US2514490A

US2514490A - Electrical musical instrument

Info

Publication number: US2514490A
Application number: US569567A
Authority: US
Inventors: John M Hanert
Original assignee: HAMMOND INSTR CO
Current assignee: HAMMOND INSTR CO; HAMMOND INSTRUMENT Co
Priority date: 1944-12-23
Filing date: 1944-12-23
Publication date: 1950-07-11
Anticipated expiration: 1967-07-11

Description

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ELECTRICAL MUSICAL INSTRUMENT Filed Dec. 25, 1944 3 Sheeis-Sheet 5 SECO/V0 D/V/DE/e 577465 Patented July 11, 1950 ELECTRICAL MUSICAL INSTRUMENT John M. Hanert, Park Ridge, Ill., assignor to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application December 23, 1944, Serial No. 569,567

(Cl. 84-L01) 25 Claims.

My invention relates generally to electrical musical instruments and more particularly to an improved instrument which is voice controlled and thus may be played by anyone capable of carrying a tune by singing, humming or whistling.

In many musical presentations the music could be greatly improved if there were provided some means for accompanying the singer without requiring the presence of a trained musician for the playing of the musical instrument. Furthermore, many people who enjoy music are deprived of the pleasure of producing instrumental music because of their inability or disinclination to pursue the long period of education and practice usually required to enable them to become proficient.

It is therefore the fundamental object of my invention to provide an improved musical instrument in which the operation of the instrument is controlled mainly by the pitch and loudness of the voice of the performer, in which various manually operable amplitude controls are provided, in which the music produced may be in any desired pitch range irrespective of the pitch of the voice used to control the instrument, and in which octave coupler effects may be obtained.

A further object is to provide an electrical musical instrument in which the pitch and loudness of the tones produced are controlled respectively by the pitch and loudness of voice or other sound made by the performer, but in which the pitch of the output tone is always exactly of a frequency of a note of the tempered musical scale even though the controlling Voice or sound is slightly off pitch.

A further object of the invention is to provide the output of the generating system of a musical instrument with a plurality of rectifying means to change the effective tone quality, such rectifying means having a common manual control to render them effective or ineffective.

A further obj ect is to provide an electrical musical instrument responsive to the pitch of an input wave, which is capable of producing pleasing musical tones of corresponding pitch or of octavely related pitches, and of selected tone quality.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Figs. l, lc and lb together constitute a schematic wiring diagram of the instrument; and

Figs. 2, 3 and 4 illustrate the forms of the signal waves appearing in various circuits of the instrument.

As shown in Fig. 1 the input to an amplifier l may be supplied by a microphone l2, which 65 may be of the usual type, but is preferably a throat microphone, or may be supplied from a special crystal microphone I4, depending upon the position of a single pole double throw switch I6. The crystal microphone I4 is preferably mounted in a case I8 having a rubber tube 20 connected thereto, the rubber tube being connected to a glass or similar tube 22 adapted to be inserted in the oral cavity of the performer. The other end of the tube 22 is closed by a suitable flexible diaphragm 24 by which saliva is excluded from the tube 22, while permitting free transmission of sound from the oral cavity to the microphone I4.

The amplifier ID is preferably of the type in which due to the provision of one or more filtering meshes, lower frequencies are amplified to a considerably greater extent than higher frequencies, as indicated by the frequency response curve i3, for convenience shown directly on the block representing the amplifier l0. By virtue of this response characteristic of the amplifier, the fundamentals of musical tones picked up by the microphone will be amplified to a greater extent than the harmonics. In most musical tone qualities the fundamental is of substantial amplitude so that even if a particular quality of tone picked up by the microphone has a second or higher harmonic of greater amplitude than the fundamental, the fundamental will nevertheless be of greater amplitude in the output of the amplifier by virtue of the progressively lesser amplification of the higher frequencies.

The output of the amplifier iD is transmitted through a coupling capacitor C26 to a conductor 28, the latter having a plurality of decoupling resistors R30 respectively connecting the conductor 28 to the control grids 32 of pentcdes 34. There are preferably 18 pentcdes 34, with their associated circuits, employed in the instrument, of which a representative group of four are illustrated in Fig. 1. Connected to the grid 32 of each of these pentodes is a parallel resonant mesh comprising an inductance L35 and a capacitor C35, these meshes being tuned to resonate at the semitone intervals in the usual vocal range from the pitch A2 at 220 C. P. S. to the pitch D4 having a frequency of 587.3 C. P. S. The cathodes of the pentcdes 34 are connected to a common conductor 42 which is connected to ground through a common self-bias resistor R44 bypassed by a capacitor C45. The resistor R44 is ofv relatively high value such that the voltage drop across it, due to the flow of plate current through any one of the pentcdes 34, will bias the other pentcdes beyond cutoff for signals of but slightly lesser amplitude than that which is imr pressed upon the grid of the conducting pentode. The suppressor grids 66 of the pentodes 32 are likewise connected to the conductor 2 while the screen grids i3 thereof are connected to a suitable source of constant potential indicated as +30 v. The plate 5i! of each of the pentcdes 34 is supplied with plate current VKfrom a suitable source, indicated as a terminal V., through a load resistor R52 which has a capacitor C54 connected in parallel therewith.

A pentode 56 has its cathode sv-and-isuppressor grid 60 connected to the +30 v. terminal of a suitable power supply whilefitS-control/grid E2 is connected directly to the plate 500i the pentode A.

The screen grids 51d of al1 of the pentodes 5t 34. are connected by a common conductores and a voltage dropping resistor R68 to a terminal +2,50 v. of the power supply. The anodes 'it vof the pentodes 56 are connected to suitable source oi" operating potential, such as af-terminal +250 V. of the powersupply, through the windings of relays 12.. respectively.

'From the foregoing it will be apparent that when an audible signal such as produced by cause a higher amplitude signal to be impressed upon its associated grid 32 than is impressed upon theremaining grids 32, and thus its associated pentode 3d will be rendered conductive. Upon the flow of Vplate vcurrent through such pentode the voltage drop across the common-selfbia-s resistor RMIA will cause the potential on the cathodes dil of the remaining pentodes to swing materiallyv in a positive direction, so that such remaining-tubes will be effectively locked out and frequencies corresponding to those of the tuned meshes Vassociated withthem would have to `be ofgreater amplitude-in -order to take away the control from the lrst pentode. When one ofthe jpentodes ,3A is rendered conducting, the flow of plate current, due to the drop across resistor Re?, causes the potentialv of the grid 62 to drop with resultant pronouncedreduction in plate current and deenergization ofits associated relay 12..

The pentode 3.4, associated with the meshL35, CS G of the highest resonant frequency, operates in the same Imanner as the other pentodes but doesnot have apentode '5,6 or relay 12 coupled At9 its output, The reason for this willgappear more clearly hereinafter but in vgeneral is based upon the fact that the instrument is normally tuned to generate a ,musical tone corresponding to the highest frequency mesh and itis therefore unnecessary to provide ,any tuning control for the musical` instrument when the audio input frequencycorresponds :t0 this highest frequency.

Jrom the foregoing it will appear that all of the relays 12 will normally be venergized. and only one relay, in the channel corresponding to the highest,amplitude-frequency in the output of amplifier il), will be deenergized. Thus, if the input signal vconsists .of a pitch glissando tone, the 'relays 'l2 corresponding to the pitch range of thev tone will be operated sequentially, one at .a time. Each relay l2 is `provided with a switch M which is normally open, i. e. when the relay 'i2 is closed. The switches it when energized connect the junctions between a series of tuning capacitors Clt (Fig. la) with a grounded conductor i8. The capacitors C15 constitute part of the tuning circuit of a master oscillator comprising a pentode i8, the output of which is supplied ;to a rectifying triode 8U. The input circuit of the pentode 'i8 includes not only the series of capacitors Clt but the parallel connected inductance L82 forming the primary winding of a tuning coil L84, the secondary winding L86 of which is connected between ground and the cathode flof the pentode 78.

tap ongthe inductance L82 is connected to a vibrato apparatus S which may be of the construction disclosed in my prior Patent No. 2,301,811, `this vibrato apparatus preferably having a control il! by which it may be turned off or on.

The ypentode 'i8 has its output coupled to the input of the triode 30 which operates in a manner to provide a rectified output signal in the form of a relatively sharp pulse wave. The output of triode S0 is coupled to the input circuits of a pair of intercoupled triodes 94 and 95 which are supplied with suitable circuit elements so that each of these tubes is responsive only to alternate Vpulses and these tubes thus constitute a pulse or'frequency divider stage. This dividing function of the triodes 9H, S5 is more fully disclosed in my copending application, Serial No. 519,838, led January 27, 1944, and since abandoned.

An output signal of one-half the frequency of the oscillator 'i3 is supplied to the second divider Vstage through a coupling condenser C95 connected between the plate of triode 95 and the grid of triode 98, the latter constituting a means for r-ectifying and sharpening the wave front of the pulse appearing in the output of triode 95. This p ulse is impressed upon the grids of intercoupled triodes 39 and i90, which together with the triode 98 constitute the second frequency divider stage. The third, fourth and fth frequency divider Ystages are similar to the first and second stages and Vare therefore illustrated as blocks 10S, H34 and 05 respectively. Thus the iirst divider stage is capable of producing a signal frequency one-half that of the oscillator 18 and the second, third, fourth and fifth divider stages produce signals which are respectiveh7 Mi, 1/8, and 3% of the frequency of the oscillator 18.

The output signal from the pulse sharpening triode 80 is derived from the junction of voltage divider resistances RIM and RIM which together constitute the plate load for triode 8U. A blocking capacitor Cl connects the junction of resistors Rll and Rl'i with the conductor Il il. A line resistor Rl l2 is connected between the conductor HS and ground. In a similar way the output of the first frequency divider stage is impressed upon a conductor l I4, that of the second divider stage upon a conductor I l5, and that of the third, fourth and iifth divider stages impressed upon conductors H6, Hl and II-B respectively.

The conductors H and H4 are respectively connected to the plates `i253 of a twin diode rectifier tube H22, the cathodes |24 of this tube being connected to ground through a conductor 25, resistor RIZS, and resistor R128, the latter having a by-pass capacitor C connected in parallel therewith. The resistor RIEB with its by-pass capacitor C| provides self-bias for the

triodes

80, 94, 95, 98, 99 and |00 and the correspending triodes in the remaining frequency dividing and rectifying stages.

In a similar manner the signal conductors ||5 and H6 are connected to the plates of a twin diode rectier tube |3, while the signal con ductors and H8 are connected to the plates of a twin diode rectifier |32. The cathodes of the rectifier tubes |30 and |32 are likewise con nected to the conductor |25. A switch |34 (Fig. 1a) is arranged to connect the conductor |25 to ground and, when the switch is in the full line position shown, the three twin diodes IZB, |30 and |32 are rendered effective to rectify the output signals of the pulse sharpening triode 8l) and the several divider stages by cutting off the positive peak portions of the signal wave outputs of these stages. When the switch |34 is moved to its dotted line position, the cathodes of the twin diodes attain substantially the relatively high positive potential of the cathodes of the

triodes

94 and 95, 98, 99 and iil, etc. so that transmission of the output signals from the various stages is not affected by the twin diodes. Since the effective power of the output signals is substantially doubled when the switch |34 is moved to its dotted line position, this switch is arranged to connect an attenuating resistance RISE in the output circuit, this resistance operating to compensate for the increase in the output of the oscillator and divider stages.

The output signals derived from the various divider stages are of the wave shape illustrated in Fig. 2. This generally rectangular wave shape grepresents a musical tone signal having an undesirably strong fundamental and also an undesirably long harmonic series. To obtain more artistic tones, the rectangular wave shape shown in Fig. 2 is modified to that shown in Fig. 3 by means of resistance capacitor meshes which are associated with the output circuits of each of the frequency divider stages. Each of these output circuits comprises a current limiting capacitor C|3'| which is effective to reduce the undesirable intensity of the fundamental component, and a capacitor C|39 which is effective to attenuate the undesirable high harmonics of the tone whose wave shape is shown in Fig. 2. A resistor RXi is connected in parallel with capacitor C|39 and a line resistor RXZ is connected between ground and each of the signal lines, such as line l 55. Capacitors C|3'| and C|39 cause the signal wave to be changed to the modified symmetrical wave shape shown in Fig. 3. This wave shape corresponds closely to those of the tones produced by the woodwind family of musical instruments comprising very predominantly the odd harmonic series and is further of a wave shape suitable for the'input to the rectifying twin diodes |29, i363 and 32.

Each of these diodes is effective to attenuate the positive peak portion of the wave, thereby destroying the symmetry of the resulting wave shape, whenever the switch |34 is connected in its full line position. The attenuation of the positive peaks of the wave shown in Fig. 3 results in a wave form representing a new harmonic series, the wave shape being shown in Fig. 4. This wave shape is characteristic of an entirely different tonal family containing all of the harmonics, and is of the string family of orchestral tones.

By movement of the switch |34 to its dotted line position, the signal applied to the output of the instrument may be of the character of Fig. 3, whereas when the switch is moved to its full line position the signal supplied to the output will be of the character represented by the wave of Fig. 4. Thus by the operation of a single switch the tone quality of the output signals of all of the frequency divider stages may be radically altered to obtain novel and interesting musical effects.

Conductors ||0 and ||4 to ||8 inclusive are adapted to be coupled to the input of a preamplifier triode |40 by selective operation of stop tablets |42 in the well known manner as disclosed, for example, in my prior Patent No.

2,357,191 dated August 29, 1944. The output of :1 trolled by adjustment of an adjustable resistor Riti).

The terminals of the secondary winding of the transformer Tiri!! are connected to the control grids |48 and |48 of volume and tone envelope controlling pentodes |50 and |5| respectively. It will be understood that the biasing potential on the grids |48 and |49 is determined by the potential at the center tap |46. In addition to being controllable by the volume control device |48 and the normal adjustable volume control Rili, there are provided other means for determining this potential which will be described hereinafter. For the present it will be noted that the push-pull output of the control tubes |59 and ii is supplied to a push-pull power amplifier iEZ and that the latter energizes a speaker |54,

In using the instrument it is desirable that the intensity of sound output, in addition to being controllable by the volume control device |48 .'1 shall be automatically controlled by the intensity of the sound input, i. e. the loudness of the voice, humming, or whistling, and this latter result is automatically accomplished as will now be described. A conductor |50 is connected to the output terminal of the amplifier Iii and supplies an input signal to a triode ft2 through a blocking condenser CIM. The triode |52 is self-biased and is coupled with a full wave rectifier tube |554 by means of a coupling transformer TISS.

' Since the anodes |68 of the rectifier tube |64 are respectively connected to the terminals of the secondary winding of the transformer Tl-n and the cathode |69 thereof is connected to the grounded center tap of this secondary winding through a rectifier load resistor RITO and filter capacitor CH2, the D. C. potential on the cathode will be substantially proportional to the amplitude of the output signal of the amplifier I0. The cathode |69 is normally connected by a conductor |14 and a switch |15 to the center tap |46 of the coupling transformer TIM. The potential on the center tap determines the grid bias and hence the degree of amplification obtained through the pentodes 15's` and |5|. Thus when the switch |18 is in its full line position the degree of amplification obtained by the control pentodes l and 5| will depend upon the ampliturie of the output signal from the amplifier I0.

It is desirable to cut off the control pentodes |5 and 5| when no signal is being supplied animee s. to theinputof-:the amplifier ||l,..but. at .the .same

time, it is essential that. .these control pentodes commence to transmit a signal shortly after .the output of the amplier l exceeds a predetermined low threshold value such .as represented, for example, bythe outputroftheamplier when the player isnot singing, whistling or humming into one of the microphones, .in which case .the output of the amplifier would be merely noise and not vsignificant. This is accomplished by means of a triode |80, the control grid |82 of which isconnected to the conductor |60'through a capacitor C|84. The control grid |52 has its biasing potential determined by an .adjustable voltage divider resistor RISE, a sliding contact of which is connected to the grid |82 through :a grid :resistor Rl, and the terminals of which are respectively connected to ground and axsuitable source of negative biasing potential indicated as -25 v. By properly adjusting the position of the slider on the adjustable voltage divider Rl the bias on the triode |80 may be made sufficient to maintain the triode cut oi until the amplitude of the signal output of the amplifier |13v exceeds the noise threshold to a signicant extent. This will occur whenever the player whistles, hums or sings into one of the microphones. When the output signal of the amplier ||l exceeds the bias potential on the triode |89, the -latter will conduct the signal. The winding of a relay |99 forms the plate load impedance for the triode |80,^being connected between the plate and a suitable source of plate potential indicated as +B. A condenser C|92 is connected in parallel with the winding of relay |90, this condenser being of small'value so as to smooth out uctuations in the plate current ow resultant from the fact that an audio frequency current is impressed upon the grid |82. The relay, upon energization, is adapted to open a normally closed switch |94 and thus break the circuit between conductors |95 and |96. Energization of the relay also results in closure of a switch |93 which connects a conductor 200 to ground. It will be noted that conductor |'95'is connected to a terminal 202 (Fig. 1b) which is normally at a suitable operating potential for the screen grids 202 of the control' pentodes |50 and |5|, this potential being determined by a suitable voltage divider comprising resistors R205 and R292 connected between a terminal of the power supply indicated as +300 v. and ground. A normally operable switch 298 is adapted to connect the junction 202 with the screen grids, the switch 208 being closed when it.is desired to produce a steady organlike sustained tone envelope and open when it is desiredto produce a piano or banjo-like percussive tone envelope.

YIt will thus appear that the opening of the switch |94 by energization of the relay |90 has no effect upon thev tone envelope when the'switch 298 is closed, since the relay switch |94 and switch 2GB are in parallel.

This percussion effect is produced by virtue of the fact that the normal screen potential at 'the junction 202 is impressed upon the screen grids 204 of the control pentodes |50, |5| through the conductors |95, |96 and switch |94, which circuit is interrupted whenever the relay |90 is energized to open switch |94. Whenever the switch 298 or relay switch |94 is opened, the potential on the screen grids 294 is sustained temporarily by a voltage storing capacitor C2|2 which's connected between the screen grids and apoint of xed' potential, indicated as ground.

Sincerthe control-,pentodes |50, |5| are of the remote .cuto type, the gradual reduction .in screen potential due to the discharge of the 'capacitor C2|2 will cause a corresponding decrease in the gain of these tubes, and a musically desirable percussive tone envelope Will result.

A single pole double throw switch 2|3 is mechanically connected to operate with the switch |16, both of these switches being either in the full line position shown in Fig. 1b, or in the dotted line position. When these switches are in the dotted line position, the tonal envelope produced is entirely independent of the performers audible input to the amplifier 9, whereas when these switches are in the full line position, the envelopes of the tones produced by the instrument are related to the audible input to the amplifier .ID through .the operation of the 'full wave rectifier tube |64.

When the switches |76 and 2|4 are in their dotted. lline positions the cathodes of the pentodes |50, ,|5| willbe connected through conductor:2|.5 to .a junction 2|.5 of a voltage divider network comprising resistors R2|8 and R2 i9 connected between ground and a terminal or" the power supply indicated as +300 v. Under these conditions the cathodes of pentodes |50, |5| are maintained at a potential of approximately +165 volts relative to ground, and the pentodes are fully cut oit. Whenever the relay is energized, as it is whenever a suitable audible signal is supplied to the amplier I0, the relay switch |98 will be closed, connecting conductor 20.0 to ground. It will be noted (Fig. 1b) that the conductor 200 is connected to the junction point 2 |6 through a resistor R222. The resistor R222 is thus effectively in parallel with the voltage divider resistor R2|9. The potential at the junction 2|-6, and hence upon the cathode of pentodes |50, |5|, is thereby reduced from a value of approximately volts to a value of approximately +50 volts. This reduction of cathode potential is suflicient to render pentodes |50, |5| conducting. 'The extent of their conductivity is lfurther controllable by means of the manually operated volume control device |49 which is effective to control the potential at a junction point 224. The potential at the junction 224 may be varied from ground to +50 volts in smoothly graded steps, depending upon the movement of the manual control of the volume control device I48. The junction point 224 is connected to the center tap |45 of the transformer Ti 1214 through a time constant mesh, comprising a resistor R226 and a capacitor C228. Theselatter circuit elements are eiective to slow the rate at which the potential at the center tap |46 may change, and thus the change in gain of theremote cutoff pentodes |50, 5| is made smooth and gradual.

Opening a manually operated switch 239 renders effective capacitor C232 which. is then connected between the cathodes and center tap |45 of the pentodes |50, |5| whenever the switches |16 and 2M are in dotted line position. Thus, when the cathodes of the tubes |50, |5| suddenly change from +165 volts to +50 volts, due to connecting the conductor 253 to ground through the relay switch |93, the potential at the junction point let` will change in a similar manner, thereby delaying the change in relative potentials o'f `the grids and-cathodes of the pentodes |50, |5|. However, after the `cathodes. have attained the +50 volt potential, the potential at the center tap |45 Will'change to the potential at the junction point 22d at a slow rate, determined by the time constant of the combined condensers C228 Aand C232 with respect to the resistor R225. Thus a slow and smooth tonal attack is obtained. When the signal from the amplifier l t disappears, deenergizing the relay |38 and opening its switch |98, the potential on the cathodes of the pentodes |56, returns to +155 volts at a rate controlled by a relatively large capacitor 023i which is connected from the cathodes to ground.

When the switches |76 and 2M are in their full line positions the volume control device ist is preferably not used and is left in the position of minimum volume. Under these conditions, the potential at the center tap |46 is determined by the potential of the cathode |69 of the full wave rectifier tube let, which in turn is a function of the amplitude of the original signal supplied to the amplifier ill. A threshold control potentiometer 24:'3 (Fig. lb) is to impart a. threshold below which extraneous and undesired signals from the amplifier i9 are not effective to cause a signal to be heard from the speaker |54. The threshold potentiometer Ritt thus serves a purpose similar to that of the potentiometer Rl, since when the switches lili and 2M are in the full line position, the latter potentiometer is not effective.

The resistor Pulli) (Fig. 1) will, in general, be

of a low Value by comparison with the resistor R225 (Fig. 1b) and therefore operation of the volume control device |43 will beineffective under these conditions. A volume control R244 is provided for adjusting` the overall gain of the amplier.

From the foregoing it will appear that the nstrument possesses a high degree of versatility as to volume, and as to the tone intensity envelopes which may be obtained by suitable operation of the various controls. For example:

l. When the switches |16 and El!! are in their full line positions and switch 263 is closed, the resulting tone intensity envelope will closely resemble that of the original signal supplied to the amplier It.

2. When the switches |76 and 2M are in their vfull line positions and the switch 263 is open, the

initial attack and peak amplitude to which the signal rises will be controlled by the corresponding initial attack and the peak amplitude of the audible signal supplied to the amplifier HJ, but the d ecay portions of the tonal envelope will be controlled by the manner in which the capacitor vC2|2 discharges. Thus there will be produced a vtone intensity envelope whose attack and decay are related to the attack and decay of the original signal supplied to the amplifier yIl! but which is automatically made percussive in its overall effect.

3. When the switches HB and 2|4 are in their dotted line positions with switch 230 closed and switch 208 closed, the resulting tonal envelope will be of a sustained organlike character having prompt attack and decay.

4. With the switches Il@ and 2|4 in their dotted line positions, switch 230 open, and switch 208 closed, the tonal envelope will be of a sustained organlike character, but will be distinguished by slow and smooth attack similar 'to the attack of a bowed string instrument.

5. with the switches ne and 2|@ in their dotted line positions and switches 298 and 23o open, the resulting tonal envelope willbe of short duration, comprising a slow attack portion followed by a slow decay. The rateof attack and l0 decay will depend upon the itors C2|2, C234 and C228.

In using the instrument the performer will sing, hum, whistle, or play on some musical instrument, a melody within the frequency range .A2-220 C. P. S. and D11-587.3 C. P. S., which is a convenient frequency range for easy rendition of a tune. Depending upon which of the coupler stop tablets |42 is operated, the fundamental frequency of the output tone of the instrument may be in the range of from 1760 to 4698.63, 880 to 2349.32, leo to 1174.66, 220 to 587.33, 110 to 293.66 or 55 to 145.83 C. P. S., or any desired combinations cf these ranges which will correspond to the octave coupler effects obtained in organs. Thus the performer has at his command the ability to produce tones ranging from the lowest bass frequencies to the highest musical frequencies corresponding to the violin, nute and piccolo. Due to the fact that the frequency responsive control means for determining the pit-ch of the master oscillator responds in a manner to tune the master oscillator exactly to the pitches of the tempered musical scale, the performer may be considerably olf key without changing the actual pitch of the tone produced. The only requirement upon the performer is that he shall hum, sing, whistle, or otherwise produce a musical tone, the pitch of which is closer to the desired note of the musical scale than to either of the adjacent semitones. This is a requirement which is easily met by most anyone capable of carrying a tune.

The tone produced may, as desired, contain a true pitch vibrato without any undesirable tremulant or unsteadiness.

The actual tone quality produced by the in strnment may be selectively varied by opening one or more of the switches |43 and by operation of the tone family control switch |34. These values of the capaccontrols will make it possible to vary the output tone over an extremely wide range of qualities including the orchestral flutes, Woodwinds, reeds, strings, brasses, organ and percussion tones.

When using the instrument the performer will usually be in a position to hear the sound output of the speaker |54 and, since the tones produced will be at exactly the proper pitch, the performer will be able easily to detect the fact that he is not singing exactly on pitch by hearing beats between his voice tone and the tone of the speaker. The instrument may serve a very useful function in vocal instruction, since the student as well as the teacher may readily detect a failure to maintain proper pitch.

While I have shown and described a particular embodiment of the invention, it will be apparent to those skilled in the art that many modifications and Variations thereof may be made without departing from the fundamental principles of the invention. I therefore desire by the following claims to include within the scope of my invention all such variations and modications by which substantially the results of the invention may be obtained by the use of substantially the same or equivalent means.

I claim:

l. In' an electrical musical instrument having kan output system including amplifying and electroacoustic translating means, the combination of an electrical generator of musical frequencies, corresponding to the semitone intervals of the tempered musical scale, means for tuning the generator to various semitone intervals of the musical-scale, a microphone, an amplifier for said lmicrophone, saidamplifier having the characteristic of increasing gain for lovver audio frequencies, za plurality of frequency responsive-devices coupled to the output of said amplifier, said devices being responsive to frequencies corresponding respectively to the semitone frequencies to which said generator may be tuned, and means operated by said devices for changing the tuning of said generator to the musical semitone nearest in frequency to that of an input signal supplied to said microphone.

2. In an electrical musical instrument having an `amplifier and electroacoustic translating means, the combination of an electric generator for electrically generating musical tone signals of the frequencies of the semitone intervals of the tempered musical scale, means coupling said generator to the amplifier, a plurality of devices for determining the pitch of the tone frequencies transmitted to said coupling means by said generator, means responsive to the frequency of an audible signal to Acause the operation of one of said devices, and means controlled by the intensity of the audible signal to determine the amplitude of the tone frequencies transmitted to said coupling means by said generator.

3. In an .electrical musical instrument having .an amplifier and electroacoustic translating means, the combination of means coupled to the amplifier for electrically generating musicaltone signals of the frequencies of the semitone intervals of the tempered musical scale, means responsive to the frequency of yan audible signal to .operate the generator'tuning means tocause the llatter to generate a frequency of a musical semitone closest to that of the controlling voice, and means responsive to the intensity of the audible signal to determine the amplitude of the tone signals transmitted from said generating meansto the amplifier.

4. In an electrical musical instrument having an output system including an electroacoustic translating means and amplication means provided With a gain control, the combination of an .electrical generator tunable to generate electrical signals corresponding to the semitones of the musical scale, means responsive to the pitch. of a :controlling voice to tune said generator .to the semitone frequency most closely approaching that of the voice, and means responsive to the .amplitude of thev controlling voice for controlling the operation of the gain control meansof the amplifier.

V5. Inv an electrical musical instrument kfor providing an independently generated musical tone 'in response to an audible signal, the combination of an electrical oscillator. having a tuning circuit including a plurality-of reactance elements, relays operable to couple the reactance elements effectively into the tuning circuit, and tuned'circuits frespectively connected to the relays and controlled by the pitch of a sound for determining which of said reactances shall be effective in determining fthe frequency of oscillation of said oscillator.

cillator, and means for translating the output of the oscillator into sound. f

7. In an electrical.musical-.instrumenthaving an output system including an electroacoustic translating means and amplification means provided with a gain control, thecombination of an electrical generator tunable to generate-electrical sign-als corresponding to the semitones of the musical scale, means lresponsive to the pitchv of a controlling sound to tune said generator to the semitone frequency most closely approaching that ofthe sound, and means to prevent the transmission of a signal to the Vamplification. means Whenever the intensity 4of the controlling sound defcreases belovv a predetermined value.

8. In an electrical musical instrument having amplification and electroacoustic translating means, the combinatie-nef a microphone, an amplifier coupled to saidvmicrophone, apluralitypf meshes resonant respectively at the frequencies of .the tones of the musical scale, a pluralityof relays each including a switch and each associated with one of said resonant meshes and adapted to be operated only when the audible input to said microphone is of a fundamental frequency near that of the-resonant frequency of its associated mesh, an oscillator for generating audio frequencies and having a plurality of reactances in its tuning circuit, means operated by said relay switches to determine which of said re.- actances shall be effective in determining the frequency of oscillation of said. oscillator, and selectively operable means for couplingl the output of said oscillator to the amplication means.

9. The combination set forth in claim 8. in Vwhich means areprovided to prevent transmission ythrough said amplification. means of a signal from said oscillator Whenever the outputv of said amplifier is of such low amplitude as to indicate that no significant-audio signal is being supplied said microphone.

10. The combination set forth in claim 8 in which there is provided means responsive to the amplitude of theoutput signal of said amplifier for controlling the gain of said amplification means.

11. The combination set forth in claim 8 in which Ia portion ofthe signal output of said amplifier is amplified and rectified to produce a voltage varying with the amplitude of' thel signal output, and in which means are provided to utilize such Voltage to control the gain of the amplification means.

12. In an electrical musical instrument controlled by an audio-frequency inputl signal, and having an output amplifier and electroacoustic -receivethe signal therefrom, said-meshesbeing resonant respectively at the frequencies of the notes of a musical scale, control devices vrespectively coupled to said frequency responsive meshes, each: of said controldevicesbeing operated When the audio-frequency input signal has la frequency nearer tov that of the resonant frequency of the mesh coupledto such control'devices than to the resonant frequencies of the other meshes, electrical means providing electrical. tone signals at the various-frequenciesof the musical scale, and meansl operatedA byr the control devices for. yrendering said -electrical means. effective to transmit to the output Yam plifler electrical musical tone signals having predetermined pitch relationships With respect to the frequencies at which said frequency responsive meshes are resonant.

13. In an electrical musical instrument controlled by an audio-frequency input signal and having an output amplifier and electroacoustic translating means; the combination of an acousticelectric transducer, an input amplifier coupled to said transducer to amplify the signals generated thereby, a plurality of frequency responsive elements coupled to the input amplifier to receive the signal therefrom, said elements being responsive respectively to the semitone frequencies of the musical scale, control devices respectively coupled to said elements to cause operation of that one of the control devices which is coupled to the one of said elements whose natural response frequency most closely approaches that of the fundamental frequency of the audio-frequency input signal, electrical means` for generating any one of a plurality of electrical tone signals of the musical scale, means operated bysaid control devices for rendering the electrical means effective to transmit to the output amplifier electrical musical tone signals having pitches the same as or octavely related to the frequencies at which said elements are respectively frequency responsive, and means responsive to the amplitude of the input signal for determining the amplitude of the tone signal produced by said electrical means.

14. In an electrical musical instrument controlled by an audio-frequency input signal and having the output amplifier and electroacoustic translating means, the combination of an input amplifier coupled to said transducer to amplify signals generated thereby, said input amplifier having a frequency response characteristic providing progressively decreased gain for signals of increasing frequency, a plurality of frequency responsive devices coupled to the input amplifier to receive the signal therefrom, said devices being responsive respectively at the various notes of a musical scale, electrical means for generating any one of a plurality of electrical tone signals of the musical scale, and means operated by said control devices for rendering said electrical generating means effective to transmit to the output amplifier electrical musical tone signals having octave relationship to the frequencies at which said frequency responsive meshes are resonant.

15. In an electrical musical instrument controlled by an audible input signal and having an output amplifier and electroacoustic translating means, the combination of a microphone, an input amplifier for the signals produced in said microphone, electrical apparatus for generating the tone frequencies of the tempered musical scale, devices for controlling frequencies of the output of said apparatus, means coupled to the input amplifier to receive signals therefrom and operative upon said devices to determine the output frequencies generated by said apparatus, and means coupled to said input amplifier and controlled by the intensity of the audible signal for determining the effective amplitude of the signal output of said apparatus.

16. In an electrical musical instrument, having a variable frequency oscillator provided with tuning means determining its frequency of oscillation, the combination of a plurality of cascaded stages of frequency dividers respectively and successively halving the frequency generated by 14 said oscillator, a signal transmission system iri-4 cluding multi-electrode electron discharge devices coupled to the oscillator and divider stages, an amplifier and electroacoustic translating means, means controlled by an audible signal for operating the tuning means to determine the frequency of oscillation of said oscillator and thereby also the frequency of operation of said divider stages, and means controlled by the amplitude of the audio-input signal to determine the gain of said electron discharge devices, whereby the signal transmitted to the amplifier and electroacoustic translating means Will vary in amplitude in accordance with the variations in intensity of the input signal.

1'7. In an electrical musical instrument having a variable frequency generator capable of generating any one of a plurality of frequencies of the tempered musical scale, means for controlling the output frequency of said generator, a plurality 0f cascaded frequency divider stages, each of said stages being capable of producing a generally symmetrical Wave representative of musical tone qualities having a relatively long series of odd harmonics of substantial amplitude, and means for changing the character of the output wave, said means comprising a rectifier optionally rendered effective to destroy the symmetry of the Wave by greatly reducing the amplitude of the peaks on one side of the zero axis Without affecting the amplitude on the other side of the axis, whereby the resultant Wave will represent a musical tone of the string type in which all audible harmonics are present.

18. In an electrical musical instrument having an apparatus for generating any one of a plurality of the frequencies of the tempered musical scale, an audible signal controlled means for conditioning said apparatus to generate a musical tone signal of pitch nearest that of the audible signal, an output system for said apparatus including an electronic control means, an amplifier, and an electroacoustic translating means, said electronic control means being normally biased to prevent transmission of a signal from said apparatus to said amplifier; and means controlled by the start of the audible signal to change the bias on said electronic control means in a direction to cause the latter to conduct the output signal of said generating apparatus to the amplifier at a predetermined controlled amplitude.

19. The combination set forth in claim 18, in which there is provided manually adjustable means for determining the intensity envelope of the transmitted tones irrespective of the intensity envelope of the controlling initial audible signal.

20. In an electrical musical instrument having an output system including an amplifier and electroacoustic translating means, a plurality of generators producing signals having a fundamental frequency and predominantly the odd harmonics thereof, a rectifier for each of said generators to alter the Wave form of the signals generated thereby, and means common to a plurality of said rectiers for selectively rendering them effective or ineffective.

2l. The combination set forth in claim 20 in which said means includes a switch and an impedance operative to adjust the output system of the instrument to reduce the gain thereof whenever the means renders the rectifiers ineffective.

l 22,. 4In an electral musical instrument .hav-ing an; outputsystemxincluding.an amplifier andelectroacoustic translating. means, a plurality of generators each producing a signal having Va fundamental frequency and `p redominantly the odd harmonics thereof,v arectiier oreachI of .said generators vto alter the Wave form of the signals generated thereby, and meanscommon .to all.v ,of said Vrectifiersfor selectively render'- ingthem-eective or ineffective.

23. In an electrical musical instrument, means for electrically converting auniformpitch glissando input signal into axchromatic scale output signal comprisingJ a plurality oi' reso-v nant elements chromatically'tuned.- inthe pitch ranger-,of the inputsignal, a local oscillator having enz-plurality of. accurate tuning means for selectively tuning the oscillator to the frequenciesfof the chromatic scale, said tuning means being coupled to -Said resonant elements andrespgectively rendered effective. by the excitation thereof, whereby the frequency of said oscillator is changed in finite interval steps ofthe chromatic scale when a smooth non-chromatic pitch. glissandoinput `signal is supplied.

24.- Infan electrical musical instrument controlled-.by an audio-frequency input signal, and

having an `output amplifier and electroacoustic translating means; the combination of a microphone, and an audio frequency input amplifier coupled to. said microphone to amplify electri- .cal signals .generated thereby, said input .ampliof theyother meshes, electrical means providing.

electrical tone .signals at the various frequencies of themusical scale, and means operated by the vcontrol devices for :rendering: saidele'cd trical- `*means effective to transmittofvtheaoutput amplifier electrical musicalftone signalsfhaw ing predetermined pitch relationshipswithre spect vto the frequencies at which said frequency responsive meshes are resonant.

25. Inan velectrical musical instrument, means foi` electrically converting a uniformy glissando input signal into an output signal of discrete tones of the tempered A,musical scale'which comf prises, a microphone for the `reception ofY a glissando tone, an audio-frequency. ampli-ner having its input connected. to the microphone and having substantially decreasedresponsefas the frequency of Vthe input signal increases, va plurality ofresonant elementsntuned to` the pitches of the:y even vtempered ,scale ande-extend ing. throughoutthe pitch rangelof therinput siglinal, means coupling said resonantl elementsito the output `of said. amplifier, Velectrical ngenerating means for producing tone signals-0f fre-` quencies of the tempered musical-scale, ari-.out-V put system, and means operated by-saidf reso.- nant elements .to control transmission: ofatone signal from said., generating meansntosaid--outf put system, the tone signal-transmittedbeinglof pitch the: sarneasor octavely related to that'fof the resonant element by which itis controlled.

JOI-IN M. HANERT.

REFERENCES CETED The following referencesare .of recordy in` .the ille of this-patent:

UNITED STATES PATENTS- Date