JPS5837816A - Pcm sound recorder and reproducer - Google Patents

Abstract

PURPOSE:To prevent assuredly the misjudgement between a carrier dropout and a data synchronizing signal, by detecting the carrier dropout when a PCM signal is reproduced and setting forcibly the data signal at a prescribed level. CONSTITUTION:A detector 15 detects the amplitude of the carrier signal of the output of an equalizer 4, and produces ''1'' when a dropout is caused and then ''0'' in the normal mode, respectively. The switching of a gate 16 is controlled by the outputs ''1'' and ''0''. When the output is ''1'', the data signal given from a comparator 14 is fed as it is to a terminal Y. While the data signal from the comparator 14 is cut off with the output ''1'' to keep the terminal Y forcibly at ''1''.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PCM recording and reproducing apparatus for recording and reproducing audio signals according to the PCM method using a video tape recorder (hereinafter referred to as a VTR) or a part thereof.

Figures 1 and 2 show the PCM signal format shown in the consumer PCM encoder/decoder technology file determined by the Japan Electronics Industry Association. Figure 1 shows the PCM signal format compliant with standard television signals. Figure 1(a) shows the data arrangement and structure of the odd field; Fig. 1(b) shows the data arrangement and structure of the even field; Fig. 1(C) shows the vertical signal section. The details of the vertical synchronization signal 1 equalization pulse signal in FIG.
Figure (d) similarly shows the details of the vertical synchronization signal and equalization pulse signal in Figure 1 (b).
This figure shows the arrangement and structure of the horizontal signal portion of the signal format, and FIG. 2 (-) excludes the arrangement and structure of each pit in one horizontal signal portion. This signal waveform conforms to the television signal, but the signal obtained by slicing this signal at level 2, that is, the PCM data signal part, is shown in Figure 2 (bl). The PCMN period signal section is shown in FIG. 2 (0).

As can be seen from these figures, a data synchronization signal "1o10" is added to the beginning of each horizontal signal section, a white reference signal is added to the end, and 1
The horizontal signal section consists of 168 bits. In addition,
Here, we are talking about a signal format that complies with the 525-line standard television system, but for the signal format that complies with the 625-line standard television system, the signal format itself differs only in some parts of the format. Since they are the same, it can be considered in the same way as the case of 625 lines.

Figure 3 shows a conventional PCM signal that records and plays back such PCM signals.
This shows part of the playback system of the CM recording and playback device.

In Figure 3, A is the spatula section of channel 1, B is the head section of channel 2, 1 and 2 are head amplifiers that amplify the outputs of head sections A and B, and 3 is the head amplifier that mixes the outputs of head amplifiers 1 and 2. mixer, 4 is an equalizer circuit, 6 is a limiter, 16 is an FM demodulator, 7 is a carrier removal filter,
8 is an amplifier, 9 is a waveform shaping filter, IQ' is an automatic gain control circuit, 11 is a clamp circuit, and 12 is a comparator.
The synchronization signal shown in Figure (C) is reproduced and output to terminal X. On the other hand, 13 is an amplifier, and 14 is a comparator. The amplifier 13 and the comparator 14 reproduce the data signal shown in FIG. 2(b), and output it to the terminal Y.

Note that the 0 point in Figure 3 indicates the FM signal played from the magnetic tape.
A carrier signal appears, and the equalizer output of the carrier signal is lost at point D.

In such conventional PCM recording and playback devices, the second
'As can be seen from the figure, in order to synchronize one horizontal period when reproducing a PCM signal, it is necessary to detect the data synchronization signal "1010#" and synchronize one horizontal period. When dropout occurs, the output of terminal Y, that is, the data signal shown in FIG. 2(b), will have a certain probability of becoming "1010".

Then, this will be mistakenly judged as a data synchronization signal, causing a problem that the synchronization of subsequent PCM signal processing will be disrupted.

The present invention provides a PCM recording/playback device that solves these problems with a simple configuration.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5.

In FIG. 4, parts having the same functions as those in FIG. 3 are denoted by the same reference numerals, and explanations thereof will be omitted.

15 detects the amplitude of the carrier signal seen at the output point of the equalizer circuit 4, and when a carrier dropout occurs, it generates "1" as the output Z, and when it is normal, that is, when there is no carrier dropout. This is a carrier dropout detector that generates 0'' as output 2. 16 is the carrier dropout detector 16 mentioned above.
When the output 2 is 0'', the data signal from the comparator 14 is output as is to the terminal Y, and when the output 2 is 1'', the data signal from the comparator 14 is cut off. This is a gate circuit that forcibly sends 1'' to terminal Y.

In this way, even if a carrier dropout occurs, the data signal at the terminal Y can be forcibly set to 1'', and a dropout can be avoided.

Note that the gate circuit 16 can be specifically constructed of a tri-state circuit G1 as shown in FIG.

As described above, the present invention detects carrier dropout when reproducing a PCM signal, and when a dropout occurs, the level of the data signal is forcibly set to "1". This can reliably prevent the signal from being mistakenly judged as a data synchronization signal. Wear.

[Brief explanation of the drawing]

Figures 1 (a) to (d) are diagrams showing the format of the PCM signal, Figures 2 (al to (C) are diagrams showing the configuration of the first signal section, and Figure 3 is the conventional PCM recording and playback. FIG. 4 is a block diagram showing a part of the reproduction system of the apparatus, FIG. 4 is a block diagram of an embodiment of the present invention, and FIG. 6 is a block diagram showing the main parts thereof.A, B... Heads Part, 1.2... to...
amplifier, 3... mixer, 4... equalizer circuit, 5... limiter circuit, 6...
...FM demodulator, 7@...l' carrier removal filter, 8...Amplifier, 9...Waveform shaping filter, 10...Automatic gain control circuit,
11...Clamp circuit, 12...Comparator, 13...Amplifier, 14...Comparator, 16...Carrier 0 knob out Detector, 1
6...Gate circuit.

Claims (1)

[Claims] P played from a hard tape for a videotape recorder
A carrier dropout detector detects the carrier amplitude of the CM signal to detect the presence or absence of carrier dropout, and the opening/closing is controlled by the output of the carrier dropout detector, and when there is no carrier dropout, the regenerated data signal is A PCM recording/playback device characterized in that it is equipped with a gate circuit that outputs the data signal as is and forcibly sets the data signal to "1" when there is a carrier dropout.