JPH04156793A - Reproducing device - Google Patents

Abstract

PURPOSE:To enable satisfactory reproducing demodulation by outputting a reproduction signal from a band filter just before at the timing of the fall of a frequency modulation signal and releasing the holding of the reproduction signal at the timing of the rise of the frequency modulation signal. CONSTITUTION:A detection circuit 30 detects dropout and the fall of the output signal is transmitted to a muting circuit 27a and a sample-and-hold circuit 27b through a delay circuit without considerable delay. In the circuit 27b, the voice signal from a band filter 16 just before receiving the signal is held, and the held voice signal is lead out to an output terminal 18 as the voice signal during the original voice signal is interrupted. When a comparison circuit signal recovered from the dropout and to be outputted to the circuit 30 is risen from a low level to a high level, the rise is transmitted through the delay circuit to the circuit 27b, and the interpolation processing due to the circuit 27b is released. Thus, the reproducing demodulation is performed with the necessary S/N and with distortion rate.

Description

[Detailed Description of the Invention] l Tojo Gogoritama 1 The present invention relates to a playback device, and more specifically to an FM (Freq
The present invention relates to a reproducing device that demodulates and reproduces a signal recorded on a magnetic tape by modulating the signal.

FIG. 3 is a block diagram schematically showing an example of the configuration of a conventional playback device that demodulates and plays back FM signals recorded on a magnetic tape.

As shown in FIG. 3, the FM signal recorded on the magnetic tape 11 is read by the reproducing head 12, and the read FM signal is amplified by the head amplifier 13 at the next stage. A limiter amplifier 14 and a monostable multivibrator 15 are sequentially connected to the next stage of the head amplifier 13, and the amplified FM signal is shaped into a rectangular wave by the limiter amplifier 14 and then sent to the monostable multivibrator 15. The waveform is shaped into a signal with a constant pulse width. A bandpass filter 16 is connected to the next stage of the monostable multivibrator 15, and the FM signal whose waveform has been shaped after passing through the limiter amplifier 14 and the monostable multivibrator 15 has its carrier wave component removed here and becomes the audio before modulation. demodulated into a signal. The audio signal demodulated through the bandpass filter 16 is then taken out from the output terminal 18 via a muting circuit or sample hold circuit 17 provided at the next stage.

In addition to the monostable multivibrator 15, at the next stage of the limiter amplifier 14, there is a device that detects missing portions of the magnetic material on the magnetic tape 11, that is, detects discontinuities that occur in the recorded FM signal in response to dropouts. A dropout detection circuit 19 is connected thereto. The detection signal of this dropout detection circuit 19 becomes a signal for controlling the subsequent muting circuit or sample hold circuit 17.

In other words, when the dropout detection circuit 19 detects a dropout or a discontinuation point in the signal, for example, when a dropout is detected, the sample and hold circuit 17 operates according to the detection signal, and the audio signal immediately before the dropout is sampled and held. The audio signal is held by the circuit 17 and outputted to the output terminal 18 . That is, during the period when the audio signal is interrupted due to dropout, the audio signal held by the sample and hold circuit 17 is supplemented. Furthermore, when a recording break point of the FM signal is detected, that is, when a non-recorded section is played back following a recorded section, the above-mentioned sample hold circuit 17 works in the same way as at the time of dropout, and the sample hold circuit 17 operates just before the recording break point. The audio signal held by the sample hold circuit 17 is output to the output terminal 1.
8, and the output audio signal gradually converges to an O (zero) signal.

On the other hand, when reproducing the starting point of recording of an FM signal, that is, the starting point of recording or the part where recording is interrupted and the next recording starts, the above-mentioned demodulation circuit method simply reproduces the starting point of recording of FM signal. Since the output of the stable multivibrator 15 rises, the rising waveform appears as noise in the output of the bandpass filter 16, that is, in the audio signal. In order to prevent this noise, the detection signal from another switching circuit 20 or the dropout detection circuit 19 is used to operate the muting circuit 17 for a certain period of time after the start of playback or the start of recording. Countermeasures such as blocking the output of signals are being taken.

However, with the conventional playback device described above, when the recording density on the magnetic tape 11 is further increased, for example, the recording density can be doubled so that 60 minutes can be recorded on a 30-minute tape. , when the recording density changes significantly, such as by enabling variable speed recording and reproduction of several tens of percent, the output of the reproducing head 12 decreases or changes significantly. Therefore, in order to obtain the necessary S/N ratio and distortion rate in response to a wide range of changes in the output of the playback head 12, it is necessary to switch the carrier wave frequency of the recording circuit so that the recording density does not become too high, or to change the carrier wave frequency of the recording circuit so that the recording density does not become too high. This necessitates measures such as switching the gain of 13, which poses a problem in that the circuit configuration of the reproducing device becomes complicated.

The present invention has been developed in view of the above-mentioned problems, and it is possible to demodulate magnetic tape recorded with a wide range of recording densities with a simple circuit configuration and with a single carrier frequency, and furthermore, it is possible to demodulate magnetic tape recorded with a wide range of recording densities using a single carrier frequency. It is an object of the present invention to provide a playback device that can perform processing for interpolating signal discontinuities and processing for removing noise generated during demodulation and playback.

F To solve the problems, in order to achieve the above-mentioned object, the playback device according to the present invention reads a frequency-modulated signal recorded on a magnetic tape with a playback head, shapes the waveform with a monostable multivibrator, and then reproduces the frequency-modulated signal recorded on a magnetic tape. A reproducing device that demodulates and reproduces the signal by removing the carrier wave component through a filter,
a bandpass filter amplifier circuit that passes a required band of the frequency modulated signal read by the playback head; a detection circuit that detects rising and falling edges of the frequency modulated signal; and a falling edge of the frequency modulated signal detected by the detection circuit. At the timing, the reproduced signal from the bandpass filter immediately before that timing is held and outputted as a subsequent reproduced signal, and at the timing of the rise of the frequency modulation signal detected by the detection circuit, the reproduced signal is held. The present invention is characterized by comprising a sample hold circuit for canceling the detection circuit, and a muting circuit for performing noise removal processing at the rising and falling edges of the demodulation system signal using the same output of the detection circuit.

■ According to the above configuration, the frequency modulation signal recorded on the magnetic tape and read by the playback head is passed through only the necessary band by the band filter amplifier circuit, and unnecessary tape running system from the frequency modulation signal is passed. Wow and flutter component signals and hum component signals coming from the power supply are removed. The monostable multivibrator then shapes the waveform into a signal with a constant pulse width, and the bandpass filter removes the carrier wave component and demodulates and reproduces the audio signal. Output to.

Further, the frequency modulation signal output from the bandpass filter amplifier circuit is input to the detection circuit, and its voltage level is compared with a required reference voltage to detect rising and falling edges of the frequency modulation signal. At this time, when a fall of the frequency modulation signal, that is, a dropout is detected, the detection signal is output to the sample and hold circuit, and the sample and hold circuit holds the audio signal from the bandpass filter immediately before the timing of receiving the signal. Then, this audio signal is output as an audio signal to compensate for the interruption of the original audio signal due to dropout.

Further, when the dropout is recovered and a rising edge is detected by the detection circuit, this interpolation processing by the sample and hold circuit is canceled. This interpolation process is started before the occurrence of transient response noise at the falling edge of the frequency modulation signal, and continues at the rising edge when the transient response noise occurs, so that the transient response noise does not appear at the output terminal. .

Further, the output of the detection circuit corresponding to the dropout is also transmitted to the muting circuit, and among the transmitted signals, the frequency modulation signal having a sufficiently long interval, such as a discontinuation point when recording on a magnetic tape, is transmitted to the muting circuit. When a signal with an interrupted signal is input, the muting circuit masks the audio signal.

Furthermore, noise generated at the rise of the frequency modulation signal is masked by the muting circuit so that it does not appear in the audio signal.

Therefore, according to the above playback device, a magnetic tape recorded with frequency modulation at a wide range of recording densities can be recorded at a single carrier frequency.
Moreover, it is reproduced and demodulated with the necessary S/N and distortion rate. Furthermore, since the detection circuit detects both the rise and fall of the frequency modulation signal and the dropout of the magnetic tape, the circuit configuration for interpolation processing and noise removal processing is simplified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, one embodiment of a playback device according to the present invention will be described based on the drawings. Note that components having the same functions as those of the conventional example are given the same reference numerals.

FIG. 1 is a block diagram schematically showing the configuration of a reproducing apparatus according to the present invention.

This playback device also has the same FM demodulation circuit configuration as the conventional playback device described above, and the FM signal recorded on the magnetic tape 11 is read by the playback head 12, and the read FM signal is transmitted to the next It is amplified by the head amplifier 13 in the second stage.

A bandpass filter amplifier circuit 26 that passes only the band of the FM modulation signal is connected to the next stage of the head amplifier 13. By passing the amplified FM signal through this bandpass filter amplifier 26, unnecessary signals are removed from the signal. The wow and flutter component signals from the tape running system and the hum component signals coming from the power supply are removed. A limiter amplifier 14 and a monostable multivibrator 15 are sequentially connected to the next stage of the bandpass filter amplifier circuit 26, and the signal sent to the limiter amplifier 14 is shaped into a rectangular wave and then converted into a single wave. The stable multivibrator 15 shapes the waveform into a signal with a constant pulse width. A bandpass filter 16 is connected to the next stage of the monostable multivibrator 15, and the carrier wave component of the FM modulated signal is removed here, and the FM modulated signal is demodulated into an audio signal.

The audio signal demodulated through the bandpass filter 16 is
The signal is taken out from the output terminal 18 via the muting circuit 27a and sample hold circuit 27b provided at the next stage.

Furthermore, a detection circuit 30 is connected to the bandpass filter amplifier circuit 26 and the limiter amplifier 14 separately from each subsequent stage, and detects the rising and falling edges of the FM signal read from the magnetic tape 11 by the reproducing head 12. It is detected by this detection circuit 30. The detection signal of this detection circuit 17 is transmitted to the above-mentioned muting circuit 27a.
The signal is output to the muting circuit 27a and the sample hold circuit 27b as a signal for controlling the sample hold circuit 27b.

The configurations of the bandpass filter amplifier circuit 26, limiter amplifier 14, and detection circuit 30 will be explained in detail below.

FIG. 2 is a circuit diagram showing specific configurations of the bandpass filter amplifier circuit 26, limiter amplifier 14, and detection circuit 30.

As shown in FIG. 2, the bandpass filter amplifier circuit 26 is composed of a bypass filter circuit 41 and a low-pass filter amplifier 42.

Of these, the bypass filter circuit 41 has an operational amplifier 43.
The output side of the head amplifier 13 is connected to the bypass filter circuit 41 of the bandpass filter amplifier circuit 26. The FM signal sent from the head amplifier 13 is filtered by the bypass filter circuit 41 to remove low frequency components below the frequency determined by the capacitors C1 and C2 and the resistors R1 and R2, and then connected to the bypass filter circuit 41. The signal is sent to a low-pass filter amplifier 42, which is connected to the low-pass filter amplifier 42.

The low-pass filter amplifier 42 is composed of an operational amplifier 44, a capacitor C3, and resistors R3 and R4. area components are removed. It is also amplified with the gain determined by the resistors R3 and R4, and the low-pass filter amplifier 42
The next stage Norimitsu amplifier 14 and detection circuit 3 connected to
0 and 0, respectively.

The limiter amplifier 14 is composed of an operational amplifier 45, capacitors C4, C5, and resistors R5, R6, and the FM signal input to the limiter amplifier 14 is
It is amplified with a gain determined by R6, and then shaped into a rectangular wave of up to ±5 cm of the power supply voltage. In addition, the limiter amplifier 14 has
A second-order low-pass filter is formed together with the low-pass filter amplifier 42 in the previous stage, and the FM signal is shaped into a short waveform as described above, and this produces high-frequency components above the frequency determined by the capacitor C5 and the resistor R6. is removed and output to the next-stage monostable multivibrator 15 connected to the limiter amplifier 14 and the detection circuit 30, respectively.

On the other hand, the detection circuit 30 includes the bandpass filter amplifier circuit 26
and limiter amplifier 14, an operational amplifier 47 that compares the voltage level of the rectified signal with a predetermined reference voltage, and an operational amplifier 46 that generates the reference voltage. The comparator circuit 34 is formed, a delay circuit 35 that performs delay processing on the output signal of the operational amplifier 47, and the like.

The rectifier circuit 31 includes a capacitor 06 and a resistor R7 that are connected in parallel with each other, and diodes D1 and D2 that are connected in series to this parallel circuit.
The FM signal sent to is first rectified into a pulsating current by the rectifier circuit 31. In addition, so that the FM signal is amplified to a level sufficient for this rectification, the gain is set up to the bandpass filter amplifier circuit 26, and the limiter amplifier 12 in the next stage is set.
By keeping the gain to a minimum, the rectifier circuit 31 functions as if it were a double-wave rectifier circuit, and performs stable pulsating current rectification for the output signal of the reproduction head 12 over a wide range.

The comparator circuit 34 is composed of an operational amplifier 46 that generates a reference voltage, a variable resistor VR1, an operational amplifier 47 whose inverting input is the signal from the rectifier circuit 31, and resistors R8, R9, etc. A reference voltage is generated so as to correct only the noise up to the filter amplifier circuit 26. This reference voltage is input non-inverted to the operational amplifier 47, and the rectifier circuit 31
The FM signal from the FM signal is inverted and input, and the operational amplifier 47 compares the voltage value of this inverted FM signal with a reference voltage. As a result of the comparison, if the voltage value of the FM signal input inverted from the rectifier circuit 31 is larger than the reference voltage, that is, if there is an FM signal input, the comparison circuit 34 outputs a high level signal to the delay circuit 35 at the next stage. is output, and the voltage value of the signal inverted and inputted from the rectifier circuit 31 is smaller than the reference voltage, that is, FM
If there is no signal input, a low level signal is output from the comparison circuit 34 to the delay circuit 35 at the next stage.

The delay circuit 27 includes a capacitor C7 and a diode D3.
When charging, that is, when the signal output from the comparator circuit 34 rises from a low level to a high level, only the resistor R11 serves as a charging path to the capacitor C7, and the time constant T1 is set large. In other words, the delay time for the rise of the output of the comparison circuit 34 is set to be relatively long. On the other hand, when discharging, that is, when the signal output from the comparison circuit 34 falls from high level to low level, the two resistors RIO1R11 connected in parallel serve as a discharge path, and the time constant T2
is small (set. In other words, the delay time is set relatively short for the falling edge of the comparator circuit 34. The output of the delay circuit 35 is used as the output of the detection circuit 30, and the output of the above-mentioned muting circuit 27a and The muting circuit 27a and the sample and hold circuit 27b are controlled based on the signal that is applied to the sample and hold circuit 27b.

In FIG. 2, the band filter amplifier circuit 26, limiter amplifier 14, and detection circuit 30 each have two power supply voltages of +5V and -5V as power supplies.
is given.

Next, each operation of interpolation processing and noise removal processing for dropout in the playback device will be explained.

As described above, the magnetic tape 1 is
The FM signal read from the FM signal is amplified by the head amplifier 13, and then filtered by the bandpass filter amplifier circuit 26, which filters noise signals in bands other than the FM signal, the wah signal of the tape mechanism, etc.
Fluff components, high-frequency tape noise, etc. are removed and the signal is input to the detection circuit 30. Furthermore, the FM signal with the opposite phase is passed through the inverting input of the Rimic amplifier 14 to the detection circuit 3.
Input to 0. The FM signal input to the detection circuit 30 is first rectified by a rectifier circuit 31 in a double-wave rectification manner, and its voltage level is compared with a reference voltage by a comparison circuit 34. In this comparison, when the head amplifier 13 is outputting an FM signal, the comparison circuit 34 outputs a high level signal, and when the FM signal is not output, a low level signal is output.

Now, if there is a dropout in the magnetic tape 11 and the FM signal output from the head amplifier 13 is interrupted, the output signal of the comparator circuit 34 will fall from high level to low level and then fall again. Bring about change by rising to a high level. That is, the detection circuit 30
detects dropouts. Because of the relatively small time constant T2 determined by the resistor RIO5R11 and capacitor C7 of the delay circuit 35 in the next stage, the fall of the output signal passes through the delay circuit 35 without much delay, and then passes through the muting circuit 27a and the sample. The signal is transmitted to the hold circuit 27b. The sample and hold circuit 27b that receives this signal holds the audio signal from the bandpass filter 16 immediately before receiving the signal, and the held audio signal is held for a period when the original audio signal is interrupted due to dropout. It is led out to the output terminal 18 as a supplementary audio signal.

In the above operation, when the FM signal falls, the limiter amplifier 14, the monostable multivibrator 15,
Although transient response noise occurs in the demodulation system consisting of the path of the bandpass filter 16, the fall of the output signal of the comparator circuit 34 corresponding to the fall of this FM signal can be sampled and held without much delay as described above. circuit 27
Since the interpolation process for compensating for the interruption of the audio signal is started before the transient response noise occurs, the transient response noise does not appear at the output terminal 18.

When the dropout recovers and the comparison circuit 34 signal output to the detection circuit 30 rises from low level to high level, this rise is transmitted to the sample and hold circuit 27b via the delay circuit 35, and the signal is output by the sample and hold circuit 27b. The interpolation process described above is canceled.

In case 2, transient response noise in the demodulation system also occurs at the rise of the FM signal, but the rise of the output signal of the comparison circuit 34 corresponding to the rise of the FM signal is caused by the resistor R11 and capacitor C7 in the delay circuit 35. Because the determined relatively large time constant Tl causes the data to be transmitted to the sample and hold circuit 27b with a slight delay, the interpolation process is still continuing at the time when the transient response noise occurs, and the transient response noise is transmitted to the output terminal 18. never appears.

The output of the detection circuit 17 in response to dropout is also transmitted to the muting circuit 27a. The muting circuit 27a can realize the following operation by being configured with a buffer, a time constant circuit, a transistor muting circuit, etc. Muting circuit 27
The time constant T3 of the delay circuit which is the time constant circuit at a is set larger than the time constants T1 and T2 of the voltage detection circuit 30 described above. Further, the transistor muting circuit is set so that muting is applied when there is no FM signal. In other words, the muting circuit 27a does not operate when the detection circuit 30 falls or rises for a short period of time, such as dropout, of the signal output from the detection circuit 30, but at the discontinuation point when recording on the magnetic tape 11. When the FM signal is interrupted at sufficiently long intervals, as shown in FIG. Conversely, when an FM signal appears on the magnetic tape 11 for the first time, for example when the tape mechanism starts playing, the above-mentioned FM signal
Demodulation noise occurs due to a transient response at the rising edge of the signal, but since the signal for canceling muting reaches the muting circuit 27a after a sufficiently large time constant T3, this noise at the rising edge is absorbed by the muting circuit 27a.
is masked so that it does not appear in the audio signal output from the output terminal 18.

As explained above, in the playback device according to this embodiment, the simple bandpass filter amplifier circuit 26 and the detection circuit 3
0, it is possible to reproduce and demodulate the magnetic tape 11 recorded with FM modulation at a wide range of recording densities with the necessary S/N and distortion ratio without switching the FM signal carrier of the recording circuit.

Further, the detection circuit 30 detects the rise and fall timings of the FM modulation signal of the magnetic tape 11 recorded at a wide range of recording densities, and the sample and hold circuit 27b performs signal interpolation processing and noise removal processing based on the detection signal. , and noise removal processing by the muting circuit 27a. In this way, one detection circuit 30 can detect both the rise and fall of the FM modulation signal and the dropout detection of the magnetic tape 18, so the circuit configuration for interpolation processing and noise removal processing is can be simplified.

! ! As is clear from the above description, the playback device according to the present invention includes a bandpass filter amplifier circuit that passes the necessary band of the frequency modulation signal read by the playback head, and a bandpass filter amplifier circuit that passes the required band of the frequency modulation signal read by the playback head, and a bandpass filter amplifier circuit that controls the rise and fall of the frequency modulation signal. A detection circuit detects, and at the timing of the fall of the frequency modulation signal detected by the detection circuit, holds the reproduction signal from the bandpass filter immediately before that timing and outputs it as a subsequent reproduction signal, and the detection circuit a sample hold circuit that releases the holding of the reproduced signal at the timing of the rise of the frequency modulation signal detected by the detector; and muting that performs noise removal processing at the rise and fall of the demodulation system signal using the same output of the detection circuit. Since it is equipped with a circuit, it is possible to reproduce and demodulate magnetic tape recorded at a wide range of recording densities from about 7 to 40 KBPS at a single carrier frequency and at the necessary S/N and distortion ratio.

Furthermore, the single detection circuit can detect both the rise and fall of the FM modulation signal and the dropout detection of the magnetic tape, simplifying the circuit configuration for interpolation processing and noise removal processing. It is possible to realize a playback device that is

[Brief explanation of the drawing]

Section 1 is a block diagram schematically showing the configuration of the reproducing device according to the present invention, FIG. 2 is a circuit diagram showing the specific configuration of the bandpass filter amplifier circuit, limiter amplifier, and detection circuit, and FIG. 3 1 is a block diagram schematically showing a configuration example of a conventional playback device. 11... Magnetic tape 12... Playback head 15
... Monostable multivibrator 16 ... Bandpass filter 26 ... Bandpass filter amplifier circuit 27a ... Muting circuit 27b ... Sample hold circuit

Claims (1)

[Claims] (1) A reproduction head that reads a frequency-modulated signal recorded on a magnetic tape, shapes the waveform with a monostable multivibrator, and then passes it through a bandpass filter to remove the carrier wave component, thereby demodulating and reproducing the signal. In the apparatus, a bandpass filter amplifier circuit that passes a required band of the frequency modulated signal read by the reproduction head, a detection circuit that detects rising and falling edges of the frequency modulated signal, and a frequency modulated signal detected by the detection circuit. At the falling timing of , the reproduced signal from the bandpass filter immediately before that timing is held and outputted as a subsequent reproduced signal, and at the rising timing of the frequency modulation signal detected by the detection circuit, the reproduced signal is outputted from the bandpass filter immediately before that timing. 1. A playback device comprising: a sample hold circuit for releasing a signal from being held; and a muting circuit for removing noise at the rising and falling edges of a signal in a demodulation system using the same output from the detection circuit.