JPH05342762A - Voice reproduction circuit - Google Patents

Abstract

PURPOSE:To reproduce voice information from an optical type recording medium with a different recording density in which video information and voice information are recorded with one device for reproducing an optical type recording medium. CONSTITUTION:An information signal in which a voice signal is recorded on a video signal multiplexed in frequency as pit train on an optical type recording medium 1 with a low density of a memory capacity is read out with an optical head 2 which is adapted to reproduce an optical type recording medium 1 with a high density of the memory capacity. An RF signal 4 generated by a pre- amplifier 3 is passed through an amplifier 5 and a peak holding circuit 6 and an envelop alone of the RF signal 4 corresponding to a land part of the optical type recording medium 1 is extracted, generated and passed through a low pass filter 4 to separate a voice signal only. Moreover, the voice signal is passed through a deemphasis 9, waveform shaper 10 and a digital voice processing circuit 11 to reproduce a voice better.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio reproduction circuit for separating and demodulating an audio signal from a reproduction signal obtained from an optical recording medium in which video information and audio information are recorded as a pit string corresponding to the video information. Regarding

[0002]

2. Description of the Related Art Video disks and compact disks are used as media for reproducing video and audio information using laser light.

Of these, in the existing video disc, an NTSC video signal is frequency-multiplexed and recorded together with a digital audio signal. By the way, in recent years, N
Research and development of high-definition video discs for recording high-definition signals instead of TSC signals are in progress. Currently, HDTV discs that record MUSE-type HDTV signals (hereinafter referred to as MUS
E-discs) and high-definition video discs (hereinafter referred to as base-band discs) that record baseband high-definition signals.

The MUSE disk is a disk for FM-modulating and recording a MUSE signal generated by band-compressing a high-definition image. On the other hand, a baseband disc is a disc in which a high-definition baseband signal is divided into two and recorded on both sides of the disc, and at the time of reproduction, two signals on both sides of the disc are combined to obtain one high-definition image. Is.

The signal band of the MUSE signal is about twice that of the NTSC signal, and the base band signal is about five times or more that of the NTSC signal. Among them, in the MUSE disc, since the linear velocity of the disc is determined so that the highest frequency of the recording signal becomes the lowest bit on the disc, it is about 2 as compared with the existing video disc recording the NTSC signal. It is necessary to play back at double the linear velocity. However, when the linear velocity at the time of reproduction doubles like this,
If the storage capacities of the discs are the same, the recordable time is half that of existing video discs.

In the base band disc,
Although the signal band is about twice that of the MUSE signal, the linear velocity is about the same as that of the MUSE disc because the method of simultaneously reading information from both sides of the disc is adopted during reproduction. However, the recordable time is 1/4 of the existing disc when the storage capacities of the discs are the same.

As described above, when the above-mentioned high-definition signal is recorded on the disc, the recording time becomes short with the current storage capacity of the optical disc. Currently, a video disc having a diameter of 30 cm which stores the NTSC signal can store for about 120 minutes, but if the storage capacity of the disc is the same, it takes about 60 minutes for a MUSE disc and about a baseband disc. I can only remember for 30 minutes. Under such a background, development of an optical disc having a larger storage capacity has been earnestly desired.

As one of the methods for increasing the storage capacity of the disk, by reducing the size of the pits, the number of pits that can be formed on the track is increased and the storage density is increased.
It is conceivable to increase the storage capacity of the optical recording medium. That is, by reducing the size of the pits, the number of pits that can be formed on the track is increased, thereby improving the recording density. Such a disc
Reproduction is possible by using a laser having a short wavelength as a light source and reducing the spot diameter on the optical disk.

[0009]

When a high-definition video disc having an existing pit shape is reproduced by the reproducing device capable of reproducing the high-definition high-definition video disc, the reproduction spot diameter is larger than that of the reproduction spot diameter.
Since the recording pit is large, RF
The signal becomes louder. In this case, the S / N ratio of the video signal increases, but the shape of the reproduced RF signal waveform on the side corresponding to the pit, which has a low disc reflectance, is distorted, and the entire RF signal on the pit side is enveloped. Also becomes saturated.

When the PCM audio signal is frequency-multiplexed in the low frequency band of the video signal, the PCM audio signal is reproduced R
It appears in the envelope of the F signal. Conventionally, the reproduced RF signal is passed through a low-pass filter to convert the reproduced signal from the PCM.
The audio signal is separated. However, play R
When the envelope of the F signal shows a saturation tendency, the separated PCM audio signal is distorted compared to the original waveform even if the PCM audio which is low-frequency multiplexed from the RF signal is frequency-separated by this conventional method. Therefore, there is a problem that the demodulated voice data has many errors.

Therefore, in the present invention, even in a reproducing apparatus set as a high density optical recording medium,
It is an object of the present invention to favorably reproduce voice data recorded on a low density optical recording medium.

[0012]

In order to solve the above-mentioned problems, the present invention uses an optical head to record an information signal in which an audio signal is frequency-multiplexed with a video signal as a pit train on an optical recording medium. In the audio reproduction circuit that reads out and separates only the audio signal component from the read signal to demodulate audio information, in the reproduction waveform obtained from the information signal on the optical recording medium, the optical head It is characterized in that a circuit for extracting an envelope component while scanning a part and a circuit for generating the extracted signal into an audio signal are provided.

[0013]

When a medium having a current pit shape in which an audio signal is frequency-multiplexed in the low frequency range of a video signal is reproduced by a reproducing device capable of reproducing a medium having a high density recording and having a small pit shape, a spot of a reproduction beam Due to the fact that the pits are larger than the diameter, the waveform of the reproduction RF signal during the period in which the beam scans the pits is distorted. However, when the beam scans the land portion between the pits, the beam is only reflected similarly regardless of the distinction between high density recording and low density recording,
No distortion occurs in the reproduced RF signal. On the other hand, the audio signal appears not only in the envelope on the pit scanning side but also in the envelope on the land scanning side in the reproduction RF signal.

In the present invention, paying attention to such a phenomenon, the extraction circuit extracts the envelope on the land scanning side, and the generation circuit generates it as an audio signal. Therefore, it is possible to extract and reproduce an audio signal without waveform distortion.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the embodiment. Figure 1
In the figure, reference numeral 1 denotes an optical disc in which a video signal and an audio signal are frequency-multiplexed and recorded. The method of frequency multiplexing these two signals is equivalent to that of the existing video disc.

Reference numeral 2 denotes an optical head, which enables reproduction even when the pit shape on the optical disc 1 is smaller than that of an existing video disc, that is, when information is recorded at high density on the optical disc 1. The shape of the spot on the disc is set.

A preamplifier 3 outputs an RF signal by converting the output from the optical head 2 into a current voltage.
The waveform of such an RF signal is shown in FIG. Here, the preamplifier 3 has a positive polarity when the beam scans the pits of the optical disk 1, and has a negative polarity when the beam scans the mirror surface (land) between the pits. Is set to indicate.

FIG. 3A shows a signal waveform when a high density recording disk having small pits is reproduced,
FIG. 3B shows a signal waveform when a low-density recording disk having large pits is reproduced.

An amplifier 5 inverts the polarity of the RF signal supplied from the preamplifier 3. A peak hold circuit 6 holds the positive peak value of the signal supplied from the amplifier 5. Details of the peak hold circuit 6 will be described later. The output signal from the peak-hold circuit 6 has a stepwise waveform as shown in FIG. Such a signal is passed through the low pass filter 7 to obtain the signal shown in FIG.
The signal has a waveform as shown in (b).

Reference numeral 9 is a de-emphasis circuit, which flattens the low-frequency portion of the waveform as shown in FIG. Reference numeral 10 shapes the waveform de-emphasized by the waveform shaper into a pulse waveform. Reference numeral 11 converts the pulse waveform whose waveform has been shaped by the digital voice processing circuit into an analog signal.

In the present embodiment, the operation when an optical disc in which recording information is recorded at a low density is reproduced will be described. First, the information from the optical disc 1 is read by the optical head 2. The read information is sent to the preamplifier 3. Reproduction RF output from the preamplifier 3
The signal is as shown in FIG.

The reproduced RF signal is inverted and amplified by the amplifier 5, sent to the video signal processing system, demodulated as a video signal, and sent to the peak hold circuit. The peak hold circuit 6 holds the positive side of the signal supplied from the amplifier 5, that is, the peak value of the signal corresponding to the land of the optical disc 1. Peak hold circuit 6
The output signal from has a step-like waveform as shown in FIG. 4 (a) in which the peak value of the RF signal is held. This signal is passed through the low-pass filter 7 to remove the high frequency component in the staircase portion, and becomes a signal having a waveform as shown in FIG. 4 (b).

In the peak hold circuit 6, since the polarity of the RF signal is inverted by the amplifier 5, the peak hold circuit 6 is
The peak on the side where the waveform distortion is not generated is held when the system scans the land. Therefore, the signal that has passed through the low-pass filter 7 is the envelope of the RF signal.
It shows the waveform on the side without waveform distortion. As described above, the envelope is a frequency-multiplexed PC.
M audio signal is shown. Therefore, the PCM audio signal can be reproduced by appropriately processing the signal that has passed through the filter 7.

The reproduction of the PCM audio signal is performed by the de-emphasis circuit 9, the waveform shaper 10, and the digital audio processing circuit 11 in the subsequent stage. That is, the signal passed through the filter 7 is passed through the de-emphasis circuit 9
The low-frequency part of the waveform is flattened, and the waveform shaper 10 shapes the pulse waveform. The pulse-shaped pulse waveform is reproduced as a good analog voice signal by passing through the digital voice processing circuit 11.

In the above embodiment, the RF signal 4 output from the preamplifier 3 is set to have a positive polarity when scanning a pit and to have a negative polarity when scanning a land. However, even when the RF signal 4 output from the preamplifier 3 is set to have a negative polarity when scanning the pit and to have a positive polarity when scanning the land, as shown in FIG. If amplifier 3 is a common-mode amplifier,
The same result as that of the above embodiment can be obtained.

Further, in the above-described embodiment, the preamplifier 3 having an output swinging in positive and negative is adopted, but the preamplifier 3 having an output swinging in positive polarity or negative polarity can be adopted. However, in this case, it is necessary to appropriately change the offset value of the amplifier 5.

In the above embodiment, the following is an example of the peak hold circuit 6 of FIG. 1 for detecting the peak hold of the RF signal.

Peak hold detection in the example of FIG.
This is a detection method in which the 0 cross point of the AC input RF signal that changes from negative to positive is detected, the zero cross point is reset for a certain period of time, peak hold is started, and the peak value of the RF signal is detected. According to this method, even if the peak value of the amplitude of the RF waveform is lower than the peak value of the previous amplitude, the value is temporarily reset, so that the previous value does not remain and the figure approximates to the envelope shape. A waveform like 4 (a) is obtained.

As another method of detecting the peak hold, as shown in FIG. 6, a peak between the zero cross point from the negative to the positive of the RF signal input to the AC and the zero cross from the positive to the negative (amplitude waveform). There is a detection method in which the level and timing of the black point are sampled by a microcomputer and only the sampled peak points are reproduced.

[0030]

By using the audio reproducing circuit of the present invention, even when the reproducing head for a high recording density optical recording medium reproduces an optical recording medium having a recording density lower than the detection capability of the reproducing head. The audio signal frequency-multiplexed in the low range of the video signal recorded on the optical recording medium can be reproduced well. This brings about an effect that the optical recording media having different recording densities can be reproduced by one reproducing apparatus for the optical recording medium.

[Brief description of drawings]

FIG. 1 is a principle / configuration diagram of an audio reproducing circuit according to an embodiment.

FIG. 2 is an RF obtained from the optical head in this embodiment.
It is a figure which shows a signal waveform.

FIG. 3 is a diagram showing an RF signal in which a PCM audio signal is multiplexed in the low frequency band of the video signal of the present embodiment.

FIG. 4 is an explanatory diagram showing an operation of separating an audio signal by peak hold according to the present embodiment.

FIG. 5 is an explanatory diagram showing an example of the operation of the peak hold circuit of the present embodiment.

FIG. 6 is an explanatory diagram showing an example of the operation of the peak hold circuit by digital processing according to the present embodiment.

[Explanation of symbols]

 1 optical disk 2 optical head 5 amplifier 6 peak hold circuit 7 low-pass filter 9 de-emphasis 10 waveform shaper 11 digital audio processing circuit

Claims (1)

[Claims] 1. An audio signal in which an audio signal is recorded as a pit train on an optical recording medium in which an audio signal is frequency-multiplexed with a video signal and recorded by an optical head, and only an audio signal component is separated from the read signal to produce a sound. A circuit for extracting an envelope component of a reproduced waveform obtained from an information signal on an optical recording medium in an audio reproducing circuit for demodulating information when the optical head scans a portion between pits. And a circuit for generating the extracted signal into an audio signal, the audio reproduction circuit.