JPS61222066A - Video disk sound processing device - Google Patents

Abstract

PURPOSE:To reproduce video disks different in kind by automatically switching from an analog sound signal processing circuit to a digital sound, signal processing device at the time of detection of a pilot signal recorded at the recording start position of the digital sound signal. CONSTITUTION:The record signals from a digital sound FM recording disk or an analog sound FM recording disk are detected by a pickup device 14 and supplied through a preamplifier 15 to a FM demodulator 16. The demodulated signals are supplied through a LPF 17 to a video signal processing circuit 18 while being also supplied through BPFs 20, 21 to FM demodulators 22, 23, respectively. The demodulated signals of a demodulator 22 is supplied to a pilot signal detecting circuit 24 and the circuit 24 detects the pilot signals recorded at the recording start position of the digital sound signals. The switching signals 25 to 27 are automatically switched at the time of detection of the pilot signals at the circuit 24. In such a manner, the video disks different in kind can be reproduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a video disc (digital audio FM recording disc) in which an analog audio signal is converted into a digital audio signal and then FM modulated and recorded, and an analog audio signal is converted into an FM signal as it is. The present invention relates to an audio processing device for a video disc playback device that is capable of playing back both a modulated and recorded video disc (analog audio FM recording disc) and a video disc recorded with modulation.

<Summary of the Invention> The present invention provides a video disc playback device that incorporates an analog audio signal processing circuit and a digital audio signal processing circuit and is capable of playing back both digital audio FM recording discs and analog audio FM recording discs. The operation is automatically switched from an analog audio signal processing circuit to a digital audio signal processing circuit when a pilot signal recorded at a recording start position of a digital audio signal is detected.

<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 digital audio FM recording 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 as an FM.
In this case, it is possible to reduce the influence of noise caused by missing reproduced signals, and it is also effective because it can reproduce audio of higher commercial quality than the analog audio FM recording method.

For this reason, a video disc reproducing apparatus capable of reproducing both analog audio FM recording discs and digital audio FM recording discs can be considered.

<Problems to be Solved by the Invention> However, in such a video disc playback device, it is necessary to use two independent circuits, one for analog signal processing and one for digital signal processing, as audio signal processing circuits. Moreover, the user had to switch the operation of the two audio signal processing circuits each time depending on the disc to be played.

<Means for Solving the Problems> The present invention has been made in view of the above points, and includes a pilot signal detection circuit that detects a pilot signal recorded at the recording start position of a digital audio signal. When the detection circuit detects the pilot signal, the operation is automatically switched from the analog audio signal processing circuit to the digital audio signal processing circuit.

<Examples> The present invention will be described below according to examples shown in the drawings. First, the operation when FM recording a digital audio signal on a video disc applied to the video disc playback apparatus according to the present invention will be explained. FIG. 2 shows a schematic block diagram of the recording system.

In FIG. 2, the first . The audio signal of the second audio channel is analog
The signal is converted into a digital signal by a digital (A/D) converter 5.6 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 outputs the signal for a predetermined time T1 immediately after the start of recording, as shown in FIG. A pilot signal maintained at only 'H' (High) or 'L' (LOW) is generated and supplied to the digital modulator 9. Note that this time width T is sufficiently long compared to the time of digital data,
For example, several hundred m5ec is appropriate. Therefore, after the predetermined time T1 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 are subjected to digital modulation such as PCM. After that, the signal is applied to the FM modulator 10 and FM-modulated using coded digital data. Here, the FM carrier frequency of the FM modulator lO is H'''It of digital data.
3,43MH where the carrier frequency of L 71 is the FM carrier frequency of the two audio channels of the VHD system
2: Select to exactly match 3.73 MHz.

In other words, as shown in FIG.
Spectral distribution with a peak at (=3.73MH2) 0
becomes.

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 waves of the digital audio obtained from the video signal processing circuit 11 and the signal-processed video signal obtained from the video signal processing circuit 11 are mixed and supplied to the FM modulator 13, where they are converted into an FM signal to be recorded on the disk. The recorded FM signal thus obtained is recorded on the disk surface by a well-known method using a magnetic head or a laser beam.

Note that the spectra of the input and output signals of the FM modulator 13 in this case are shown in FIG. 5 and FIG. 6, 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 an audio signal is digitally coded and recorded on a disc.

FIG. 1 shows one embodiment of the video disc audio processing apparatus of the present invention. Here, the reproduction operation of a digital audio FM recording disc recorded in the above method will first be explained.

In FIG. 1, a disk recording FM signal is detected by a pickup device 14, and after being amplified by a preamplifier 15, it is supplied to an FM demodulator 16 where it is FM demodulated. As shown in FIG. 5, 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 17.
The signal is supplied to the video signal processing circuit via the video signal processing circuit, where appropriate signal processing such as dropout compensation, chroma high frequency conversion, time pace correction, etc. is performed, 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, f+ and T2, via bandpass filters 20 and 21, and is supplied to the next stage FM demodulator 22 and 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 81.32.

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, a pilot signal maintained at the "H" level for a time T1 is derived before the digital audio signal. The pilot signal detection circuit 24 is composed of, for example, a one-shot multi-circuit 33 of the ridrigger type and a flip-flop circuit 34, as shown in FIG. 8, 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 the resistor R1 and capacitor C1 attached to the one-shot multi-circuit 33 so as to satisfy the following relationship: T3 << Tz << T+. However, here T3 is the unit pulse width of digital data, which is usually 1
Since the one-shot pulse width T2 is less than μsec, the one-shot pulse width T2 may be selected to be, for example, about 1"SeC. At this time, the output of the one-shot multi-circuit 33 is only within the detection period T of the pilot signal, as shown in FIG. It is inverted from "H" to L, and is always maintained at "H" level during other periods, that is, during digital data periods. Then, at the falling edge when the output of the one-shot multi-circuit 33 changes from "H" to "L", the flip-flop circuit 34 in the subsequent stage is set, and its output is reversed from 'L' to 'H' as shown in FIG. and thereafter maintained at the "Hjl 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, a detection signal of "H" level is always applied to the switching circuit 25. As described above, the switches of each of the switching circuits 25, 26, and 27 are switched to the terminal (2) side.

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 pink-up device +4, preamplifier 15, FM demodulator 16, low-pass filter 8, and video signal processing circuit are the same as in the case of the reproduction operation of the digital audio FM recording disk described above. The explanation will be omitted.

The demodulated output of the FM demodulator 16 is passed through a bandpass filter 20.
2] into two FM carriers, fl and 12, and are supplied to FM demodulators 22 and 23, 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 "Ln level", and the switches of the switching circuits 25, 26, and 27 are on the terminal 0 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 appropriate signal processing such as decoding and noise reduction is performed. After that, the audio signal of the second channel is outputted to the audio output terminal 31 via the switching circuit 26.Similarly, the audio signal of the second channel is subjected to appropriate signal processing in the analog audio signal processing circuit 29, and then outputted via the switching circuit 27. and is led out to the audio output terminal 32.

<Effects of the Invention> Thus, according to the video disc audio processing device of the present invention, the pilot signal recorded in advance on the disc, especially at the recording restart position of the digital audio signal, is detected in advance by the pilot signal detection circuit 24, and this detection output is detected in advance. The switching circuits 25, 26, and 27 are switched based on the disc being played, and the signal processing circuits 28, 29, and 30 according to the disc to be played perform appropriate audio signal processing operations. There is no need to switch modes.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of one embodiment of the video disc audio processing device of the present invention, Fig. 2 is a block diagram of a recording system for FM recording a digital audio signal on a disc, and Fig. 3 is a waveform of the digital audio signal. Figure 4 is F in Figure 2.
The modulation operation characteristic diagram of the M modulator lO, FIG. 5 shows the input signal spectrum of the FM modulator 13 in FIG. 1, and FIG. 6 shows the input signal spectrum of the FM modulator 13 in FIG.
The output signal spectrum of the same FM modulator, Fig. 7 is a signal waveform diagram for explaining the operation of the pilot signal detection circuit, and Fig. 8
The figure is a specific circuit configuration diagram of the pilot signal detection circuit. 22, 23... FM demodulator, 24... Pilot signal detection circuit, 28.29... Analog audio signal processing circuit, 30... Digital audio signal processing circuit. Agent Patent Attorney Aihiko Fukushi (and 2 others) - 11 - Shu d! Figure 4 Figure 5 Figure 11m &/MHz Figure 7

Claims (1)

[Claims] 1. A video disc that has a built-in analog audio signal processing circuit and a digital audio signal processing circuit, converts the analog audio signal into a digital audio signal, and then performs FM modulation and records it;
A pilot signal detection method for detecting a pilot signal recorded at a recording start position of a digital audio signal in a video disc playback device capable of playing back both a video disc and a video disc recorded by FM modulating an analog audio signal. 1. A video disc audio processing device comprising: a circuit for automatically switching operation from an analog audio signal processing circuit to a digital audio signal processing circuit when the detection circuit detects a pilot signal.