JPS58105413A - Pcm magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To absorb completely the wow and flutter, by setting the distance between a reproducing head and a recording head at an integer-fold value of the circumference of a capstan. CONSTITUTION:The relation of the distance I between heads 3 and 15 and the diameter D of a capstan 1 is set as I=DXnuXN (nu: pi; and N=an integer). As a result, the signal 24 is recorded double on a magnetic tape 2 which is driven with a press-contact to a pinch roller 25 and synchronously the phase of with the recorded signal 23 although the tape 2 travels with the wow and flutter. The tape travelling speed varies in a period of nuD/v and on the basis of the prescribed value (v), and the N-fold time of the tape travelling speed coincides with the time T which is needed for the shift of a point on the tape 2 and between the heads 3 and 15 in the following relation, that is, T=1/v=nuD/vXN. In other words, the recording signal 24 which is started with a delay of T sec. later than the synchronizing signal SYo is synchronous with the signal 23 recorded on the tape 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PCM magnetic recording/reproducing device using a magnetic tape, and relates to a PCM magnetic recording/reproducing device that uses a magnetic tape to record a new signal overlapping a previously recorded portion of the magnetic tape. The objective is to minimize the phase difference between a pre-recorded signal at a point, that is, the phase difference between the data frame at that point, and obtain a correct reproduced signal.

In a PCM magnetic recording and reproducing apparatus using a magnetic tape, a jitter absorbing memory on the reproducing circuit side generally suppresses wow and flutter contained in the reproduced output signal to zero. However, when another signal is overwritten on an already recorded tape (generally called pan-nine), the recorded signal at the start point of overlapping recording and the newly recorded signal are Disturbance occurs in the phase of a data frame composed of a pattern, that is, a digital signal, an error detection/error correction signal, a synchronization signal, etc. added according to a certain rule. This is because a capstan in principle generates wow, 7, 3, and 3 vectors, and the magnetic tape driven by this capstan runs with a wow and flutter component, so new signals are added to the recorded signals on the tape, which does not run constantly. It is difficult to record signals with perfectly aligned phases.

When a disturbance occurs in the phase of the recording signal at the recording start point in this way, the number of data in the vicinity becomes smaller or larger than the number of data included in the normal magnetic recording pattern.

Therefore, the number of data input to the jitter absorption memory mentioned above during playback may be less than or greater than the predetermined value.
In the worst case, the jitter absorption memory, which has little margin, will not be able to absorb the wow and flutter. Therefore, muting occurs in the playback output signal, so PCM
This is a serious drawback for magnetic recording and reproducing devices.

In addition, since the recording signal pattern phase changes suddenly at the point where overlapping recording starts, it is very difficult to extract (separate) the synchronization signal after this point, and in the worst case, the PC
The present invention, in which the M reproducing circuit system can be synchronized, solves the above-mentioned conventional drawbacks, and is characterized in that the distance between the reproducing head and the recording head is an integral multiple of the circumference of the capstan.

An embodiment of the present invention will be described below based on the drawings.

In this embodiment, the data frame is generally constructed by adding error detection and error correction signals and a synchronization signal for bit synchronization to an A/D converted digital signal. FIG. 1 is a configuration diagram of this embodiment, and the signals reproduced by the reproduction head 3 located upstream in the running direction of the magnetic tape 2 driven by the capstan 1 are as follows:
The signal is passed through a reproducing circuit 4 and a demodulating circuit 5 and is separated into a synchronizing signal 6 and a first PCM signal 7. This first PCM signal 7
The second PCM signal 1o obtained by passing the analog signal input from the input terminal 8 through the A/D conversion circuit 9 is:
The signals are respectively input to signal switching circuits 11, and their output signals are sent to delay circuits 12. Modulation circuit 13. It passes through the recording circuit 14 and is recorded on the magnetic tape 2 by the recording head 16 located on the downstream side in the running direction of the magnetic tape 20.

In addition, a first recording command signal (REC') is sent from the control circuit 17 which receives the signal from the operation switch 16 and controls each part.
1s is input to the timing adjustment circuit 19. The timing adjustment circuit 19 controls the signal switching circuit 11 in response to the first recording command signal 18, and also adjusts the timing of the recording clock generation circuit 2o based on the synchronization signal 6, and further controls the recording clock generation circuit 2o. A second recording command signal (REC) 21 is output to the circuit 14.

FIG. 2 is a time chart of signals in the main part of the embodiment shown in FIG. Therefore, it is ahead by Tsec shown by the following formula.

speed, l is the distance between both heads 3 and 15) Therefore, when the first recording command (REC') 1s occurs at point A,
The timing adjustment circuit 19 receives the immediately preceding synchronization signal SYo.
After Tsec, the timing of the recording clock generation circuit 20 is taken, so the modulation circuit 13 operates in synchronization with it, and the recording circuit 14 operates at point B in response to the second recording command signal (REC) 21'i. It is set as follows. In other words, the signal 24 recorded by the recording head 16 can synchronize with the phase of the recorded signal 230 and start overlapping recording as shown in FIG. 2 if the magnetic tape travels at a constant rate. contains a wow and flutter component, so correct overlapping recording is impossible with the above timing settings alone.

Here, in the present invention, the diameter of the capstan 1 and the distance l between both heads 3.16 are set to the relationship l = D x π x N - (where π = pi, 1IJ = integer). , capstan 1 and pinch roller 2
Although the magnetic tape 2 running while being pressed at 5 is actually running with wow black, the second
As shown in the figure, a signal 24 is superimposed and recorded by the recording head in synchronization with the phase of the recorded signal 23.

This is because, as shown in FIG. 3, the tape running speed πD -do fluctuates at a cycle of - around the specified value V;
The time N times that time corresponds to the time T required for one point on the magnetic tape 2 to move between both heads as follows.

T=±-ρ×N v v That is, if the time when one point on the magnetic tape 2 passes the reproducing head 3 is tl in FIG. 3, the error with respect to the specified speed V at that time is the recording head 16'f: passing It is nothing but the same as time 2.

Therefore, as shown in FIG. 2, the synchronization signal SY.

The recording signal 4, which is started after Tsec, is synchronized with the signal 23 already recorded on the tape 2.

In addition, in Fig. 3, the wow and flutter component is limited to a component that occurs once per rotation of the capstan πD (glue period = -).
This is because tape recorders usually have the most amount of this component.

In addition, although the delay circuit 12 is provided between the signal switching circuit 11 and the modulation circuit in FIG.
A configuration may also be adopted in which a delay circuit is provided between 1 and 1.

According to the configuration of the above embodiment, by setting the distance l between the playback head 3 and the recording head 16 and the diameter of the capstan that drives the tape to 1=πXDXN, the recorded signal pattern can be Overlapping recording can be started at the phase of . Therefore, since the data amount near the overlapping recording start point does not change to the specified amount, the jitter absorption memory can completely absorb the wah 7 rack during playback, and it is possible to prevent muting from occurring in the playback output signal around that point. . Furthermore, since the phase of the recording pattern near the overlapping recording start point does not change suddenly, it is possible to prevent the PCM reproducing circuit system from becoming out of synchronization.

As described above, according to the present invention, by setting the distance between the reproducing head and the recording head equal to an integral multiple of the circumference of the capstan, even when the magnetic tape is running in a state where it has wows and 7 rattles, It is possible to overwrite a new signal with the same phase from the recording head on the already recorded signal on the magnetic tape. Therefore, during reproduction, wow and flutter can be completely absorbed by the jitter absorption memory, and a correct reproduction signal can be obtained without losing synchronization.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a PCM magnetic recording/reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a time chart of important signals, and FIG. 3 is a diagram showing tape running speed with respect to time. 1... Capstan, 3... Playback head, 6... Demodulation circuit, 9... Mountain A/D conversion circuit,
11... Signal switching circuit, 12... Delay circuit, 14... Recording circuit, 16... Recording head, 19... Timing adjustment circuit.

Claims (1)

[Claims] A reproducing head and a recording head are arranged sequentially from the upstream side with respect to the traveling direction of the magnetic tape driven by the capstan, and the first digital signal reproduced from the reproducing head is transmitted to the recording head, which is calculated from the tape traveling speed. A second digital signal delayed by a time corresponding to the distance and a third digital signal obtained by converting an analog signal inputted from an input terminal into a digital signal are subjected to fade processing and then synthesized. means for recording a recording head, or means for recording said first digital signal and said second digital signal;
means for performing fade processing on each of the digital signals and recording the signals on the recording head after delaying the signals by a time corresponding to the distance between the two heads,
A PCM magnetic recording and reproducing device characterized in that the distance between the reproducing head and the recording head is set to an integral multiple of the circumference of the capstan.