JPH0725842Y2 - Audio carrier recording judgment device in video tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a video tape recorder which is FM-modulated according to an audio signal and reproduces audio from an audio carrier recorded on a video tape. The present invention relates to an audio carrier wave recording / judging device for judging the presence / absence of an audio carrier wave recorded on a video tape.

(Prior Art) The requirements for high-quality recording and reproduction of voice band signals are as follows.
It is also strong against devices other than dedicated devices that only record and play voice. Therefore, the video tape recorder meets the above-mentioned demand by adopting a recording method in which an audio carrier wave FM-modulated according to an audio signal is recorded on a video tape and reproduced.

When reproducing audio in this recording method, it is premised that a video tape on which an audio carrier is recorded is used. However, in order to ensure compatibility with conventional audio recording methods, the audio carrier is detected from the video tape. If not, it is determined that the recording is performed by the conventional method, and the sound is reproduced according to the method.

The circuit used for this determination is, as shown in FIG.
Amplifies the output of the rotary head 31 using the head amplifier 32,
After extracting only the signal component of the required frequency by the bandpass filter 33, the output level of the bandpass filter 33 is detected and compared by using the envelope detection circuit composed of the diode D, the capacitor C, and the resistor R. By using the instrument 34, the determination is made depending on whether the detected level is higher than a preset reference level 34a.

(Problems to be Solved by the Invention) Since the above circuit is configured to make a determination based on the level of the sound carrier detected by the rotary head 31, when the determination level is set low, Even if the voice carrier is not detected, the noise component detected by the rotary head may erroneously determine that the voice carrier is detected. In other words, the carrier wave modulated by the voice has a low frequency, so that it is easily affected by the low-frequency converted chroma component and the lower sideband of the FM luminance signal, making it difficult to detect the presence or absence of the voice carrier in the level comparison. There was such a problem. Therefore, the level that serves as the criterion for the determination, including such interference as the chroma component and the lower sideband of the FM luminance signal,
The level is set to have a sufficient margin against noise.

On the other hand, the video tape is often played back by a model other than the recording device and the device in which the recording is performed. Then, when the recording level of the sound carrier on the recording side is low and the reference level of the determination on the device side for reproduction is set high between the two models used at that time, at the time of reproduction, Since the detected level often becomes smaller than the reference level even though the audio carrier is being detected, it may be determined that the audio carrier is not recorded. Then, there was a problem that the sound was interrupted.

The present invention was devised to solve the above problems, and an object thereof is to provide an audio carrier recording / judging device in a video tape recorder, which is capable of judging that an audio carrier is recorded without error. It is in.

(Means for Solving the Problems) In order to solve the above problems, an audio carrier recording / judging device in a video tape recorder according to the present invention rotates an audio carrier recorded on a video tape while being FM-modulated according to an audio signal. By detecting with the head,
When the audio reproduction is performed and the phases of the two signals are compared, the comparison output showing the phase difference between these two signals and the lock output showing that the phases of the two signals are in the locked state Phase detector that sends two outputs, a low-pass filter that guides the comparison output sent from the phase detector, and an oscillation frequency that changes according to the output of the low-pass filter, and a voltage-controlled oscillator circuit that sends the output to the phase detector. And a detection determination circuit that outputs a determination output indicating the detection of the voice carrier when the lock output transmitted by the phase detector indicates the lock of the phases of the two signals, and is detected by the rotary head in the phase detector. The phase of the audio carrier wave and the phase of the output of the voltage controlled oscillator are compared. It is intended to.

(Operation) Since the phase comparison performed by the phase detector is performed based on the phase difference between the two signals, if the signal introduced to one input is a noise component having no phase continuity, the noise component Irrespective of the level of, the lock output does not show a signal indicating that the two signals are in phase lock. However, if the signal detected by the rotary head is a voice carrier, then when the level of the signal is within comparable levels, a signal will appear at the lock output indicating lock, even if the level of the voice carrier is low. The detection determination circuit sends a determination output according to the state of the lock output signal. With such a configuration, the presence or absence of the FM voice carrier can be detected reliably regardless of the level of the noise component, and at the same time, the dropout can be detected. Further, the comparison output output from the phase detector shows the audio signal carried by the carrier in the phase locked state, and by introducing this to the low-pass filter, the FM detection output of the audio can be obtained at the same time. It is possible.

(Embodiment) FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

In the figure, the output of the rotary head 11 that detects the voice carrier is guided to the head amplifier 12 that amplifies the detection signal, and the output of the head amplifier 12 passes only the component corresponding to the frequency of the voice carrier. , And is sent to one of the comparison inputs of the phase detector 14 through the bandpass filter 13 that attenuates other unnecessary signal components.

Comparative output 14a output from this phase detector 14
Of the voltage controlled oscillator circuit 16 via the low pass filter 15 which is a loop filter for removing the high frequency component contained in the comparison output 14a and holding the locked state of the two signals input to the phase detector 14. It is being sent to the control input. The output of the voltage controlled oscillator circuit 16 is
It is led to the other comparison input of the phase detector 14.

On the other hand, the lock output sent from the phase detector 14
14b is led to the plus input of the comparator 182, to which the reference voltage 18a is applied to the minus input, via the low-pass filter 181, which is a component of the detection determination circuit 18. The output of the comparator 182 is sent to the outside as the determination output 18b. Also, the comparison output 14 from the phase detector 14
a is sent to the outside as a demodulation output indicating voice.

The operation of one embodiment of the present invention having the above configuration will be described below.

The voice carrier detected by the rotary head 11 is amplified by the head amplifier 12 and unnecessary components are removed by the bandpass filter 13, so its output 13a is at the level required by the comparison input of the phase detector 14. The signals are in phase with each other while satisfying the above conditions.

Further, since the voice carrier (output from the bandpass filter 13) and the output of the voltage controlled oscillator circuit 16 are guided to the phase detector 14 and the phases of these signals are compared, the comparison output 14a is output. A signal corresponding to the phase difference between the phase of the output signal from the voltage controlled oscillator circuit 16 and the phase of the sound carrier appears.

Since this signal is guided to the control input of the voltage controlled oscillator circuit 16 via the low pass filter 15, the voltage controlled oscillator circuit is controlled.
The output frequency sent by 16 gradually converges in the direction in which it matches the frequency of the voice carrier. After the matching of the frequencies occurs, the phase of the output of the voltage controlled oscillator circuit 16 shifts, and the phase of the output 16a matches the phase of the voice carrier. After that, as long as the frequency of the voice carrier does not exceed the lock range, the phase detector 14 and the low-pass filter 15 are changed by following the change of the frequency of the voice carrier and changing the frequency of the voltage controlled oscillator circuit 16. The phase lock loop including the voltage controlled oscillator circuit 16 maintains the locked state.

In this locked state, when the frequency of the voice carrier changes, it follows the change. Therefore, the average level of the comparison output 14a (the average of about half the time required for one cycle of the highest frequency of the recorded voice signal) level)
Changes. This change is indicative of the audio signal carried by the carrier since the audio carrier is FM modulated. Therefore, in an external circuit to which the comparative output 14a is guided, the comparative output 14a is guided to the low-pass filter, so that the audio signal recorded by the audio carrier appears at the output.

On the other hand, when the phase lock loop is in the above lock state, a signal indicating lock appears at the lock output 14b. The lock output 14b is at the “H” level when the lock is shown, and at the “L” level in other states, the “H” level is input to the plus input of the comparator 182 via the low pass filter 181. Led to
The determination output 18b which is the output thereof is set to the "H" level. Therefore, in the external circuit to which the determination output 18b is guided, the signal based on the comparison output 14a is used as the audio signal, assuming that the video tape on which the audio carrier is recorded is being reproduced.

On the other hand, when the video tape on which the audio carrier wave is not recorded is being reproduced, the noise component whose phase is not uniform appears at the output 13a of the band pass filter 13, so that the phase detector 14 is always out of lock. ,
Lock output 14b remains at "L" level. Therefore, the determination output 18b also becomes "L" level, and it is assumed that audio recording is being performed along one end of the tape, and the tape is reproduced. Depending on the circuit configuration of the phase detector 14, "H" and "L" may be reversed.

As described above, in this embodiment, since the low-pass filter 181 is provided in the detection determination circuit 18, due to the disturbance of the detection of the instantaneous audio carrier caused by the elongation of the video tape, etc. Even if the lock loop is locked for a very short time and a short "L" level pulse appears at the lock output 14b,
Since the “L” level is absorbed by the low-pass filter 181 without being sent to the comparator 182, it is possible to prevent an unnatural interruption of voice that occurs when a short-time lock release is sent to the outside. ing.

Note that the present invention is not limited to the above-mentioned embodiment, and the demodulation output is described as a configuration in which the comparison output 14a is sent to the outside as an output indicating an audio signal.
It is possible to adopt a configuration in which the 15 outputs are sent to the outside as demodulation outputs.

(Effects of the Invention) The audio carrier determining device in the video tape recorder according to the present invention includes a phase detector for comparing the phase of the audio carrier detected by the rotary head with the phase of the output of the voltage controlled oscillator, and a loop filter. Since the audio carrier detection is determined based on the lock output of the phase-locked loop consisting of the low-pass filter, the level of the audio carrier detected by the rotary head is large in this lock output. Even when modulated, as long as the phase of the output of the voice carrier is aligned, a signal indicating lock appears, so it is possible to accurately determine whether the voice carrier is recorded regardless of the noise component. It is possible to detect the dropout at the same time. Further, since the comparison output output from the phase detector shows the voice signal carried by the carrier wave in the phase locked state, by guiding this to the low pass filter, the FM detection output of the voice is also obtained at the same time. There are various effects such as being possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing an electrical configuration of a conventional technique. 11 ... Rotating head 14 ... Phase detector 15 ... Low pass filter 16 ... Voltage controlled oscillator 18 ... Detection judgment circuit

Claims (1)

[Scope of utility model registration request] 1. A video tape recorder which reproduces audio by detecting an audio carrier, which is FM-modulated in accordance with an audio signal and recorded on a video tape, by using a rotary head, to detect the phase of two signals. A phase detector that sends out two outputs, a comparison output indicating the phase difference between these two signals and a lock output indicating that the phases of the two signals are in a locked state by performing comparison, and this phase detector A low-pass filter to which the comparison output to be sent is guided, a voltage-controlled oscillator circuit that changes the oscillation frequency according to the output of the low-pass filter, and sends the output to the phase detector, and a lock output that is sent by the phase detector. When the phase lock of the two signals is And a detection determination circuit for transmitting a determination output, wherein the phase detector compares the phase of the sound carrier detected by the rotary head with the phase of the output of the voltage controlled oscillation circuit. Audio carrier recording judgment device in recorder.