JPS6237444B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a method for transmitting an audio signal together with a television signal.
The present invention relates to an automatic audio signal format identification device that can automatically identify the format of an audio signal when recording on a VTR.

[Summary of the invention]

The present invention relates to an automatic audio signal type identification device suitable for application to the audio system of a VTR, and in particular uses a signal related to the frequency of a vertical synchronization signal of a television signal as an identification signal for identifying multiplexed audio signals, etc. When reproducing the identification signal, this identification signal is reliably detected without being affected by jitter, etc. by phase-detecting and reproducing the identification signal using the reproduction synchronization signal related to the vertical synchronization signal. be.

[Conventional technology]

When recording television signals on a VTR,
When the audio signal is a TV audio multiplex signal, a pilot signal (signal corresponding to the multiplex control signal), which is an identification signal for identifying the multiplex audio signal, should also be recorded at the same time. This pilot signal was not recorded for the reason shown below.

In other words, when recording this pilot signal on an existing audio track by superimposing it on the audio signal,
This pilot signal has a frequency (low frequency, e.g. 30 Hz or less) and a level (e.g. 40 dB relative to the audio signal level (0 dB)) that does not affect the audio signal.
(below). However, it is impossible to accurately separate the pilot signal having such frequencies and levels from the audio signal. This is because the S/N of the reproduced pilot signal is very poor due to the effects of jitter, etc., so it is a very low frequency band below 30Hz, and it is a pilot signal that shows a stereo signal and a two-audio signal (bilingual broadcasting). ) must be recorded at different frequencies, but it is practically impossible to construct a circuit for frequency-separating these pilot signals in a reproduction system. It is also very susceptible to jitters and noise.

Therefore, among the VTR playback output terminals, VHF and
A pilot signal for this multiplexed audio signal is not superimposed on the high frequency signal (VHF television signal, UHF television signal) obtained at the UHF output terminal. Therefore, simply by receiving this high frequency signal, the mode corresponding to the multiplexed audio signal will not be automatically selected.

Therefore, it is conceivable to record this pilot signal on another track, for example a control track.

[Problem that the invention seeks to solve]

By the way, even when identifying the format of the recorded audio signal by recording the pilot signal using the control track, the format of the recorded audio signal may be at least a stereo signal or two audio signals. Since there are three types of pilot signals, a monaural signal and a monaural signal, it is insufficient to record one type of pilot signal on a single control track. When using two or more types of pilot signals, there are disadvantages similar to those described in the ``Prior Art'' section. It is also not very advisable to provide a track for recording pilot signals. This is because, if possible, it would be preferable to be able to process using only existing control tracks or audio tracks.

Furthermore, even in the case of recording such a pilot signal, there is a drawback that it is susceptible to the effects of jitter and noise.

Therefore, the present invention proposes an automatic audio signal type identification device that does not require changing the track pattern or the like and is less susceptible to the effects of jitter and the like.

[Means for solving problems]

In order to solve the above-mentioned problems, in this invention, as shown in FIGS. 2 and 3, the pilot signal
The frequencies of Pb and Pc are formed in relation to the frequency of the vertical synchronization signal of the television signal, and during playback, the pilot signals Pb and Pc are phase-detected using the reproduction synchronization signal related to this vertical synchronization signal, and the pilot signals A control signal P _W ' corresponding to the signal is obtained.

[Effect]

In this configuration, the pilot signals Pb and Pc are phase-detected using the reproducing synchronization signal related to the vertical synchronization signal, so even if jitter occurs, the pilot signal
Pb and Pc can be reliably phase detected.

〔Example〕

An example of the present invention will be explained in detail with reference to FIG.

In FIG. 1, 10A indicates a recording system, and 10B indicates a reproduction system. In the recording system 10A, 1 is a tuner, 2 is a video intermediate frequency amplification circuit, and 3 is a video detection circuit. The video output S _V after detection is sent to the signal conversion circuit 4 where the luminance signal is FM modulated in this example.
The chroma signal is low frequency converted and then recorded on the magnetic tape 5 by the rotating magnetic head H _A.

On the other hand, a part of the output of the video intermediate frequency amplification circuit 2 is supplied to a first FM detection circuit 8 constituting a multiplex demodulator through a detection circuit 7 for an audio intermediate frequency signal.
The output is supplied to a low-pass filter 9 to reproduce the main channel signal S _M of the multiplexed audio signal. This detection output is further transmitted to the second FM detection circuit 1.
1, and its output is supplied to a low pass filter 12.
is supplied to reproduce the sub-channel signal _S.sub.S.

These two channel signals S _M and S _S are supplied to the switching circuit 13, and if the multiplexed audio signal is a stereo signal, it is separated into a left signal and sent out from the respective output terminals b and c, and if the multiplexed audio signal is a stereo signal, it is sent out from the respective output terminals b and c. For example, one output terminal b outputs a German audio signal, and the other output terminal c outputs an English audio signal, for example.

In order to determine whether the multiplex audio signal is a stereo signal, a dual audio signal, or a monaural signal, and to control the corresponding switching operation, a multiplex control signal is provided at the subsequent stage of the second FM detection circuit 11. A detection circuit 15 is provided, and its output (output corresponding to stereo/monaural/bilingual) is used as the control signal P _W . It should be noted that since this detection circuit 15 can be a conventionally known one, its details will be omitted.

Demodulated audio signals output from output terminals b and c
Sb and Sc are a pair of audio heads H, respectively, as is well known.
The demodulated audio signals Sb and Sc are recorded on the corresponding audio tracks of the magnetic tape 5 at _B and _Hc , but coded single-frequency pilot signals Pb and Pc corresponding to the multiplexed control signals are included in these demodulated audio signals Sb and Sc. are superimposed. 20 is a circuit for forming these pilot signals Pb and Pc.

Pilot signals Pb and Pc should be 30Hz or less (for example, 25
Hz), and in this invention, the magnetic tape 5
The 50Hz control signal CP used for speed control, that is, the vertical synchronization signal of the television signal, is used, and this is used in the counter 21 to
low pass filter 2 after counting down to
2 to form a 25 Hz sine wave signal CW, which is supplied to the phase selection circuit 25.

As shown in the figure, the phase selection circuit 25 has a pair of switching circuits (actually electronic switches) SW _B and SW _C configured in a 1-circuit, 3-contact type, and one switching circuit SW _C receives a sine wave signal CW. In addition to the,
An inverter 26 supplies a sine wave signal whose phase is inverted. For example, the phase relationship between the multiplexed audio signal and the pilot signals Pb and Pb is selected as follows.

That is, as shown in FIG. 3, when the signal is a stereo signal, the pilot signal Pb superimposed on the demodulated audio signal Pb and the pilot signal Pc superimposed on the other demodulated audio signal Sc are in opposite phase relation to each other. (Japanese language broadcasting), the in-phase relationship is selected (see Figure 2), and when monaural signals, the pilot signals Pb and Pc are not superimposed at all.

A pair of switching circuits SW _B and SW _C are constructed to obtain such a relationship. Of the symbols attached to each terminal, S indicates a stereo signal, B indicates a two-audio signal, and M indicates a monaural signal. Each signal switching terminal is shown. The switching timing is controlled by a three-value control signal (for example, a stereo signal is a negative output, a two-audio signal is a positive output, and a monaural signal is a zero output).
Controlled by _W.

Note that in this example, the pilot signals Pb and Pc are at a predetermined level (for example, -30 to
-40dB) and recorded.

Next, the reproduction system 10B will be explained.

A video output S _V played back at head H _A and a pair of audio signals played back at heads H _B and H _C
Both Sb and Sc (including pilot signals Pb and Pc) are supplied to the switching circuit 26, the video output S _V is output as is, and the audio signals Sb and Sc are
are appropriately switched and converted into channel signals S _M and S _S of multiplexed audio signals.

Pilot signals Pb, Pc reproduced for that purpose
is supplied to the control signal forming circuit 30 to form a control signal P _W ' for multiplex audio signal conversion, which is then supplied to the switching circuit 26. This control signal P
_W ' is further supplied to a multiplex control signal CS forming circuit 40 to form a multiplex control signal CS corresponding to the pilot signals Pb and Pc.

FIG. 4 shows a concrete example of these forming circuits 30, 40.

Pilot signal reproduced by heads H _B and H _C
Pb and Pc are separated from the audio signals Sb and Sc by bandpass filters 31 and 32. On the other hand, the control signal CP reproduced from the control head (not shown) is counted down to 1/2 by the counter 34 to form a 25Hz sine wave signal CW, which is separated by bandpass filters 31 and 32. Together with the pilot signals Pb and Pc, they are supplied to multipliers 35 and 36, respectively, where multiplication processing for phase detection is performed.

Since the pilot signals Pb and Pc are also formed based on the 50Hz signal, this sine wave signal CW
Even if the pilot signals Pb and Pc fluctuate due to jitter, etc., the control signal CP
Since the signal itself fluctuates due to jitter, etc., the multiplication process is not affected by the jitter, and its polarity does not change. 2
The two multiplication outputs are further supplied to a third multiplier 37 to determine the phases of the pilot signals Pb and Pc.

That is, if it is a stereo signal, the output will be negative, if it is a two-audio signal, it will be a positive output, and if it is a monaural signal, the output will be zero. This multiplication output is supplied to a three-value comparator 39 through a low-pass filter 38 to form a three-value output corresponding to the level of the multiplication output, that is, a control signal P _W '.

The other forming circuit 40 is provided with two oscillators 41 and 42 as shown. These oscillators 41,
42 is for multiple control signals, one is 982.5
Hz, the other oscillates at 922.5Hz. These control signals are selected in the switching circuit 43 according to the multiplexed audio signal, and which one is selected is determined by the value of the control signal P _W '. The selected control signal is supplied to the AM modulator 44 and subjected to AM modulation. 45 is a subcarrier (55.125kHz) oscillator, and a terminal 46 outputs a multiplex control signal CS.

50 is an RF modulator for forming a television signal. First, the sub-channel signal S _S converted by the switching circuit 26 is combined with the multiplexed control signal CS by the combiner 51, and then the first FM The signal is FM modulated by the modulator 52, and this FM modulated signal is combined with the main channel signal S _M output from the switching circuit 26 as well. 53 is a synthesizer. This combined output is further supplied to a second FM modulator 54.

On the other hand, the video output S _V is output from the AM modulator 55
After being subjected to AM modulation in the synthesizer 56, the signal is synthesized into an FM modulated multiplex audio signal to form a target television signal.

〔Effect of the invention〕

As explained above, in the present invention, the pilot signal frequency is formed in relation to the vertical synchronizing signal frequency of the television signal, and at the time of reproduction, the reproduced pilot signal is phase-detected using the reproduced synchronizing signal related to the vertical synchronizing signal. This allows the pilot signal to be detected.

According to this, the pilot signal is distorted due to jitter etc.
Even if Pb and Pc fluctuate on the time axis, the reproduction control signal CP will also fluctuate accordingly, so there is no effect of jitter or the like on the multiplication process for phase detection. That is, the pilot signal can be detected accurately even if there is jitter or the like.

In addition, as in the example, it is possible to add
When recording single-frequency pilot signals Pb and Pc with each channel signal by selecting them in an in-phase or anti-phase relationship depending on the form of the audio signal and superimposing them,
During playback, multiple audio signals can be distinguished by determining their phases.

That is, in the case where the pilot signal is frequency-separated to distinguish between multiplexed audio signals, etc., it is quite difficult to distinguish between the pilot signals. On the other hand, when a single set of pilot signals is used for recording as described above, it is only necessary to separate them from the audio signal, and the discrimination can be made reliably.

Furthermore, since the pilot signals Pb and Pc are sine wave signals, there is no spurious interference.

In addition, in the embodiment described above, the pilot signal
In order to prevent the audio signals Sb and Sc from being degraded by Pb and Pc, the pilot signal level was lowered below the audio signal level (e.g. -30 to -40 dB) and recorded.
Instead of recording at almost the same level, the playback system (1
A switching circuit 26 provided in the switching circuit 0B) may be provided to cancel the pilot signals Pb and Pc. In this case, each audio signal before being converted into main and sub channel signals S _M and S _S
These pilot signals Pb and Pc can be easily canceled by adding a signal having the opposite phase to the superimposed pilot signals Pb and Pc at the Pb and Pc stages.

Since the audio signals Sb and Sc are combined in the monaural signal, the pilot signals Pb and Pc are canceled at this time without using any special means.

Further, according to the present invention, VHF and VTR
Each UHF output terminal outputs a television signal containing multiplexed control signals, so if you use this television signal, you can automatically select the audio signal playback mode even if it is output from a VTR. So it's very convenient.

Note that in the above embodiment, the pilot signals Pb and Pc were formed using a 50Hz vertical synchronization signal.
When recording a video signal of a standard format different from that described above, it goes without saying that the frequencies of the vertical synchronization signals used as pilot signals Pb and Pc will be different.

Another possible application of the present invention is that even when an audio signal is recorded using an audio recording system with different characteristics, such as the Dolby recording system, the present invention can be used to easily record audio signals that are not a normal recording system. can be identified. As described above, according to the present invention, the format of the audio signal to be recorded (monaural, stereo, bilingual, Dolby) can be easily and reliably identified.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of the present invention, FIG. 2 is a system diagram showing an example of a pilot signal forming circuit,
FIG. 3 is a waveform diagram showing an example of a pilot signal, and FIG. 4 is a system diagram showing an example of a control signal forming circuit. Sb and Sc are audio signals formed from the main and sub channel signals S _M and S _S , Pb and Pc are pilot signals, 20 is a forming circuit thereof, 25 is a phase selection circuit,
30 is the control signal P _W ', 40 is the multiplexed control signal CS
This is the formation circuit of

Claims (1)

[Claims] 1. An identification signal that identifies the form of the audio signal according to the form of the audio signal to be recorded is mixed with the audio signal and recorded on a magnetic tape, and during playback, the audio is detected by the identification signal reproduced from the magnetic tape. In the automatic audio signal type identification device for a video tape recorder, the signal reproduction system is switched according to the recording format, the identification signal frequency is formed in relation to the vertical synchronization signal frequency of the television signal, and the identification signal frequency is formed in relation to the vertical synchronization signal frequency of the television signal. An audio signal type automatic identification device that detects the identification signal by phase-detecting the identification signal using a reproduction synchronization signal related to the vertical synchronization signal.