CA1091069A - Piano action magnetic tape recording process for player piano playback - Google Patents

Abstract

A PIANO ACTION MAGNETIC TAPE RECORDING
PROCESS FOR PLAYER PIANO PLAYBACK
ABSTRACT

A process is provided for recording electric signals corres-ponding to piano key operation and for reproducing the piano key operation. The process includes switching a discrete frequency oscillator corresponding to each piano key, algebraically adding the outputs of each oscillator, processing the algebraic sum of the oscillator outputs, recording the processed signal, reproduc-ing the processed signal, reprocessing said recorded signal, detecting each frequency in the reprocessed signal, and energizing an electromechanical device so as to actuate the piano key which had switched the discrete frequency oscillator.

Description

lO~lOt;'3 NO ACTION ~IA(',NETIC Tir~PE RFCORDING
PROCESS FOR PLAYER PIANO PL.AYBACK
BACKGROUND OF THE INVENTION

Player pianos have been in common usage for many years. While player pianos differ in their general configuration, they usually function in substantially the same manner.
A typical player piano has a keyboard containing 88 keys simi-lar to the keys of most other pianos. Above the keyboard of most player pianos is a mechanism which provides for the automatic oper-ation of the piano. This mechanism in most player pianos employs a t~acker bar in which is situated an array of pneumatic holes. Each hole corresponds to a single key of the keyboard.
The typical player piano control apparatus also includes two spindles which cooperate to hold the ends of a scroll so the center of the scroll is stretched tightly across the tracker bar. The scroll, which is often called a tape, is usually made of paper.
The typical player piano utilizes a source of power and inter-ior mechanical parts which wind the scroll from one spindle to the other across the tracker bar at a predetermined speed and which also include a pneumatic system that applies suction to each tracker bar hole on the side opposite the paper scroll. The pneumatic system detects a pressure differential in the tracker bar holes to operate the piano keyboard action in a predetermined manner.
The player piano action is controlled by putting openings of predetermined size and length in the paper scroll so the openings cross the tracker bar holes in a predetermined manner.
When a paper scroll hole is aligned with a tracker bar hole, the corresponding pneumatic system detects normal atmospheric pressure in the tracker bar hole. When a solid portion of the paper scroll covers a tracker bar hole, it prevents the passage of air through the tracker bar hole and the pneumatic mechanism there-fore senses a different air pressure in the tracker bar hole than

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the level of air pressurc existing therein when a hole in the paper scroll permits ambient air pressure surrounding the piano to commun-icate with the tracker bar hole.
The aforedescribed paper scroll and player piano mechanics in operation are attractive in a nostalgic sense, but have certain in-herent disadvantages. For example, the paper scroll can easily be torn or damaged. The paper scroll is also relatively bulky. The scroll drive mechanism requires maintenance, and the paper roll may tear. Paper is also subject to distortion and warping from humidity changes and moisture content in the atmosphere. In addition, the whole paper drive process of winding the paper roll across a tracker bar involves a delivery apparatus especially vulnerable to mechanical failure from breakage and wear of parts, which generally include electric motor or vacuum drives, speed control governors, braking mechanisms, and tracking devices controlling paper alignment.
It is therefore an object of this invention to provide a process for reproducing key action of a piano by generating AC signals which are unique to the operation of each key, but unrelated to the musical instrument function performed by such key, recording such sig-nals, reproducing such signals, and operating the keys correspondingto such signals.
It is a further object of this invention to provide a process of generating unique electric signals corresponding to key operation using only AC signals and in which the total energy responsive to each key cperation is magnetically recorded at the same level to facilitate recording maximum data in a given recording medium.
For purposes of describing the subject process, it should be noted that the term "key" may be any apparatus having two discrete positions. While the term "key" is primarily directed to those applications in which the key is one of a standard set of keys in a player piano, it will be apparent to persons versed in the art that for purposes of the subject process, a key may also be a key on

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; ~n organ or a corresponding actuation mechanism on a different musi-cal instrument and may also be a control unit on an instrument such as the sustain pedal on a piano or a stop on an organ which enhances particular sounds emanating from the organ.
SUMMARY OF THE INVENTION
This invention is of a unique process for reproducing key action of a piano or other musical instrument having a set of keys or the equivalent which are manually operable to produce a desired noise or other signal. As each of said keys are switched from a first posi-tion to a second position, a predetermined AC signal is generated byan oscillator. Each of the AC signals are algebraically added and their combined sum is processed so as to generate a processed signal in which the energy level attributed to each AC signal is the same and the processed signal is recorded in magnetic tape. On playback, the recorded signal is processed and each of the AC signals is detected and used to energize an electromechanical device that operates each of the keys to reproduce the original key action.
_ESCRIPTION OF TEE PREFERRED EMBODIMENT
All of the components to be used in the subject process are standard units which are conveniently available to persons versed in the art and are used in numerous applications. Persons versed in the art will recognize immediately the various components and realize that various other components could be substituted so long as they have similar functions while still accomplishing the same result as the subject process and thus without departing from the spirit of the invention.
To record electric signals which correspond to unique opera-tional sequence of a set of keys on a musical instrument according to the subject invention, the first step is generating a discrete fre-quency AC signal as each of the keys of a musical instrument isswitched from a first position to a second position. As persons versed in the art will appreciate, the subject process could easily be applied to a piano, an organ, or various other musical instruments

-4-having numerous keys. For purposes of describing the process, it will be assumed that the process applies to the instrument commonly ~nown as a piano.
Each piano key has a first position in which the key is normally biased to a raised position by a suitable mechanical device. When the piano is played, the key is switched from the first position to a second position by depressing the key. To practice the subject process, a key switch is provided adjacent each of the piano keys.
Each key switch may be an opto-interrupter saturated transistor switch, a suitable mechanical contact switch, or another suitable switch which can detect piano key movement from the first position to the second positiDn without interfering with the piano action.
Each of the key switches may be mounted on a suitable frame out of sight inside the piano so as to follow piano keyboard action as the keys are depressed and released.
Each of the key switches is in series with the power supply of a standard oscillator which generates an AC signal on an oscillator output terminal when the key switch is closed. Each of the oscilla-tors are selected to have a discrete frequency in the audio range.
While various oscillators may be used, operational amplifier oscillators in a wein bridge configuration would be an example of a suitable oscillator. The oscillator output on the terminal is a sine wave of maximum amplitude available without clipping. Each of the oscillators have an identical amplitude and a unique frequency.
The second step in the subject process is generating an electric signal which is the algebraic sum of the AC signals generated by the oscillators. Persons versed in the art will appreciate that the oscillators are signal generating devices of low power capability.
Accordingly, to generate an electric signal which is the algebraic sum of the AC signals produced by the oscillators, each of the AC
signals should first be passed through a buffer stage, such as an emitter follower which has a high input impedance and low output

-5-10910~9 impedance. The buffered signal can then be passed through a passive voltage divider network having suitable input impedances from each buffer stage so that each of the AC signals are algebraically combined.
As persons versed in the art will appreciate, an electric signal is thus generated which is the algebraic sum of the AC signals produced by each of the operational amplifiers. Obviously the electric signal which is so produced contains components of equal amplitudes but different frequencies. It is then processed and recorded in a suit-able recording medium, such as magnetic tape or magnetic wire. Since tape decks using magnetic tape in conventional cassettes are in common usage, the processed signal could be preserved by recording it in a suitable tape deck.
Tape decks generally have from one to four channels for record-ing. A conventional piano has 88 keys. Persons versed in the art will appreciate that 88 oscillators can easily be provided in a com-pact package. For example, each of the oscillators may be a 741 type operational amplifier integrated circuit. However, tape recorder capability generally is limited to approximately 15,000 Hertz (cycles per second). Accordingly, to facilitate recording electric signals corresponding to operation of 88 keys while maintaining adequate separation of signals, it is best to divide the keys into four 22 tone groups and record the signals from only 22 keys on each channel of the tape deck.
The process for reproducing mechanical action of a plurality of keys in addition to the above steps for recording electric signals corresponding to a unique operational sequence of a set of keys also includes the steps of playing back the recorded signal from tape deck and processing it so the processed signal is the algebraic sum of the AC signals recorded as aforementioned.
The next step in the reproduction process is detecting each of the AC signals in the processed playback signal. As persons versed in the art will appreciate, such a detection stage should have a high 10'31(~;9 impedance stage, which may be high input impedance operational amplifiers having their outputs connected to suitable decoders such as the 567 tone decoder integrated circuit which are in common usage in push button telephone equipment. As persons versed in the art will appreciate a frequency sensitive decoder such as the 567 unit operates as a frequency sensitive switch.
When the frequency to which the decoder is preset is not present in its input, the decoder input is an open circuit but when the fre-quency for which the decoder is preset is present in its input its output becomes a closed circuit. Each of the decoders is provided preset to the frequency generated by one of the oscillators.
Accordingly, in a piano there would be 88 of the decoders.
As persons versed in the art will appreciate, each of the decod-ers are often termed a detector oscillator in reference to their frequency sensitivity.
The final step in the process for reproducing the mechanical action of a plurality of keys is energizing a suitable electromechan-ical device which operates the key associated with an oscillator having the same frequency as the frequency detected by the corres-ponding detector. The electromechanical device may include a relaycoil which operates an electromagnet core in such a manner as to physically strike the mechanism associated with a key so as to cause movement of the piano key. In the alternative, persons versed in the art will appreciate that in a player piano a pneumatic mechanism exists in which a tracker bar is provided with an array of pneumatic holes which are permitted to communicate with the atmosphere in a predetermined manner controlled either by a paper tape having open-ings which alternately cover the holes or the holes may be controlled by individual control valves. Accordingly, the electromechanical device may be a solenoid operated control valve controlling the communication of a tracker bar hole with the a~mosphere.
In summary, the process for reproducing mechanical action of a plurality of keys includes the process for recording electric (,~

lO9iO~;9 8ignals corresponding to a unique operational sequence of a set of keys that each have first and second positions comprising the steps of generating a discrete frequency AC signal as each of the keys is switched from a first position to a second position, algebraically adding each of the AC signals, processing the sum of the algebraic signal addition, and recording the processed sum signal in a suitable recording medium. The process for reproducing mechanical action of a plurality of keys also includes a process for switching a plurality of keys in accordance with a recorded signal, which includes playing 10 back the recorded signal, processing the playback signal to reproduce a signal that is the algebraic sum of the AC signals, detecting each of the AC signals in the processed playback signal, and energizing an electromechanical device so as to switch each of the keys from the first position to the second position in accordance with each of the AC signals detected on playback.

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`~J -8-1091~'~
IN THE CANADIAN PATENT OFFICE

. --HARRY A. POMBER AND GARY T. BRUSH EXAMINER: Y. Toyooka (Harry A. Po~ has been deleted as Applicant) SERIAL NO. 281,876 SECTION: E-3 FILED: July 29, 1977 CLASS: 84-1.1 A PIANO ACTION MAGNETIC TAPE RECORDING PROCESS FOR PLAYER PIANO
PLAYBACK

THE COMMISSIONER OF PATENTS
Ottawa, Hull KlA OEl Canada SUPPLEMENTARY DISCLOSURE

When recording electric signals which correspond to a unique operational sequence of a set of keys, once an electric signal is generated which is the algebraic sum of the AC signals produced by each of the operational amplifiers consideration must be given to the practical limitations of the recording medium to absorb data in large quantities. Magnetic recording tape which is currently in wide supply has approximately a 24 decibel saturation level.
By employing the step of processing the electric signal which is the algebraic sum of the AC signals through a low pass filter prior to recording the f~ltered signal, the amplitude of higher frequency signals is lowered more than the amplitude of lower frequency signals.
The low pass filter thus functions as a saturation control. The filterjed signal which is being recorded contains components derived from each of the AC signals and each of the components has an energy level identical to each of the other components. The saturation on the magnetic tape thus remains constant for each signal that is being recorded.
In the reproduction process to reproduce the signal which is the algebraic sum of the AC signals where the sum was processed through a ~low pass filter prior to recording it is necessary to provide the additional step of filtering the playback signal throuqh a high pass filter which reverses the effect of the low pass filter r~
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~rior to recording. The high pass filter has little effect on the high frequency signal components but as frequency decreases the limitation effect of the high pass filter increases so the output of the high pass filter is a filtered signal that is the algebraic sum of the AC signals, which are each detected in the processed playback signal. Upon detection, a suitable device is energized so as to switch each of the keys from the first position to the second position in accordance with the AC signals detected on playback.
Persons versed in the art will appreciate that when the detec-tion of the respective frequencies takes place instead of energizing one of the keys the energization could be made of an indicator lamp or other electrical device. The energization of an indicator lamp above each of the various keys on a piano could be employed as a teaching device to show a student pianist which keys must be played to dupli-cate the sèquence ~f key operation which had produced the recorded signal.

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Claims (11)

The embodiments of the invention in which an exclusive pro-perty or privilege is claimed are defined as follows:

1. A process for recording electric signals corresponding to a unique operation sequence of a set of keys that each have first and second positions comprising, in combination, the steps of generating a discrete frequency AC signal as each of said keys is switched from said first position to said second position; al-gebraically adding said AC signals ; processing the sum of said algebraic addition so as to generate a processed signal in which the energy level components of each AC signal are substantially equal; and recording said processed signal in a recording medium.

2. A process for reproducing mechanical action of a plural-ity of keys which each have first and second positions comprising, in combination, the steps of generating a plurality of AC signals which are each of a unique frequency and which each correspond to movement of a key from said first position to said second position;
generating an algebraic sum signal which is the algebraic sum of said AC signals; processing said algebraic sum signal so as to gen-erate a processed signal in which the energy level components of each AC signal are substantially equal; recording said processed signal; generating a playback signal by playing back said recorded signal; processing said recorded signal so as to generate a pro-cessed playback signal that is the algebraic sum of said AC sig-nals; detecting each of said AC signals in said processed playback signal; and energizing an electromechanical device so as to switch each of said keys corresponding to each of said detected AC sig-nals from said first position to said second position.

3. The process of Claims 1 or 2 in which said AC signals cor-responding to key movement signals are sine waves of substantially identical amplitudes.

4. The process of Claim 1 or 2 in which said recording medium is a magnetic tape.

5. The process of Claim 1 or 2 in which said electromechani-cal device is a solenoid control valve.

CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE

6. A process for recording electric signals corresponding to a unique operation sequence of a set of keys that each have first and second positions comprising, in combination, the steps of generating a discrete frequency AC signal as each of said keys is switched from said first position to said second position; algebraically adding said AC signals; filtering the sum of said algebraic addition through a low pass filter so as to generate a filtered signal in which the energy level components of each AC signal are equal; and recording said filtered signal in a recording medium.

7. A process for reproducing mechanical action of a plurality of keys which each have first and second positions comprising, in combination, the steps of generating a plurality of AC signals which are each of a unique frequency and which each correspond to movement of a key from said first position to said second position; generating an algebraic sum signal which is the algebraic sum of said AC signals;
filtering said algebraic sum signal through a low pass filter so as to generate a filtered signal in which the energy levels of each AC
signal component are equal; recording said filtered signal; gener-ating a playback signal by playing back said filtered signal; fil-tering said playback signal through a high pass filter so as to generate a filtered playback signal that is the algebraic sum of said AC signals; detecting each of said AC signals in said filtered playback signal; and energizing an electromechanical device so as to switch each of said keys corresponding to each of said detected AC
signals from said first position to said second position.

8. The process of Claim 1 or 2 in which said AC signals corresponding to key movement signals are sine waves of substantially identical amplitude.

9. The process of Claim 1 or 2 in which said recording medium is a magnetic tape.

10. The process of Claim 1 or 2 in which said electromechanical device is a solenoid control valve.

11. A process for energizing electrical devices according to a plurality of key movements between first and second positions comprising, in combination, the steps of generating a plurality of AC signals which are each of a unique frequency and which each correspond to movement of a key from said first position to said second position; generating an algebraic sum signal which is the algebraic sum of said AC signals; filtering said algebraic sum signal through a low pass filter so as to generate a filtered signal in which the energy levels of each AC signal component are equal; recording said filtered signal; generating a playback signal by playing back said filtered signal; filtering said play-back signal through a high pass filter so as to generate a fil-tered playback signal that is the algebraic sum of said AC signals;
detecting each of said AC signals in said filtered playback signal;
and energizing said electrical devices according to detection of each of said AC signals corresponding to key movement between said first and second positions.