Electrical musical instrument

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for generating musical sounds, more particularly, the ³⁵sound of any desired instrument.

Many devices have been invented in past which simulate the sounds of the standard musical instruments, notably that of the pipe organ. A few have used the technique of recording the audio signal of every note of the musical scale on a magnetic drum or disc, and, at the desired moment of play, reading the note into an amplifier and, in turn, a loudspeaker. This latter system has the advantage that it may literally reproduce the sounds of ₄.the best instruments in the world. If the generation of a violin sound is desired, for example, a Stradivarius instrument might be used in the original drum or disc recording.

This system as described has never been practical for κη the reason that only the steady state sound of any instrument could be recorded. An important characteristic of the tone of any musical instrument is the sound it makes when the tone is begun. This characteristic, called the. attack,” is a transient which varies from instrument 55 to instrument, from note to note. It is an extremely complicated addition of harmonics with time varying amplitudes, which, for all practical purposes, defies direct generation. '

The present invention additionally relates to a method ₆₀and apparatus for playing a device which generates musical sounds, more particularly for receiving musical sounds of one instrument, detecting level and pitch, and controlling the production of sounds, by the generator, of another musical instrument. _6g

There has long been a need, in the musical circles, for a device which would enable the player of one instrument to play another. Musicians have learned to play a plurality of instruments in the past, but have invariably found that best proficiency came with specialization. Various 70 mechanical devices have been invented to bring similarity between the “operation” of instruments, however, none have used the actual sound of one instrument to choose the notes of another.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a musical signal generator of the recording type which also reproduces the attack characteristic of the instrument recorded.

It is a further object of the present invention to provide method and apparatus for the generation of musical sounds of one instrument in accordance with the notes played on another.

These and other objects which will hereafter become apparent are achieved by a device consisting of a number of bandpass filters each adjusted to pass only the frequencies in the immediate vicinity of one note of the well tempered scale, a corresponding number of threshold level detectors each connected to a bandpass filter for determining when a note has been played, and a magnetic recording drum, having two tracks per note, one track capable of reproducing the attack characteristic, the other, the steady state of any musical instrument, operatively connected to the threshold detectors so that first the attack and then the steady state of any note is generated in response to a signal therefrom. The device is thus capable of “hearing” what note is sung or played by the musician, converting this information into signals denoting the pitch and level of the sound heard, and reproducing the sound of any desired instrument, in accordance with these signals, at the same pitch and level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the overall system which forms the basis of the instant invention.

FIG. 2A is a schematic diagram showing the pitch and level detector of the preferred embodiment of the instant invention.

_ FIG. 2B is a schematic diagram showing the musical signal generator according to the preferred embodiment of the present invention.

FIG·· 3 is a schematic diagram showing one type of magnetic head control switch that may be used with the signal generator of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawings is a block representation of the apparatus and method that forms the basis of the invention: apparatus and method wherein musical sounds of one instrument may be converted to the musical sounds of another. Sound waves of any pitch, level and quality impinge on microphone 100 where they are converted to corresponding electrical oscillations. The pitch of the fundamental note, as well as the level or intensity of the tone is isolated in electronic device 200 and the information transmitted to a musical tone generator 300. The generator 300 is capable of producing the electrical signal facsimile of the musical note of any given musical instrument, with the possible exception of the human voice, at an intensity corresponding to that detected by the device 600 ^el^ecfri^cal signal is then passed to a loudspeaker

It will be appreciated that the system shown in FIG. 1 is neither limited to a single pitch and level detector nor a single producer. One detector may be used, for example to feed a number of electronic tone producers each generating the sounds of a different musical instrument. Likewise a single tone producer generating, say, the sounds of an organ, may be fed by various detectors adjusted to detect the pitch and level of various other instruments to provide a number of organ “voices” or simultaneous lines of music.

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A complex system is readily contemplated whereby any number of detectors may be switched into service to control any desired number of tone generators. As will be explained in more detail below, the tone generators need not necessarily produce sound at the pitch emitted by the _gsource instrument but might be further switchable to permit the production of music in any desired key.

FIG. 2A depicts the preferred embodiment for detecting pitch and level. Electrical oscillations in the audio range originate at the sound source 101 which may be a jq microphone; a magnetic tape, magnetic drum, phonograph or motion picture reproducing head; a ratio or television audio output or any similar device. These oscillations may be amplified if necessary by introducing a preamplifier 102 into the circuit. 15

The electrical oscillations are then fed to a number of bandpass filters 201 to 225 of conventional design arranged in parallel. These filters are each tuned to a note in the welltempered scale with a “Q” sufficient to distinguish notes a “half-tone” apart. Since the welltempered scale 20 consists of thirteen notes in an octave, each, as is well known, defined by a particular frequency, a pitch detector with the normal musical instrument and singing voice range of two octaves must comprise twenty-five such filters. If the musical sounds to be detected are to occur 25 in the lower musical registers it might be necessary to insert a frequency doubler in the circuit after the preamplifier and to set all bandpass filters to a frequency an octave higher. This technique will overcome the practical difficulties of obtaining the necessary “Q” where the 30 difference of a half-tone is but a few cycles per second.

The output of each bandpass filter is connected to the input of a separate adjustable threshold gate. Twenty-five threshold gates 226-250 have been indicated for this purpose in the diagram. The object of the threshold gates, 35 which are of conventional design, is to produce a voltage at the output if the input voltage exceeds a given value. If the input voltage is less than the “threshold” the output is either at ground or at least at some other potential. It is common in the art to call the former output a “1,” the ⁴θ latter a “0”; this nomenclature will hereinafter be used. The threshold gate is commonly called a “Schmitt trigger.”

The circle in the center of blocks in FIG. 2A, as well as FIG. 2B, from which emanate the short hash marks is 45 intended to indicate that the device represented by the block is subject to the manual adjustment of some parameter. The threshold voltage of the threshold gates must here be adjustable so as to cause a “1” only when the fundamental of any note has passed through the band- 50 pass filter. Harmonics as well as unwanted background may, in this simple manner, be excluded from detection. Since the amplitude range of any given note varies from instrument to instrument, and of any given instrument even from note to note, the use of the detector to dis- 55 tinguish notes of more than one instrument necessitates the availability of manual adjustment.

The outputs “1” or “0” of the parallel threshold gates may be directly connected to the musical signal generator shown in FIG. 2B and discussed in detail below. In 60 this case they would each be simply connected to a separate magnetic head control switch; if there be 25 threshold gates, to 25 control switches.Two further features are shown in FIG. 2A, however, which may be inserted intermediate between the threshold gates and the control 65 switches. The first permits the manual operation of the signal generator by keyboard, and the second the selection of musical key.

Since the musical signal generator is capable of producing the sounds of practically any musical instrument, it 70 permits the musician to conveniently “play” all instruments without laboriously learning their technique. If the musician can operate a keyboard, as for example, a piano keyboard, he can “operate” the musical instrument which the musical signal generator is designed to imitate. Single- 75 ,701 pole, single-throw switches 251-275 biased with a mechanical spring or some other device to hold them normally open, serve, when manually depressed, to provide a “1” signal to the magnetic head control switch of the musical signal generator. When open they provide a “0.” These switches are physically in the form of push buttons, piano keys, or any other configuration which is easy to “play.”

One terminal or circuit point of the switches 251-275 is connected to a source of voltage V, which potentially represents a “1.” The other terminal or circuit point is connected through switch 276 to the magnetic head control switch of the musical signal generator. Multiple pole, double throw switch 276 permits setting the apparatus to “automatic,” whereby the pitch and level detector are connected into the circuit, or to “manual.” In the manual setting terminal switches 251 to 275 as well as a level potentiometer are connected to the musical signal generator. It will be appreciated that the “1” signal, which is to be generated by closing the switches 251-275, can be represented by any other potential as well, including a negative potential or even ground.

The output of either the pitch detector (automatic setting) or the manual keyboard (manual setting) may then either be connected directly to the magnetic head control switch of the musical signal generator or to a key control switch 277, as shown in FIG. 2A. The key control switch is simply a multiple pole (one per input note channel) multiple throw (one per output note key) switch which connects all input note channels to a number of possible magnetic head control switches. This switch enables the operator to “play” the input in one key, say C major, and produce signals and, of course, by loudspeaker, sounds in any other. If the keyboard is used, this feature would permit an operator to always play in his most accustomed key while choosing any other. If the pitch and level detector is used to detect, for example, voice sounds from a microphone, the singer need only sing in his most comfortable register.

The switch 277 comprises a number of input circuits 290 which each may be selectively connected to a number of output circuits 281 to 289. The output circuits pass through a cable 299 to the musical signal generator where each is connected to a magnetic head switch. The output circuits can thus be connected with any desired magnetic head switch to give the desired key; the simplest and most obvious format would be a connection of the input notes so as to selectively generate notes up to, say 4 half notes below, and 4 half notes above the note played as well as the note itself.

The sound source generated signal is also connected to a level detector 291 which produces a D.C. voltage output in proportion to the A.C. voltage input. Any known technique such as integration may be used to obtain this result. The D.C. output is passed through switch 276 on line 298 to the musical signal generator where it is used to control the level of the output as described in detail below.

In the event that the operator wishes to control the output level manually, either switch 276 or a separately provided switch may be used to disconnect the level detector and connect a potentiometer 294. This potentiometer permits setting the D.C. voltage on line 298, at will, anywhere from zero to “V” as shown in FIG. 2A. The signal generation mechanism thus normally operates to produce higher musical volume the greater the voltage.

FIG. 2B, showing the preferred embodiment of the musical signal generator, will now be described. This device employs a magnetic drum 351 of conventional design having two tracks for every note to be produced. The steady state tone of a musical instrument is recorded completely around one track at a constant level so that the drum may turn more than one complete revolution without any consequent break in the signal. This requirement necessitates more than the mere recording of a note

3,539 5 on one circumference of the drum; the tail of a single circumference must be placed in phase with the head of the recorded signal so that no audible change in the tone occurs at the joinder of head and tail. The phase may be adjusted by slightly increasing or decreasing the fre- _rquency of the entire recorded signal, a process best car- ’’ ried out by adjusting the speed of the recording from which the drum recording is made.

The second track for each note recorder on the magnetic drum carries the starting transient or “attack” char- ₁₀acteristic of the musical instrument represented. This characteristic is recorded in one circumference of the drum beginning in the case of every note at a certain reference line drawn in the axial direction along the face of the drum. Since the time length of the attack character- 15 istic varies from instrument to instrument and even with one instrument from note to note it will be necessary either to adjust the circumference of the drum or the speed of the drum’s rotation so that the attack transients are completely damped for all the notes in exactly one revolu- 20 tion.

The magnetic drum shown in the diagram is provided with forty-nine dual tone tracks, twelve per octave for four octaves and an additional one making the highest note four octaves above the lowest. The drum has a single ad- 25 ditional timing track on which, precisely where the track crosses the reference line, is recorded a timing mark or blip. Ninety-nine magnetic recording heads 352 to 450 are arranged in an axial line, one per track, to read the tracks described above. The tone track heads are con- 30 nected directly to the magnetic head control switches 302350, of which there are also forty-nine, one per dual tone track, or in other words, one for every two heads. The timing track magnetic head 352 is connected through a preamplifier 301 to each of the magnetic head control 35 switches. The magnetic heads 352—450, the preamplifier 301 and the control switches 302-350 constitute means, according to this embodiment of the present invention, for reading first the attack transient and then the steady state characteristic of a desired musical note or notes from the ⁴⁰plurality of recorded notes.

The reference line described above need not, of course, be a physical line drawn on the magnetic drum. Its purpose is merely to insure that the start of the attack characteristics are all aligned with the timing mark as record- 45 ed on their respective tracks. It may be helpful during drum recording to actually have a visible line; however, this depends on the manufacturing processes used.

The magnetic head control switches 302 to 350¹ will be further described below in connection with FIG. 3 and 50 the discussion of operation of the musical signal generator. Suffice it now to say that the output of each is the composite of the transient and the steady state recorded signals; that is, a single musical note. Each control switch is connected to its own level preamplifier 451 to 499 55 wherein the signal is amplified an adjustable amount. Not shown but useful is an adjustable note “end” control connected in each channel and to the pitch and level detector which anticipates the end of the note and drops the volume gradually, not abruptly as would be the case 60 with the presently shown apparatus.

To the level preamplifiers or note end control devices may be attached other commonly known devices 500 to 548, such as the echo, vibrato or tremolo generators. These devices should be individually manually adjustable 65 in all the significant parameters; namely period, amplitude, attack and damping transients, etc., or attached to some device which detects these parameters in the input to the pitch and level detector for automatic control of same. The various channels are finally combined in a 70 mixer 562, and fed through a final amplifier 549 which includes the level control. This amplifier 549 responds to the voltage on line 298- to produce an output signal of corresponding amplitude. This control function is most easily accomplished by using the voltage from line 298 75 ,701 to bias the first stage of amplification. The lower the bias the lower the output signal from that particular stage.

The final signal emerging from the amplifier 549 is fed to a sound sink, which can be a loudspeaker, magnetic tape or phonograph recording head, motion picture sound recording head or the like.

Turning now to FIG. 3, which illustrates one type of magnetic head control switch that may be used with the present invention, it is necessary to briefly state the modus operandi of the musical signal generator. The two recording heads for any note constantly read the transient as well as steady state tone tracks and pass these to the magnetic head control switches. As soon as the control switch receives a “1” input from the pitch detector described in connection with FIG. 2A:

(a) it waits until it receives the next timing signal from timing track head 352 and preamplifier 301;

(b) upon receipt of the first timing signal it connects the transient recording head, through a preamplifier, to the output;

(c) upon receipt of the second timing signal (denoting one complete revolution of the drum), it disconnects the transient recording head and connects the steady state recording head, through a preamplifier, to the output;

(d) it maintains the final connection mentioned above, the receipt of further timing signals notwithstanding, until the input from the pitch detector returns to “0.” While the input is “0,” of course, both recording heads remain disconnected from the output.

It is therefore seen that first the transient, then the steady state is read from the recording of any given note. There is a short waiting period between the “playing” of a note and the production of same until the magnetic heads next cross the reference line but, as the length of the attack characteristic is short, usually in the neighborhood of Jo second, this period will not be noticeable. It is interesting to note in this regard that these instruments with the longest attack characteristic are just those instruments that must be played the slowest and for which, therefore, the waiting period will be less noticeable. Compare, for example, the bass (slow, long characteristic) and the violin (fast, short characteristic).

FIG. 3 depicts two flip-flops 555 and 557, capable of being triggered by positive going pulses, AND gates 553 and 558, inverter 554, differentiator 556, mixer 561 and controllable preamplifiers 559 and 560. The input 551 from the pitch detector, normally “0” but in the “1” state when a note is to be played, passes through AND gate 553 upon coincidence with a timing signal on line 550 from magnetic head 352 and preamplifier 301. Since the flip-flop 555 was held in its reset state “R” by the positive signal from inverter 554, it will change to the set state “S” on the occurrence of the “1” and the first timing mark. The AND gate 558 will then pass the set output signal to preamplifier 559 to enable the transient signal from magnetic head 353 to pass through mixer 561 to the output line 552. The other input to AND gate 558 will be “1” since flip-flop 557 has been constrained to start in the reset state by a signal from inverter 554. The preamplifiers 559 and 560 operate as signal gates, permitting the recording signal to pass from the magnetic heads 353 and 354 to mixer 561 if and only if a “1” appears on the respective enable inputs.

When the second timing mark is read the signal is passed through AND gate 553 to reset flip-flop 555. The set output signal ceases and the recorded signal from head 353 is halted at preamplifier 559. The presence of a sudden increase in voltage at the reset output of flip-flop 555, however, causes the differentiator 556 to produce an output pulse setting flip-flop 557 and enabling the recorded signal from the steady state magnetic head 354. This signal is also passed through the mixer 561 to the output line 552.

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Flip-flop 557 will remain in the set position until the input on line 551 changes from a “1” to a “0.” The inverter 554 will then reset both flip-flops and hold them there until the note, which the particular magnetic head control switch controls, is played again. It will be noted that flip-flop 555 oscillates between the set and reset conditions while the note is played but is only functional in the control switch while flip-flop 557 remains reset.

Although this invention has been described with reference to a specific illustrative embodiment thereof, it will be understood that various modifications, elaborations and alterations will occur to those skilled in the art which do not depart from the essential spirit of the invention.