US2500820A - Electrical musical instrument - Google Patents

Description

March 14, 1950 Filed Sept. 13, 1945 J. M. HANERT ELECTRIC AL MUSICAL INSTRUMENT ALTERNATE PULSERESPONSIVEFRE'QHENCY 'lI//DERSI March 14, 1950 J. M. HANERT 2,500,820

ELECTRICAL MUSICAL INSTRUMENT Filed Sept. 13, 1945 3 Sheets-Sheet 2 sr/:JQE z vvvvv AAA.

March 14, 1950 J. M. HANERT 2,500,820

ELECTRICAL MUSICAL INSTRUMENT Filed sept. 13, 1945 s sheets-sheet s U26@ zsz 5719652 5719053 A JL r 44 d 46 Z4 n //?z/e/? for L/O/w? M Hanne/"2* Patented Mar. 14, 1950 UNITED STATES4v PATENT OFFICEl ELECTRICAL MUSICAL INSTRUMENT John M. Hanert, Park Ridge, Ill., assigner to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application September 13, 1945, Serial No. 616,079

t 12 Claims. (Cl. Sli- 1.19)

My invention relates generally to electrical musical instruments and more particularly to electrical organs, melody instruments and other keyboard instruments.

In the past, electrical musical instruments have been provided with means for imparting variousforms of tonal animation such as tremulants, that is, amplitude modulation devices, and vibratos, that is, frequency modulation devices. While it is true that these two effects, especially the vibrato, are productive of a certain degree of tonal warmth, it has been found that neither of them is a tonal substitute for the grand chorus effect of a very large number of the same kind of orchestral instruments sounding the same note simultaneously, nor of a large number of organ pipes sounding simultaneously, nor of a large chorus of voices.

To the listener and musician alike the chorus effect possesses an incomparable appeal because of its tonal grandeur. The random acoustic character of the chorus is unique among musical tonalities. In the chorus tonality the partials of a single tone are replaced by bands of numer-` ous fundamental frequencies and bands of numerous harmonic frequencies.

Musical instrument builders have endeavored to produce the chorus effect by simultaneously` a pleasing narrow chorus effect with two or' three generators, the effect becomes inharmonious or out-of-tune if an attempt is made to increase the width of the chorus effect by further detuning the generators. It has also been found that this inharmonious effect can be removed only by providing many more generators whose itches are intermediate those of the first mentioned group. However, the cost of providing the necessary large number of individual generators for each note or key of the instrument is prohibitive for all practical purposes.

From an analytical aspect, the full chorus effeet may be viewed as an extension of the vibrato effect. In both effects a band of frequencies is substituted for a single frequency. The physiological reason that the vibrato and chorus effectsv are pleasant is that more elemental organs of` hearing, such as the nerve endings at the bases' of the arches of Corti, are excited. However, each nerve ending is excited to a lesser degree than in the case of a single loud tone devoid of vibrato or chorus effect in which the energy is concentrated on but a few frequencies, resulting in but a few nerves being violently excited. The important differences between the vibrato and chorus effects are: (l) There are many more frequencies of comparable amplitude present in` the wide chorus effect than in the Wide vibrato.

nomena occurring during one complete cycle areso complex and the cycle is of such long duration that the listener cannot identify corresponding cyclic events, and thus cannot assign any overall regular periodicity to the effect. This effect is produced by combining the outputs of as few as three generators each tuned to a slightly different pitch and each frequency-modulated at-I a different rate.

Experiments have shown that as few as three such frequency-modulated generators, carefully tuned to pitches lying in a relatively wide chorus frequency band, produce chorus effects of the maximum Width desirable in music, and exhaustive tests have proved that these are equivalent,

i in the chorus effect, to as many as 20 simultaneously sounding melody instruments of the type shown in my prior Patent No, 2,254,284.

As is well known in the `electrical art, frequency modulation is productive of a series of X strong side band frequencies of decreasing amplitudes above and below the modulated frequency. In the musical art, frequency modulation is commonly called vibrato when produced by a single generator, and usually occurs at modulation rates i in the order of 6 C. P. S. For a more complete discussion of the side band theory as applied to vibrato, reference may be had to my previous Patent No. 2,382,413. The degree of the vibrato effect is inherently limited because the side band frequencies are always separated by frequency increments equal to the rate of the vibrato, and the frequency increments are constant regardless of the Width of the vibrato. Since the frequency increments are equal to the vibrato rate,

c the number of frequencies obtainable in a band of given width is limited. rfhis fundamental limitation of the vibrato is obviated in the instrument of the invention by providing three or more generators which are frequency-modulated at different rates, such as 5, 6 and '7 C. P. S.

Under these conditions the various beats and other repetitions effects are of an extremely complex character due to the simultaneous generation of sound signals by the three frequencymodulated systems. Due to the fact that lthe modulating rates, as well as the modulated frequencies, are diierent, the various beat rates are mutually masked to such an extent that the ear is unable to detect a repititious cycle, and instead senses the tone as comprising a large number of randomly spaced frequencies in a band which is wide but in which there is no dissonance. The different sets of side band frequencies as thus generated by the three frequency-modulated systems are very great in number and tend to lie between each other and thus provide many frequencies of comparable amplitude in the band which, in turn, makes it permissible to detune the three `generators to a considerable extent without causing inharmonious effects. On the contrary, they are then effective to produce -a very wide and rich chorus effect of satisfying Vmusical quality.

It is therefore the primary object of my invention to provide a novel apparatus for producing tones having a random chorus quality.

Another object'oi my yinvention is to provide an electrical organ in which complex -as well as pure harmonic tones are generated.

Another object is to provide means for generating a complex 'odd harmonic series of tones with which the event harmonics may be synthetically combined.

Anotherobject `is to-pr'ovidea chorus generator tuning system'in 'which the degree of detuning may be easily and accurately determined by a aero-beat tuning method.

Another object -is to provide a tone generating system capable of simultaneously generating a complex odd harmonic series, a string tone odd and -even harmonic series, Aand a relatively pure sinusodial 'tone vin which the phases of the three systems are substantially uniform and additive in all the 'notes of the instrument.

`A further object is to provide a multiple channel vibrato `rapparatus in which vibratos of different rates are produced.

`A further object is to kprovide a stable electronic `alternate-pulse-responsive frequency divider tone generating system for organs.

HA further object is to provide a simple `and easily operated stop switch control mechanism.

.A further object is to `providean electric organ by which, upon the depression vof a single playing key, a `tone of extremely complex quality may be produced.

A further object is to provide an improved output system for an electric organ 'in which some of the components of a complex tone may be quality controlled while other components thereof are not affected by such controls.

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

Figure l is in part a block diagram and in part a wiring diagram of the complete musical instrument;

Figures 2 and 2a together constitute a wiring diagram of a representativeportion of the instrument; and

Figure 3 is a wiringdiagram showing two stop switch units.

In Fig. l the generatingsystem of the instrument is represented by blocks, whereas the output system is shown mainly in the `form of a schematic wiring diagram. As shown by the block diagram, the signal generating system comprises a sharp signal generating channel comprising the first horizontal row of blocks at the top of the diagram, a hat signal generating channel comprising the second row of blocks, and a normal pitch `generating channel comprising the third row of blocks. The sharp signal generating channel comprises a frequency modulating vibrator' apparatus 18 which supplies a modulating frequency, such as l C. P. S., to a vibrato control apparatus 551. The vibrato effects change in the frequency of the output of a master oscillator 5 l The master oscillator 5l supplies a controlling frequency signal to the second stage of a cascaded series of alternate pulse responsive frequency dividers 52 to 51, these divider stages each successively dividing frequency supplied thereto by 2. The flat signal generating system comprises a frcquency modulating vibrato apparatus 48, operating at 5 C. l?. S., a vibrato control BD, a master oscillator Si, and frequency divider stages 62 to 61. The normal pitch signal generating channel comprises a frequency modulating vibrato apparatus d8, operating at '1 C. P. S., a vibrato control ?U, a master oscillator 1'I and divider stages 12 to 11. Each of the master oscillators 5|, El, 1| supplies a signal toa transformer unit 8l, which has two secondary windings, each having `a grounded terminal and having their other terminals connected respectively to conductors 81S and I8|B, the outputs differing in harmonic content. Conductor HiB provides a 'wave representing a string-like or brilliant (B) quality while the signal supplied to the conductor 81S is substantially a pure sine (S) wave.

Each of the divider stages such as the stages 52, 62 and 12 supplies a signal to a transformer unit 82, the secondary of which produces a brilliant signal in the conductor 82B. In a similar manner each of the divider stages 52, 62, 12 supplies a signal to a transformer 82A having two secondary windings, one supplying a sine wave to conductor 82S and the other supplying a wave representing the odd harmonic series to a conductor 82D.

Stages53 to 51, 63 to 61, 13 to 11 respectively supply signals through transformer units 83 to 81 and 33A to 81A and provide signals of brilliant quality in conductors 83B to 81B, ton@ signals of `sine wave form in conductors 83S to 81S, and signals representing the odd harmonic series in 'conductors 83D to 81D respectively.

The electric organ herein described is assumed to have an upper manual of playing keys, a lower manual, and a pedal clavier. For the purposes of illustration there is shown one playing key representative of all of the lzeys of the upper manual, a key 9| representative of all of the playing keys of the lower manual, and a pedal 92 representative of the usual 32 pedals. The instrument would also include a plurality of stop switch units 94, each of which represents a pair of stop tabletsl for controlling the tone quality. These tablets and the switches operated thereby are shown in Fig. 3 and will hereinafter be described in detail. In addition, for determining which of a plurality of preselected tone qualities shall be used for either of the manuals, preset keys may be provided, in the manner shown in the patent to L. Hammond, N o. 1,956,350, for rendering operative drawbars whereby the relative intensities of the individual components of the tone to be sounded may be controlled.

For purposes of illustration it is assumed that the outputs of the master oscillator 1| and of the divider stages 12 to 11 are respectively of the frequencies of the notes C6, C5, C4, C3, C2, Cl and C of the tempered musical scale, namely the following frequencies: 2093.00, 1046.50, 523.25, 261.626, 130.81, 65.406, and 32.703 C. P. S. It is also assumed that the keys 90 and 9| represent the note C3 while the pedal 92 represents the note C2. Each `of the keys 90, 9| is arranged, upon depression, to close a plurality of key switches 98, herein illustrated as 8 in number. Each of the key switches 98 has connected to one pole thereof a decoupling resistor` Rl02. In the switches operated by the playing keys 90, and 9| the resistors R|02 are respectively connected to conductors 84B, 83B and 84D, 85S, 84S, 83S, 82S and I8|S representing the eight foot string, the four foot string, eight foot odd harmonic series, subfundamental, fundamental, and second, fourth, and eighth harmonics of the note C3 respectively.

The switches 98 make contact with bus bars |04,

of which there is a group of eight for the upper manual, and a similar group of eight for the lower manual.

There are five matching transformers T|05, TIOB, T|0'|, T|08 and T|09, each having a primary winding, one terminal of which is grounded, and each having a plurality of taps illustrated as having conductors I0, and ||2 connected thereto. The stop switch units 94 are arranged to connect the bus bars |04 to selected conductors H0, or ||2. The switches 98 of the pedalboard are similarly adapted to be connected to selected conductors ||0, and ||2 by the stop switch units 94 associated therewith.

The conductors I0, and ||2 may be more or less permanently connected to preselected taps on the transformers T|05 to T|09 or these conductors may be considered as representative of sliding contactors which may be individually adjusted to make contact with selected taps on these transformers.

Thesecondaries of the transformers T l 05 to TI 01 are connected in series between ground and a conductor ||4, while the secondaries of transformers T|08 and T|09 are connected between ground and a conductor ||5. The secondary of transformers T|05, T|01 and T|08 are each adapted to have one of a plurality of tone quality determining meshes ||6 connected in parallel therewith by opening one or more of the switches ||8, one of which normally shunts each of these meshes.

It will be noted that only the bus bars |04 which carry complex wave form frequencies in the upper manual may be connected to the taps of the primary winding of transformer T|05, only the complex wave bus bars |04 of the lower manual may be connected to the taps of the primary` winding of transformer T|0|, and that only the complex wave bus bars |04 of the pedal clavier may be connected to the taps on the primary winding of transformer T|08. The conductors I0, and |2 for the upper and lower manuals, which conduct only sine wave signals, are connected to taps on the primary of transformer TI06, while the corresponding conductors for the pedal clavier are connected to taps on transformer T|09. The readily apparent reason for this is that the tone quality of the sine wave signal cannot be altered by means of ltering meshes such as meshes |6, and it is only the initially generated complex waves which may have their tone quality readily change by the use of such meshes.

The conductor I4 carries the combined signal from the three transformers T|05 to TIU'I to a pre-amplifier triode |24 through a resistor R|25 and volume control variable resistor R|25. The resistor R|26 is connected to ground through a bass compensation capacitor C|28, while the grid or triode |24 is connected to ground through a grid resistor Rl30. The cathode of the triode |24 is connected to ground through a self-bias resistor R|32 which has a by-pass condenser C|34 in parallel therewith. The anode of pentode |24 is connected to a suitable source of plate current, indicated as a +B terminal, through a load resistor Rl 35. The triode |24 is coupled to the input of an amplifying and reverberation apparatus |38, and the output of the latter is translated into sound by a speaker |40. The reverberation apparatus may be of the type shown in the patent to L. Hammond, No. 2,230,836. The reverberation apparatus is preferably-provided with suitable control switches so that it may be used or not at will.

The resistors R|02 are of high value relative to the output impedances of the transformer units 8|, 82, 82A, 83, 83A, etc. and relative to the input impedances of transformers Tl 05 to T|09 so that completion of several circuits by the closure of switches 98 connected to the same transformer unit or transformer will cause substantially arithmetic addition of the signals and there Will not be any appreciable feedback from one transformer unit to another through the several circuits which are completed upon closure of the key switches 98. The taps on each of the transformers 'N05 to T|09 are preferably at geometrically increasing number of turns from the grounded ends of the transformers.

The secondaries of the transformers T|08 and T|09 are connected in series and coupled through conductor H5, resistor R|4|, volume controlling variable resistor Rl42, and bass compensation capacitor CH3, to a preamplifier and reverberation control apparatus |39, the latter being coupled in push-pull to a push-pull amplifier |45. The output of the amplier |45 is transformer coupled to the inputs of parallel pushpull triodes |49 forming a power amplifier, and the output circuit of the latter is coupled by a transformer Tl5| to a speaker |53. It will be noted that the push-pull power amplifier, comprising the triodes |49, operates as a class B amplifier', thereby providing high power output.

While the generating system employed may be of any desired type of electronic oscillator and cascaded frequency dividing system such, for example, as that shown in the patent to Laurens Hammond, No. 2,126,682, there is a great advantage in employing oscillators and alternate pulse responsive frequency divider systems of the type shown in Figs. 2 and 2a.

A preferred form of master oscillator such as the oscillator 5| comprises a triode |44 having a variable inductance L|46, one terminal of which is connected to ground and the other terminal of which is connected to the grid |41 through a capacitor C|48 having a grid leak resistor R|50 in parallel therewith. A capacitor C|52 is connected in parallel with the inductance LI 46. Upon closure of a switch |54 by means of the chorus control 49, the plate |56 of triode |44 is connected to a suitable source of plate voltage indicated as a terminal +300 v. through a plate load resistor R|58. The closure of the switch |54 also applies operating plate voltage to the master oscillator 6| as well as the remaining master oscillators oi the chorus generatory channels. A1 pair of switches- |60, IBI, each has one pole connected to a tap. on the. inductance L|46-and when in the full line position shown, connect this tap to ground through condensersA C|62 and C|63. When in their dotted line positions the switches |60; connect the tap on the inductance Limite ground through parallel capacitors CIM, C 65 and a switch |66 which. is openedI and closed at a periodicity such as 7 C. P. S. by the vibrato switch operating apparatus 48.

The latter apparatusmay comprise an electromagnetically energized vibratory reed such as disclosed in the patent to D. Hancock, Jr., No. 2,301,870, preferably. operating in a manner to maintain the switch closcdduringonly one half of the cycle. It will be clear that when the switch |65 is closed the capacitors C|64, C|65 will be effectively in the resonant tuning mesh of the oscillating triode |44, and that when this switch is open these capacitorsare ineffective. The frequency of oscillation is therefore decreased when the switch |66 is closed and increased when the switch |66 is open. The value of the capacitor C|62 is substantially one half that of CB4, and C|63is one half that of Clil. Thus, when, ior example, the switches |60, are` in their full line. positions, the frequency of oscillation will be the average of the two vibrato frequencies produced when these switches are in their dotted line positions. Three degrees of frequency modulation are available since the capacitors CI 64 and C|i5fare ofI different values. Thus, for example, when switch |S| only is in its dotted line position a narrow frequency modulation may be produced. When the switch |60 only is in its dotted line position a frequency modulation of medium width may be produced. Whenrboth switches |60 and |6| are in the dotted line positions a widel frequency modula tion will be produced.

The master oscillators 6| and 1| are identical with theroscillator 5| except that the osciilators 5| and El are provided with additional means to facilitate their being tuned the desired degree sharp and flat relative to the normal pitch frequency generated by the oscillator 1|,

To initially tune the master oscillators, the oscillator 1| is rst tuned to its required pitch by adjustment of its variable inductance LMB. Itk will be noted that there is provided a pair of capacitors Cile, C|1I, each having one terminal grounded and its other connected" respectively to single pole double throw switches |12, |73. With both f the switches |12, |13 in an intermediate position both capacitors C|10 and CE1| are inclective. The flat oscillator 6| is then tuned to the same pitch as that of the oscillator 1| by adjustment of its variable inductance LMS. Thereafter, either the switch |12 or the switch H53, or both of these switches (depending upon whether a medium, a narrow or a wide chorus effect is desired) are moved to full line position, thus including capacitors C|10 or Ci'll, or both, in the resonant mesh of oscillator GI and thereby lowering its frequency of oscillation a desired amount.

To tune the oscillator sharp the switch |12, or switch 13, or both of these switches, are moved to upper dotted line position so as to bring capacitor CHQ or Cl1i, or both of these capacitors, in the tuning circuit o 'l oscillator 5|. With the switches in the latter position the inductance L|46 of oscillator 5| is adjusted to cause it to oscillate at the same frequency as the normal pitch oscillator 1|.v Thereafter; the switch |12, or |13, or both, are again moved to full line position with the result that the oscillator 5| will be sharp to substantially the same degree that the oscillator 6| is at. rlhe capacitors CHD and Cl'll together with their associated switches #Hand |13 thus form a simple and convenient means for timing the sharp and nat master oscillators. This tuning operation, using the zero beat technique, is so simple that the user of the instrument may do it should it ever become necessary.

The oscillators have been found to be very stable in operation, so that such tuning should be necessary but very infrequently. It will be noted that the feedback circuits of these oscillators are through connection of their cathodes to taps on their inductances LMB somewhat above ground potential, sufficient to provide adequate feedback for self-oscillation.

The output circuit of the oscillator 5| is coupled to the input circuit of a rectifying and pulse sharpening triode |16 through a blocking capacitor C|18 connecting the plate |56 of triode |44 with the grid |19 of triode |16. Negative grid bias is applied to the grid |15 through a resistor Rice connected to a suitable source of cutoff potential indicated as a terminal C-. The triode |16 is supplied with plate current through a load resistor R182 connected to a suitable source o plate voltage indicated as a terminal B+.

The outputs of the oscillators 6| and 1| are similarly coupled to rectiiying and pulse sharpening triodes |16 and the cathodes |84 0i all three triodes |16 are connected to a common conductor la. This conductor connects the cathodes to ground through the transformer unit 8|. This unit comprises a pair of transformers TISS and TiBS, the primary windings L| and Lil of which are connected in series between the conductor |86 and ground, there being a capacitor C|92 in parallel with the winding LISU, and a capacitor C|94 in parallel with the winding L|9|. Separate secondaries LISB and LI 91, respectively forming parts of the transiormers T538 and T|89, each has one terminal grounded and the other terminal connected respectively to the conductors 8|B and BIS. Due to the iiltering action of the capacitors C|92,

C|94 and the inductances oi transformers TISS and TISS, the signal appearing on the conductor SIS will be substantially a sine wave while the signal appearing on conductor 8|B will he a iSeries of spaced positive peaks which will be in phase with the positive peaks of the sine wave on conductor SES.

The alternate pulse responsive frequency divider stages arev preferably of the form shown in my copending application Serial No. 519,838, filed January 27, 1941i, now abandoned. Each of these stages comprises a pair of triodes 200, 20| having their grids 202, 203 connected to the plate |8| of triode |lt through capacitors C204 and C2D5.

"The gri- ds 202, 203 are connected to a suitable source of negative grid bias indicated as terminals -C through grid resistors R206 and R201. The plates 208 and 2D!! of these triodes are connected to a source of plate current indicated as terminals B-lthrough load resistors R2|0 and R2||. The plate 298 connected to the grid 203 by a mesh comprising a resistor R2 I2 having in parallel therewith a resistor R2|3 in series with a capacitor C2l4. Similarly the plate 209 is connected to the grid 202 through a resistor 9 R2I6 having in parallel therewith a resistor R2 I1 in series with a capacitor C2I8. As more fully described in my aforesaid copending application, the triodes 200, alternately conduct plate current as negative impulses are impressed upon their input circuits. It will be noted that the cathodes 220 of the triodes 20| are connected to ground whereas the cathodes 222 of the triodes 200 are connected to a common conductor 224. This conductor is connected to ground through the primary windings L226 and L221 of transformers T228 and T229 respectively comprising the transformer unit 82. L226 and L221 have capacitors C230 and C23I connected in parallel therewith respectively. The

secondary winding L232 of transformer T228 has one terminal grounded and the other terminal connected to the conductor 82D while the secondary winding L233 of T229 has one terminal connected to ground and its other terminal connected to its conductor 82S. Upon alternate pulses impressed upon the inout circuit of triode 200, the cathode current will rapidly increase, and on the intermediate pulses, it will rapidly decrease, and the current wave on the cathodes 222 therefore tends to be of rectangular shape. Due to the filtering action of the meshes comprising the capacitors C230, C23| and transformers T228, T229, the signal appearing on the conductor 82S will be substantially a sine wave, while that appearing on the conductor 82 will be of complex shape as indicated in Fig. 2 adjacent the conductor 82D. The harmonic analysis of the wave of this shape shows it to be a fundamental with the long series of odd harmonics of progressively decreasing intensity without any even harmonics. The sound equivalent of this wave shape is very pleasing to the ear, its tone quality resembling that of the clarinet more than that of any other conventional musical instrument. Since this wave is produced only upon each alternate impulse supplied to the triodes 200, 20| it will be apparent that the frequency of the signals on the conductors 82D, 82S will be one half of that of the signals appearing on the conductors 8| S and 8|B.

A rectifying and pulse sharpening triode 236 (Fig. 2a) has its grid 231 connected to the plate 209 of triode 20| through a blocking capacitor G238. The triode 236 operates in a manner similar to the operation of the triode |16. The cathodes 240, for the triodes 236 of the divider stages 52, 62 and 12 are connected by a common conductor 242 to the transformer unit 82A which comprises a transformer T244 having a primary L245 and a secondary L246. A capacitor C241 is connected in parallel with the primary winding L245. L246 has one terminal grounded and the conductor 82B connected to its other terminal. Due to the rectifying action of the triode 236, the wave appearing upon the plate thereof will comprise sharp negative pulses which are impressed upon the input circuits of triodes 250 and 25| which form part of the third stage of frequency division, the circuit elements associated with the triodes 248 and 25| being the same as those shown in connection with the triodes 200 and 20|. The values of some of the elements of the circuit may differ to accord with their different operating frequencies.

The subsequent stages 4 to 1 inclusive of each of the frequency generating channels are like- Wise similar to the second stage except for differences in the values of some of the components.

Referring to Fig. 3 each of the stop switch The windings' units 94 comprises a soft stop tablet 260, and a medium intensity stop tablet 262. Stop tablet 260 operates a single pole single throw switch 264, a single pole double throw switch 266 and a single pole single throw switch 268. Stop tablet 262 operates a similar group of switches 210, 212 and 214. The switch arms of switches 264 and 266 are connected to one of the conductors |04 and when neither of the stop tablets 260 and 262 is depressed, the conductor |04 is connected to ground through the switch 264, conductor 216, the switch 210 and grounded conductor 218.

When it is desired to utilize the signal supplied over the conductor |04 at low intensity the stop tablet 260 only is depressed, thereupon completing a circuit from conductor |04 through switch 266, conductor 280, switch 212, conductor 282, switch 268 and conductor 284 to a tap on the associated matching transformer such as the transformer TI05. The tap to which the conductor 264 is connected utilizes the lowest nurnber of turns on the primary of the transformer and thus the output of the transformer is at low amplitude.

When it is desired to utilize the signal on conductor |04 at medium intensity the stop tablet 262 only is operated, whereupon, the signal is transmitted from the conductor |04 to the transformer TI05 through switch 266, conductor 286. switch 214, and conductor 288 to the intermediate tap on the primary of TI05 thereby causing the signal in the output of this transformer to be at medium amplitude.

When the signal on conductor 04 is to be vutilized at full amplitude, both stop tablets 260 and 262 are depressed, whereupon the signal from the conductor |04 flows through switch 266, conductor 280, switch 212 and conductor 290 to the ungrounded terminal of the primary of TI 05.

By virtue of the use of this type of stop switch unit the amplitudes of the complex and sine wave components of each tone may be individually controlled in any one of three degrees of intensity. Thus a large variety of extremely complex qualities may be selected and made available for each of the manuals and for the pedal clavier. In addition, the quality may further be controlled by selective operation of the switches |I8 to render effective one or more of the filter sections I I6.

` of both upper and lower manuals, which control the substantially sine wave signals from the generating system, are connected to the transformer TI06 while the tablet switch units 94 of the upper manual which control the complex quality outputs of the generating system are connected to transformer TI05. Similarly the tablet switch units 94 of the lower manual controlling the cornplex waves are connected to TI01, and the tablet switch units 94 for the pedal controlling the complex waves are connected to TI08. Inasmuch as each of these latter three transformers has tone quality filtering meshes I |6 associated therewith, the complex quality tone signals may have their harmonic content substantially altered by appropriate operation of the switches II8. Thus the tone qualities lavailable on the two manuals,

the vibrato apparatus.

.ably 1% of the pitch of the note.

as well as on the pedal'clavier, Ymay beindividually selected, making it vpossible to Vutilize a Aregistration technique substantially lilre that employed in playing the pipe organ.

The instrument is played in the usual manner, the musician selecting desired tone qualities by the operation of the stop tablets 260,252. The quality of the components other than the sine Wave components may be varied from time to time by selective operation oi the tone control switches I'I8.

Dueto the fact that there are three signal generating channels by which a chorus ol any one of three selective widths may be obtained, and due to the fact that each of the three generating channels has a different vibrato periodicity, it is clear that by depression of a single lrey `a tone of utmost complexity may be produced. The tone is equivalent to that produced by a large number of mechanical musical instruments simultaneously playing the same'note, such, for example, as the sound produced by ,a large orchestral string section when all the musicians are playing the same note. The richness and harmonic complexity of the tones produced far eX- ceed those previously obtainable from any othesingle musical instrument known to applicant.

Since the three signals (sine wave, brilliant, and odd harmonic series) are in phase, they will be additive when used simultaneously. It will be noted that in synthesizing a tone quality by the voperation or" the stop switch units E4 controlling the sine wave output signals of the generating system, only even harmonics are utilized so'that it is not necessary to borrow odd harmonics `of lthe tempered scale from other generators. Instead, a signal comprising the exact odd harmonic series signals may be synthesized with the sine wave even harmonic signals to produce substantially any desired tone quality.

As previously pointed out, the output signals of the generating system may comprise solely the output of the normal pitch channel, or 'may comprise the outputs of all three channels, by kselective operation of the chorus control 49 (switch |54, Fig. 2) which renders operative the flat and sharp signal generating channels.

Furthermore, the player may, by appropriate `operation of the switches l'ill, H3, determinethe width of the chorus effect desired, and, by ap propriate operation of switches H35, may control By Virtue of the fact that the normal pitch, sharp pitch and hat pitch generating channels may each have a diilerent vibrato rate, the overall eiect of tone produced is `extremely complex and the musical tones pro- 4relative to the third generator by amounts inthe Vorder of 1% of the pitch of the note. jgree of sharpness ornatness to which'the gen'- .erating systems Vare .tuned should not be more `than 1.7%, but may be considerably less than 11%,

The de such as and still produce a desirable chorus effect, although of course not as pronouncedas when the frequency difference is greater.

The vibrato rate is preferably in the range of f from 5.5 to 7.5 C. P. S. and the extent of variationfinlrequency due to the vibrato is preier However, the pitch Achange du@ to the vibrato effect may vary 12 somewhat from this percentage and still produce musically advantageous results. A 'frequency change due to the vibrato of from .25% to 1.5 it above and below the average frequency may be employed.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such similar and modilied forms of the apparatus disclosed, byvvvhich substantially the results of the invention may be obtained by substantially the `same or equivalent means.

I claim:

l. In an electrical musical instrument the combination of a generating system producing irequencies of the musical scale at normal pitch, u generating system producing frequencies slightly a generating system producing. frequencies slightly i'lat, means individual to eachlgenerating system and coupled therewith for frequency modulating the signals produced thereby to an extent to cause the introduction of the vibrato effect, each of said last named means operating at a rate dil-lering from that of the others, the respec tive rates being approximately 5, G and 'l cycles per second, and means for combining the signals produce by the three generating systems and translating the combined signalintcvsound.

2. An electrical musical instrument comprising three generating systems, each system including a plurality of generators of different musical tone frequencies, the first system generating electrical signals respectively of the nominal frequencies of the tempered musical scale, the second system generating ectrical signals which are respcctively sharp relative to the nominal frequencies of the musical scale by 0.25 to 1.7 per-:entend the third systemgenerating signals which are respectively flat relative to the vnominal fre quencies of the musical scale by 0.25 to 1.7 percent, the extent to which the second system is sharp and the third system is flat beingr suilicient to produce a readily perceptible chorus effect, vibrato means individual to each generating system to frequency modulate the signals generated thereby at slightly different `rates within the range of 5 to 7.5 cycles per second, an output system, and key roperated means for causing simultaneous transmission tothe output system of signals from corresponding generators of the three generating systems.

3. An electrical musical instrument comprising electrical signal generating systems, each capable of producing signals of all of the notes oi the musical scale within the gamut of the instrument, the frequencies of the signals generated by at least two of thesystems differing from the stand- Yard-frequenciesof the tempered musical scale by y0.25 to.l.7 percent'toproducea wide chorus effect when combined. and .translated into sound, .means iortirerniencyv modulating the signals produced by the generating systems atdiierent vibrato rates, and selective means for combining the signals .from the Agenerating systems and translating the combined signal intosound.

fl. A qualitycontrol apparatus for selectively connecting a signal carrying bus bar to one of .four different amplitude determiningterminals, comprising; apairof manually'operable elements,

a plurality of switchesoperated by each element,

four circuits for connecting the bus bar respectively to said four terminals, each circuit including at least one switch operated by each of said elements, said circuits being completed respectively when neither of the elements is operated, when the first of the pair 0f elements is operated, when the second of the pair of elements is operated, and when both elements are operated.

5. In a generating system capable of producing musical tone frequencies of complex wave form and of sine wave form, a pair of matching transformers having tapped primary windings, a plurality of bus bars, key operated switches for selectively connecting said signal generators to said bus bars, means to connect sine wave signal collecting bus bars to selected taps of the primary of one of said matching transformers, means to connect the bus bars carrying complex Wave signals to selected taps of the primary of the other of said transformers, a plurality of selectively coupled filtering meshes associated with the latter transformer, and means for combining the outputs of both of said transformers and translating the combined signal into sound.

6. In an electrical musical instrument having a signa1 generating system producing complex quality and substantially sine wave signals of octave relationship, signal collecting bus bars, playing key operated switches for connecting the generating system to the bus bars, a pair of transformers having tapped primaries arranged to be coupled to the bus bars, one of said transformers being arranged to be coupled to bus bars carrying complex quality representing signals, the other to bus bars carrying signals of substantially sine wave form, a filtering mesh having a plurality of adjustable impedance varying filtering means associated with the rst transformer, and means for amplifying and translating into sound the combined signals derived from both of said transformers.

'7. In an electrical musical instrument, the combination of three generating channels, each comprising a master oscillator and a plurality of frequency divider stages connected thereto in cascade so as respectively to generate frequencies corresponding to the pitch of corresponding notes in the successive octaves of the musical scale, one of said channels generating signals of normal frequency and the other two channels generating signals respectively sharp and nat relative to the normal pitch frequencies, each of said channels including means for frequency modulating the frequencies generated thereby, said frequency modulating means operating at different rates within the range of 4.5 to '7.5 cycles per second, means for combining the signal outputs of corresponding stages of said generating channels, and playing key operated switch means for selectively transmitting signals from a plurality of said stages to the output system of the instrument.

8. In an electrical musical instrument having an output system, the combination of three signal frequency generating systems, each generating all of the frequencies corresponding generally to the notes of the musical scale, one of said systems generating signals of the frequencies of the musical scale with substantial exactness and the other two systems generating signals respectively sharp and flat relative to the substantially exact frequencies, each of said systems including means for frequency modulating the signals generated thereby, said frequency modulating means operating at different rates Within the range of 4.5 to 7.5 cycles per second, and playing key operated switch means for selectively transmitting signals from the generating systems to the output system of the instrument.

9. In an electrical musical instrument having a plurality of frequency generating channels, each channel generating octavely related frequencies, means for frequency modulating the signals produced in said channels at a rate in the order of 6 cycles per second and to an extent in the order of 1.5% of the modulated frequency, an output system for the instrument, key controlled means for selectively connecting corresponding generators of the several channels to the output system, and means for selectively adjusting one of the channels to generate frequencies in the order of 1% higher than another of the channels and a third channel to generate frequencies in the order of 1% lower than those generated in the first channel.

l0. In an. apparatus for controlling the degree of coupling of a signal carrying conductor with an output device, in which the device has three input terminals, each for a different degree of attentuation of the signal in the output device, the combination of two manually operable tablets, a break and make switch and a make switch operable by each of the tablets, said signal carrying conductor being connected to one of the break and make switches, and conductors connecting at least two of said switches of different tablets in series between the signal conductor and the input terminals, the connections of the conductors being arranged to Cause the signal conductor to be connected to the high attenuation terminal when one of the tablets is operated, to connect the signal conductor to the intermediate attenuation terminal when the other tablet is operated, and to connect the signal conductor to the low attenuation terminal when both switches are operated.

11. The combination set forth in claim 10 in which each tablet is provided with an additional break switch normally connected in series between the signal conductor and ground.

12. An electrical musical instrument comprising, a plurality of electrical signal generating systems, each capable of providing a signal for each note within the gamut of the instrument, the frequencies of the signals for corresponding notes generated by said systems differing from each other by from 0.25 to 1.7 percent to produce a perceptible chorus effect, means for frequency modulating the signals produced by the generating systems at different vibrato rates between 5 to '7.5 cycles per second, an output system, a plurality of playing keys, and means operated by each key to select corresponding frequency signals from each of the generating systems and to transmit the signals to the output system.

JOHN M. HANERT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,128.367 Kock Aug. 30, 1938 2,159,505 Hammond May 23, 1939 2,201,388 Curtis May 21, 1940 2,220,709 Demuth Nov. 5, 1940 2,310,429 Hanert Feb. 9, 1943

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