JPH0557668B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to a digital signal reproducing device.

BACKGROUND TECHNIQUE Conventionally, there is a reproducing device that reproduces a digital signal obtained by A/D converting an analog signal from a recording medium on which the digital signal is recorded, and extracts the original analog signal by D/A converting the digital signal. There is. Disks, magnetic tapes, etc. are used as recording media for recording the above-mentioned digital signals. For this reason, the digital signal reproduced due to variations in the rotation of the disk and variations in the running of the magnetic tape during reproduction inevitably becomes a signal containing variations in the time axis.

FIG. 3 shows a block system diagram of an example of a conventional digital signal reproducing device. In the figure, reference numeral 1 denotes a rotary head type video tape recorder, which reproduces and outputs a pseudo video signal recorded on a track inclined in the longitudinal direction of a magnetic tape. This pseudo video signal is a signal in which a digital signal such as an NRZ modulated PCM signal is superimposed on a standard television system composite synchronization signal. The reproduced pseudo video signal is supplied to the PCM audio processor 2, where each bit of the NRZ modulated PCM signal is extracted and NRZ demodulated. The PCM signals obtained by this are sequentially written to memory,
After processing such as deinterleaving, the signals are sequentially read out using a stable clock signal generated within the processor 2 with no time axis fluctuations. The PCM signal thus obtained is subjected to processing such as error correction and then D/A converted into an analog signal, and if this analog signal is an audio signal, it is supplied to the speaker 3 and made to produce sound. Further, the PCM audio processor 2 supplies a composite synchronizing signal to the video tape recorder 1 to cause it to operate in synchronization.

Problems to be Solved by the Invention Since the conventional PCM processor 2 processes digital signals, jitter and ripples in the playback signal do not affect the recording and playback of audio signals, which are analog signals. Jitter, which is a problem during demodulation, is absorbed by the memory in the PCM processor 2, so a device to remove jitter and ripples is installed between the video tape recorder 1, which is the recorded signal playback section, and the PCM processor 2. It was considered pointless to do so. However, according to the applicant's experimental results, the reproduced audio obtained by inputting the signal from which jitter and ripples have been removed to a PCM processor has no distortion in the reproduced audio signal, and the jitter and ripples are not removed. It has become clear that this method is more audible than the conventional one.

Means and Effects for Solving the Problems The present invention provides a recorded signal reproducing section that reproduces a signal recorded on a recording medium in synchronization with a composite synchronization signal generated by a digital signal demodulating section, and A signal reading means generates a first clock signal synchronized with the reproduced signal, and reads the digital signal in the reproduced signal in synchronization with the first clock signal.
A second clock signal is generated based on the composite synchronization signal generated in the memory and the digital signal demodulator, and the digital signals are sequentially read out from the memory using the second clock signal to generate the reproduced signal. a digital signal waveform substitution section that is composed of a signal substitution means and has a power supply and ground independent of the recording signal reproducing section and the digital signal demodulation section; and a digital signal that generates a composite synchronization signal and substitutes it. This is a digital signal reproducing device consisting of a digital signal demodulating section that demodulates and converts the digital signal into an analog signal, and the digital signal waveform substitution section is installed between the recorded signal reproducing section and the digital signal demodulating section, and The waveform substitution section substitutes the reproduced signal with a signal having the same information as the reproduced signal and outputs the signal to the digital signal demodulation section. An embodiment thereof will be explained with reference to FIG. 1 and the following figures.

Embodiment FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, the same parts as in FIG. 3 are given the same reference numerals. In FIG. 1, numeral 1 denotes a video tape recorder which is a rotary head recording signal reproducing section, which reproduces and outputs a pseudo video signal recorded on a track inclined in the longitudinal direction of a magnetic tape. As shown in FIGS. 2A and 2B, this pseudo video signal is obtained by superimposing a digital signal such as an NRZ modulated PCM signal on a standard television system composite synchronization signal. The digital signal consists of 247 pulses following the equivalent pulse of one field's worth of composite sync signal.
It exists in a horizontal scanning period (the horizontal scanning period is represented by "H" in the figure), and a 128-bit digital signal a, for example, to which a synchronization bit is added is superimposed on each horizontal scanning period. The video tape recorder 1 described above is operated in synchronization with a composite synchronization signal c from a PCM audio processor 2, which will be described later, but the reproduced pseudo video signal b includes time axis fluctuations due to fluctuations in the running speed of the magnetic tape, etc. There is.

This reproduced pseudo video signal b is supplied to a data reading circuit 10 and a synchronizing signal separation circuit 11 in a signal waveform substitution device (digital signal waveform substitution section) 5. Here, the signal waveform substitution device 5 is separate from the video tape recorder 1 and the PCM audio processor 2, which will be described later, and has an independent power supply and ground. The synchronization signal separation circuit 11 separates and generates a composite synchronization signal from the reproduced pseudo video signal b and supplies it to the oscillation circuit 12 and the reading control circuit 13. The oscillation circuit 12 has a horizontal synchronizing signal separation circuit and a phase signal separation circuit.
It consists of a locked loop (PLL).
The horizontal synchronizing signal component of the composite synchronizing signal which is separated from the reproduced pseudo video signal and which itself includes time axis fluctuation is extracted, and is synchronized with this horizontal synchronizing signal to generate a first clock signal having a repetition frequency of 12 MHz, for example. This clock signal is supplied to the read control circuit 13.

The reading control circuit 13 uses the vertical and horizontal synchronizing signals of the composite synchronizing signal as a reference, and divides the frequency of the clock signal, for example, during the existence period of the digital signal a of the reproduced pseudo video signal as shown in FIGS. 2A and B. A latch pulse with a repetition frequency of 3 MHz is generated and supplied to the data reading circuit 10. At the same time, a write enable signal obtained by inverting the latch pulse and an address signal obtained by counting the latch pulse are supplied to the memory 14. As a result, the data reading circuit 10 latches only the digital signal a in the reproduced pseudo video signal and supplies it to the memory 14, and the digital signals are sequentially written into the memory 14. The data reading circuit 10, the synchronization signal separation circuit 11,
The oscillation circuit 12 and the reading control circuit 13 constitute a signal reading means.

The oscillation circuit 15 is composed of a horizontal synchronization signal separation circuit, a frame synchronization signal separation circuit, and a phase locked loop (PLL), and the PCM audio processor 2 generates a composite synchronization signal shown in FIG. c, extracts the horizontal synchronizing signal component of this composite synchronizing signal c, synchronizes with this horizontal synchronizing signal, and generates a second clock signal with a stable repetition frequency of 12 MHz with no time axis fluctuation. The signal is supplied to the read control circuit 16. Further, this second clock signal is frequency-divided to obtain a pulse signal with a repetition frequency of 3 MHz, and this pulse signal and a frame synchronization signal separated and generated from the composite synchronization signal c are supplied to the video signal generation circuit 17.

The video signal generation circuit 17 has the above repetition frequency.
A stable composite synchronization signal that is supplied with a 3MHz pulse signal and a frame synchronization signal, is delayed by time nH (n is a natural number, and H is one horizontal scanning period) from the composite synchronization signal c, and has no time axis fluctuation. d is generated and supplied to the read control circuit 16 and mixer 18. Note that the above-mentioned time nH is set to a value that is sufficiently larger than the time axis variation α of the reproduced pseudo video signal b output from the video tape recorder 1 with respect to the composite synchronization signal c. In this connection, the memory 14 has a storage capacity sufficient to store digital signals read within a time nH.

The readout control circuit 16 uses the vertical and horizontal synchronizing signals of the composite synchronizing signal d as a reference, divides the frequency of the pulse signal from the oscillation circuit 15, and divides the frequency of the pulse signal from the oscillation circuit 15 to generate a signal at the same timing as the digital signal presence timing in FIGS. 2A and B. An address signal and a read permission signal for reading out the digital data to be superimposed on the composite synchronization signal d from the memory 14 are generated and supplied to the memory 14. As a result, the digital signal a is read out from the memory 14 in the same order as when it was written, and is supplied to the mixer 18. The mixer 18 superimposes the digital signal a on the composite synchronization signal d, thereby obtaining a stable pseudo video signal e without time axis fluctuations shown in FIG. 2E, which is supplied to the PCM audio processor 2. . The oscillation circuit 15, readout control circuit 16, video signal generation circuit 17, and mixer 18 constitute a signal substitution means.

A PCM audio processor 2, which is a digital signal demodulator, supplies a composite synchronizing signal c to a video tape recorder 1 and a signal waveform substitution device 5. Further, the digital signal a is dispersed from the pseudo video signal e and NRZ demodulation is performed. obtained by this
PCM signals are sequentially written into memory, subjected to processing such as deinterleaving, and sequentially read out using a stable clock signal with no time axis fluctuations. The PCM signal thus obtained is subjected to processing such as error correction, then D/A converted to an audio signal which is an analog signal, and is supplied to the speaker 3 for sound generation.

Since the pseudo video signal e from which time axis fluctuations have been removed is supplied to the PCM audio processor 2, the arithmetic units that perform various processes within the processor 2 are not affected by time axis fluctuations, and the power supply of the processor 2, Ground potential etc. will not fluctuate. Therefore, the clock signal and PCM signal in the D/A converter become stable, and the obtained analog signal becomes distortion-free.

Note that the present invention is applicable not only to a digital signal reproducing apparatus that reproduces an audio PCM signal using a video tape recorder, but also to a digital signal reproducing apparatus using a fixed head digital tape recorder, or a digital signal reproducing apparatus such as a digital audio disk. It can also be applied to a playback device, and is not limited to the above embodiment.

Effects of the Invention As described above, the digital signal reproducing apparatus of the present invention includes a recording signal reproducing section that reproduces a signal recorded on a recording medium in synchronization with a composite synchronization signal generated by a digital signal demodulating section, and a recording medium. A signal reading means generates a first clock signal synchronized with the reproduced signal, and reads the digital signal in the reproduced signal in synchronization with the first clock signal; A second clock signal is generated based on the composite synchronization signal generated in the memory and the digital signal demodulator, and the second clock signal is used to sequentially read the digital signals from the memory and replace the reproduction signal. a digital signal waveform substitute section, which is composed of a substitute means and has a power supply and ground independent of the recorded signal reproducing section and the digital signal demodulating section; and a digital signal waveform substitute section that generates a composite synchronization signal and demodulates the substituted digital signal. A digital signal reproducing device comprising a digital signal demodulating section that converts a digital signal into an analog signal; Since the section replaces the reproduced signal with a signal having the same information as the reproduced signal and outputs it to the digital signal demodulation section, the processing circuit that is supplied with the substitute signal from the digital signal waveform substitution section and outputs the analog signal is jittered. The processing circuit's power supply and ground potential do not fluctuate, and the clock signal and digital signal in the D/A converter are stable, making the resulting analog signal distortion-free and of high quality. It has the following features:

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an embodiment of the present invention.
Figure 2 is a signal waveform diagram of each part of the device shown in Figure 1.
The figure is a block system diagram of an example of a conventional digital signal reproducing device. 1... Video tape recorder, 2... PCM audio processor, 5... Signal waveform substitution device,
10...Data reading circuit, 11...Synchronizing signal separation circuit, 12, 15...Oscillating circuit, 13...Reading control circuit, 14...Memory, 16...Reading control circuit, 17...Video signal generation circuit, 18...Mixer.

Claims (1)

[Claims] 1. A recorded signal reproducing section that reproduces a signal recorded on a recording medium in synchronization with a composite synchronization signal generated by a digital signal demodulation section; a signal reading means for generating a first clock signal and reading a digital signal in the reproduced signal in synchronization with the first clock signal; and a signal reading means for synchronizing the read digital signal with the first clock signal. A second clock signal is generated based on a memory to be written in sequentially and a composite synchronization signal generated within the digital signal demodulation section, and digital signals are sequentially read out from the memory using the second clock signal to replace the reproduced signal. a signal alternative means, and
a digital signal waveform substitution section having a power supply and ground independent of the recording signal reproducing section and the digital signal demodulation section; generating the composite synchronization signal and demodulating the substituted digital signal into an analog signal; A digital signal reproducing device configured with the digital signal demodulating section for converting the digital signal, the digital signal waveform substituting section being installed between the recording signal reproducing section and the digital signal demodulating section, and the digital signal waveform substituting section 2. A digital signal reproducing device, wherein the reproduced signal is replaced with a signal having the same information as the reproduced signal and outputted to the digital signal demodulator.