US2139023A - Electrical generation of musical tones - Google Patents

Description

Dec. 6, 1938. w. E. KOCK 2,139,023

ELECTRICAL GENERATION OF MUSICAL TONES Filed Aug. 23, 1935 3 smeris-sheet 1 L P fg-@- P d We f`f6`. FIG'. Z f'fl 3 1 p1 Pa 2B F/G'. 4

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ELECTRICAL GENERATION OF MUSICAL TONES Filed Aug. 23, 1955 5 Sheets-Sheet 2 BY I Mam Dec. 6, 1938.

w. E. KocK 2,139,023

ELECTRICAL GENERATION OF MUSICAL TONES 3 Sheets-Sheet .'5

Filed Aug. 25, 1935 Mmmm UNITED STATES PATENT OFFICE Winston E. Kock, Cincinnati, Ollio, assigner to l 'Ille Baldwin Company. Cincinnati, Ohio Application August 23, 1935. Serial No. 37,547

My invention relates to improvements in musical instruments of the type employing electrical voscillators of audible frequency for the production of tone.

It is found desirable in such electrical muslcal instruments to be able to produce many types of timbres or tone colors with one oscillator or with one set of oscillators in order to permit variations in registration. In the present invention I present several methods of improving the performance of an electrical musical instrument by providing distinct and novel means for varying its tone quality and tonal effects.

More specifically, I propose to set forth the manner of combining certain circuits to form tones resembling the diierent stops of a pipe organ or that can be combined in such a manner as to imitate some of the orchestral timbres.

One such method is the introduction of socalled formants or damped oscillations. It is known, for example, that the characteristic tone color of brass instruments, such asv the trumpet or trombone, is imparted by the bell of the instrument. The pulsations of air being expelled from the trumpet set the iiared bell into damped vibrations and these are heard superimposed upon the pulsating note issuing from the instrument. Excessive damping of these already slightly damped oscillations by means of a mute inserted into the trumpet completely changes the timbre of the instrument.

In order t'o reproduce faithfully these characteristic tone colors by electrical means, it is therefore necessary to be able to set up oscillations which are not excessively damped. Now an ordinary electrical circuit with inductance and capacity is capable of being jarred into damped electrical waves by means of a suitable excitation or shock. However, due to the fact that the inductance will of necessity possess a cer tain amount of electrical resistance these electrical waves are of very short duration, i. e., they are strongly damped, because the pulsating iiow of energy is rapidly absorbed by this resistance. Means for overcoming this difficulty are herein described.

A modification of this method consists in combining one or more harmonics of constant intensity together with the basic tone and formant. For example, certain orchestral timbres, in addition to possessing one or more formants, are known to possess strong fourth and fifth harmonies throughout their entire register. In'an electrical musical instrument of the electric organ type this can be accomplished by arranging several contacts on one key so that in addition to the basic tone being heard along with its electrically excited formant. the oscillators generating those tones which would correspond to the desired partials are connected to the amplifier and impart their timbre to the final tone.

Referring now to the drawings, Fig. 1 is a diagram of a circuit for producing formants of any desired damping.

Fig. 2 is a diagram of a heavily damped wave form.

Fig. 3 is a weakly damped wave form.

Fig. 4 is a periodic recurrence of damped oscillations.

Fig. 5 shows a formant circuit excited by an inductive glow discharge oscillator.

Fig. 6 shows the impulses of the voltage of the inductive glow discharge oscillator which act upon the formant circuit.

Fig. 7 shows the wave form of the output voltage and indicates how the formants are generated by the excitation impulses of Fig. 6.

Fig. 8 shows a formant circuit arranged for the production of low formants and excited by an inductive glow discharge oscillator.

Fig. 9 shows a formant circuit excited by a plurality of oscillators.

Figs. 10, l2 and 13 are modifications of formant circuits.

Fig. 11 is a, graph showing the eiect of the formant circuit on the oscillator characteristics.

Fig. 14 is a complete diagram of a number of notes.

Figs. 15, 16 and 17 are diagrams of filter circuits.

In Fig; 1 of the drawings, the circuit consists of the glow lamp G, the condenser C, and inductance L, a resistance R, and a source of current B. The circuit is tuned to the desiredy frequency by varying the values of L and C. As the voltage B is increased, a point is reached Where the oscillations break off and the glow lamp G remains ignited all the time. 'I'he circuit is then in a condition to produce damped oscillations; and, when a shock of some kind is introduced, there is produced a wave form as shown in Fig, 2, possessing a frequency determined by the values of L and C. By decreasing the voltage B slightly, but still maintaining a suilciently high voltage on the glow lamp toinsure that it remains ignited continuously, andv then again exciting the circuit, a wave formas shown in Fig. 3 is created with the frequency unchanged from that of Fig. 2, that is, the damping can be decreasedby decreasing the voltage B. In the application to produce formants, a periodic succession of shocks is applied in order to produces. series ofdamped waves as shown in Fig. 4. If this periodic succession possesses a frequency of only several shocks per second, a tone similar to that of a xylophone or marimba is produced. As the frequency of the shocks is increased so as to reach the audible range, say several hundred shocks per second, the damped oscillations impart a characteristic tone'color to the fundamental tone which produces the shocks, and the frequency of these periodic shocks as shown at the peaks P, determines the pitch of the tone. i

Oscillators which generate the shocks can be any of several types, such as: vacuum tube, neon oscillator, Thyratron, or inductive glow discharge oscillator. A

For example, in Fig. 5 a circuit is shown of an inductive glow discharge oscillator O as set forth in my United States Patent No. 2,046,463, issued July 7, 1936, from a copending application Serial #701,1'13, filed December 6, 1933. Each time the tube G ignites or goes out a discontinuity occurs in the wave form of the voltage across the tube and hence also across the inductance. Transferring this voltage by condenser C1 to a formant circuit M, the discontinuities will be accentuated and there will be produced in the output a wave form similar to that of Fig. 6. The high peaks in Fig. 6 are produced when the glow discharge tube G in the oscillaor circuit ignites and the part of the wave form represented by S occurs when the tube goes out.

Since this voltage from the oscillator circuit is impressed on the formant circuit, the peaks shock the circuit, producing damped waves, as represented by Fig. '7, and impart a pronounced tone color to the wave sent to the amplifier.

In the circuit as shown in Fig. 5 the condenser C1 is very small, thus causing a high frequency formant with the effect of the oboe, bassoon or trumpet. To accentuate the lower frequencies as shown in Fig. 8, the condenser C2 is larger than that shown in Fig. 5. 'Ihe condenser C3 in Fig. 8 is made variable to permit the performer to execute a continuous change of tone color.

Many fundamental tones may be played at the same time and then be made to excite the same formant circuit as shown in Fig. 9. One formant can be used with a number of notes in a certain part of the scale, although the formants will have to change as the frequency rises. In Fig. 9 circuits O and O1 correspond to the oscillator in Fig. 5 and the condensers C4 and C5 act the same as condenser C1 in Fig. 5, the value depending on the part of the scale in which the generators are located. The same generators may excite several formant circuits at the same time and reproduce a number of orchestral tone timbres, as will be clear from the circuit arrangement ,of Fig. 9, if O and O1 are considered as formant circuits and M as an oscillator circuit.

The damping must not be decreased too far because the non-linearity so produced would cause objectionable distortion in amplifying sev- 'eral notes at a time.

In Fig. 10, in place of a simple inductance in the inductive glow discharge oscillator, atransformer is used having a fairly high impedance in both legs and a very small condenser "is connected across the secondary. I'his secondary circuit is capable of producing strongly damped formants, as mentioned above, and the excitation shocks of the primary inductive glow oscillator circuit, transferred by means of the transformer action to the secondary circuit, will excite formants of a frequency determined by the size of Cs and of the transformer constants. In thismanner a very simple method of adding a formant to its output wave is obtained (it will be observed that this formant will be transferred to the primary and hence to the output wave) and each note of the scale can have its resonator" adjusted to reproduce any desired organ pipe. This composite oscillator would replace. in an electrical organ, for example, my inductive glow oscillator as set forth in my copending application referred to, and one oscillator would be employed for each note.

A further advantage of this method is that the formant circuit is reflected by the transformer into the generating circuit and, having a resonant period of its own, tends to exert a control over the-frequency of the oscillator. and the oscillator is forced to oscillate at one of the sub-harmonics of the secondary circuit. This is illustrated in Fig. 11, which shows a typical curve of frequency vs. voltage. It is observed that the frequency does not increase uniformly to the resonant frequency, as in my inductive glow discharge oscillator, but increases stepwise, and the topmost step is extremely fiat. Thus the pitch stability against voltage fluctuations and other variables is increased over that of the inductive glow discharge oscillator.

A somewhat similar effect can be obtained by placing this small condenser Cs directly across the main inductance as shown in Fig. l2. Here the circuit consisting of L and Cs constitute the formant circuit and stabilization is also obtained.

When a transformer is used having a high distributed capacity, it is sometimes unnecessary to connect the additional condenser Cs across the secondary. Fig. 13 illustrates how the distributed capacity of the inductance may produce the same effect as a small condenser. The condensers C7 are merely representative of the distributed capacity of the inductance L.

It will be noticed that the circuit of Fig. l0 is really a two section filter and therefore presents a narrower resonance band to the oscillator frequencies and increases the stabilization of the generator.

'I'hus any filter circuit which can improve the sharpness of resonance of the simple filter circuit (inductance and condenser) in my inductive glow discharge oscillator will improve its stability. Additional types of 2-section filters, coupled to a neon oscillator, are given in Figs. 15, 16 and 17. Fig. 15 shows a two section filter with inductive coupling, Fig. 17 one with capacity coupling, and Fig. 16 shows a still different type of filter coupling. All three of these circuits improve the stability by presenting a sharper resonance band which tends to hold the oscillator frequency at the proper pitch against larger voltage variations.

This improvement in stabilization can be applied to almost any type of relaxation oscillator, for example the dynatron or the relaxation inverter. By using a filter of several sections in place of the simple circuit of inductance and capacity, the sharpness of resonance can be increased so that the relaxation oscillator is held 70 more firmly to the frequency desired.

In Fig. 14 a circuit of three notes is shown where the tone generators T1, T2 and Ta are connected thru the switches or keys S to a pre-amplifier A where the tones are amplified. They then this composite tone.

may be passed thru lters controlled by switches S1 and Sz if desired, or,v may be passed to a formant circuit M controlled by switch Sa.

If the switch controlling the tone generator T1 were closed and the switch Sz were closed, the current generated in Ti would pass thru the preamplifier and the low harmonics would be filtered out, while if switch S1 were closed the high harmonies would be filtered out. If the switch S3 were closedinstead, the tone generated would excite the formant circuit F3 to produce the combination of the basic tone and a formant before going to the main ampliner and sound producing means. As many tones can be played as desired and all will undergo the particular tone color modification introduced by closing any of the switches Si, Sz, and S3. The main amplifier then increases their intensity to the desired level and the loudspeaker converts the electrical oscillations into sound waves.

As mentioned earlier in the specification, it is sometimes desirable to add to a particular tone certain harmonics of definite intensity, in addition to a formant. One possible method of accomplishing this is given in Fig. 14. Consider that the generators T1, T2 4and T3 are each an octave apart, T1 oscillating, let us say, at 440 cycles, T2 at 880 and T3 at 1760 cycles. T2 would then produce a frequency which corresponds to the second harmonic of T1, and T3 a frequency which corresponds to the 4th harmonic of T1. By aiiixing three contacts S to the key corresponding to the generator T1, as that particular note of the scale is depressed, all three frequencies will be heard. Their relative amplitudes can be adjusted to the desired level by properly selecting the resistances R. This produces a note of a particular tone color, possessing :T 2nd and 4th harmonic of a definite intensity. If switch Ss is closed, Ithe formant will be heard along with In the diagram, the frequencies T2 and T3 also excite the formant circuitwhich may or may not be desirable. It is a simple procedure to have the switches S corresponding to the two frequencies T2 and T3 connected directly (or through a different fiiter system from F1) to the amplifier so that only the formant excited by the basic tone T1 is heard along with the composite tone.

Many other modifications may be made and still come within the scope of my invention. What I claim as my invention is:

1. In an electrical musical instrument, a tone generator consisting of a source of current, a resistance and glow tube and an inductance and condenser connected in series across the glow tube, another circuit consisting of a source of current, a resistance and glow tube, and an inductance and condenser in series across the glow tube, the output of the first named circuit being connected to the second named circuit and the output of the second named circuit being connected to an amplier and sound producing means.

2. vIn an electrical musical instrument, a tone generator consisting of a source of current, a resistance, a glow tube and an inductance and condenser connected in series across the glow tube and a second circuit consisting of a source of current, a resistance, a glow tube and an inductance and a condenser in series across the glow tube, the output of the first named circuit being connected to the second named circuit with a condenser in between and the output of the second named circuit being connected to an amplifier and a sound producing means.

3. In an electrical musical instrument, a tone generator in one circuit and a tone timbre modifier in another circuit, the output of the first named circuit being connected to the input of the second named circuit thru a condenser and the output of the second named circuit being connected to an amplifier and sound producing means.

4. In an electrical musical instrument, aplurality of means for generating oscillations of predetermined different frequencies, an intermediate circuit arranged in conjunction therewith, means for selectively associating said intermediate circuit with one or more of said generating means so as to transfer to said intermediate circuit electrical oscillations of desired frequencies, at least one formant circuit comprising oscillation generating means arranged, upon excitation, to produce damped oscillations, a connection between said intermediate circuit and said formant circuit for exciting said formant circuit, an output circuit for said electrical musical instrument, means for selectively connecting said output circuit to said intermediate circuit for the transference of substantially unmodified oscillations therefrom, and for selectively connecting said output circuit to said formant circuit for the transference of oscillations from said formant circuit comprising the combined frequencies of the oscillations in said intermediate circuit and the damped oscillations generated in said formant circuit.

5. In an electrical musical instrument, a plurality of means for generating oscillations of predetermined diiferent frequencies, at least one formant circuit comprising oscillation means arranged, upon excitation, to produce damped oscillations, means for selectively connecting said formant circuit with one or more of said generating means so as to transfer to said formant circuit electrical oscillations of desired frequencies, an output circuit for said electrical musical instrument, means for selectively connecting said output circuit with one or more of said generating means for the transference of substantially unmodified oscillations therefrom, and for selectively connecting said output circuit to said formant circuit for the transference of oscillations fromv said formant circuit comprising the combined frequencies of the oscillations of at least one of said generating means and damped oscillations generated in said formant circuit.

6. In an electrical oscillator a glow discharge tube, a feed circuit therefor comprising a resistance and a source of potential, and a control circuit therefor which is a tuned circuit comprising a capacity and an inductance, and means for further stabilizing the glow tube oscillator thus formed, said means comprising a second tuned circuit coupled to said control circuit.

7. In an electrical oscillator a glow discharge tube, a feed circuit therefor comprising a resistance and a source of potential, and a control circuit therefor which is a tuned circuit comprising a capacity and an inductance, and means for further stabilizing the glow tube oscillator thus formed, said means comprising a second tuned circuit coupled to said control circuit, said last mentioned tuned circuit comprising an inductance and a capacity and an inductance in said first mentioned control circuit acting as the coupling means between said two circuits.

8. In an electrical oscillator a glow discharge tube, a feed circuit therefor' comprising a resistance and a source of potential, and a control circuit therefor which is a tuned circuit comprising a capacity and an inductance, and means for further stabilizing the glow tube oscillator thus formed, said means comprising a second tuned circuit coupled to said control circuit, said second tuned circuit comprising a capacitg7 and an inductance, and coupling means between said second tuned circuit and said irst mentioned control circuit comprising a capacity.

9. .an electrical glow discharge tube oscillator comprising a glow discharge tube, a fed circuit therefor containing a source of potential and a resistance, and a control circuit therefor containing a capacity and inductance, said inductance comprising in part at least a winding of a transformer, said transformer having a second winding and a capacity connected across said second winding whereby to tune the same.

lll. in combination an input circuit, a source ci electrical oscillations in said input circuit, an output circuit and a formant circuit, said formant circuit comprising an over-damped glow discharge tube oscillator, a connection between said input circuit and said formant circuit, and a connection between said formant circuit and said output circuit.

li. lin combination an input circuit, a source oi electrical oscillations in said input circuit, an output circuit and a formant circuit, said formant circuit comprising an over-damped glow' discharge tube oscillator, a connection between said input circuit and said formant circuit, a connection between said formant circuit and said output circuit, and a connection between said input circuit and said output circuit whereby said output circuit will receive electrical oscillations from said and said formant circuit comprises a series capacity.

13. In combination in an electrical musical instrument a plurality of oscillation generators, an input circuit, means for connecting said generator selectively to said input circuit, a. formant circuit having means therein for producing damped oscillations, an output circuit, a connection between said formant circuit and said input circuit, a. connection between said formant circuit and said output circuit, and a connection between said input circuit and said output circuit, whereby said output circuit receives oscillations from said input circuit plus modied oscillations as produced by said formant circuit.

14. Means as set forth in claim 13, wherein said connection between said input circuit and said output circuit contains illter means.

15. A glow discharge tube circuit adapted to produce damped oscillations comprising a glow discharge tube, a feed circuit therefor containing a source of potential and a resistance, and a control circuit therefor comprising at least a capacity and an inductance. said source of potential being high enough to maintain said tube in a state o! continuous discharge.

16. In a glow discharge tube oscillator comprising a glow discharge tube, a feed circuit therefor, and a tuned stabilizing circuit controlling the frequency of oscillations of said oscillator, means for further stabilizing said oscillator comprising a second tuned circuit inductively coupled to the first-mentioned tuned circuit of said oscillator. WINSTON E. KOCK.

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