JPS61222068A - Video disk sound recording system - Google Patents

Abstract

PURPOSE:To prevent beat interference and to discriminate a recording system by setting the FM carrier frequency of a digital sound signal to the FM carrier frequency of a sound channel of an analog sound FM recording system and recording a pilot signal at the recording start position. CONSTITUTION:The first sound channel signal and the second sound channel signal inputted at input terminals 1, 2 are supplied through AD converters 5,6 to a digital modulator 9. The recording start signal inputted at an input terminal 3 is supplied to a pilot signal generator 7 and an address signal generator 8 and the pilot signals are supplied for a prescribed time period to the modulator 9 from the start of recording. The modulated digital signals from the modulator 9 are supplied to a FM modulator 10 while the modulator 10 has the FM carrier frequency of the 'H' and 'L' levels of the digital sound signals set to the same frequency as the FM carrier frequency of the first and second sound channels adopted at the analog sound FM recording system. The resulting signals are recorded, the beat interference is prevented and the reproduction is carried out in which the recording system can be discriminated.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention is a method for recording audio signals on video discs. In the audio recording method that records
The FM carrier frequency is selected to be a specific frequency, and a pilot signal is recorded at the recording start position of the digital audio signal.

<Prior art> An analog audio FM recording method is normally used to record audio signals on a video disc. Generally, the analog audio signals of the second two channels are each FM-modulated and recorded on the disc together with the video signal, but due to scratches on the disc itself, the signals may be lost during playback, resulting in the reproduced audio being lost. Noise may occur. Therefore, a method has been proposed in which the audio signal is converted into a digital signal, further code-modulated, and this digitally coded audio signal is recorded on FM. It is effective because it can reproduce higher quality audio than the FM recording method.

<Problems to be Solved by the Invention> However, the problem with digitally encoding this audio signal and recording it on FM is that beat interference occurs between the FM modulation wave of the digitally encoded audio signal and the video signal. .

<Means for Solving the Problems> The present invention has been made in view of the above-mentioned points, and when recording a digitally coded audio signal with FM modulation, the H# and L'' of the coded signal are Each FM carrier frequency of the level is the same frequency as the FM carrier frequency of the first and second two audio channels adopted in the current analog audio FM recording system, for example, in the current VHD system, 3 .43 MHz and 3.73 MHz are selected and recorded, and a pilot signal is recorded at the digital audio recording start position for discrimination between digital audio recording and analog audio recording.

Function> As in the recording method of the present invention, the FM carrier frequency of digital audio is converted to the first FM carrier frequency of analog audio FM recording method. If the FM carrier frequency is selected to match the FM carrier frequency of the second audio channel, the FM carrier frequency of this first and second audio channel
The carrier frequency is set to a value that minimizes beat interference with the video signal, so audio beats will never appear on the screen.

In addition, a video disc player capable of playing back both video discs in which digital audio is recorded in FM using the frequency relationship of the recording system of the present invention and video discs recorded in the existing analog audio FM recording system. In this case, it becomes possible to share some circuits of the audio signal processing circuit system such as the FM demodulator, and in this case, the pilot signal can be detected and the existing analog audio FM recording system and the digital audio FM according to the present invention can be used in common. The recording system is discriminated, and the operation of the audio signal processing circuit is automatically switched based on the output of the discrimination, thereby making it possible to reproduce discs of both systems.

<Examples> The present invention will be described below according to examples shown in the drawings. 1st
The figure shows a schematic block diagram of a recording system when the audio recording method of the present invention is adopted.

In FIG. 1, the first . The audio signal of the second audio channel is analog
Digital (A/D) ffi converter 5.

6, the signal is converted into a digital signal and supplied to a digital modulator 9. On the other hand, the recording start signal inputted to the input terminal 3 is supplied to the pilot signal generator 7 and the address signal generator 8, and at this time, the pilot signal generator 7 sends the signal for a predetermined period of time T1 immediately after the start of recording, as shown in FIG. Only'H
” (High) or °% L u (Low) is generated and the digital modulator 9
supplied to Note that this time width T1 is sufficiently longer than the time of digital data, and is suitably several hundred m5ec, for example. Therefore, after the predetermined time T has elapsed, the digital audio signal from the A/D converter 5.6 and the address signal from the address signal generator 8 are added with an error correction code in the digital modulator 9 and converted into digital signals such as PCM. After being modulated, the signal is applied to an FM modulator 10, where it is FM-modulated using coded digital data. Here, as the FM carrier frequency of the FM modulator 10, the carrier frequency of "Hn,""L" of digital data is V
It is selected to exactly match the FM carrier frequencies of 3.43 MHz and 3.73 MH2 for the two audio channels of the HD system. In other words, as shown in Figure 3, FM
The input gain data string to the modulator IO is f+1=1
The spectral distribution becomes 0 with peaks at 43 MHz) and f2 (=3.73 MHz).

On the other hand, the video signal input to the input terminal 4 is supplied to a video signal processing circuit 11, where it is subjected to appropriate signal processing such as chroma low-frequency conversion and pre-emphasis, and then supplied to a mixing circuit 12. In the mixing circuit 12, the FM modulator 10
The FM wave of digital audio obtained from the video signal processing circuit 11 and the video signal after signal processing obtained from the video signal processing circuit 11 are mixed and supplied to the FM modulator I3, where they are modulated into an FM signal to be recorded on the disk. The spectra of the input and output signals of this FM modulator 13 are shown in FIGS. 4 and 5, respectively.

This is the same as in the case of FM recording on a disc according to the conventional general analog audio FM recording method.

The above is an overview of the digital audio processing and pilot signal processing operations of the recording system when audio signals are digitally coded and recorded on a disc according to the method of the present invention.

Next, an example of a video disc reproducing apparatus suitable for reproducing a disc recorded according to the recording method of the present invention will be described with reference to the drawings in FIG. 6 and subsequent figures.

Pick-up device in Figure 6! 4 detects a disk recording FM signal, which is amplified by a preamplifier 15 and then supplied to an FM demodulator 16 where it is FM demodulated. As shown in FIG. 4, this demodulated signal is obtained in a state in which a video signal of a luminance signal and a color signal and an audio FM signal are mixed. The middle video signal component is filtered through a low-pass filter I7.
The signal is supplied to the video signal processing circuit via the video signal processing circuit, where it is subjected to appropriate signal processing such as dropout compensation, chroma high-frequency conversion, and time base correction, and a standard color video signal is derived to the video output terminal 19.

On the other hand, the audio FM signal is separated into two FM carriers, fl and T2, through a bandpass filter 20.degree. 21, and is supplied to the next stage FM demodulator 22, 23 for FM demodulation.

The demodulated output of the FM demodulator 22 is sent to the pilot signal detection circuit 2.
4, and the pilot signal is detected by an operation described in detail later.

When the pilot signal is detected in this detection circuit 24, the switches of the switching circuits 26, 27, and 28 are respectively switched to the terminal (2) side. In this case F
The digital audio signal obtained as the demodulated output of the M demodulator 22 is supplied to the digital audio signal processing circuit 30 via the switching circuit 25, where it undergoes appropriate processing such as digital code demodulation, error detection and correction, and D/A conversion. As a result, a high quality audio signal is delivered via the switching circuit 26.27 to the audio output terminal 31.32.

Next, the above pilot signal detection operation will be explained in more detail. When a digital audio FM recording disk is played back, since a pilot signal is recorded in advance at the recording start position of the digital audio signal, a digital signal as shown in FIG. 7 is output as the demodulated output of the FM demodulator 22. The signal is supplied to the pilot signal detection circuit 24. In this case, before the digital audio signal, for the time T1
A pilot signal maintained at a level is derived. The pilot signal detection circuit 24 is composed of a one-shot multi-circuit 33 of a ridrigger type and a seven-lip-flop circuit 34, as shown in FIG. 8, for example, and the digital signal shown in FIG. 33, the one-shot multi-circuit 33 is triggered at the rising edge of the pulse. Here, it is assumed that the time width T2 of the one-shot pulse is set in advance by a resistor R1 and a capacitor C+ attached to the one-shot multi-circuit 33 to satisfy the following relationship: T3 << T2 << T + . However, here T3 is the unit pulse width of digital data, which is usually 1.
Because it is less than μsec? The one-shot pulse width T2 may be selected to be, for example, about I"Sec. At this time, the output of the one-shot multi circuit 33 changes from 'H# to "L" only within the pilot signal detection period Tl, as shown in FIG. During other periods, that is, during digital data periods, it is always maintained at the "H" level. When the output of the one-shot multi-circuit 33 transitions from 'Hn to L', the subsequent 7-rip 70-tube circuit 34 is set, and its output is inverted from L to H as shown in FIG. 7O. Thereafter, it is maintained at the "H" level.As a result, when the pilot signal detection circuit 24 detects the pilot signal recorded at the recording start position of the digital audio signal, the detection signal is always at the "H" level. The voltage is applied to the switching circuits 25, 26, and 27, and the switches of each of the switching circuits 25, 26, and 27 are switched to the terminal (2) as described above.

Next, the operation when an analog audio FM recording disk is played back in the above playback device will be explained. In this case, the operations of the pickup device +4, the preamplifier I5, the FM demodulator 16, the low-pass filter 18, and the video signal processing circuit are the same as in the case of the reproduction operation of the digital audio FM recording disk described above. Explanation will be omitted.

The demodulated output of the FM demodulator 16 is passed through a bandpass filter 20.
The signal is separated into two FM carriers, fl and 12, by 21 and supplied to FM demodulators 22 and 28, respectively. The FM demodulator 22 demodulates the analog audio signal of the first audio channel, and the FM demodulator 23 demodulates the analog audio signal of the second audio channel.

In this case, the demodulated analog audio signal does not contain the pilot signal, so the output of the pilot signal detection circuit 24 is always at the "L" level, and the switches of each switching circuit 25, 26, and 27 are connected to terminal 0. It has been switched to the side. Therefore, in this case, the audio signal of the first channel is supplied to the analog audio signal processing circuit 28 via the switching circuit 25, where it is subjected to appropriate signal processing such as decoding and noise reduction, and then transferred to the switching circuit 25. 26 to the audio output terminal 31. Similarly, the audio signal of the second channel is subjected to appropriate signal processing in the analog audio signal processing circuit 29 and then sent to the audio output terminal 32 via the switching circuit 27.
is derived.

<Effects of the Invention> According to the video disc audio recording method and formula of the present invention, when a digital audio signal converted into a digital signal as described above is FM modulated and recorded on a disc, the "H" of the digital audio signal is , "L" signal level carrier frequency is used in the first . Since the frequency is set to be the same as the FM carrier frequency of the second audio channel, there is no risk of beat interference with the video signal.

Furthermore, according to the recording method of the present invention, since a pilot signal is recorded at the recording start position of a digital audio signal, the video disc player detects the presence or absence of this pilot signal to determine whether the disc is analog audio recording. It is possible to determine whether the disc is digital audio recording, and by switching the audio processing circuit, it is possible to play back discs with both recording systems.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a recording system according to the video disc audio recording method of the present invention, FIG. 2 is a waveform diagram of a digital audio signal according to the same recording method, and FIG. 3 is an FM in FIG.
A modulation operation characteristic diagram of the modulator 10, FIG. 4 shows the input signal spectrum of the FM modulator 13 in FIG. 1, and FIG. 5 shows the input signal spectrum of the FM modulator 13 in FIG.
The output signal spectrum of the M modulator 13, FIG. 6 is a block diagram of a video disc playback device for playing back a video disc recorded by the recording method of the present invention, and FIG. 7 shows the pilot signal generation in the same video disc playback device. FIG. 8 is a signal waveform diagram for explaining the operation of the circuit, and is a specific circuit configuration diagram of the pilot signal generation circuit. 5.6... A/D converter, 7... Pilot signal generator, 8... Address signal generator, 9... Digital modulator, ]0... FM modulator. Oshiiri #Oshite 児 + Hibiki Sound C Sen 9 &) JLJ Chou 3 Figure 84 Figure Attribute 5 Figure

Claims (1)

[Claims] 1. In an audio recording method in which an audio signal converted into a digital signal is FM-modulated and recorded on a video disc, the FM carrier frequency of the "H" and "L" signal levels of the digital audio signal is used in an analog audio FM recording method. A video disc audio characterized in that the frequency is set to be the same as the FM carrier frequency of the adopted first and second audio channels, and a pilot signal is recorded at the recording start position of the digital audio signal. Recording method.