodes

31, 32, 33, 34 and 35 are reversely biased and are all switched off when all of the

selectingkeyswitches

21, 22, 23, 24 and are opened.

The terminal 42, i.e. the junction between two biasresistors 52 and 53, is connected to a decoupling-capacitor 76 which in turn is connected to the reference potential 60.

Terminals

43, 45 and 48, i.e. the respective junctions of the

bias resistors

53 and 54, 55 and 56, and 56 and 57, are also connected to

decoupling capacitors

77, 78 and 79 6, which in turn are also connected to the reference potential 60, respectively.

Additional capacitors

71, 72, 73, 74 and 75 are connected between the common output conductor 50 and

output terminals

6, 7, 8, 9 and 10, respectively.

The reference character R indicates the resistance values of the reverse-

bias resistors

66, 67, 68, 69 and 70, respectively. The reference character R indicates the resistance value of the shunt-resistor 59. The reference character R indicates the resistance values of thhe separating-

resistors

36, 37, 38, 39 and 40. The reference character r r r r r r and r indicate the resistance values of the bias-

resistors

51, 52, 53, '54, 55, 56 and 57, respectively. The values of the respective resistances are in the following relation:

Diodes

31, 32, 33, 34 and 35 are reversely biased and all switched off, thus preventing the tone signals of the frequencies f f f f and f of the

tone generators

26, 27, 28, 29 and 30 from passing to the

output terminals

6, 7, 8, 9 and 10, respectively, when all of the

selectingkeyswitches

21, 22, 23, 24 and 25 are opened. Therefore, there is no selected-tone signal at the common output conductor 50.

When only the selecting-keyswitch 21 is closed by the depression of the corresponding key, the diode 31 is forwardly biased so as to be switched on, thus allowing a tone signal of a frequency f to pass from the tone generator 26 to the common output conductor 50. Each of the

other diodes

32, 33, 34 or 35 is also forwardly biased so as to be switched on thus allowing the respective tone signal of frequencies f f or L, to pass from the

respective tone generator

27, 28, 29 or 30 to the common output conductor 50, when the respective selecting-

keyswitchs

22, 23, 24 or 25 are closed by the depression of the corresponding keys.

Upon the simultaneous closing of two selecting-keyswitches, for example 21 and 22, only the diode 32 is forwardly biased and thus switched on in order to pass a tone signal, having a frequency of f from the tone generator'27 to the common output conductor 50. On the other hand, the diode 31 is reversely biased and is switched off due to the common potential of about V which is produced at the common output conductor 50, because R R and V V In the same manner as described above, the signalselecting system of the present invention is capable of switching on only the single diode corresponding to the h ghest bias potential from among the bias potentials corresponding to any two or more of the selecting-keyswitches which are simultaneously closed by the depression of the corresponding keys, and is also capable of passing the lowest frequency tone signal corresponding to said highest bias potential through a single diode to the common output conductor 50 and of producing a selectedtone signal at said common output conductor 50. On the other hand, the signal-selecting system of the present invention is capable of switching off the other diodes corresponding to all the bias potentials except said highest bias potential by means of a common potential which is produced at the common output conductor 50 and which is almost equivalent to the highest bias potential among the bias potentials corresponding to the selecting-keyswitches which are simultaneously closed by the depression of the corresponding keys.

' Therefore, the signal-selecting system of FIG. 1 is capable of selecting the lowest frequency tone signal from among the tone signals produced by the keys simultaneously depressed, when the bias potentials opposed to the reference potential 60 are arranged in an ascending order of the absolute value of the potential in relation to a descending order of the frequencies of the tone generators and a descending order of the notes of the keys corresponding to the selecting-keyswitches, respectively.

Suitable specification for resistances, capacitances, and bias voltages are shown below by way of example.

1'1, 7'2, C =1000 pf., C ,uf., C =1500 pf. V -V 1=0.3-1.2v. (111:2, 3, 4

Decoupling-

capacitors

76, 77, 78 and 79 prevent the tone signal from a tone generator from being coupled to the other tone signals from the other tone generators. In the absence of the decoupling-

capacitors

76, 77, 78 and 79, the tone signal from one tone generator is undesirably coupled with the tone signals from other tone generators having essentially the same amplitude even if the bias resistors 51-57 have a much smaller resistance than the separating-resistors 36-40. In the absence of the decoupling capacitor 76, for example the tone signal from the tone generator 26 is coupled through the source-resistor 61, the separating-resistor 36, the bias-resistor 52 and the separating-resistor 37 to the tone signal from the tone generator 27 at the anode of diode 32. Therefore, when the selecting-keyswitch 22 is closed, a mixture of the two tone signals from

tone generators

26 and 27 is fed to the common output conductor 50. Consequently, the mixture causes

frequency dividers

83 and 84 to operate incorrectly. The decoupling-capacitor 76 prevents the tone signal from tone generator 26 being coupled to the tone signal from the tone generator 27 by bypassing the tone signal from tone generator 26 to the reference potetnial 60. Decoupling-capacitors can practically be used in connection with a plurality of bias-terminals in order to prevent the tone signals from mutually coupling. The decoupling-

capacitors

76, 77, 78 and 79 are not required to have the same capacitance as each other. For example, it may be practical to use a large value capacitance as a decoupling-capacitor in connection with a bias-terminal corresponding to a low frequency tone generator, and a small value capacitance as a decouplingcapacitor in connection with a bias-terminal corresponding to a high frequency tone generator.

Reverse-bias-

resistors

66, 67, 68, 69 and 70 are used for biasing reversely and for switching off

diodes

31, 32, 33, 34 and 35 when the selecting-keyswitches are opened. Upon the removal of the reverse-bias-

resistors

66, 67, 68, 69 and 70, the tone signals of the tone genertors 26, 27, 28, 29 and 30 are partially fed through the

additional capacitors

71, 72, 73, 74 and 75 to the common output conductor 50 as noise signals. The reason for this is that the cathodes of

diodes

31, 32, 33, 34 and 35 are normally opened and therefore no reverse bias is imparted to said diodes when the selecting-keyswitches are opened. Reverse-bias-

resistors

66, 67, 68, 69 and 70 do not influence the operation of the tone signal-selecting system, because their resistance values are much larger than the resistance value of the shunt-resistor 59.

The

additional capacitors

71, 72, 73, 74 and 75 account for the stable operation of the signal-selecting system." of the present invention. In the absence of these

additional capacitors

71, 72, 73, 74 and 75, the repetitive switching, for example the repetitive switching on and off of selecting-keyswitch 21, produces noise pulse signals at the common output conductor 50 while the selecting-keyswitch 25 is closed during the repetitive switching. Said noise pulse signals cause

frequency dividers

83 and 84 to operate incorrectly. Although the reason for the noise pulse signals is not clearly understood, the noise pulse signals may be attributable to capacitances produced between the anodes and the cathodes of the

diodes

31, 32, 33, 34 and 35 when said diodes are reversely biased. The

additional capacitors

71, 72, 73, 74 and.75 completely remove the trouble caused b the noise pulsesignals and ensure the smooth operation of the signal-selecting system, although the appearance of the selected-tone signal at the common output conductor 50 is.a little delayed after switching on of a selecting-keyswitch. A

smaller capacitance value for said additional capacitance does not effect the operation, but a larger capacitance value causes the selected-tone signal to be delayed too c Theshunt-capacitor 20 removes the noise due to leakage signals from the

tone generators

26, 27, 28, 29 and 30; which appears at the common output conductor 50 when all of the selecting

keyswitches

21, 22, 23, 24 and 25 are opened. Said noise attributable to leakage signals has relatively high frequency components and causes the

frequency dividers

83 and 84 to operate incorrectly when the shunt-capacitor '20 is removed. The shunt-capacitor 20 acts as a low-pass-filter having a very low cut-off frequency 'due to the large resistance value R of the shunt-resistor 59 and thus attenuates the leakage signals which are present when all of the selecting-keyswitches are opened. On the other hand, when a single selectingkeyswitch is opened, the shunt-capacitor 20 acts as a low-pass-filter having a relatively high cut-off frequency due to the relatively small resistance value R /R of the parallel resistance of the shunt-resistor 59 anda separating-resistor and, therefore, as a practical matter, does not distort a selected-tone signal and cause it to be attenuated. Thus, the portion 70, enclosed within the dotted line of FIG. '1, will be referred to as a signal-selecting circuit for convenience. I However, a selected-tone signal cannot be fed directly to the tone forming means 15 or to the frequency dividing means 14, because the selected-tone signal derived from the common output conductor 50 has a large D.C. potential superposed thereon, as shown in FIG. 2(a). A selected-tone signal having a large DC. potential produces large clicks synchronously with the switching on and off of the selecting-keyswitch and cannot be used as a tone signal for a musical instrument. The selected-tone signal containing the large DC. potential causes a breakdown of the transistors of the frequency divider or causes the frequency divider to act irregularly during the first few cycles of the. selected-tone signal.

FIG. 2 shows the voltage waveforms in various parts of the signal-selecting system of the invention, when selecting-keyswitches, for example, 21, 25 and 23, are successively closed by depressing corresponding keys. The horizontalaxis istime, and the vertical axes are voltage amplitudes. The selected-tone signals of the common output conductor 50 are superposed on DC voltages V V and'V as shown in part .(a). Said selected-tone signals superposed on the DO voltages are differentiated by ditferentiatingcircuit 81 so they are no longer superposed on the DC. voltages and to produce differentiated signals as shown in part'(b) at the output of the differentiating circuit 81.

The wave shaping circuit 82 eliminates large amplitude pulses of positive or negative polarity, which are present in the differentiated signal and are synchronized with the times t t t and 1 The time t corresponds to a time whenthe sele'cting-keyswitch 21 is closed; the time 1 corresponds to a time when the selecting-keyswitch' 25 is closed; the time t corresponds to a time when the selecting-keyswitch 25 is opened and selecting-keyswitch 23 is, ,.simult aneously closed; and the time 1.; corresponds to a time when all selectingkeyswitches' are opened. The wave shaping circuit 82 also converts the waveforms of the differentiated signals into pulse-train signals having uniform amplitudes and uniform pulse widths as shown in part (c). Said pulse-train signals trigger the frequency divider 83. The frequency divider 83 divides the frequencies of the input pulse train signals by-a factor of two and produces divided signals having a rectangular waveform as shown in part (d).,S aid divided signals further trigger the frequency-divider 84. The frequency divider 84 further dividesthe frequencies of the input divided signals by'a factor of two and produces further divided signals havin rectangular waveforms as shown in part (e).

After having been modified by the differentiating circuit 81, wave shaping circuit 82 and

frequency dividers

83 and 84, selected-tone signals of the common output conductor 50, can be used for tone signals of electronic musical instruments.

The tone signals of tone generators 26-30, shown in part (a) of FIG. 2 by way of example, are rectangular wave signals. However, the tone signals of the tone generators 26-30 can also have sawtooth waveforms, sine waveforms or other waveforms.

'FIG. 3 shows another embodiment of the signal-selecting system of the present invention, in which tone signal coupling means are transformer-type means. The tone signal coupling means comprise

transformers

236, 237, 238, 239 and 240 having the primary coils coupled to tone

generators

26, 27, 28, 29 and 30, respectively and having the secondary coils coupled between

terminals

41, 42, 43, 44 and 45 and

input terminals

1, 2, 3, 4 and 5, respectively. The secondary coils of

transformers

236, 237, 238, 239 and 240 have an impedance very much smaller than the shunt-resistor 59. The remainder of the signalselecting system shown in FIG. 3 and its operation is the same as that shown in FIG. 1.

FIG. 4 is a circuit diagram of an embodiment of the differentiating circuit 81, the wave shaping circuit 82 and

frequency dividers

83 and 84. The differentiating circuit 81 has a capacitance of 2700 pf. and an input impedance to a transistor amplifier circuit of 50kt The wave shaping circuit 82 is composed of four transistor amplifiers and a clipper circuit.

Frequency dividers

83 and 84 are composed of flip-flop circuits.-

The portion surrounded by the dotted 'line of FIG. 5 is an embodiment of the foot-switching means 87 of FIG. 1. The foot-switching means 87A comprises a gate circuit 101, an envelope controlling means 16A, a source of power 106 and a switch 102. The gate circuit 101 is coupled between the tone forming means 15 and the amplifying means.88. The envelope controlling means 16A is composed of a capacitor 105 and

resistors

103 and 104 connected in series between a reference potential, e.g. ground with the junction between capacitor 105 and -resistance 104, connected to a control terminal of the gate circuit 101 in order to actuate the gate circuit 101 and to control the envelope of the output signal of the gate circuit 101. The switch 102 is operated by the foot pedal 98 and is coupled between the source of power 106 and the junction between

resistors

103 and 104 in the envelope controlling means 16A. The capacitor 105 is charged in order to switch on the gate circuit 101 and to provide an output signal for the output of the gate circuit 101 when the switch 102 is closed by depressing the foot pedal 98. The output signal decays gradually after the switch 102 is opened by removing the force on the foot pedal 98. Therefore, the switching means 87A shOWn in FIG. 5 is capable of producing signals having an organ type envelope and is also capable of producing signals of the sustain type envelope when the resistance value ofthe resistor 103 is large. The decay rate can be changed by changing the resistance value of the variable Y resistor 103.

The portion surrounded by the dotted line of FIG. 6 is another embodiment of the foot-switching means 87 of FIG. 1. The envelope controlling means 16B is composed of

capacitors

107 and 110, resistors 103 and 109 and a diode 108. The resistor 109, capacitor 107 and variable resistor 103 are connected in a manner similar to the corresponding elements of the circuit 16A of FIG. 5. Diode 108 and capacitor 110 are connected in parallel with velope. The decay rate can also be changed by changing the resistance value of the resistor 103.

The portion surrounded by the dotted line of FIG. 7 is a further embodiment of the foot-switching means 87 of FIG. 1. The foot-switching means 87C comprises a light responsive resistance element 151, a shutter 153 and a light source 152. The input tone signal passes through the light responsive resistance element 151 to the amplifying means 88. The shutter 153 is coupled to the foot pedal 98 and is actuated in response to movement thereof in order to vary the amount of light falling on the resistance element 151 and thus to vary the strength of the output tone signal. Therefore, the volume of the output signal can be varied in accordance with the movement of the foot pedal 98. The output signal of the foot-switching means 87C is thus controllable. Therefore the attack and decay of the ouput signal can be controlled so as to be smooth by controlling the rate of depression and the rate of lifting of the foot-pedal 98.

FIG. 8 shows a further embodiment of the signal-selecting system. Reference number indicates the same signal-selecting circuit as that surrounded by the dotted line of FIG. 1. The foot switching means 87 is coupled between the frequency dividing means 14 and the tone forming means 15, and is operated by the foot pedal 98 in the signal-selecting system of FIG. 8. The system is otherwise the same as that of FIG. 1.

FIG. 9 shows a single keyboard type electronic musical instrument which employs the signal-selecting system of the invention. The electronic musical instrument of FIG. 9 has a single keyboard, a foot pedal 98 for controlling the output of the output system 12 and an expression pedal means 99 for controlling volume of sound. Said keyboard has sixty-one keys and is divided into a melody keyboard 203 and an accompaniment keyboard 202 at the key corresponding to middle C.

FIG. 10 shows an embodiment of a circuit diagram of the electronic musical instrument shown in FIG. 9.

Tone generators

111, 112, 113, 114 and 115 generate melody tone signals for the melody keyboard 203.

Tone generators

26, 27, 28, 29 and 30 generate tone signals which are both accompaniment tone signals and tone signals for feeding to a signal-selecting circuit 80B controlled by the accompaniment keyboard 202. The signal-selecting circuit 80B has the same construction as the signalselecting circuit 80 surrounded by the dotted line of FIG. 1 and can select the lowest frequency tone signal from among the tone signals generated when a plurality of accompaniment keys are depressed simultaneously.

The melody manual keyboard 203 has melody keys for operating

melody keyswitches

126, 127, 128, 129 and 130 which control melody tone signals supplied through

resistors

116, 117, 118, 119 and 120 from

tone generators

111, 112, 113, 114 and 115, respectively. The accom paniment manual keyboard 202 has accompaniment keys for simultaneously operating selecting-

keyswitches

21, 22, 23, 24 and 25 and

accompaniment keyswitches

121, 122, 123, 124 and 125, respectively.

Accompaniment keyswitches

121, 122, 123, 124 and 125 control accompaniment tone signals fed through

resistors

66, 67, 68, 69 and 70 from

tone generators

26, 27, 28, 29 and 30, respectively.

Selecting-

keyswitches

21, 22, 23, 24 and 25 control the signal-selecting circuit 80B and provide a selected-tone signal for the common output conductor 50. The selectedtone signal from the common output conductor 50 is controlled through an output system 128 comprising a differentiating circuit 81, a wave-shaping circuit 82, a frequency dividing means 14, a foot-switching means 87 and a tone forming means 15 which is the same as the output system 12 of FIG. 1. A foot pedal is coupled to the foot-switching means 87 and controls the output of the output system 12B.

A melody tone forming means 204 is coupled to an out-put conductor 208 connected to the

melody keyswitches

126, 127, 128, 129 and 130. An accompaniment tone forming means 205 is coupled to another output conductor 209 connected to the

accompaniment keyswitches

121, 122, 123, 124 and 125. An amplifying means 88 is coupled to the melody tone forming means 204, the accompaniment tone forming means 205 and the output system 12B of the signal-selecting system of the invention, and amplifies the tone signals fed thereto. An electroacoustic translating means, for example, a loud-speaker 89, is coupled to the output of the amplifying means 88 and produces musical sounds. An expression pedal means 99 is connected through a volume controlling means 100 to the amplifying means 88, and controls the volume of the sounds.

The signal-selecting system of FIG. 10, therefore, comprises

tone generators

26, 27, 28, 29 and 30', the signal selecting circuit 80B, selecting-

keyswitches

21, 22, 23, 24 and 25, the common output conductor 50 and the output system 12B, and is operatedby selecting-

keyswitches

21, 22, 23, 24 and 25 of the accompaniment manual keyboard 202 so as to select the lowest frequency tone signal from among the tone signals generated when a plurality of accompaniment keys are depressed simultaneously.

The electronic musical instrument of FIG. 10 can produce musical sounds as shown, for example, by the musical notes of part (c) of FIG. 12, when accompaniment keys are played according to musical notes of part (a) of FIG. 12, and the foot pedal 98 is depressed with a rhythm as shown in part (b).

The foot switching means 87A shown in FIG. makes it possible for the electronic musical instrument of FIG. to produce musical sounds, for example, in accordance with the musical notes of part (a) of FIG. 13, when accompaniment keys are played according to the musical notes of the upper row of part (a) and the foot pedal 98 is depressed with a rhythm shown in part (b).

The foot switching means 87B shown in FIG. 6 makes it possible for the electronic musical instrument of FIG. 10 to produce musical sounds, for example in accordance with the musical notes of part (a) of FIG. 14, when accompaniment keys are played according to the musical notes of the upper row of part (a) and the foot pedal 98 is depressed with a rhythm shown in part (b).

FIG. 11 shows a circuit diagram of another embodiment of the electronic musical instrument shown in FIG. 9.

Tone generators

111, 112, 113, 114 and 115 generate melody tone signals in response to depression of the keys on the melody keyboard 203.

Tone generators

151, 152, 153, 154 and 155 generate tone signals for feeding to a signal-selecting circuit 80A for the melody keyboard 203.

Tone generators

26, 27, 28, 29 and 30 generate tone signals which are both accompaniment tone signals and tone signals for another signal-selecting circuit 80B for the accompaniment keyboard 202.

The signal-selecting circuit 80A has a construction similar to that of the signal-selecting circuit 80 sur rounded by the dotted line of FIG. 1, and is capable of selecting the highest frequency tone signal from among the tone signals generated when a plurality of melody keys are depressed simultaneously, because the bias potentials set against the reference potential 60 are arranged in an ascending order of the absolute value of the potential in relation to both the ascending order of frequencies of the

tone generators

151, 152, 153, 154 and '155 and the ascending order of the notes corre' sponding to the keys, respectively. The signal-selecting circuit 80B has also the same construction as that of the signal-selecting circuit 80 surrounded by the dotted line of FIG. 1 and is capable of selecting the lowest frequency tone signal from among the tone signals generated when a plurality of accompaniment keys are depressed simultaneously.

The melody manual keyboard 203 has melody keys for simultaneously operating selecting-keyswitches 131,

12 r 132, 133, 134 and 135 and

melody keyswitches

126, 127, 128, 129 and 130. Melody keyswitches 126, 127, 128, 129 and 130 control the melody tone signals fed through

resistors

116, 117, 118, 119 and 120 from

tone generators

111, 112, 113, 114, and 115, respectively. Selecv ing-

keyswitches

131, 132, 133, 134 and 135 control the signal-selecting circuit A and provide a selected-tone signal for a common output conductor 210. The selected-tone signal at the common output conductor 210 is fed to an output system 12A comprising a differentiating circuit 81A, a wave shaping circuit 82A, two

frequency dividers

83A and 84A, three tone-selecting switches A, 96A and 97A and a tone forming means 85A.

Accompaniment keyswitches

121, 122, 123, 124 and 125 control accompaniment tone signals fed through

resistors

66, 67, 68, 69 and 70 from

tone generators

26, 27, 28, 29 and 30, respectively. Selecting-

keyswitches

21, 22, 23, 24 and 25 control the signal-selecting circuit 80B and provide a selected-tone signal for a common output conductor 50. The selected-tone signal at the common output conductor 50 is fed to an output system 12B which is the same as that shown in FIG. 10. A foot pedal 98 is coupled to the foot-switching means 87 and controls the output of the output system 12B.

A melody tone forming means 204 is coupled to an output conductor 208 for the melody keyswitches 12 6, 127, 128, 129 and 130. An accompaniment tone forming means 205 is coupled to the output conductor 209 for the accompaniment keyswitches '121, 122, 123, 124 and 125. An amplifying means 88 is coupled to the output system 12A, the melody tone forming means 204, the accompaniment tone forming means 205, and the output system 12B, and amplifies the tone signals fed thereto. An electro-acoustic translating means, for example a loudspeaker 89 is coupled to the output of the amplifying means 88 and produces musical sounds. An expression pedal means 99 is connected through a volume controlling means 100 to the amplifying means 88 and controls the volume of the sounds.

One of the signal-selecting systems of FIG. 11 comprises

tone generators

151, 152, 153, 154 and 155, the signal-selecting circuit 80A, selecting-

keyswitches

131, 132, 133, 134 and 135, the common output conductor 210 and the output system 12A, and is operated by selecting-

keyswitches

131, 132, 133, 134, and 135, controlled by the melody manual keyboard 203, and is capable of selecting the highest frequency tone signal from among the tone signals produced when a plurality of melody keys are depressed simultaneously. The other of the signal-selecting systems of FIG. 11 comprises

tone generators

26, 27, 28, 29 and 30, the signal-selecting circuit 80B, selecting-

keyswitches

21, 22, 23, 24 and 25, the common output conductor 50 and the output system 12B, and is operated by selecting-

keyswitches

21, 22, 23, 24 and 25 controlled by the accompaniment manual keyboard 202, and is capable of selecting the lowest fre quency tone signal from among the tone signals produced when a plurality of accompaniment keys are depressed simultaneously. The frequencies of

tone generators

151, 152, 153, 154 and 155 are higher, for example, by one octave than those of tone generators 111, 112, 113-, 114 and 115, respectively.

The foot switching means 87A shown in FIG. 5 makes it possible for the electronic musical instrument of FIG. 11 to produce musical sounds, for example, in accord ance with musical notes of part (b) of FIG. 15 when melody keys, accompaniment keys and the foot pedal are played according to musical notes of the first row, the second row and the third row, respectively, of part (a). Musical sounds corresponding to the first row of part (b) of FIG. 15 are produced by the signal-selecting circuit 80A and the output system 12A and are three note tones, each of which extends over two octaves. The second row of part (b) of FIG. 15 shows musical sounds produced by the melody keyswitches and the melody tone 13 forming'means 204. Thethird row of part (b) 'of FIG. shows the musical sounds produced by the accompaniment keyswitches and the accompaniment tone forming means 205. Musical sounds corresponding to the fourth row of part (b) are produced by theslgnal-selecting circuit 80B.and the output system IZ B'and have a pitch lowerfby one octave than the sounds corresponding to the lowest notes of the third row of part (b), and have a rhythm shown in the fourth row of part (b) and envelopes of the sustain type. The output system 128 can also,.produce simultaneously two or more musical sounds related octavely to notes of the fourth row of part (b) of FIG. 15 when the frequency dividing means 14 is provided with two or more frequency d1- viders whichdivide the frequencies of input signals by I a factor of two.

Therefore,- .the electronic musical instrument of FIG. 111 having the signal-selecting system of the invention can easily produce versatile musical sound effects when the operator is playing only a single manual keyboard divided intotwo parts, i.e. a melody manual keyboard and an accompaniment manual keyboard, and a foot edal. p Frequency dividers dividing the frequencies of input signals by a factor of two as described above can be replaced by frequency dividers which divide the frequencies of input signals by a factor of three or more.

The signal-selecting system of the invention is reliable even when composed of a plurality of keyswitches which are widely used, and can be constructed by utilizing inexpensive and simple keyswitches of the bus bar type. Consequently, the signal-selecting system of the invention is capable of selecting reliably only one tone sign-a1 from a plurality of tone signals.

The selected-tone signals can be supplied to the tone form-ing means without producing clicks and to the frequency dividing means without causing faulty operation thereof in association with the pulse generating means which comprises the differentiating circuit and the wave shaping circuit and can eliminate disadvantage due to the variation of the D.C. voltage superposed on the selectedtone signals. Therefore, the signal-selecting system can be operated with a high stability.

Thus, the signal-selecting system of the invention makes possible an electronic musical instrument characterized by ease of playing and superior operation, particularly in the embodiments as shown, for example, in FIGS. 9-11.

The signal-selecting system of the invention can be used not only for an electronic musical instrument having a single keyboard, but also for an electronic musical instrument having two or more keyboards, for example, a spinet type electronic organ or a full sEale electronic organ.

While particular embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that numerous modifications and variations can be made in the form and construction thereof without departing from the fundamental principles of the invention. It is, therefore, desired by following claims, to include within the scope of the present invention all similar and modified forms of the apparatus disclosed and by which the results of the invention can be obtained.

What is claimed is:

1. A signal-selecting system for a keyboard type electronic musical instrument comprising:

a plurality of tone generators which generate tone signals having frequencies corresponding to the notes of a musical scale;

a plurality. of switching devices each having input terminals and output terminals;

a plurality of selecting-keyswitches each having one side coupled to said switching devices and operable by the keys of said keyboard;

a common output conductor to which the other sides of said keyswitches are connected;

a shunt resistor connected between said common conductor and a reference potential;

a plurality of tone signal coupling means coupled between said tone generators and said input terminals;

an output system connected to said common output conductor; and

a bias system which produces a plurality of bias potentials, said system being coupled to the said switchingdevices for feeding the respective bias potentials" to the switching devices with the order of the magnitude of potential in a sequential relationship both to the order of frequencies of said tone generators and the order of notes of the keys corresponding to the selecting-keyswitches, whereby said tone signals passing to said output terminals from said input terminals are switched on or olf when said selecting-keyswitches are closed and opened respectively.

2. A signal-selecting system as claimed in claim 1, wherein said bias potentials are arranged in an ascending order of absolute magnitude of potential relative to said reference potential and correspond both to an ascending order of notes of said keys corresponding to said selecting-keyswitches, respectively, said signal-selecting system being capable of selecting the highest frequency tone signal from among the tone signals generated when a plurality of keys are depressed simultaneously.

3. A signal-selecting system as claimed in claim 1, wherein said bias potential are arranged in an ascending order of absolute magnitude of potential relative to said reference potential and correspond both to a descending order of frequencies of said tone generators and a descending order of notes of said keys corresponding to said selecting-keyswitches, said signal-selecting system being capable of selecting the lowest frequency tone signal from among the tone signals generated when a plurality of keys are depressed simultaneously.

4. A signal-selecting system as claimed in claim 1, wherein said switching devices are diodes and have input terminals to which said bias system is connected and which function as bias terminals.

5. A signal-selecting systemas claimed in claim 1, wherein said tone signal coupling means are RC-coupled type means and comprise separating-resistors coupled between said bias system and the respective input terminals, and source-resistors and coupling-capacitors connected in series, respectively and connected between said tone generators and said input terminals, said separatingresistors having a smaller resistance than said shuntresistors.

6. A signal selecting system as claimed in claim 1, wherein said tone signal coupling means are transformercoupled type means and comprise transformers having respective primary coils coupled to said tone generators and respective secondary coils coupled between said bias system and said input terminals, said secondary coils having a smaller impedance than said shunt-resistor.

7. A signal-selecting system as claimed in claim 1, wherein said bias system comprises a plurality of biasresistors in a series connection, one end terminal of said system being connected directly to said reference potential and a source of power connected to said reference potential and to which the other end terminal of said series connection is connected, said system having intermediate terminals between adjacent resistors for connection to the respective switching devices for providing bias potentials therefor and also providing bias potentials at said end terminals, said bias-resistors having a smaller resistance than said shunt-resistor.

8.'A signal-selecting system as claimed in claim 1, wherein said bias system comprises a plurality of biasresistors in a series connection, one end terminal of said system being connected directly to said reference potential and a source of power connected to said reference potential and to which the other end terminal of said series connection is connected, said system having intermediate terminals between adjacent resistors for connection to the respective switching devices for providing bias potentials therefor and also providing bias potentials at said end terminals, said bias-resistors having a smaller resistance than said shunt-resistor, a decoupling-capacitor connected between each intermediate terminal and the respective switching device.

9. A signal-selecting system as claimed in claim 1, further comprising reverse-bias-resistors connected to the respective switching devices, for feeding a plurality of reverse-bias potentials to said switching devices, said reverse-bias-resistors having a larger resistance than said shunt-resistor.

10. A signal-selecting system as claimed in claim 1,

wherein said signal-selecting system further comprise additional capacitors coupled between said common output conductor and the respective output terminals of said switching devices. 11. A signal-selecting system as claimed in claim 1, wherein said signal-selecting system further comprises a shunt-capacitor coupled between said common output conductor and said reference potential.

12. A signal-selecting system as claimed in claim 1, wherein said output system comprises:

a pulse generating means connected to said common output conductor for removing a DC. voltage superposed on a selected-tone signal from said common output conductor and converting said selected-tone signal into a pulse-train signal;

a frequency dividing means connected to said pulse generating means and having at least one frequency divider for dividing the frequency of said pulse-train signal by an integral factor and producing a divided signal;

a tone forming means which is connected to said frequency dividing means; and

a tone-selecting means which is connected to said tone forming means and is capable of selecting said at least one tone-formed signal, said tone forming means changing the tone color of said divided signal by said tone-selecting means and producing at least one toneformed signal.

13. A signal-selecting system as claimed in claim 12,

wherein said tone forming means is also connected to said pulse generating means and changes the tone color of said pulse-train signal. I 14. A signal-selecting system as claimed in claim 12, wherein said pulse generating means comprises a differentiating circuit which comprises at least one capacitor coupled between the input and the output of said differentiating circuit and at least one resistor coupled between the output of said differentiating circuit and said reference potential and which removes DC. current and provides a differentiated signal at the junction of said at least one capacitor and said at least one resistor, and a wave shaping circuit connected to said junction and converts said differentiated signal into a pulse-train signal.

15. A signal-selecting system as claimed in claim 12, wherein said frequency dividing means has at least one frequency divider which divides the frequency of the input pulse-train signal by a factor of two.

16. A signal-selecting system asblaimed in claim 12,

wherein said frequency dividing means has at least one frequency divider which divides the frequency of the input pulse-train signal by a factor of three.

17. A signal-selecting system as claimed in claim 12, said output system further comprises an amplifying means, and a foot-pedal actuated foot-switching means coupled to said output system for passing said tone-formed signal to said amplifying means synchronously with depression of the foot-pedal of said switching means.

18. A signal-selecting system as claimed in claim 17, wherein said tone forming means is also connected to said pulse generating means and is capable of changing the tone color of said pulse-train signal.

19. A signal-selecting system as claimed in claim 17, wherein said pulse generating means comprises a differentiating circuit which comprises at least one capacitor coupled between the input and the output of said differentiating circuit and at least one resistor coupled between the output of said differentiating circuit and a reference potential and which removes direct current and provides a differentiated signal at the junction of said at least one capacitor and said at least one resistor, and a wave shaping circuit which is connected to said junction and converts said differentiated signal into a pulse-train signal.

20. A signal-selecting system for a keyboard type electronic musical instrument as claimed in claim 17, wherein said frequency dividing means has at least one frequency divider which divides the frequency of the input pulse-train signal by a factor of two.

21. A signal-selecting system as claimed in claim 17, wherein said frequency dividing means has at least one frequency divider which divides the frequency of the input pulse-train signal by a factor of three.

22. A signal-selecting system as claimed in claim 17, wherein said foot-switching means is connected to the output system between said tone forming means and said amplifier.

23. A signal-selecting system as claimed in claim 17, wherein said foot-switching means is coupled to said output means between said frequency dividing means and said tone forming means for passing said divided signal to said tone forming means synchronously with the depression of the foot-pedal.

24. A signal-selecting system as claimed in claim 23 wherein said foot-switching means is further coupled between said pulse generating means in said tone forming means for passing said pulse-train signal to said tone forming means synchronously with the depression of the foot-pedal.

25. A signal-selecting system as claimed in claim 17, wherein said foot-switching means comprises a circuit including a light responsive resistance element through which said tone-formed signal passes, and means coupled to said foot-pedal and actuated in response to movement thereof for varying the light imparted to said resistance element so that the strength of said tone-formed signal varies in accordance with the movement of said foot-pedal.

26. A signal-selecting system as claimed in claim 17, wherein said foot-switching means comprises a gate circuit, an envelope controlling means connected to a control terminal of said gate circuit to control said gate circuit, a source of power, and a switch operated by the foot pedal and coupled between said source of power and said envelope controlling means.

27. An electronic musical instrument as claimed in claim 1 further comprising:

a further plurality of tone generators for generating melody tone signals;

a melody manual keyboard having a plurality of melody keys;

a plurality of melody keyswitches coupled to and actuated by said melody keys and coupled to said melody tone generators for controlling output of said melody tone signals;

an accompaniment manual keyboard having a plurality of accompaniment keys;

a plurality of accompaniment keyswitches coupled to and actuated by said accompaniment keys and coupled to said first mentioned plurality of tone generators for controlling output of accompaniment tone signals, respectively;

a foot-pedal coupled to said signal-selecting system and controlling the output of said signal-selecting system;

a melody tone forming means coupled to said melody keyswitches;

an accompaniment tone forming means coupled to said accompaniment keys-witches;

an amplifying means coupled to said melody tone forming means, said accompaniment tone forming means and said signal-selecting system;

an electro-acoustic translating means for producing sound coupled to said amplifier; and

an expression pedal means coupled to said amplifier for controlling the volume of sounds amplified by said amplifier;

said selecting keyswitches in said signal-selecting system being coupled to and operated by said keys oi said accompaniment manual keyboard, and capable of selecting the lowest frequency tone-signal from among the tone signals generated when a plurality of accompaniment keys are depressed simultaneously. 28. An electronic musical instrument as claimed in claim 1, further comprising:

a further plurality of tone generators for generating accompaniment tone signals;

a melody manual keyboard having a plurality of melody keys;

a plurality of melody keyswitches coupled to and actuated by said melody keys and coupled to said firstmentioned plurality of tone generators for controlling the output of melody tone signals;

an accompaniment manual keyboard having a plurality of accompaniment keys;

a plurality of accompaniment keyswitches coupled to and actuated by said accompaniment keys and coupled to said further plurality of tone generators for controlling output of accompaniment tone signals;

a melody tone forming means coupled to said melody keyswitches;

an accompaniment tone forming means coupled to said accompaniment keyswitches;

an electro-acoustic translating means for producing sounds coupled to said amplifying means; and

an expression pedal means coupled to said amplifying means for controlling the volume of sounds amplified thereby;

said selecting-keyswitches in said signal-selecting system being coupled to and operated by said keys of said melody manual keyboard, and being capable of selecting the highest frequency tone signal from among the tone signals generated when a plurality of melody keys are depressed simultaneously.

29. An electronic musical instrument as claimed in claim 1 and further comprising:

a further signal selecting system having tone generators for generating selected tone signals;

a further plurality of tone generators for generating melody tone signals;

a melody manual keyboard having a plurality of melody keys;

an accompaniment manual keyboard having a plurality of accompaniment keys;

a plurality of accompaniment keyswitches coupled to and actuated by said accompaniment keys and coupled to said first mentioned tone generators for controlling output of accompaniment tone signals;

a melody tone forming means coupled to said melody keyswitches;

an accompaniment tone forming means coupled to said accompaniment keyswitches;

an amplifying means coupled to said melody tone forming means, said accompaniment tone forming means, said signal-selecting system and said further signalselecting system;

an expression pedal means coupled to said amplifying means and controlling the volume of sounds amplified thereby;

said selecting keyswitches in said signal-selecting system being coupled to and operated by said keys of said accompaniment manual keyboard and selecting the lowest frequency tone signal from among the tone signals produced when a plurality of accompaniment keys are depressed simultaneously; and

said selecting keyswitches in said further signal-selecting system being connected to and operated by said keys of said melody manual keyboard and selecting the highest frequency tone signal from among the selector tone signals produced by the tone generators of said further signal selecting system when a plurality of melody keys are depressed simultaneously.

References Cited UNITED STATES PATENTS 2/ 1959 Bode. 7/1968 Hurvitz.

3,417,188 12/1968 Munch.

T. VEZEAN, Assistant Examiner U.S. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 509 I 265 Dated April 28 r 1970 Inventor) MASAO TSUKAMO'IO, MASAHIKO TSUNOO and TAKATSUGU NAKAJIMA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 3, for "R =829KQ" read R =820KQ and for "R =220MQ" read R =220K2 Column 7 line 6 for "V V read n. 1

Signed and sealed this 6th day of July 1 971 (SEAL) Attest:

EDWARD M .FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents