US2036892A - Art of producing musical sounds electrically - Google Patents

Description

April 7, 1936. G. SMILEY 2,036,892

ART OF PRODUCING MUSICAL SOUNDS ELBCTRICALLY Filed Dec. 4, 1933 2 Sheets-Sheet 1 Ill a G P 5 1; 5 n w- -mm Time In Time 1P2 lr ngzNToR BY 2 M4... Quil ATTORNEYS Eci Ajaril 7, 1936. 4 G. SMILEY 2,036,892

ART OF PRODUCING MUSICAL SOUNDS ELECTRiCALLY Filed Dec. 4, 1933 2 Sheets-Sheet 2 5 g INVENTOR ATTORNEYS Patented Apr. 7, 1936 UNITED STATES her or raonucme MUSICAL sounns amc'rmcmr Gilbert Smiley, Brighton, Masm, assignor to Pratt,

Read a company, Deep River. W com- R S S U E D Application December 4, 1933, Serial Nil- 700,837

ration of Connecticut Claims.

My present invention has for its object to produce musical sounds electrically. A more specific object of my invention is to provide a circuit arrangement for producing an output wave which 5 possesses the harmonics, required under certain conditions, to render a given note musically desirable or pleasing to the ear.

Still another object contemplated is the provision of means for adding to a more or less pure 1o sinusoidal wave of given frequency, as derived from an appropriate oscillator or appropriate oscillators, one ormore additional harmonics of the fundamental of said wave at a proper amplitude, or for the reinforcement of harmonics already present but of insuflicient amplitude, by

the use of a vacuum tube repeater from the output of which the resultant wave form may be amplified and reproduced by a loud speaker.

To these and other ends my invention comprises further improvements all of which will be more fully set forth in the following specification and the novel features pointed out in the accompanying claims.

In the drawings:

Fig. 1 is a diagrammatic illustration of a ,vacuum tube circuit for repeating audible frequency oscillations and applying thereto the desired characteristic wave form.

"Figs. 2 to 5 are plate-current curves versus grid-potential curves, illustrating the manner in which invention is accomplished.

Fig. 6 is a schematic illustration of a means for effecting simultaneous adjustments of grid supply-potential and input wave amplitude.

Similar reference characters in the several figures indicate like parts.

In illustrating my invention I have shown a repeater circuit comprising a vacuum tube V having a plate P, a grid G and a cathode K. The 40 input circuit, across which the incoming oscillations are impressed, comprises the conductors l and 2, the former leading through a blocking condenser Co to one end of a voltage-divider 3 the slider 3a of which is connected by a conductor 5 4 to the grid G, and the latter leading directly to the cathode K. The other end of the divider 3 is connected to the cathode by a conductor 5 in which a biasing source of potential Ec for the grid is provided. The output circuit comprises the plate and cathode leads 6 and I, which may be connected to an amplifier 8 in turn feeding into aloud speaker 9, as will be understood. The plate lead 6 has a blocking condenser Cp connected therein. The plate-cathode circuit comprises the source Eb for supplying the operating potential to the plate P and the resistance R through which said potential is supplied and which serves as a coupling resistance in the output circuit. The condensers Co and Cp prevent the operating D. C. potentials from being transmitted through the input and output terminals to the instrumentalities connected thereto.

Any convenient source or sources of oscillations feed into the input conductors l and 2. In Fig. 1 I have shown a single source S connected to these conductors. In my development of musical instruments for the playing of chords, however, I employ a series of independent or dependently related sources of oscillations, such as vacuum tube oscillatory circuits, tuned to the various frequencies called for by the various keys of the keyboard. I'hus several or all of these oscillatory circuits may be adapted to feed into the repeater circuit shown in Fig. 1, each oscillatory circuit so connected being arranged to supply a proper proportion of its output when the key associated with the frequency or note which it produces is struck or depressed. If desired, a separate repeater circuit may nevertheless be provided for each of the sources, each repeater circuit receiving the proper intensity of output from its associated source when the latters key is depressed. Forthe production of single notes, the repeater circuit of Fig. 1 may be associated with a single oscillator, the frequency of which is controllable by suitable means cooperating with the keyboard.

I have found in practice that in many "of the types of oscillators or generators of audible frequency voltage waves, the wave form produced is too pure, 1. e., too close to a sinusoidal wave to create various desirable musical effects. In other words, such a wave form does not reproduce a musical note acceptable for many purposes, as it is lacking in timbre.

My invention contemplates broadly introducing an oscillatory wave of a pure or insufficiently impure form into a repeater circuit and there introducing the necessary harmonics to produce what is known in a musical sense as overtones, the final output from the repeater being a wave form which, by proper control, is caused to render a note similar or identicalto that sounded by an instrument it may be desired to simulate, or, moreover. to create discrete tonal effects, not necessarily imitative of existing instruments, but none the less pleasing and desirable. In general this is accomplished by the introduction in the repeater circuit of such controlling elements that the harmonic content of the output wave may be widely varied to permit desired and desirable tonal effects to be attained.

The object desired may be accomplished by controlling both the grid bias of the repeater tube V and the amplitude of the inputwave and taking advantage of the repeater tube characteristics. The grid bias may be controlled by proper adjustment of the potential of the supply Ec, and the amplitude of the input wave may be controlled by proper adjustment of the slider 3a on the voltage-divider 3.

The curve I shown in Figs. 2 to 5 inclusive illustrates the plate-current characteristic of a. repeater tube V such as I may employ in accordance with my invention. In Fig. 2 this tube is operated as a linear repeater, in which case the output wave, which corresponds to the plate current wave I2, is an amplified facsimile of the grid potential wave I I produced by the influence of the incoming fluctuating wave. In operating the repeater circuit in this instance the grid bias potential is selected, as indicated by the axis Eel, to fall at about the center of the straight portion of the plate current" characteristic curve Hi. This bias is such that equal grid potential changes, within certain limits, produce equal plate current changes about the steady plate current, indicated by the axis Ipl, resulting under the steady bias conditions. Thus, practically no distortion results when alternating potential of amplitude Al is applied to the grid G, causing an output wave of double amplitude B between crests to be established about the plate axis Ipl.

A comparison of the figure just described with Fig. 3 shows how harmonics of appreciable magnitude may be introduced in the-output wave by increasing the grid operating potential in a negative direction. The amplitude of the grid potential wave is at the same time slightly increased to the value A2, which 'is done to maintain the desired double amplitude B of the output wave in the plate circuit. As seen, the input wave I3 is established along the new axis E02, which results in shifting the plate axis to 1122 along which the output wave I4 is correspondingly distorted from its former approximately sinusoidal form shown in Fig. 2. p

In Fig. 4 I have illustrated the bias of the grid of the repeater tube adjusted to place the input axis at the cut-off point E03. of the plate current characteristic curve It). In this case the amplitude of the input voltage must be considerably increased, as its new value A3 indicates, in order to maintain the output corresponding to a fluctuating flow of current in the plate circuit at the same amplitude as before. As observed, the output wave 96 established along the new axis Ip3 as a result of the grid potential fluctuations i5 is in this instance definitely distorted, its wave form introducing such harmonics as to adapt it for certain musical purposes.

5 shows a further adjustment of the grid bias to a point E04 beyond the cut-oil point of the tube and it is seen that, in order to continue the output at the same double amplitude B, it is necessary to still further increase the amplitude of the input wave, as shown by A4. The input wave is indicated by IT and, as observed, the form of the corresponding output wave l8 es- .tablished along the axis Ip4 departs to a still greater degree from that supplied to the repeater input, plate current passing only during the crests of the more positive half cycles of the input wave.

From the above description it is apparent that the present invention provides the distinct advantage that yarious musical efi'ects as to timbre or tone quality of the notes produced may be obtained by proper adjustment of the operating parameters of the tube V. Satisfactory control of the resultant wave form supplied to the amplifier 8 and loud speaker 9 is in this manner eiiected without the use or variable filter means otherwise necessary for such control, were a sutflciency of harmonics in the first place available. In practice, the operating parameters of the tube may be made variable, either continuously or in predeterminedsteps, between conditions for maximum linearity or minimum distortion and conditions for any selected maximum of distortion. In either case, the amplitude of the input wave and the operating potential at the grid may be adjustable simultaneously to maintain their proper relationship for an essentially constant apparent volume output. An arrangement ior such simultaneous adjustment is shown schematically in Fig. 6. A voltage-divided 20 is connected across the source E0 and its slider 20a is operated conjointly with the slider 30. of the divider 3, as by a common handle 2!. If desired, tle amplifier 8 may include suitable filter means for the elimination of undesirable or over-amplitude harmonics or their attenuation to negligible or desirable amplitude in the manner known in the art. parameters of the tube may be selected to produce desired harmonics of a desired amplitude and thereafter made permanent. In this instance a filter means is provided for controlling the harmonic content.

It is understood that, if desired, such values 0! operating potential Ec may be provided at the rid of the tube V as to cause the input potential changes to swing through the upper portions 10a (Fig. 2) of the characteristic curve Hi. The distorting effects which are obtained in this manner are similar to those which have been described. In this instance the more the grid supply-potential is increased in a positive direction, the richer is the harmonic content of the output wave. It is, of course, understood that the more the grid supply-potential is increased in a positive direction, the greater the amplitude to which the input wave should be adjusted to maintain the intensity of the output wave substantially constant. However, this distortion is much the same as will be realized by operation on the low plate current end of the curve l0, and has the disadvantage that, in some instances, the grid of the tube V will draw current placing an appreciable load on the oscillatory source, which may, in some instances, destroy stability of fundamental frequency. Further, in drawing current, the grid may introduce certain high order harmonics which are usually musically undesirable. For these reasons it is generally preferable to operate the grid in the more negative region, though the invention comprises all possibilities of deliberate distortion in repeater circuits.

Although the invention is illustrated in the drawings and described herein in connection with a single repeater tube, it is understood that circuits involving a plurality of repeater tubes, each of which is operated in a. manner as described, may be used to produce other desirable musical efiects. For example, a pair of non-linearly operated repeater tubes may be used in a pushpull arrangement, i. e., symmetrically disposed in a back-to-back circuit connection. Assuming It is understood that the operating aoaasaa 3 the required balance between such tubes, no even harmonics will be found to exist in the output wave other than those already present in the input wave.

What is claimed is:

1. In a musical instrument, the combination with means for producing electrical oscillations of audible frequency, of a harmonic introducing thermionic tube repeater circuit to which said oscillations are supplied, said repeater circuit comprising means for varying its grid operating potential to vary the harmonic content of its output oscillations, said repeater circuit also comprising means for varying the amplitude of the input oscillations at its grid to maintain the intensity of its output oscillations substantially constant.

2. In a musical instrument, the combination with means for producing an audible frequency electrical wave of substantially pure sinusoidal form, of a wave distorting thermionic tube repeater circuit to which said wave is supplied, said repeater circuit comprising means for varying its grid supply-potential to vary the form of its output wave, said repeater circuit also comprising meansfor varying the amplitude of the input wave at its grid to maintain the intensity of its output wave substantially constant.

3. In a musical instrument, the combination with means for producing electrical oscillations of audible frequency, of a harmonic introducing thermionic tube repeater circuit to which said oscillations are supplied, said repeater circuit comprising means for varying its grid supplypotential to vary the harmonic content of its output oscillations, said repeater circuit also comprising means for varying the amplitude of the input oscillations at its grid to maintainthe intensity of its output oscillations substantially constant, -said supply-potential varying means in one of its positions of adjustment effecting a bias value at cut-off or beyond causing maximum introduction of harmonics.

4. In a musical instrument, the combination with means for producing an audible frequency electrical wave of substantially pure sinusoidal form, of a wave distorting thermionic tube repeater circuit to which said wave is supplied, said repeater circuit comprising means for varying its grid supply-potential to vary the form of its output wave, said repeater circuit also comprising means for varying the amplitude of the input wave at its grid to maintain the intensity of its output wavesubstantially constant, said supply-potential varying means in one of its positions of adjustment effecting a bias value at cut-off or beyond causing maximum wave distortion.

5. In a musical instrument, the combination with means for producing electrical oscillations .of audible frequency, of a harmonic introducing simultaneously.

eflecting harmonic introduction between conditions for substantial absence of harmonic introduction and conditions for a predetermined maximum of harmonic introduction.

6. In a musical instrument, the combination with means for producing an audible frequency electrical wave of substantially pure sinusoidal form, of a wave distorting thermionic tube repeater circuit to which said wave is supplied, said repeater circuit comprising means for varying its grid supply-potential to vary the form of its output wave, said repeater circuit also comprising means for varying the amplitude of the input wave at its grid to maintain the intensity of its output wave substantially constant, said supply-potential varying means effecting wave distortion between conditions for substantial absence' of wave distortion and conditions for a predetermined maximum wave distortion.

'7. In a musical instrument, the combination with means for producing electrical oscillations of audible frequency, of a harmonic introducing thermionic tube repeater circuit to which said oscillations are supplied, said repeater circuit comprising means for varying its grid operating potential, to vary the harmonic content of its output oscillations, said repeater circuit also comprising means simultaneously operated with said operating potential varying means for varying the amplitude of the input oscillations at its grid to maintain the intensity of its output oscillations substantially constant. I

8. In a musical instrument, the combination with means for producing an audible frequency electrical wave of substantially pure sinusoidal form, of a wave distorting thermionic tube repeater circuit to which said wave issupplied, said repeater circuit comprising means for varying its grid supply-potential to vary the form of its output wave, said thermionic circuit also comprising means simultaneously operated with said supply-potential varying means for varying the amplitude of the input wave at its grid to maintain the intensity of its output wave substantially constant.

9. In a musical instrument, the combination with means for producing electrical oscillations of audible frequency, of a harmonic introducin thermionic tube repeater circuit tov which said oscillations are supplied, said repeater circuit comprising an adjustable source of grid-supply potential for varying the harmonic content of its output oscillations and a voltage-divider for varying the amplitude of the input oscillations at its grid to maintain the intensity of its output oscillations substantially constant.

10. In a musical instrument, the combination with means for producing electrical oscillations of audible frequency, of a harmonic introducing thermionic tube repeater circuit to which said oscillations are supplied, said repeater circuit comprising an adjustable source of grid-supply potential for varying the harmonic content of its output oscillations and a voltage-divider for varying the amplitude of the input oscillations at its grid to maintain the intensity of its output oscillations substantially constant, said voltagedivider and said adjustable source being operated GILBERT SMILEY.

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