JPH0380463A - Fm modulated signal reproducing device - Google Patents

Abstract

PURPOSE:To automatically discriminate the sort of information on an FM modulated signal which is recorded by detecting the level change of the carrier of the FM modulated signal and processing an FM-demodulated information signal according to the detection output. CONSTITUTION:A gate pulse GP is inputted to gate circuits 4a and 4b through the outputs of differentiation circuits 3a and 3b an a terminal 7. Thus, only a differentiation waveform caused as the level of the carrier of an AMF signal in a vertical flyback term is higher than the other term is passed through them and inputted to Schmitt trigger circuits 5a and 5b. The outputs of the circuits 5a and 5b are inputted to one terminal of AND gates 8a and 8b and a dropout detection signal DO is inputted to the other terminal of them through a terminal 9. The outputs of the circuits 5a and 5b when dropout occurs are made invalid by gates 8a and 8b. It is correctly detected by the circuits 4a and 4b and the gates 8a and 8b whether a stereo-voice signal is recorded or a main and sub voice signal is recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM modulated signal reproducing device, and particularly to an FM modulated signal reproducing device in which any of a plurality of types of information is FM modulated.

[Prior art] In recent years, even in camera-integrated video tape recorders,
Stereo audio is being promoted, but conventionally it was 1.5M.
Even if you use a VTR that records monaural audio signals with FM modulation using a 1.5 MHz carrier wave, in order to maintain compatibility with the conventional version and create stereo, the 1.5 MHz FM modulated carrier wave is used to record monaural audio signals. A method is adopted in which the sum signal of the L channel and the R channel is recorded, and a 1.7 MHz FM modulated carrier wave is newly provided to record the difference signal between the L channel and the R channel.

A VTR that records stereo audio signals using this type of sum-difference method.
When attempting to record so-called main and sub-audio signals, such as Japanese on the L channel and English on the R channel, in which left and right independent audio signals are recorded, the recorded signal It is necessary to determine whether the signal is a stereo audio signal or a main/sub audio signal to determine whether or not to pass it through the matrix circuit.

[Problems to be solved by the invention] Manually switching the processing as described above becomes complicated and causes confusion, and if the switching is performed incorrectly, the playback quality in particular will be significantly impaired. Because of this problem, it has been desired to automatically switch the processing mode. In order to perform such switching of processing modes, identification information for identifying the type of audio signal must be recorded in some form on the recording medium, and the switching described above must be performed in accordance with this identification information.

However, recording and reproducing such identification information separately from the audio signal is not preferable because it interferes with high-density recording and requires a dedicated recording and reproducing means. Furthermore, if an error occurs in this identification information, large noise will occur in the reproduced audio, so care must be taken to ensure that there is no error in the identification information.

In view of the above-mentioned background, the present invention is an FM system that can detect the type of modulation information of an FM modulation signal without separately reproducing the information.
An object of the present invention is to provide an M modulation signal reproducing device.

[Means for Solving the Problems] With this purpose in mind, according to the present invention, an FM modulated signal is reproduced in which the carrier wave level in a specific period is different from that in other periods only when specific information is modulated. An apparatus comprising: FM demodulation means for demodulating an FM modulation signal; detection means for detecting a level change of a carrier wave of the FM modulation signal; and processing means for processing an FM demodulated information signal according to a detection output of the detection means. The structure was designed to include the following.

[Function] By configuring as described above, the FM carrier wave itself can be used as identification information, and it can be determined that the information of the FM modulated signal is specific information without providing a separate reproduction means for identification information.

[Example] Examples of the present invention will be described below.

FIG. 2 is a diagram showing a schematic configuration of a reproduction system of a VTR as an embodiment of the present invention. The VTR of this example uses the left and right sum signals and left and right difference signals of stereo audio signals, or the aforementioned main and sub audio signals as 2-channel audio signals.
Record modulation.

Here, the audio FM modulated signal (hereinafter referred to as AFM signal) is magnetically recorded and reproduced in the form of the FM modulated audio signal obtained by FM modulating the audio signal, but the frequency spectrum of the AFM signal is as shown in Figure 3. It is shown in the figure below.

fl to f4 shown in FIG. 3 are the frequencies of the tracking pilot signal ATF according to the well-known four-frequency system, and f
c is the carrier frequency of the low frequency converted chroma signal CL, fm and fs are the AFM signals AFM-main, AFM-s
u is the carrier wave frequency of b, and the AFMFM modulation signal A
When recording a stereo audio signal, a signal obtained by converting the L (left) channel and R (right) channel signals into their sum signal is recorded as the M-main, and when recording the main and sub audio signals, for example, Main audio signals such as words are recorded.

On the other hand, when recording a stereo audio signal, the AFMFM signal FM-sub records a signal obtained by converting the L channel and R channel signals into a difference signal between them, and when recording a main/sub audio signal, it records a signal obtained by converting the L channel and R channel signals into a difference signal between them. An audio signal is recorded. Note that if this AFMFM modulation signal is not recorded, the AFM main signal is recorded as a monaural audio signal.

fsy is the luminance signal sync chip frequency, fwh
is the peak white frequency. It is well known that these frequency allocations differ depending on the format, such as so-called high band mode and normal mode recording.

FIGS. 4(a) and 4(b) show the AFMFM signals F M -m a i n and A F at the time of recording the main and sub audio signals.
It is a figure which shows the amplitude of the carrier wave of M-sub.

As shown in FIGS. 4(a) and 4(b), the amplitude level of the carrier wave of the AFM signal in the vertical retrace section of the luminance signal is set higher than that in the other than the vertical retrace section.

This will be explained below with reference to FIG. The signals recorded on the magnetic tape 10 in FIG.
and preamplifiers 13 and 14, and these signals are made continuous by a switch circuit 15 switched by a head switching pulse (HSWP) synchronized with the rotational phase of the helad 11 and 12 from a terminal 16, and then converted into a band. Pass filter (BPF)17. Bypass filter (HPF) 18, B
It is input to PF24 and BPF25.

The low-frequency color signals separated by BPF17 undergo color signal processing (
Process C) The color signal is processed by the circuit 19 to return it to its original band, and is outputted from the color signal output terminal 21 and inputted to the mixing circuit 22 .

The FM modulated luminance signal separated by the HPF 18 is subjected to processing such as FM demodulation by a luminance signal processing (Y process) circuit 20, outputted from a luminance signal output terminal 24, and inputted to a mixing circuit 22. The output of the mixing circuit 22 is outputted from an output terminal 23 as a decoded video signal. Note that the Y process circuit 20 has a well-known dropout compensation circuit, and supplies a dropout detection signal DO to the mode detection circuit 36.

The AFM main signal separated by the BPF 25 is input to the mode detection circuit 30 and the limiter 27, and the AFM main signal output from the limiter 27 is input to the FM demodulation circuit 29.
The signal is FM demodulated into the original audio signal, and then sent to the stereo matrix circuit 33. The a terminal of the switch 31 is input to the b terminals of the switches 31 and 32.

The AFM sub-signal separated from the BPF 26 is input to the mote detection circuit 30 and the limiter 2B.
The signal input to 8 is FM demodulated by the FM demodulation circuit 30 to the original audio signal, and is input to the a terminal of the matrix circuit 33 and the switch circuit 32.

When a stereo audio signal is recorded, the switch circuits 31 and 32 transmit the stereo audio signal demodulated by the matrix circuit 33 to each C terminal according to a 2-bit mode detection signal outputted from the mode detection circuit 36, which will be described later. is output to the output terminals 34 and 35 via the matrix circuit 33, and when the main and sub audio signals are being recorded, the F
The audio signals output from the M demodulation circuits 29 and 30 are outputted to output terminals 34 and 35 via each a terminal. Thereby, the stereo audio signal and the main and sub audio signals are selectively output as appropriate.

When both switches 31 and 32 are connected to the b terminal, the AFM main signal, that is, a monaural audio signal, is output from the terminal 34.35, and when they are connected to the d terminal, the audio signal is output to the terminal 34.35. No output is performed.

The mode detection circuit 36 in FIG. 2 will be explained in detail below.

1 is a diagram showing a specific configuration example of the mode detection circuit of FIG. 2. In FIG. 0, 1a and lb are the BPF 25.
This is a terminal into which the AFM signal separated by 26 is input,
These AFM signals are sent to envelope detection circuits 2-a and 2b, respectively.
Yubako 1I7f 1-line detection circuits 2a, 2b (,
Detect the carrier wave level of the tAFM signal. The output signals of the envelope detection circuits 2a and 2b are respectively sent to differentiating circuits 3a.

3b, and the differential waveform of the level change portion is output.

The outputs of the differentiating circuits 3a and 3b are gated by gate circuits 4a and 4b for a predetermined period including the vertical retrace period, for example, the vertical retrace period and several horizontal operation periods immediately before and after the vertical retrace period. This gate circuit 4a.

The gate pulse GP supplied to 4b is generated by the gate pulse generating circuit 37 in FIG. 2 in synchronization with HSWP,
The signal is input to this mode detection circuit 36 via the terminal 7 in FIG. As a result, only the differential waveform caused by the carrier wave level of the AFM signal during the vertical retrace period being higher than other periods can be passed, and the effects of noise and dropouts outside the above-mentioned predetermined period can be eliminated. be able to.

The differential waveforms passed through gate circuits 4a and 4b are input to Schmitt trigger circuits 5a and 5b.

The Schmitt trigger circuits 5a and 5b are set to have a dead zone below a predetermined threshold, and are not sensitive to differential waveforms whose amplitude is below that corresponding to switching of the carrier wave level during recording.

That is, the presence of the Schmitt trigger circuits 5a, 5b can also reduce the influence of noise within the predetermined period gated by the gate circuits 4a, 4b.

Moreover, this Schmitt trigger circuit 5a.

Depending on whether the threshold level 5b is set in the positive or negative direction, only positive or negative differential waveforms will be detected. That is, if the threshold values of the Schmitt trigger circuits 5a and 5b are set to either positive or negative, only either the rise or fall of the FM carrier level will be detected. In this example, the Schmitt trigger circuit 5 is set to a negative level, which is the threshold value.
A and 5b detect the fall of the carrier wave level after the vertical retrace period, and in response to the detection of the fall, the outputs of the Schmitt trigger circuits 5a and 5b become a logical high level (Hi).

The outputs of the Schmitt trigger circuits 5a, 5b are input to one terminal of AND gates 8a, 8b. and gate 8
The dropout detection signal Do from the Y process circuit 20 described above is inputted to the other terminals a and 8b via the terminal 9. This dropout detection signal is a signal that becomes a logical low level (LO) when a dropout occurs, and the outputs of the Schmitt trigger circuits 5a and 5b are invalidated by AND gates 8a and 8b when a dropout occurs.

The outputs of the ant gates 8a, 8b are input to retriggerable mono multivibrators 43a, 43b. The time constants of the retriggerable mono-multivibrators 43a and 43b are set so that they remain Hi for several fields after the trigger. The reason for this will be explained below. The outputs of the AND gates 8a and 8b are the main and sub audio signals, and when the outputs are not recorded, the gate circuit 4a.

4b and AND gates 8a and 8b, pulses are almost never output, but due to dropouts, etc., pulses are not output during the vertical retrace period even though the main and sub audio signals are being recorded. This is a possible situation.

That is, just because pulses are not obtained from the ant gates 8a and 8b during 2 to 3 fields, it cannot be assumed that the main and sub audio signals are not recorded. The time constants of the mono-multivibrators 43a and 43b are set with these considerations in mind.

A signal obtained by inverting the above-mentioned dropout detection signal DO by an inverter 45 is input to the integrating circuit 41, and the output of the comparator 42 becomes Hi when the output of the integrating circuit 41 exceeds a predetermined level. That is, the comparator 42
The output becomes Hi when dropout continues for a predetermined period or more or occurs at a predetermined frequency or more.

Output di, d of mono multivibrator 43a, 43b
2 and the output of comparator 42 are read-only memory (
This is the read address of ROM) 50. The 2-bit data stored in each address of the ROM 50 is as shown in Table 1.

Table 1 In Table 1, “0” is a logical low level (Lo)
, "1" corresponds to Hi. Mode data md, which is the output of this ROM 50, becomes control data for the switches 31 and 32 in FIG. 2 via the terminal 51. That is, as shown in Table 1, when md is "OO", switches 31 and 32 are connected to the d terminal, and similarly when md is "O1", "IO", "1"
1'', switches 31 and 32 are connected to the so, c, and a terminals.

Kokote, let me explain the idea behind this MD. First, if the output d3 of the comparator 42 is Hi, dropouts occur frequently and good audio signal reproduction cannot be expected, so even if the outputs dl and d2 of the mono multivibrators 43a and 43b are both Hi, the switch 31.3
Connect 2 to the d terminal to disable audio output.

Next, a case where d3 is Lo will be explained.

In this case, if dl=d2, the reliability of this information is extremely high. Therefore, if di and d2 are both Hi,
Switches 31 and 32 are connected to terminal a, and FM'41. m
The main and sub audio signals output from the circuits 29 and 30 are connected to the terminal 34.
．． It is output from 35. Further, if both di and d2 are Lo, the switches 31 and 32 are both connected to the C terminal, and the L channel and R channel signals of the stereo audio output by the matrix circuit 33 are output from the terminals 34 and 35. However, if d1≠d2, the reliability of this information is low, and even if processing is performed for either the main/sub audio signal or the stereo audio signal, there is a possibility that incorrect processing will be performed. If incorrect processing is performed, unlistenable audio will be output. Therefore, in this example, dl*d2
In this case, the output signal of the FM demodulation circuit 29, that is, the sum signal of the stereo audio or the main audio signal of the main and sub audio is outputted from the terminals 34 and 35 as a monaural audio signal.

At this time, the display section 38 displays whether the output audio signal is a stereo signal, a monaural signal, or a main/sub signal according to the 2-bit mode information md.

According to the configuration as described above, the gate circuit 4a.

4b and AND gates 8a and 8b, it is possible to detect with almost no error whether a stereo audio signal or a main/sub audio signal is being recorded. Moreover, this identification information is recorded by increasing the level of the FM carrier wave during the vertical retrace period, and the above identification is performed simply by detecting the change in the level of the carrier wave, so special recording and reproducing means are not required. do not need.

In the above embodiment, the FM41 transmission level during the vertical retrace period was set high when recording the main and sub audio signals.
Increase the FM carrier level when recording stereo audio signals,
The reproduction system may also be configured to detect that a stereo audio signal is recorded.

In addition, in the configuration shown in FIG. 1, an ant gate is provided to take an AND of the dropout detection signal and the gate pulse, and this AND signal is used to generate the gate circuit 4a.

Almost the same effect can be obtained even if the AND gates 8a and 8b are controlled and the AND gates 8a and 8b are eliminated.

[Effects of the Invention] As explained above, according to the present invention, an FM that can automatically determine the type of information of a recorded FM modulation signal and perform desired processing as appropriate without providing any special reproduction means. A modulated signal reproducing device is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a mode detection circuit of a VTR according to an embodiment of the present invention, FIG. 2 is a diagram showing a schematic configuration of the entire reproduction system of a VTR according to an embodiment of the present invention, and FIG. FIG. 4 is a diagram showing the frequency spectrum of the recorded signal. FIG. 4 is a diagram for explaining the carrier wave level of the recorded FM modulated audio signal. In the figure, 2a and 2b are envelope detection circuits, and 3a. 3b is a differential circuit, 4a and 4b are gate circuits, 5a and 5b
is a Schmitt trigger circuit, 8a. 8b is an AND gate, 10 is a magnetic tape, 11.12 is a playback head, 20 is a brightness signal processing circuit, 25.26 is a band pass filter, 27.28 is a limiter, 29.30
is an FM demodulation circuit, 31.32 is a changeover switch, 33 is a matrix circuit, 34.35 is an audio output terminal, 36 is a mode detection circuit, 37 is a gate pulse generation circuit, 43a, 4
3b is a retriggerable monomultivibrator, Do is a dropout detection signal, HSWP is a head switching pulse, and GP is a gate pulse.

Claims (5)

[Claims] (1) A device for reproducing an FM modulated signal in which the carrier wave level in a specific period is different from that in other periods only when specific information is modulated, comprising: FM demodulation means for demodulating the FM modulated signal; FM
detection means for detecting a change in the level of a carrier wave of the modulated signal;
FM modulated signal reproducing apparatus comprising processing means for processing an FM demodulated information signal according to a detection output of the detection means. (2) An FM modulated signal reproducing device according to claim (1), wherein the detection means detects a rise in the level of the carrier wave. (3) The FM modulated signal reproducing device according to claim (1), wherein the detection means detects a fall of the carrier wave level. (4) The FM modulated signal reproducing device according to claim (1), wherein the detection output is not obtained except for a predetermined period including the specific period. (5) The apparatus according to claim (1) includes a dropout detection means, and the detection output is not obtained for a predetermined period including the dropout detection period. FM modulation signal reproducing device.