JPS6250916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The following US patent applications are related to this application: Namely, Application No. 681093, filed on April 28, 1976, ``Method and Apparatus for Reproducing Musical Performances,'' invented by Joseph Maxx Campbell, and Application No. 681098, filed on April 28, 1976,
``Demultiplexing and Storage Apparatus for Time-Division Multiplexed Frames of Musical Data,'' Invented by William Solon Finley and Application No. 680996, filed April 28, 1976, ``Demultiplexing and Storage for Time-Division Multiplexed Frames of Musical Data.''"Solenoid hammer control device for the reproduction of expressive effects", Joseph Maxx.
Campbell and William Solon Finlay invention patent application.

The patent applications listed above are incorporated herein by reference.

The present invention relates to an improved apparatus for reproducing magnetic tapes containing digitally recorded musical performances of keyboard instruments.

No. 681,093, cited above, discloses a clock recovery circuit which is set by an adjustable resistor (resistor R9) to accommodate the nominal data rate and which provides playback. Determined by the speed of the tape recorder. Typically, this will increase the tape speed by approximately ±
It can be changed by 5%. When you adjust the tape recorder's playback speed to speed up or slow down the tempo, the clock data
The recovery circuit is unable to keep up with this large change (the large phase change in our US patent application Ser. No. 681,093 was considered insufficient data), and the operation of the circuit is hampered by the large change in data rate. It will be done. Accordingly, the present invention seeks to provide a circuit for obtaining a clock signal from a very short train of pulses representing the edges of biphasic marks or spaces or other encoded digital data. . The circuit includes a non-retriggerable monostable multivibrator to which a short train of pulses representing the edges of phase encoded digital data is applied. The non-retriggerable multivibrator has a period determined by an external circuit, which in our above-cited patent application uses fixed resistors to adjust the timing of the multivibrator. The present invention uses a DC voltage that varies directly with the change in edge pulse speed, and this DC voltage is applied via a feedback circuit to reduce the current in the control transistor.
This will reduce the pulse width. A variable resistor adjusts the nominal pulse width to three quarters of the total time for normal data recovery operation.
As the spacing between narrow trigger pulses or edge pulses increases, the number of positive pulses increases and recovery of encoded data becomes possible. Hereinafter, the present invention will be explained in detail with reference to the drawings.

Referring to FIG. 1, a piano keyboard or keyboard, for example, is designated by number 10 as a source of keyboard data. This can be any keyboard instrument, such as a harpsichord, chime, organ, piano, etc., and each output or switch actuation is indicated by a line 11-1 through 11-N, the number of which is the number of output lines that can be sensed and recorded. corresponds to the number of key switch actuations to be performed. These keyswitch actuation signals are provided to a multiplexer 12 which scans or views the individual lines 11-1 through 11-N sequentially in time to form a data frame. Also shown in the block diagram of FIG. 1 is a synchronization signal source 10S which provides a synchronization signal to multiplexer 12 on line 11S. A timing source 12T provides a timing signal to multiplexer 12. Thus, key switches, sustained tone and loud pedals and actuations are sensed by multiplexer 12 one at a time and generally in a sequential manner. Without transposition, these need not be sensed sequentially, but may be viewed or scanned in groups in any manner or order. The only criterion in this case is that the scan time or position of a particular switch in a cell be maintained throughout the device. As a result, the multiplexer 12
The parallel data of the key switch actuation is translated into a serial data stream along output line 13.

This data and timing signal for timing source 12T is preferably biphasic space/
The signal is applied to an encoder 14, which is a mark encoder, and then this signal is recorded on a magnetic tape in a tape recorder 15. The tape recorder 15 is conventional in all major respects, and a detailed explanation thereof will be omitted. The device also includes various forms of recording expression data, but these are not relevant to the present invention. Additionally, tape can be used to pre-record performances by famous or outstanding performers, either in home recordings or as punch paper rolls with expressive signal information, and thus allows specific sources of musical information to be transferred to tape format. During playback by tape recorder 15, the encoded data appears at the output of a read head (not shown) and is sent out via a correction network and an amplifier. to recover digital data. The data from the read head includes clock data to be recovered and used in the demultiplex operation. A key aspect of the invention is that the speed of the tape recorder can be adjusted during playback to change the tempo of the playback of music data, and a key feature of the invention is a circuit that can follow this speed change;
Data can therefore be recovered and used without any adverse effect on playback operations.

The signal on line 16 from the tape recorder is applied to a decoder 17 which transfers the decoded data to a demultiplexer and latch circuit 1.
Give to 8. Time Recovery Bit Dropout Synchronization Counter, Bit and Frame
The circuits of the counter operate the device and are detailed in the patent application cited above and are part of the prior art used in the present invention.
A detailed explanation thereof will be omitted. keyboard, expression,
The pedals and auxiliary devices accept the data and reproduce the performance. The effect of the present invention is that the device clock
in the recovery and follow-up circuit.

The signal read from the tape is applied to an amplifier, the output of which is applied to an edge detector 40. Edge detection circuit 40 generates a series of narrow pulse voltages called . These pulses correspond to the edges of the input rectangular waveform and its speed, which in the present invention can vary according to the speed of the tape recorder. If you adjust the speed of the tape recorder to make the tape move faster, these pulses will occur at a faster rate; if you adjust the speed of the tape recorder to slow down the tempo, these pulses will occur at a slower rate. Occurs at speed. Therefore, even though the recording is at a constant speed, the speed changes during playback according to the speed of the tape recorder.

These pulses are applied to a non-retriggerable monostable multivibrator 41 whose output is high for a period of time determined by capacitor 45 and resistors 46 and 47. Resistor 47 is adjusted so that for normal tape recorder speeds the D pulse output is three-quarters of the information bit time. In the biphase codes used, there is a transition at the beginning of each bit period or data cell, which is the source of the "edge" pulses. The transition that occurs in the middle of the bit period is controlled by the monostable multivibrator 41 (clock
recovery generator).

This D pulse accompanying the data detector 48
The output of this data detector is used to provide information for driving a keyboard instrument. The waveform of the D pulse is equivalent to a clock pulse and is shown in Figure 3.
And for the purpose of explaining the invention, it includes a portion marked C' in which the digital voltage is high during period t ₁ and a portion where it is low during period t ₂ . When the speed of the tape recorder changes from a normal constant speed, such as the recording speed, the length of time T1 decreases, and if this change is too large, the clock signal is distorted and lost. The pulses generated by edge detection circuit 40 vary according to the speed of the tape recorder and are applied to a monostable multivibrator or clock recovery generator 41.

In FIG. 2, clock recovery generator 4
1 is shown as in the prior art and is a non-retriggerable one-shot monostable multivibrator that begins to time out when set by a positive pulse, such that the time-out period is three-quarters of the bit time. It is set.
And when the change in pulse exceeds the time set by resistors 46 and 47 and capacitor 45, the circuit ceases to operate properly. The output of circuit 41 is essentially a recovered clock signal, shown as a D pulse in FIG. generate. This D or clock pulse is connected to the retriggerable data detector 4.
4, this detector is used to provide input to
Creates output signal pulses used for data recovery and data dropout.

Next, referring to Fig. 3, the circuit components shown in Fig. 2 are used, and are the same as those shown in Fig. 2 except for the addition of a resistor R6 and a capacitor C2. The output of stable multivibrator 41' is filtered and/or integrated. The DC voltage appearing across capacitor C2 is applied to a feedback circuit and connected to voltage divider resistor R4.
and the base b of transistor Q1 via R5
given to. The emitter e of the transistor Q1 is connected to the power supply voltage via a resistor R3, and the collector c is connected to one end of a resistor 46', which is connected to control the period of the monostable multivibrator 41'. ing. Therefore, transistor Q1 is a monostable multivibrator 41'
connected to automatically adjust the period of the In this way, the pulses appearing at the output of monostable multivibrator 41' effectively track changes in the speed of the pulses applied to monostable multivibrator 41'. This circuit thus operates on the principle that as the pulse width at the output on terminal 6 of the monostable multivibrator changes, the DC voltage appearing on capacitor C2 changes. Therefore, as the potential at point 5 on capacitor C2 increases in a positive direction due to the large positive pulse width at point 6, the current through transistor Q1 decreases, and this increases the current through transistor Q1 through timing resistors 46' and 47'. This results in a change in impedance and a reduction in the pulse width at point 6 on the output of monostable multivibrator 41'. A variable resistor 47' allows the nominal pulse width to be adjusted to three quarters of the total time, as in the prior art. Therefore, as the spacing of the narrow pulses on line 3 increases, the positive pulses on output line 7 increase and recovery of the encoded data occurs. Thus, the circuitry follows tempo changes for the player piano, allowing the device to operate very effectively even when changing the tempo and/or speed of the playback tape device by ±20%.

The ability to follow and accommodate changes in tape recorder speed is not limited to the embodiments described above. Various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an electronic recorder and player for a musical instrument, and Fig. 2 shows a part of a playback circuit showing a conventional clock data recovery device and a conventional structure to show the relationship with the present invention. Partial Block Diagram FIG. 3 is a block diagram of a circuit according to the invention which has been improved to track tempo changes and derive a clock signal from a phase encoded digital signal. 41': Monostable multivibrator, 46', 4
7': Timing resistor, C2: Capacitor, Q
1: Transistor, R4, R5: Voltage divider resistance, R
6: Resistance.

Claims (1)

[Scope of Claims] 1. A magnetic tape playback device for reproducing musical expressions having a variable speed magnetic tape playback unit, wherein the musical expressions are recorded on a magnetic tape using a biphasic self-clocking code, A clock recovery generator 41 is connected to receive the input data pulses and includes electronic timing members 45, 46, 47;
Data detection means 48 are connected to receive the input data pulses and the recovered clock signal from the clock recovery generator 41 to detect notes in the data stream and to detect notes in the data stream accordingly. In a magnetic tape playback device for playing keys on a keyboard of the device, an integrator circuit R ₆ , C ₂ is connected to receive the recovered clock signal and to generate a signal voltage corresponding to changes in the clock signal. , a feedback circuit connects the signal voltage to the clock recovery generator 41 to vary the pulse width as a function of changes in tape speed of the tape playback unit so that track tape speed changes cause the player piano to A magnetic tape playback device characterized by being able to follow tempo fluctuations. 2 A transistor circuit in which the feedback circuit is connected together with the timing member.
2. The magnetic tape reproducing apparatus according to claim ₁ , wherein the magnetic tape reproducing apparatus includes a clock recovery generator 41 and changes the timing of the clock recovery generator 41. 3. The magnetic tape reproducing apparatus according to item 1, wherein the clock recovery generator 41 is adapted to tolerate speed fluctuations of plus or minus 20%.