JPS5922284B2 - signal processing device - Google Patents

Abstract

PURPOSE:To enable obtaining the highest articulation at anytime, by such a way that reproducing sound is automatically changed by a certain ratio even when the reproducing speed of magnetic tape etc. is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a magnetic recording system that enables the reproduction and listening of the contents recorded on a magnetic tape to the extent that the contents recorded on the magnetic tape can be understood even when the magnetic tape is played back at a speed higher than the tape speed at the time of recording, for example. The present invention relates to a signal processing device that can realize a playback device and the like.

Generally, when a magnetic recording/reproducing device is used to reproduce and listen to a signal recorded on a magnetic tape, there are cases where it is desired to reproduce the signal faster (or slower) than the tape speed at which it was recorded.

For example, if you want to listen to a recording of a meeting faster, you may want to double the tape speed. This is based on the fact that the speed at which humans can hear is several times higher than the speed at which humans speak, but if we simply doubled or tripled the tape speed, the pitch of the original audio signal would also change at the same time. Therefore, the content cannot be understood. For this reason, special equipment was used to shorten the duration without changing the pitch of the original signal, thereby satisfying the above requirements. It has been experimentally determined that by shortening the playback time without changing the pitch of the original signal, the playback speed at which the content can be understood is two to three times faster. On the other hand, people with intellectual disabilities or for language practice may wish to play the audio signal at a slower than normal speed to improve their understanding.

In this case as well, it was not practical to simply slow down the tape speed, and it was still necessary to use special equipment to extend only the duration of the signal without changing the pitch of the original signal. The conversion function that attempts to maintain the original pitch by converting the frequency of the reproduction signal even if the tape running speed is changed in this way will be referred to as the reproduction pitch control function.

Conventionally, as a means of realizing such a playback pitch control function, a rotating head is used, and the rotational speed of the rotating head is changed in conjunction with changes in the tape running speed, and the relative speed between the two is adjusted to the tape speed at the time of recording. There are some devices that try to maintain the same playback pitch by equalizing the pitch, but this type of device is extremely difficult to realize in practice due to the small diameter of the rotating magnetic head, so here we will try to satisfy the above function electronically. The conventional means for doing so will be explained.

First, before explaining the configuration of a conventional device, a process in which an audio signal is processed will be explained using FIG.

FIG. 1 shows the process by which an audio signal is processed, taking as an example a signal that is reproduced at twice the normal speed. Figure 1a shows the original signal recorded on the magnetic tape.When the magnetic tape on which this original signal is recorded is run at twice the recording speed and reproduced, the original signal is reproduced as shown in Figure 1b. against 2
played at twice the frequency. When this reproduced signal is passed through an analog delay element, a signal having the frequency of the original signal can be obtained as shown in FIG. 1c. In this case, as is clear from the figure, the odd-numbered segments A, C, . . . of the original signal
are processed and used, but even-numbered segments B, D, . . . are picked up without being used. FIG. 2 shows the main structure of an apparatus that realizes the process described in FIG. 1 and facilitates understanding of the principle of the present invention.

To explain this, the magnetic tape 1 is held between a capstan 3 driven by a motor 2 and a pinch roller 4 pressed against the capstan 3, and runs in proportion to the rotation of the motor 2. The motor 2 is configured to rotate in proportion to a voltage obtained by dividing the DC voltage +B applied to both ends of the speed control variable resistor 5. Note that 6 indicates a motor drive circuit for driving the motor 2. The DC voltage divided and extracted by the variable resistor 5 is applied to the DC voltage amplification circuit 7. This DC voltage amplification circuit 7 is a voltage amplification circuit for supplying the optimum voltage necessary for pitch control to the pitch control circuit 8 at the next stage. Further, the signal reproduced from the tape 1 by the reproduction head 9 is amplified by the preamplifier 10, and then
The analog signal is transmitted to the delay element 11. This analog signal delay element 11 is a circuit that receives a control signal from the pitch control circuit 8 and converts the frequency of the reproduced pitch signal so that it always has a constant pitch. This circuit generates the control signals necessary for frequency conversion. As the analog signal delay element 11 used here, for example, a charge transfer type semiconductor element (bucket brigade device, so-called BBD element, or charge coupled type element) is effective.

Note that since the above-mentioned BBD element is already well known, a description thereof will be omitted here. The audio signal subjected to frequency conversion processing by the analog signal delay element 11 passes through a power amplifier 12 at the next stage, and then sounds at a speaker 13.

The details of signal frequency conversion have already been published in the published patent publication in 1982.
89002, a detailed explanation thereof will be omitted and only a summary of the operations related to the present invention will be provided.

In FIG. 1, which shows an example where the running speed of tape 1 is faster than the steady speed, the audio signal (
(shown as a sine wave signal in Figure 1) is several tens of milliseconds
A number of segments A, B, C with a duration of
, D, . . . and the odd-numbered segments (A, C, . . .) are stretched in time to
A', C', etc. in figure c.

If the length of this segment is too short, pitch changes will occur, and if it is too long, consonants may be dropped or vowels may overlap, so in the case of speech, 20 to 30 ms-Ec is considered to be appropriate. It has been confirmed experimentally.

When the tape running speed is high, in order to return the audio signal played at a high pitch to its original frequency (pitch), the clock signal applied to the analog signal delay element 11 is applied within the time corresponding to the segment as shown in FIG. As shown in
KHz).

This clock signal is generated from the pitch control circuit 8.

The pitch control circuit 8 includes a first constant current charging/discharging circuit 8a, a second constant current charging/discharging circuit 8b, and a waveform shaping circuit 8c as circuits for generating the clock signal. The range of change in the output voltage of the first constant current charging/discharging circuit 8a is configured to vary between the upper limit voltage Vu and the lower limit voltage d, as shown in FIG. The range of change in the output voltage of the charging/discharging circuit 8d is configured to be between an upper limit voltage Vu and a lower limit voltage d, as shown in FIG. 3d.

As can be seen from FIGS. 3D and 3e, the output waveform of the first constant current charging/discharging circuit 8a changes within the variation range of the second constant current charging/discharging circuit 8b, and as a result, The period of the output of the charging/discharging circuit 8a changes with time. Here, the period t of the second charging/discharging circuit 8b corresponds to the length of the segment. On the other hand, the second charging/discharging circuit 8
What changes the period t of b is the charging/discharging current value of the same circuit, and in the case of Fig. 3, when the discharge current is large, the period t
is short, and conversely, when it is small, it becomes long.

In addition, the charging/discharging current value of the circuit is configured to be controlled by the voltage of the DC voltage amplifier circuit 7 in the previous stage, so when the output voltage of the DC amplifier circuit 7 changes, the length of the segment changes, resulting in In other words, the rate of change of the clock signal frequency within a segment varies. If the rate of change in this clock signal frequency always matches the tape running speed, the playback pitch will always remain constant even if the tape running speed changes, but the rate of change is faster than the standard. In case,
If the pitch conversion becomes excessive and slow, the pitch conversion becomes insufficient.

The above is the principle of pitch control disclosed in Publication No. 50-89002.

However, the ability to always keep the reproduced pitch constant even if the tape running speed changes is often inconvenient depending on the application.

In addition, as mentioned above, the conversion of audio pitch using the playback pitch control function involves dividing the continuous signal into segments, deleting part of the signal during high-speed playback, and repeating the signal during low-speed playback. The original signal (original audio)
The intelligibility of the signal after pitch conversion is somewhat worse than the intelligibility of the signal. Therefore, if the voice played at high or low speeds is not completely converted to the original pitch, and if the rate of pitch conversion is controlled to such an extent that the unnaturalness caused by insufficient conversion is not noticeable, the clarity of the voice can be further improved. has been experimentally confirmed.

In other words, if we take for example high-speed playback where the tape running speed is twice as high, the pitch will be approximately 10
The clarity is better when the pitch is ~15% higher, and the clarity is better when the pitch is about 10-15% lower during low-speed playback where the tape speed is 0.5 times. The present invention is intended to achieve the above-mentioned improvement in clarity. For example, when the tape running speed is changed to higher or lower speed than the normal tape running speed, the optimum clarity is obtained in accordance with the above-mentioned tape running speed. The aim is to automatically perform pitch conversion so that

An embodiment of the present invention will be described below with reference to the drawings from FIG. 4 onwards.

Reference numerals 5, 7, and 8 in FIG. 4 are the same as those in FIG. A constant direct current amplifier circuit 15 is connected between the input terminal of the reproduction pitch control circuit 8 and the input terminal of the reproduction pitch control circuit 8 by switching the changeover switch 14 to the contact b side. Reference numerals 15a and 15b indicate input and output terminals of the circuit 15.

FIG. 5 shows a specific circuit of the constant direct current amplifier circuit 15. By the way, as described above, the pitch control circuit 8 controls the period t of the clock signal that drives the analog signal delay element 11 by the DC voltage applied to the second charging/discharging circuit 8b inside the pitch control circuit 8.

Therefore, when the changeover switch 14 is switched to the fixed contact a side and the DC voltage amplification circuit 7 and the pitch control circuit 8 are directly connected, the clock voltage increases in proportion to the DC voltage that controls the rotation of the motor 2. The signals are also controlled, so that
The pitch is controlled to remain constant even if the playback speed changes, but if the input DC voltage of the pitch control circuit 8 is changed at this time, the pitch will also change accordingly.

The constant direct current amplifier circuit 15 is a circuit for shifting the input direct current voltage of the pitch control circuit from the reference voltage.

Here, the operation of the constant direct current amplifier circuit 15 will be explained. In FIG. 5, the constant direct current amplifier circuit has an input terminal 1
When a certain voltage Ei is applied to 5a, the amplification degree of the circuit is 1, and when the voltage Ei changes by K times, the output terminal 1
The output voltage ED at 5b is configured to be Ei (1+Kγ).

Here, γ is the voltage amplification factor of the transistors Ql and Q2. That is, when the voltage ED divided by the bias resistors RA and RB is equal to the input voltage Ei, the input voltage appears almost as is at the output terminal 15b. Also, the input voltage Ei
is K times as large as the divided voltage ED, the base voltage EB of the transistor Q1 can be approximately determined by the following equation. EB=EI(K-1)XRc/(Rv+RO
)+E1=EI{1+(K-1)Rc/(Rv+RO)
}When EI, Rc, and Rv are determined using this formula, it can be seen that EB changes by multiplying the input voltage multiplier K by the resistance division ratio. Therefore, when the variable resistor R is fixed at a certain value and the input voltage Ei is varied, the output voltage ED changes while satisfying the above equation.

Since the input voltage Ei changes in conjunction with the tape running speed during playback, the output voltage ED also changes in conjunction with the tape running speed during playback. When the output voltage ED changes, the pitch change rate also changes. For example, if the tape running speed is doubled and the variable resistor R shown in FIG. 5 is shorted,
A specified DC voltage is applied to the pitch control circuit 8, and the pitch returns to its original value, but when the variable resistor R has a certain value, the base voltage EB of the transistor Q1 becomes lower than the specified voltage, and the pitch returns to its original value. do not have.

Therefore, the pitch becomes high as a result. In FIG. 5, the value of the variable resistor Rv can be changed, but the output DC voltage can also be changed by changing other resistance parts, such as RA, RB, and RC. Furthermore, FIG. 5 shows an embodiment of a constant direct current amplifier circuit,
Needless to say, a DC amplifier having the above-mentioned functions is effective. Figure 7a shows the relationship between the tape speed ratio and pitch change rate during playback when the variable resistor Rv is fixed at a certain value and the voltage applied to the base of the transistor Q1 is lower than the specified voltage. You can see that when the playback tape speed changes, pitch conversion is automatically performed to always maximize clarity. Next, FIG. 7b shows the relationship between the tape speed ratio and pitch change rate when varying the variable resistor R.

In this case, by adjusting the variable resistor R while keeping the reproduction speed constant, the pitch can be changed within the shaded range. In place of the variable resistor Rv, the sixth
Resistors Rd with different resistance values as shown in figure a or b,
Re and Rf can also be selectively switched by a switch S, and in this case the relationship between the reproduction tape speed ratio and the pitch change rate is as shown in FIG. 7c.

In FIG. 7c, p', q', and r' represent relationship curves when the switch S in FIGS. 6A and b is switched to contact points P, q, and r, respectively. As described above, the device of the present invention has the great feature that even if the playback speed is changed, the playback pitch automatically changes at a constant rate, and the best clarity can always be obtained.

Furthermore, the apparatus of the present invention can be applied not only to the magnetic recording/reproducing apparatus shown in the embodiment, but also to magnetic disk players, record players, etc.

[Brief explanation of the drawing]

FIGS. 1A, b, and c are diagrams explaining the signal processing process of a conventional signal processing device, and FIG. 2 is a diagram illustrating the signal processing in FIG. A block diagram of the processing device, FIG. 3D, e, and f are waveform diagrams of the main parts of the same device, FIG. 4 is a block diagram of the main parts of the signal processing device in an embodiment of the present invention, and FIG. 5 is the same device A circuit diagram showing a constant direct current amplification circuit constituting the circuit, FIGS. 6A and 6B are circuit diagrams of a manual voltage switching means that can be used in place of the variable resistor Rv in FIG. 5,
7A and 7B are reproduction tape speed ratio vs. pitch change rate characteristics diagrams of a signal processing device using the circuit shown in FIG. 5 above, and FIG. FIG. 6 is a characteristic diagram of reproduction tape speed ratio versus pitch change rate of a signal processing device having the circuit shown in FIG. 5; 1...Magnetic tape, 2...Motor, 3
... Capstan, 4 ... Pinch roller, 5 ... Variable resistor for speed control, 6 ...
... Motor drive circuit, 7 ... DC voltage amplification circuit, 8 ... Pitch control circuit, 9 ... Playback head, 10 ... Preamplifier, 11.・・・・・・
Analog signal delay element, 12... Main amplifier, 13... Speaker, 14... Changeover switch, 15... Constant direct current amplifier circuit.

Claims (1)

[Scope of Claims] 1. Reproducing means for reproducing signals recorded on a recording medium, speed variable means for varying the reproduction speed of the recording medium, and temporarily storing signals reproduced from the reproducing means. and an analog signal delay element driven by a clock signal, a clock signal generation means for generating a clock signal for driving the analog signal delay element, and a signal that controls the clock signal generation means and is reproduced by the reproduction means. A dividing signal generating means for dividing into a large number of minute segments, and a dividing signal period of the dividing signal generating means are controlled in conjunction with the speed variable means, so that the reproduction pitch is kept approximately constant even if the reproduction speed of the recording medium changes. DC voltage amplification means that operates as shown in FIG. A signal processing device comprising amplification means. 2. A reproduction means for reproducing a signal recorded on a recording medium, a speed variable means for varying the reproduction speed of the recording medium, and a speed variable means for temporarily storing the signal reproduced from the reproduction means and driven by a clock signal. an analog signal delay element, a clock signal generation means for generating a clock signal for driving the analog signal delay element, and a clock signal generation means for controlling the clock signal generation means and dividing the signal reproduced by the reproduction means into a large number of minute segments. and a DC voltage that operates to control the divided signal period of the divided signal generating means in conjunction with the speed variable means so as to keep the reproduced pitch substantially constant even if the reproduction speed of the recording medium changes. an amplification means; a constant direct current amplification means that is located between the DC voltage amplification means and the divided signal generation means and amplifies the output voltage from the DC voltage amplification means at a constant rate to change the playback pitch; A switching means that can select between a first position in which the voltage amplification means is directly connected to the divided signal generation means and a second position in which the constant direct current amplification means is interposed between the DC voltage amplification means and the divided signal generation means; A signal processing device comprising: