JPH0520828B2 - - Google Patents

Description

[Detailed description of the invention] For example, an audio signal is encoded by PCM etc.
When recording and reproducing (transmitting) information on a magnetic tape or the like, a correction code is added to detect and correct errors during transmission.

For example, CRC (Cyclic Redundancy)
In an error detection code called CRC, a code expressed as a polynomial whose coefficients are information bits is divided by a generator polynomial, and the remainder is encoded to be added to the information bits as a CRC code. In decoding, the received code including the CRC code is divided by the generator polynomial, and if the remainder is 0, it is determined that no error has occurred, and if there is some remainder, it can be detected that an error has occurred. It is.

In this way, errors can be detected. Furthermore, errors can be corrected using this code signal.

By the way, when an audio signal is converted into PCM and magnetically recorded as described above, the magnetic tape that was once recorded may be reused to record another audio signal. In that case, the PCM signal is generally a high frequency, so
By re-recording, the previous recording is automatically erased, and there is no need to provide a special erasing head or the like.

However, when re-recording, if there is dust or the like on the tape, the head and tape will separate at that part and re-recording will not take place. Previously recorded signals are not erased and the original signal remains between newly recorded signals. In other words, the continuity of the signal is lost.

When such a tape is played back, if the above-mentioned dust and the like are removed, the original signal is played back in the middle of the new signal. If the original signal reproduced here has a very short period of time, it is detected as an error by the above-mentioned CRC, and the signal is corrected or removed.

However, the disturbances caused by the above-mentioned dust and the like often occur over a wide area, and may extend to several blocks of information bits forming the above-mentioned CRC.
In that case, if the remaining original signal is a PCM signal similar to the new signal, no errors will be detected by the CRC in the reproduced signal, and the reproduced signal will be demodulated in the same way as the new signal and the reproduced audio It makes noise inside.

For example, it has been proposed to provide an index bit in the information bits and set a different index value each time the data is rerecorded, thereby distinguishing between the original signal and the newly recorded signal. . In this way, it is possible to determine that the original signal is being reproduced in a portion of the reproduced signal where the index is different from the others, and this portion can be removed to prevent the occurrence of abnormal noise.

However, in this case, for example, if the index bit is 2 bits, there are four possible index values, and on a tape that has been repeatedly re-recorded, the index value of the newly recorded signal and the index value of the original signal will be different. There is a risk that they will match. Therefore, if the number of index bits is increased, signal redundancy increases and signal recording efficiency deteriorates.

In view of these points, the present invention is designed to enable multi-digit index signals to be transmitted without providing index bits and therefore without increasing redundancy. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the recording system. In the figure, 1 is an input terminal for audio signals. This audio signal is supplied to the PCM circuit 2 to be converted into a PCM signal, and this PCM signal is supplied to the signal addition circuit 3. Further, the PCM signal is supplied to the signal adding circuit 4, and an arbitrary index signal from the index forming circuit 5 is also supplied to the adding circuit 4. This additional signal is CRC
CRC supplied to code forming circuit 6 and formed
The code is supplied to an additional circuit 3. This additional signal is then supplied to the head 8 through the modulation circuit 7.

In this circuit, when the PCM signal D shown in FIG. 2A is generated, an index signal ID is added in the addition circuit 4 as shown in FIG. 2B. This signal is supplied to the CRC code forming circuit 6, where it is divided by, for example, a generator polynomial, and from this remainder, a second
A CRC code signal CRC shown in FIG. C is formed.
This code signal CRC is then supplied to the addition circuit 3 and added to the PCM signal D as shown in FIG. 2D, and this signal is modulated and recorded.

Figure 3 shows the reproduction system. In the figure, head 11
The signal is supplied to the error correction circuit 13 through the demodulation circuit 12. The demodulated signal is also supplied to the CRC decoder 14, where it is divided by the generator polynomial.

The CRC code formed at the time of recording is formed for the signal to which the index signal ID is added. On the other hand, since the recorded signal does not include the index signal ID, when the decoder 14 performs division, a remainder always occurs. This remainder corresponds to the value obtained by dividing the index signal ID by the generator polynomial, and will be a constant value if there is no error in the signal.

Therefore, this remainder is supplied to the index detection circuit 15 and monitored over a plurality of CRC codes.
If the constant remainder continues, it is determined that there is no error in the signal. In that case, correction circuit 1
The demodulated signal supplied to PCM 3 is supplied as is to the PCM reproduction circuit 16, and the reproduced audio signal is taken out to the output terminal 17.

Furthermore, if different remainders occur discontinuously, it is determined that an error has occurred in the signal. In this case, error correction or the like can be performed by removing the specific influence of the index signal ID from the detected remainder and supplying the remainder from which this influence has been removed to the correction circuit 13. The corrected signal is then supplied to the PCM reproducing circuit 16.

On the other hand, if equal remainders different from the normal remainders occur consecutively, it is determined that the above-mentioned original signal has been reproduced. And in this case,
A correction stop signal is supplied to the correction circuit 13,
Either the signal supply to the PCM reproduction circuit 16 is stopped, or the signal interpolated with an arbitrary signal is
The signal is supplied to the PCM reproducing circuit 16.

In this way, recording and reproduction (transmission) of PCM signals is performed. According to the present invention, the original signal remaining during re-recording can be reliably removed by using the index signal, and a special signal for this index signal can be removed. Since no bits are provided, signal redundancy does not increase.

In the above example, the number of bits of the index signal is
The number of bits can be equal to the number of bits of the CRC code.

Further, the index signal may be changed by 1 when the apparatus is switched on or when recording is started, or the index of the original signal may be detected in advance and set to a value different from this. Additionally certain rules, e.g. CRC
The number may be increased by 1 for each block, and in this case, the detection circuit 15 performs monitoring according to this rule. Since these index signals have a large number of bits, there are many types of indexes, and the probability that the index of the recorded signal matches the index of the original signal is low.

Furthermore, in the above example, when a tape with the original signal remaining is played back, the remainder changes slightly, and then other values continue.
Therefore, in such a case, it can be determined that the original signal already remains in the slightly changed part, and the correction may be stopped from this part.

Further, in FIG. 1, the index signal may be added at a subsequent stage of the CRC code forming circuit 6, as shown by a broken line. In this case, for the PCM signal D shown in FIG. 4A, the signal shown in FIG. 4B is
A CRC code signal CRC is formed, and an index signal ID shown in FIG. 4C is added to this signal.
Then, this added signal becomes as shown in Fig. 4D.
Added to PCM signal D.

In this case as well, the remainder is detected in the decoder 14 of FIG. 3, and the same operation as described above can be performed. In this case, since the index signal itself is taken out as the remainder of the decoder 14, monitoring becomes easier.

Furthermore, in the present invention, the index signal may be transmitted together with the PCM signal for each predetermined block. In this way, the index can be detected more reliably.

As described above, according to the present invention, since an error detection code is generated that includes an index signal for identifying the continuity of code signals, code signals and index signals can be transmitted without increasing redundancy. can do.

[Brief explanation of the drawing]

Figures 1 and 3 are system diagrams of an example of the present invention;
The figure is a diagram for explaining the same, and FIG. 4 is a diagram for explaining another example. 5 is an index forming circuit, 6 is a CRC code forming circuit, 14 is a CRC decoder, and 15 is an index detecting circuit.

Claims (1)

[Claims] 1. A code for detecting signal errors is generated based on a code signal and an index signal for identifying the continuity of the code signal, and is transmitted together with the code signal. Characteristic code signal transmission method. 2. A first signal adding means for adding an index signal for identifying the continuity of the code signal to the code signal, and detecting a signal error in the signal output from the first signal adding means. A code signal comprising: an error detection code generation means for generating a code for the error detection code; and a second signal addition means for adding a signal output from the error detection code generation means to the code signal. transmission equipment. 3. An error detection code generation means for generating a code for detecting signal errors in the code signal, and an index signal for identifying the continuity of the code signal in the signal output from the error detection code generation means. 1. A code signal transmission device comprising: signal addition means for adding; and signal addition means for adding a signal output from the signal addition means to the code signal.