05/262229

03/27/1973

06/13/1972

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Nippon Gakki Seizo Kabushiki Kaisha (Hamamatsu-shi, JA)

84/698

984/325, 84/699, 84/678

G10H1/08; G10H1/06; G10H5/12; G10H1/06

84/1.01,1.11-1.13,1.17,1.19-1.23,1.26,DIG.9

3150228	Electronic musical instrument	September 1964	Gibbs et al.
3535969	MUSICAL INSTRUMENT ELECTRONIC TONE PROCESSING SYSTEM	October 1970	Bunger
3571481	MARIMBA TONE FORMING SYSTEM FOR AN ELECTRONIC MUSICAL INSTRUMENT	March 1971	Adachi
3610804	COMBINATION OF SELECTOR SWITCH AND EXPRESSION CONTROL OF ELECTRONIC MUSICAL INSTRUMENT	October 1971	Matsuura
3694561	ANIMATION CIRCUIT FOR A MUSICAL INSTRUMENT	September 1972	Morez
3697664	ELECTRONIC MUSICAL INSTRUMENT HAVING AUTOMATIC BASS TONE SELECTOR	October 1972	Hiyama

Wilkinson, Richard B.

Witkowski, Stanley J.

What is claimed is

1. In a keyboard electronic musical instrument having pedal keys, a bass tone producing device comprising:

2. A bass tone producing device according to claim 1 wherein said harmonic bass tone signal source comprises two units for generating different harmonic bass tone signals, and there is further provided another signal composing means for mixing in a preset ratio two output signals from both said harmonic bass tone signal source units.

3. A bass tone producing device according to claim 1 wherein said fundamental and harmonic bass tone signal sources comprise a frequency divider chain comprised of a plurality of cascade-connected bistable multivibrators each including two transistors, and said keyer circuits comprise emitter follower circuits each including a transistor which has its base connected via a diode to the collector of one of the two transistors included in the corresponding one of said bistable multivibrators and its emitter connected via a resistor to a line which is connected to one of a pair of positive and negative power sources via a resistor and a normally open switch closed upon depression of a corresponding key on said pedal keyboard, said transistor having its collector connected to the other power source with a resistor network connected between the collector and emitter of said transistor.

4. A bass tone producing device according to claim 1 further including a trigger circuit wherein said fundamental and harmonic bass tone signal sources comprise a frequency divider chain comprised of a plurality of cascade-connected bistable multivibrators each including two transistors, and said keyer circuits comprise a first group of emitter follower circuits each including a transistor which has its base connected via a diode to the collector of one of the two transistors included in the corresponding one of said bistable multivibrators and its emitter connected via a resistor to a line which is connected via a capacitor to one of a pair of positive and negative power sources, said transistor having its collector connected to the other power source and said line being connected via a resistor and a diode to the output terminal of said trigger circuit rendered conductive upon depression of one of said pedal keys and also connected via a series circuit of a diode and a resistor network to the other power source; and a second group of emitter follower circuits each including a transistor which has its base connected via a diode to the collector of the other transistor included in the corresponding one of said bistable multivibrators and its emitter connected via a resistor to another line which is connected via a capacitor to said one power source, said transistor having its collector connected to the other power source line and said line being connected via a resistor to the output terminal of said trigger circuit and also connected via a resistor network to the other power source.

5. A bass tone producing device according to claim 1 wherein said first tone coloring filter is a low pass filter.

6. A bass tone producing device according to claim 1 wherein said second tone coloring filter is a band pass filter.

7. A bass tone producing device according to claim 1 wherein said first signal composing means comprises a plurality of resistors connected at one end to the corresponding output terminals of said keyer circuits, said resistors being jointly connected at the other ends thereof.

8. A bass tone producing device according to claim 1 wherein said final signal composing means comprises two resistors connected at one end to the corresponding tone coloring filters, said resistors being jointly connected at the other ends thereof.

9. A bass tone producing device according to claim 4 wherein said trigger circuit includes a one-shot multivibrator.

10. A bass tone producing device according to claim 1 wherein said means for reversing the phase of said harmonic bass tone signal in said second composite signal comprises a phase inverter coupling the harmonic bass tone signal from said keyer circuits to said second tone coloring filter.

11. A bass tone producing device according to claim 1 wherein said means for reversing the phase of said harmonic bass tone signal in said second composite signal comprises means in said harmonic bass tone signal source for generating pairs of opposite phase harmonic bass tone signals, one of said bass tone signals being coupled to said first tone coloring filter, and the other of said bass tone signals, which is out of phase with respect to said one of said bass tone signals, being coupled to said second tone coloring filter.

BACKGROUND OF THE INVENTION

This invention relates to a bass tone producing device for use in an electronic musical instrument and more particularly to a bass tone producing device in which a bass tone is composed of a fundamental signal and harmonic signal.

As is well known, the bass tones of a musical instrument are played by the pedal keys to beat the rhythm of the music and to support melody and chord tones which are played by manual keys. A keyboard electronic musical instrument such as an electronic organ is so designed as to produce desired base tones upon its pedal key depression. The bass tone consists of a fundamental tone and harmonic tones mixed in a proper ratio. Bass tones thus composed can have an excellent sound effect where the performance is given in a relatively limited room, but have a drawback where the performance is given in an appreciably spacious hall, the bass tones presenting a muffled sensation rich in lower components due to the acoustic character of the hall that the lower components have longer reverberating time.

It is accordingly the object of this invention to provide a bass tone producing device for an electronic musical instrument capable of producing bass tones having a tone color like that of a tuba, for example, sounding clear even in a relatively large spacious hall.

SUMMARY OF THE INVENTION

The bass tone producing device of this invention delivers, upon depression of a pedal key of an electronic musical instrument, an ordinary bass tone signal consisting of a fundamental bass tone having a prescribed pitch and harmonic signals having pitches of a higher octave than that of the fundamental base tone mixed in a proper ratio as well as an additional bass tone signal consisting of the harmonics. The former bass tone signal is conducted through a first tone coloring filter having a relatively low peak frequency, while the latter bass tone signal is passed through a second tone coloring filter having a peak frequency higher than the first tone coloring filter. The filtered two bass tone signals are blended in a proper ratio with the phase of the latter reversed or suitably shifted so as to produce final desired bass tone signals, which are composed in good condition free from mutual complicated interference among the component signals. Tones reproduced by these composite bass tone signals have peak tone pressures (formants) in not only a relatively low frequency region but also a higher frequency region, so that where an electronic musical instrument is played in a spacious hall, the tones display an excellent rhythmical effect without presenting a muffled sensation rich in low pitch components as is often the case with the prior art bass tone producing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block circuit diagram of a bass tone producing device for a keyboard electronic musical instrument according to an embodiment of this invention;

FIG. 2 is a concrete circuit arrangement of the bass tone producing device of FIG. 1;

FIG. 3 is a curve diagram showing the rising and decaying characteristics of output bass tones from the device of FIG. 2;

FIG. 4 is a chart showing curves of the frequency characteristics of the respective filters included in the device of FIG. 2 and a curve of the actually measured frequency characteristics of composed bass tone signals;

FIG. 5 is a schematic block circuit diagram of a bass tone producing device according to another embodiment of the invention;

FIG. 6 is a concrete circuit arrangement of the device of FIG. 5;

FIG. 7 is a curve diagram showing the rising and decaying characteristics of two types of bass tone signals delivered from the different groups of keyer circuits of FIG. 6;

FIGS. 8A to 8E show actually measured frequency spectra of final output signals produced from the circuitry of FIG. 6 at different times in its decay; and

FIG. 9 indicates curves of the frequency characteristics of the filters and the mixed output in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A bass tone producing device according to the preferred embodiments of this invention will now be described by reference to the appended drawings.

FIG. 1 is a schematic block circuit diagram of a bass tone producing device according to an embodiment of the invention. There are provided, for each one of the keys (actually 13 or 25 or 32 keys are arranged in the order of musical notes, though only one of them is indicated), a 16' tone signal source 12 as a fundamental bass tone signal source, 8' and 4' tone signal sources 13 and 14 as harmonic bass tone signal sources. The source 12 is generally so designed as to generate a tone signal whose pitch is one octave lower than the notation notes in a musical staff, and is known as a 16-foot tone signal. Likewise, the harmonic bass tone signal sources generate an 8-foot tone signal and a 4-foot tone signal, respectively.

Output signals from the 16' tone signal source 12 and the 8' and 4' tone signal sources 13 and 14 are conducted via respective keyer circuits 15, 16 and 17 gang-actuated with the depression of the corresponding pedal key 11, and individual resistors R ₁ , R ₂ and R ₃ connected to the output terminals of the keyer circuits 15 to 17 to be mixed in a predetermined ratio. The bass tone signals thus mixed are supplied to a tone coloring filter 18 having a relatively low peak frequency to form a first composite signal. On the other hand, output signals from the 8' and 4' tone signal sources 13 and 14 are passed through the corresponding keyer circuits 16 and 17 and separate resistors R ₄ and R ₅ connected to the output terminals of the keyer circuits 16 and 17 to be mixed in a predetermined ratio and, after the phase is reversed by a phase inverter 19, are supplied to another tone coloring filter 20 having a higher peak frequency than the tone coloring filter 18 to form a second composite signal. The above-mentioned two composite signals delivered from both tone coloring filters 18 and 20 are introduced via individual resistors 6 and 7 to be blended finally in a predetermined ratio. The bass tone signal thus blended is properly amplified by an amplifier 21 to be fed to the next stage (not shown) in the instrument.

FIG. 2 is a concrete circuit arrangement of the bass tone producing device of FIG. 1. The fundamental bass tone signal source 12, and the harmonic bass tone signal sources 13 and 14 are constituted by a frequency divider chain 31 consisting of three cascade connected bistable multivibrators 121, 131 and 141 respectively including two transistors as TR ₁ -TR ₂ , TR ₃ -TR ₄ and TR ₅ -TR ₆ .

It will be noted that the tone signal sources (generally provided in a number of 85 or 97 corresponding to musical notes of C ₁ to C ₈ or C ₁ to C ₉ ) are formed of 12 master oscillators representing one octave of the highest musical scale and a plurality of frequency dividers cascade connected to the respective oscillators in turn. Accordingly, the first stage bistable multivibrator 141 constituting the 4' tone signal source 14 included in the frequency divider chain 31 has its input terminal 32 impressed with an output signal from a preceding frequency divider stage (not shown).

The keyer circuits 15 to 17 are constructed of emitter follower keyer circuits 151, 161 and 171 including transistors TR ₇ , TR ₈ and TR ₉ respectively whose bases are connected via forwardly directed diodes D ₁ , D ₂ and D ₃ to the collectors of the corresponding transistors of the bistable multivibrators 121, 131 and 141, for example, the right side transistors TR ₂ , TR ₄ and TR ₆ respectively. The aforesaid transistors TR ₇ , TR ₈ and TR ₉ have their collectors directly connected to a grounded positive source line 33, and their emitters connected via resistors R ₁₂ , R ₁₃ and R ₁₄ to a line 36 which is connected to a negative source line 35 via a resistor R ₁₁ and a normally open key switch 34 closed upon depression of the pedal keys 11. Between the line 36 and the negative source line 35 is connected a capacitor C ₁ . Between the line 36 and the positive source line 33 is connected in parallel a resistor R ₁₅ and a series circuit consisting of a resistor R ₁₆ and a variable resistor VR ₁ having a movable contact 37 connected to the positive source line 33.

The emitters of the transistors TR ₇ , TR ₈ and TR ₉ are respectively connected via the resistors R ₁ , R ₂ and R ₃ of the indicated values and a capacitor C ₅ to the base of a transistor TR ₁₁ included in an emitter follower amplifier 39 provided if required.

The tone coloring filter 18 is comprised of a low pass filter 181 including an inductor L ₁ and a capacitor C ₃ connected between one end of the inductor L ₁ and the positive source line 33. The inductor L ₁ has the other end connected via a coupling capacitor C ₄ to the emitter of the transistor TR ₁₁ .

The emitters of the transistors TR ₈ and TR ₉ are also connected to the base of a transistor TR ₁₀ included in a grounded-emitter amplifier 191 constituting the inverter 19 via the resistors R ₄ and R ₅ of the indicated values as well as via a coupling capacitor C ₂ connected to the common connection 38 of the resistors R ₄ and R ₅ .

The tone coloring filter 20 is formed of a band pass filter 201 including a group of an inductor L ₂ and a capacitor C ₇ and another group of an inductor L ₃ and a capacitor C ₈ , the two groups being connected in parallel between the positive source line 33 and the collector of the transistor TR ₁₀ via a coupling capacitor C ₆ and a resistor R ₁₇ . The amplifier 21 is formed of an emitter follower amplifier 211 including a transistor TR ₁₂ having its base applied through a coupling capacitor C ₉ with the aforesaid two mixtures of bass tone signals delivered from the low pass filter 181 and the band pass filter 201 after the mixtures are further blended together through the resistors R ₆ and R ₇ of the indicated values.

The operation of a bass tone producing device according to this invention will now be described by reference to FIG. 2. While any of the pedal keys 11 is not depressed, the corresponding key switch 34 remains open, the capacitor C ₁ is charged with source voltage through a parallel circuit consisting of the resistor R ₁₅ and the series circuit of variable resistor VR ₁ and resistor R ₁₆ . Accordingly, the line 36 has substantially the same voltage as the positive source line 33 to keep the transistors TR ₁₂ , TR ₁₃ and TR ₁₄ of the switching circuits 151, 161 and 171 nonconducting, deriving no bass tones.

Where, under this condition, a pedal key 11 is depressed by a player's foot, the corresponding key switch 34 is closed to cause the voltage stored in the capacitor C ₁ to be discharged through the resistor 11. In the later described length of transient time t ₁ after key depression, the line 36 has its voltage brought to substantially the same level as that of the negative source line 35. At this time, the transistors TR ₇ , TR ₈ and TR ₉ of the keyer circuits 151, 161 and 171 are triggered to be changed from a nonconducting to a conducting state, bringing the entire circuitry of FIG. 2 to a stationary operating condition. Thus the fundamental bass tone signal having a predetermined pitch and the harmonic bass tone signals thereof derived from the collectors of the respective right side transistors TR ₂ , TR ₄ and TR ₆ included in the bistable multivibrators are mixed through the corresponding diodes D ₁ to D ₃ , the now triggered keyer circuits 151, 161 and 171 and the corresponding resistors R ₁ to R ₃ . The mixed bass tone signals are properly amplified by the amplifier 39 and conducted to the low pass filter 181 to form a first composite signal. On the other hand, the harmonic bass tone signals from the corresponding triggered keyer circuits 161 and 171 are mixed through the corresponding resistors R ₄ and R ₅ and, after reversed in phase and properly amplified by the common emitter amplifier 191, conducted to the band pass filter 201 to form a second composite signal. The two composite signals obtained from both the filters 181 and 201 are further mixed together through the resistors R ₆ and R ₇ and properly amplified by the amplifier 211.

Where, under this condition, the depressed pedal key 11 is released, the corresponding key switch 34 is opened to have the capacitor C ₁ charged again with source voltage in the later described sustain time t ₂ after the release. Accordingly, the entire circuitry of FIG. 2 is rendered inoperative until the pedal key 11 is depressed next time.

The curve 41 of FIG. 3 shows the operating condition of the circuitry of FIG. 2 resulting from depression of a pedal key 11. The circuitry is brought to a stationary operating condition in the prescribed length of transient time t ₁ after key depression which is defined by a time constant representing the product of the capacitance of the capacitor C ₁ and the resistance of the resistor R ₁₁ . This operating condition is sustained until the release of the depressed pedal key 11. Upon the release, the circuitry of FIG. 2 is again rendered inoperable in the prescribed sustain time t ₂ determined by a time constant representing the product of the capacitance of the capacitor C ₁ and the composite resistance of the parallel circuit consisting of the resistor R ₁₅ and the series circuit of variable resistor VR ₁ and resistor R ₁₆ . The sustain time t ₂ can be freely varied within the range of t ₂ maximum and t ₂ minimum by the adjusted sliding of the movable contact 37 of the variable resistor VR ₁ . According to the circuitry of FIG. 2, the aforesaid prescribed length of transient time t ₁ and the maximum and minimum sustain times t ₂ maximum and t ₂ minimum are chosen to be t ₁ = 10 to 20 milliseconds, t ₂ maximum = 1.5 seconds and t ₂ minimum = 0.2 second respectively.

FIG. 4 shows curves 51 and 52 showing the actually measured frequency characteristics of the low pass filter 181 (together with the CR coupling network) and the band pass filter 201 of FIG. 2 according to a preferred design and a curve 53 indicating the actually measured frequency characteristics of mixed bass tone signals delivered from the last output. As apparent from FIG. 4, the low pass filter 181 (together with the CR coupling network) has the frequency characteristics that it has a peak frequency around 300 Hz and causes signals passing therethrough to attenuate 3 dB around 150 Hz and 600 Hz. In contrast, the band pass filter 201 has the frequency characteristics that it has a peak frequency around 1,000 Hz and causes signals passing therethrough to attenuate 3 dB around 800 Hz and 1,300 Hz. Since the two composite signals obtained from filters 181 and 201 are satisfactorily blended together, as previously described, in reverse phase, so that the mixtures are prevented from mutual complicated interference.

The bass tone produced by the mixture of the two composite signals has a peak tone pressure level around a relatively low frequency portion (around 300 Hz according to this embodiment) and also around a higher frequency portion (around 1,000 Hz according to this embodiment). The present inventor has experimentally found, therefore, that even where an electronic musical instrument is played in a spacious hall, the resultant bass tones obtained by the device of this invention do not present a muffled sensation rich in the aforesaid low frequency component as is often the case with the prior art bass tone producing device but bear a tone color like that of a tuba, providing a clear and distinctive tone effect.

FIG. 5 is a schematic block circuit diagram of a bass tone producing device according to another embodiment of this invention.

The point at which the embodiment of FIG. 5 differs from the preceding one is that the two composite signals have different amplitudes and different decaying envelopes, and that the harmonic bass tone signals are derived in both of the opposite phases for dispensing with a phase inverter. To this end, the circuitry of FIG. 5 causes a pair of 8' bass tone signals and a pair of 4' bass tone signals to be generated in the reverse phase from the 8' tone signal source 13a and the 4' tone signal source 14a respectively. The opposite-phase paired 8' tone signals from the 8' tone signal source 13a are respectively conducted to separate keyer circuits 16a ₁ and 16a ₂ . Similarly, the opposite-phase paired 4' tone signals from the 4' tone signal source 14a are respectively supplied to separate keyer circuits 17a ₁ and 17a ₂ . The circuitry of FIG. 5 causes the 8' and 4' tone signal sources 13a and 14a concurrently to act as the inverter 19 of FIG. 1, eliminating the necessity of providing a separate inverter. The other parts of the circuitry of FIG. 5 have substantially the same arrangement as the corresponding parts of FIG. 1 and are denoted by the corresponding numerals, description thereof being omitted.

FIG. 6 is a concrete circuit arrangement of FIG. 5. As in FIG. 2, the 16' tone signal source 12a and the 8' and 4' tone signal sources 13a and 14a jointly constitute a frequency divider chain 31a consisting of three cascade connected bistable multivibrators 121a, 131a and 141a, each including two transistors as TR ₂₁ -TR ₂₂ , TR ₂₃ -TR ₂₄ and TR ₂₅ -TR ₂₆ . Keyer circuits 15a, 16a ₁ and 17a ₁ are constituted of emitter follower circuits 151a, 161a ₁ and 171a ₁ including transistors TR ₂₇ , TR ₂₈ and TR ₂₉ respectively which have their bases connected via forwardly directed diodes D ₁₁ , D ₁₂ and D ₁₃ to the collectors of respective left or right side transistors included in the bistable multivibrators 121a, 131a and 141a, for example, the left side transistors TR ₂₁ , TR ₂₃ and TR ₂₅ of each of the aforementioned three groups. The transistors TR ₂₇ to TR ₂₉ have the collectors directly connected to the grounded positive source line 33 and the emitters connected via resistors R ₂₁ , R ₂₂ and R ₂₃ respectively, to a line 36a ₁ which is connected to the negative power source line 35 via a capacitor C ₁₁ . Output signals delivered in the later described manner from the emitters of the transistors TR ₂₇ to TR ₂₉ are supplied to a low pass filter 181a through corresponding resistors R _1a to R _3a , the coupling capacitor C ₅ , an emitter follower circuit 39a and the coupling capacitor C ₄ in turn. On the other hand, the aforesaid keyer circuits 16a ₂ and 17a ₂ are comprised of emitter follower keyer circuits 161a ₂ and 171a ₂ including transistors TR ₃₀ and TR ₃₁ which have their bases connected via forwardly connected diodes D ₁₄ and D ₁₅ to the collectors of the right side transistors TR ₂₄ and TR ₂₆ of the respective groups of transistors included in the 8' and 4' tone signal sources 131a and 141a which correspond to the keyer circuits 16a ₂ and 17a ₂ . The transistors TR ₃₀ and TR ₃₁ have their collectors directly connected to the positive power source line 33 and their emitters connected via resistors R ₂₄ and R ₂₅ to a line 36a ₂ which is connected via a capacitor C ₁₂ to the negative power source line 35. Output signals delivered in the later described manner from the emitters of the transistors TR ₃₀ and TR ₃₁ are supplied, as in the case of FIG. 2, to a band pass filter 201a through corresponding resistors R _4a and R _5a and the coupling capacitor C ₆ .

There is further provided a trigger circuit 61 of the undermentioned arrangement so as to trigger the aforementioned keyer circuits 15a, 16a ₁ , 17a ₁ , 16a ₂ and 17a ₂ upon depression of a pedal key 11. The trigger circuit 61 includes a series circuit of a resistor R ₂₆ , the normally open key switch 34 and a capacitor C ₁₃ connected across the positive and negative source lines 33 and 35. A common connection 62 to the key switch 34 and the capacitor C ₁₃ is connected to a common connection 64 to two resistors R ₂₇ and R ₂₈ connected in series between the base of a transistor TR ₃₂ included in a common emitter trigger circuit 63 and the negative source line 35. The transistor TR ₃₂ has its emitter connected via a resistor R ₂₉ to the negative source line 35 and also via a resistor R ₃₀ to the positive source line 33. Further, the transistor TR ₃₂ has its collector connected via a resistor 31 to the positive source line 33 and also via a coupling capacitor C ₁₄ to the input terminal 66 of a one-shot multivibrator 65 which includes two transistors TR ₃₃ and TR ₃₄ , and further a feedback capacitor C ₁₅ connected between the collector of the rear side transistor TR ₃₄ used as the output terminal 67 of the one-shot multivibrator 65 and the base of the front side transistor TR ₃₃ used as the input terminal of the one-shot multivibrator 65. The transistor TR ₃₃ has its base connected via a resistor 32 to the positive source line 33. Both transistors TR ₃₃ and TR ₃₄ have their collectors connected via resistors R ₃₃ and R ₃₄ to the positive power source line 33 and also their emitters jointly connected to the negative source line 35.

The collector 67 of the transistor TR ₃₄ constituting the output terminal of the one-shot multivibrator 65 is connected to the line 36a ₁ via a diode D ₁₆ of the indicated polarity and a resistor R ₃₅ and also to the line 36a ₂ via a resistor R ₃₆ . Between the line 36a ₁ and the positive power source line 33 is connected a series circuit consisting of a diode D ₁₇ of the indicated polarity, a resistor R ₃₇ and a variable resistor VR ₁₁ . The variable resistor VR ₁₁ has its movable contact 68 connected to the positive power source line 33. There is further provided a diode D ₁₈ of the indicated polarity between a common connection 69 to the diode D ₁₇ and the resistor R ₃₇ and a common connection 70 to the resistor R ₂₆ and the key switch 34.

The operation of a bass tone producing device arranged as described above according to the second embodiment will now be described by reference to FIG. 6.

While the pedal key 11 is not depressed, the corresponding key switch 34 remains open and the one-shot multivibrator 65 has its front side transistor TR ₃₃ rendered conductive and its rear transistor TR ₃₄ rendered nonconductive. Accordingly, the collector 67 of the transistor TR ₃₄ has substantially the same voltage as that of the positive source line 33, so that the capacitor C ₁₁ is charged with source voltage through the series circuit of the variable resistor VR ₁₁ , resistor R ₃₇ and forwardly biased diode D ₁₇ , and the capacitor C ₁₂ is charged with source voltage through the series circuit of the resistors R ₃₄ and R ₃₆ . In this case, the diode D ₁₆ is reversely biased electrically to insulate the lines 36a ₁ and 36a ₂ from each other. Accordingly, the lines 36a ₁ and 36a ₂ have substantially the same voltage as the positive power source line 33, keeping nonconducting all the transistors TR ₂₇ to TR ₃₁ included in the keyer circuits 15a, 16a ₁ , 17a ₁ , 16a ₂ and 17a ₂ . As the result, there is not delivered any bass tone.

Where, under this condition, a given pedal key 11 is depressed, the corresponding key switch 34 is closed to cause the capacitor C ₁₃ to be charged with source voltage through the resistor R ₂₆ and also the transistor TR ₃₂ of the trigger circuit 63 to have its base supplied with the now stepped-up voltage. Since the transistor TR ₃₂ is brought from a nonconducting to a conducting state, its output signal triggers the one-shot multivibrator 65 to reverse the condition of the transistors TR ₃₃ and TR ₃₄ included in the multivibrator 65, that is, to render the former nonconductive and the latter conductive. But after the predetermined short time (e.g. 10 ms), the one-shot multivibrator comes back to the original state. Accordingly, the collector 67 of the transistor TR ₃₄ has the voltage momentarily brought up to substantially the same level as that of the negative power source line 35 decaying subsequently. As the result, the capacitor C ₁₁ has its stored energy discharged through the resistor R ₃₅ , the forwardly biased diode 16 and the energized transistor TR ₃₄ included in the multivibrator 65 in turn. Similarly the capacitor C ₁₂ has its charged voltage released through the resistor R ₃₆ and the now energized transistor TR ₃₄ .

The lines 36a ₁ and 36a ₂ have their voltages changed from that of the positive power source line 33 to a level substantially equal to that of the negative power source line 35 in the later described lengths of transient time t ₁₂ and t ₁₃ after depression of a pedal key 11, thus bringing the entire circuitry of FIG. 6 including the keyer circuits 151a to 171a ₂ to a momentarily operating condition. Accordingly, all the transistors TR ₂₇ to TR ₃₁ included in the keyer circuits 151a to 171a ₂ are triggered to a conducting and then back to a non-conducting state. Thus the fundamental bass tone signal having the predetermined pitch and the harmonic bass tone signals thereof which are delivered from the collectors of the respective left side transistors TR ₂₁ , TR ₂₃ and TR ₂₅ included in the bistable multivibrators 121a, 131a and 141a are mixed through the separate keyer circuits 151a, 161a ₁ and 171a ₁ and resistors R _1a to R _3a and, after properly amplified by the amplifier 39a, supplied to the low pass filter 181a to form a first composite signal having a percussive envelope. On the other hand, the harmonic bass tone signals which are delivered from the collectors of the respective right side transistors TR ₂₄ and TR ₂₆ included in the bistable multivibrators 131a ₂ and 141a ₂ in reverse phase to those obtained from the collectors of the left side transistors TR ₂₃ and TR ₂₅ are mixed through the corresponding keyer circuits 161a ₂ and 171a ₂ and resistors R _4a and R _5a and conducted to the band pass filter 201a to form a second composite signal having a percussive envelope. The two composite signals delivered from both the filters 181a and 201a are further blended together through the respective resistors R _6a and R _7a and amplified by the amplifier 211a.

The curves 71 and 72 in FIG. 7 illustrate the rising and decaying characteristics of output level of the respective composite signals upon depression of the pedal key 11. As apparent from FIG. 7, the transistor TR ₃₂ of the trigger circuit 63 is brought from a nonconducting to a conducting state and as the result, the transistors TR ₃₃ and TR ₃₄ of the one-shot multivibrator 65 have their conditions reversed, that is, the front side transistor TR ₃₃ is momentarily rendered nonconductive and the rear side transistor TR ₃₄ conductive but subsequently both of the transistors come back to original states. Thus the collector 67 of the transistor TR ₃₄ has the voltage abruptly changed from that of the positive power source line 33 to a level substantially equal to that of the negative power source line 35 and gradually back to the former. According to the aforesaid discharge of the capacitor C ₁₁ , the line 36a ₁ has its voltage brought from that of the positive power source line 33 to a level substantially equal to that of the negative power source line 35 in the prescribed length of transient time t ₁₂ which is defined by a time constant representing the product of the capacitance of the capacitor C ₁₁ and the series composite resistance of the resistor R ₃₅ , the forwardly biased diode D ₁₆ and the energized transistor TR ₃₄ . Similarly according to the aforesaid discharge of the capacitor C ₁₂ , the line 36a ₂ has its voltage brought from that of the positive power source line 33 to a level substantially equal to that of the negative power source line 35 in the prescribed length of transient time t ₁₃ (in the circuitry of FIG. 6 t ₁₂ is chosen to be equal to t ₁₃ ) which is defined by a time constant representing the product of the capacitance of the capacitor C ₁₂ and the series composite resistance of the resistor R ₃₆ and the energized transistor TR ₃₄ . Accordingly, the entire circuitry of FIG. 6 is brought to a full operating condition quickly and then is subjected to gradual change to non-operating state. As the collector 67 of the transistor TR ₃₄ has the voltage again changed from that of the negative power source line 35 to a level substantially equal to that of the positive power source line 33, the line 36a ₁ has its voltage changed again due to the aforesaid change of the capacitor C ₁₁ from that of the negative power source 35 to a level substantially equal to that of the positive power source line 33 after the sustain time t ₁₄ for the first composite bass tone signals composed of a 16' bass tone and an 8' and a 4' bass tone, the sustain time t ₁₄ being represented by the product of the capacitance of the capacitor C ₁₁ and the internal resistances of the working transistors TR ₂₇ , TR ₂₈ and TR ₂₉ and the resistors R ₂₁ , R ₂₂ and R ₂₃ , as the point 69 is made negative through the diode D ₁₈ . Similarly, the line 36a ₂ has its voltage changed from that of the negative power source line 35 to a level substantially equal to that of the positive power source line 33 after the sustain time t ₁₅ for the second composite bass tone signals free from the 16' bass tones and only consisting of the 8' and the 4' bass tones, the sustain time t ₁₅ being represented by the product of the capacitance of the capacitor C ₁₂ and the internal resistances of the working transistors TR ₃₀ and TR ₃₁ and the resistors R ₂₄ and R ₂₅ . At this time, the entire circuitry of FIG. 6 is brought to a fully inoperable state. Upon release of a pedal key 11, the transistor TR ₃₂ of the trigger circuit 63 is brought from a conducting to a non-conducting state but the transistors TR ₃₃ and TR ₃₄ of the one-shot multivibrator 63 are not affected at all. If the pedal key is released amidst the decaying period, the point 69 is released from the negative potential, and then the capacitor C ₁₁ is also charged through the diode D ₁₇ , the resistor R ₃₇ and the variable resistor VR ₁₁ expediting the charging operation. Thus the decaying envelope would be changed to 71a or 71b, the slope being controlled by the variable resistor VR ₁₁ .

FIGS. 8A to 8E are the frequency spectra of the finally produced bass tone as measured at certain time intervals. FIG. 8A shows the spectrum of the bass tone when the entire circuitry of FIG. 6 is in a full operating condition, and FIGS. 8B to 8E indicate the spectra measured about 100, 200, 300 and 400 milliseconds after the condition of FIG. 8A.

Referring to the circuitry of FIG. 6, the low pass filter 201a is chosen to have such frequency characteristics that as shown by the curve 51a of FIG. 9, the filter has a peak frequency of about 150 Hz and causes signals passing therethrough to attenuate 3 dB at about 80 Hz and 200 Hz. This arrangement enables bass tones of lower frequency than those possible with the preceding embodiment to be reproduced. Obviously, the frequency characteristics of the low pass filter 201a and band pass filter 181a may be suitably designed to meet the object and applications of an electronic musical instrument intended.

While the resistors R _1a to R _7a may also be chosen to have such resistance as conforms with the object and applications of the electronic musical instrument, the circuitry of FIG. 6 uses resistors having the values of resistance indicated therein.