JPH0158574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixed head type multi-channel PCM recording and reproducing apparatus.

FIG. 1 is a diagram showing the recording format of a multi-channel PCM recording and playback device.
1 is a magnetic tape; 2-1 to 2-8 are information tracks on which information for one audio channel is recorded; 5-1;
5-2 is a redundant track on which a redundant signal, for example a parity check code, for error correction of the audio information data of the information track 2 is recorded.

FIG. 2 is a diagram showing a method of adding the redundant tracks 5-1 and 5-2, in which a ₁ to a ₈ are information tracks 2
- information signals recorded in 1 to 2-8, respectively;
c ₁ and c ₂ are redundant signals for error correction recorded on the redundant tracks 5-1 and 5-2, and b is the bit length.

In order to create redundant tracks 5-1 and 5-2, information signals a1 _and b bits each are input from adjacent positions in the tape width direction from the information tracks 2-1 to 2-8.
~ _a8 is extracted, error correction signals _c1 and _c2 are obtained from a total of 8b-bit information signals, and these are sent to redundant track 5.
-1, Record at 5-2.

In FIG. 3, a large number of data shown in FIG. 2 are arranged in the tape running direction, and redundant signals are also added in the tape running direction. In the figure, S is a synchronization mark, and d ₁ to _{d 10} are information tracks 2-1 to 2-
8. Both redundant tracks 5-1 and 5-2 are redundant signals added every 7b bits.

The redundant signals d ₁ to _{d 10} are usually generated by a CRC code algorithm, and a synchronization mark S is further added to each track to the CRC code (information signal + redundant signal) generated in this way. Hereinafter, the period from the synchronization mark S to the redundant signal di (i=1 to 10) will be referred to as a frame.

A collection of 10 tracks of these frames constitutes one code block CB.

There is a multi-track PCM recording/playback device shown in FIG. 4 that records in a format as described above. In the figure, 1 is tape, D
7 is a multi-track playback head, 101 is an amplifier that amplifies the output of the playback head 7, and 201 is a time axis correction circuit that temporarily accumulates the output of the amplifier 101 and outputs it with crystal oscillator precision timing. , 102 is an error correction circuit for error correcting the output of the circuit 201, and 103 is the error correction circuit 1.
D/A converter for D/A converting the output of 03, 10
4 is an audio amplifier that amplifies the output of the D/A converter 103, and the circuit elements 101, 201, 1
02, 103, and 104 form a reproduction side digital circuit 9 (hereinafter referred to as reproduction circuit),
8 is an output terminal of the circuit 9. Further, 11 is an input terminal, 106 is an audio amplifier that amplifies the audio signal from the input terminal 11, and 107 is the audio amplifier 106.
Both of them form an input side digital circuit 10 (hereinafter referred to as input circuit). 12 is the output of the error correction circuit 102 on the reproduction side and the input circuit 1 on the recording side.
105 switch for selecting and switching between 0 and 0 outputs;
108 is a delay circuit for head interval compensation that delays the input signal from the switch 12 by a predetermined time; and 108 is an error correction circuit that adds a synchronization mark S and an error correction code di (i=1 to 8) to the output of the delay circuit 105. code addition circuit; 109 is the error correction code addition circuit 10;
8, both of which are connected to the recording side digital circuit 15 (hereinafter referred to as the recording circuit).
is formed. Reference numeral 6 denotes a multi-track recording head for recording the output of the recording circuit 15 onto the tape 1.

Although FIG. 4 shows only the circuits on the reproduction side and the recording side of the information track for simplicity, the configuration of the redundant track is different from the above, and the reproduction side circuit has only circuits 7, 101, 201, and 102. , its output is supplied to all error correction circuits of the information track for error correction. Furthermore, the recording signals of all the information tracks are supplied to the recording side circuit of the redundant track, and furthermore, during overdubbing, all the reproduction signals of the information tracks other than the recording track are supplied to the recording side of the redundant track via the switch 12 of each track. It is now being supplied to the circuit. Furthermore, the reproduction side circuit of the information track is not as shown in FIG. 4, but the error correction circuit of each track is supplied with reproduction data of all other tracks for error correction.

Next, the operation will be explained.

The output of the reproduction head 7 is amplified by a reproduction amplifier 101 and applied to a time axis correction circuit 201. Then, the playback information signal is subjected to time axis correction circuit 201 that absorbs time axis fluctuations (hereinafter referred to as jitter) caused by uneven running of the tape, etc.
02, the code error is corrected, and the D/A converter 103
The signal is converted back to an analog signal, amplified by the audio amplifier 104, and output to the outside from the output terminal 8.

On the other hand, the audio signal applied to the input terminal 11 is amplified by the audio amplifier 106, and the A/D converter 10
7, it is converted to a PCM signal. The output of this A/D converter 107 is sent to the delay circuit 1 via the switch 12.
05 and is delayed for a predetermined time by the delay circuit 105, a synchronization mark S and a redundant signal di (i=1 to 8) are added by the error correction code addition circuit 108, and amplified by the recording amplifier 109. It is recorded on the tape 1 by the recording head 6.

Note that the switch 12 and the recording amplifier 10
9 is controlled by an external operation button (not shown), and when switch 12 is connected to the output side of error correction circuit 102, recording amplifier 109 does not operate.

A conventional multi-channel PCM recording/playback device is configured as described above, and the PCM recorder can completely absorb jitter during playback using the time axis correction circuit shown in Figure 4. This is one of the features of PCM recorders.

By the way, in order to completely absorb jitter with the above-mentioned time axis correction circuit, tape running is controlled by a phase-controlled servo system that compares the reference phase of the crystal oscillator precision with the reference reproduction phase of the reproduction information signal. I need to be there. It is generally known to use the detection information of the synchronization mark of any track shown in FIG. 3 as the reference reproduction phase of the reproduction information signal. However, if a servo system is constructed that is controlled using the position of the synchronization mark of one existing track as a reference reproduction phase, the following problem will occur if the track becomes unreproducible for some reason. That is, according to the above recording format, a one-track error can be completely corrected.
Although the information signal within the frame can be reproduced by error correction, since there is no synchronization mark, a reference reproduction phase cannot be obtained, the tape running is disturbed, and normal reproduction cannot be performed.

Furthermore, even if a dedicated servo track for recording the reference reproduction phase is provided in addition to the track for recording PCM information, if the servo track becomes unreproducible, normal reproduction of PCM information will become impossible. Unfortunately, it was a problem.

Also, one of the functions of the multi-channel PCM recording/playback device is overdubbing processing.
Overdubbing refers to recording on another track after a predetermined time delay in synchronization with the playback sound of a previously recorded track. However, when overdubbing is performed, the following problems occur.

In FIG. 4, during overdubbing, the audio information signal _a2 of a certain information track 2-2 is transferred from the input circuit 10 to the redundant tracks 5-1 and 5-2 via the switch 12 of the track 2-2. circuit (not shown) and other information tracks 2-1,
The information signals _a1 , _a3 to _a8 of 2-3 to 2-8 are sent from the reproducing circuit 9 to the recording circuits (not shown) of the redundant tracks 5-1 and 5-2 via the switches 12 of each track. and the recording circuit outputs redundant signals c ₁ ,
c ₂ is generated. In this case, information track 2-
If the information signals a ₁ , a ₃ to a 8 of 1, 2-3 to _2-8 are newly recorded, the deterioration due to code errors will increase, so the track on which the recording is performed during overdubbing and the redundant signal accordingly It is necessary to rerecord only the redundant tracks 5-1 and 5-2 to be changed.

FIG. 5 is a diagram showing how the information on each track changes due to overdubbing. In the figure, the shaded area is the re-recorded area, and A is one section on the tape 1.

FIG. 6 is an enlarged view of section A in FIG.

In the overdubbing process, the playback head 7
Redundant signals c ₁ and c ₂ are created based on the information signals a ₁ , a ₃ to a ₈ of the reproduced frames other than the second channel reproduced in , and the information signal a ₂ of the second channel to be newly recorded. 2 channel information and redundant signals c ₁ , c ₂
In order to record only the second channel, frames excluding the second channel, which is not recorded this time, and frames to be newly recorded must be correctly recorded on the tape as shown in FIG. Therefore, it is necessary to delay the signal to be recorded by a predetermined time and to make the sum of this delay time and the time required for signal processing exactly match the tape running time from the playback head 7 to the recording head 6. PCM recording and playback device has delay circuit 1
It is equipped with 05. The function of this delay circuit ensures that one code block is composed of 10 frames arranged in the vertical direction as shown in FIG.

However, if the tape running time from the playback head to the recording head varies due to jitter, etc.
The recording state of the overdubbed tape is 7th.
As shown in figure a, the positional deviations Δ ₁ , Δ ₂ , Δ ₃ , Δ ₄ , Δ ₅ , Δ ₆
As a result, the reference reproduction phase becomes random as shown in FIG.

That is, after performing overdubbing as shown in FIG. 7a, when reproducing this tape, the reference phase reproducing circuit shown in FIG. The present invention is characterized by making the delay time of this circuit and the delay circuit longer, and the following explanation does not describe the disadvantages of the present invention. A reference reproduction phase signal is obtained. In FIG. 8, 811 to 818 are synchronization mark detection circuits;
821 to 828 are one-shot multivibrators, 803 is an AND gate, 806 is a clock generation circuit, 804 is a phase comparator, and 805 is a capstan motor. This signal in FIG. 7b corresponds to the output of the AND gate 803 in FIG.
Pulse signals B and C are generated at the rear end of the synchronization mark, respectively, of which pulse B corresponds to the falling edge of the reproduction synchronization mark of the track as originally recorded. C corresponds to the trailing edge of the reproduction synchronization mark of the track re-recorded during overdubbing.

The above-mentioned positional deviation between tracks accumulates as overdubbing is repeated, and the reference playback phase is affected by jitter and other effects each time overdubbing is repeated, and the affected phase information is transferred to the playback turbo. It will be sent to the system. As a result, the positions of the frames on the reproduction track and the frames on the recording track become unstable, resulting in the problem that code blocks cannot be reconstructed.

The present invention has been made to eliminate the drawbacks of the conventional ones as described above, and it generates a reference reproduction phase from synchronization marks of a plurality of tracks, and also
When overdubbing, by always recording the signal at a position that is behind or ahead of the playback track, normal playback can be performed even if one track's synchronization mark is missing, and it is possible to avoid time axis fluctuations in the tape running direction. Since the time base correction circuit absorbs some jitter and other deviations between synchronization marks, the synchronization mark detection signal detected earliest or latest among multiple tracks becomes the reference reproduction phase, and the code block is The purpose is to provide a PCM recording and playback device that can be reconfigured correctly.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 8 shows a reference phase regeneration circuit according to an embodiment of the present invention. In the figure, 811 to 818 are synchronization mark detection circuits for each track that are included in the time axis correction circuit 201 and detect synchronization marks; 821 to 82;
8 is a one-shot multivibrator that outputs "0" for half the repetition period of the synchronization mark after detecting the synchronization mark in the synchronization mark detection circuits 811 to 818; 803 is the output of the one-shot multivibrator 821 to 828; It is an AND gate that takes AND, and both are the reference phase regeneration circuit 8.
07 is formed. 806 is a clock generation circuit that generates a reference phase with crystal oscillator precision; 804 is a phase comparator that compares the phase of the output of the clock generation circuit 806 with the phase of the output of the AND gate 803; and 805 is the phase comparator. This is a capstan motor whose rotation is controlled by the output of 803.

Further, in the present invention, the delay time T _d of the delay circuit 105
Set as follows.

Td = (d/v - T _p ) + ΔT ₁ (1) where d (cm): Head spacing V (cm/s): Average tape speed T _p : From playback head 7 to recording head 6 excluding delay circuit 105 Average signal processing time ΔT ₁ : Expressed as a predetermined time longer than the maximum value or effective value of the variation in tape running time d/v.

However, ΔT ₁ must satisfy the following formula.

ΔT ₁ ≧ 1/2 dΔ/V where dΔ (cm): Maximum value or effective value of variation between frames during overdubbing Figure 9 is a time chart showing the signal waveform of each signal line of this embodiment circuit. be.

In the figure, 901 is a synchronization mark detection circuit 81
902 is the output waveform of the synchronization mark detection circuit 811, 903 to 911 are the output waveforms of the one-shot multivibrators 821 to 828, and S' in format 901 is the erroneous synchronization signal. , X in the signal waveforms 902 and 903 is a point where the synchronization signal that should have been detected due to the erroneous synchronization signal S' was not detected, and this is the point where the synchronization signal that should be detected is not detected in the signal waveforms 904 to 9.
The same applies to 10, and illustration of the format of each track is omitted for these other tracks.

Next, the operation will be explained using FIG. 9 as well.

First, when only reproduction is performed, as shown in FIG. 9, the synchronization mark detection circuits 811 to 818 output a detection output as a pulse only after inspecting the last part of the synchronization mark S of each track. The one-shot multivibrator 821-82 is activated by the pulse output.
8 continues to output "0" for half the period of the synchronization mark S. Further, when the synchronization mark S cannot be detected, the one-shot multivibrator does not operate. Therefore, the signal waveforms 902 and 903 corresponding to the format 901 become as shown in FIG. 9b and c, and the signals 904 to 91 corresponding to the other tracks
0 is also as shown in d to h in the figure, and the locations where the synchronization mark S cannot be detected remain "1". However, by ANDing the outputs of the one-shot multivibrators 821 to 828 using the AND gate 803, the synchronous arc S can be obtained from one track.
Even if you cannot detect the synchronization mark S of other tracks
As a result, the output 911 of the AND gate 803 becomes a rectangular wave signal that regularly inverts at a constant period, as shown in FIG. 9h.

Next, the operation during overdubbing will be explained.

In this embodiment, the delay time of the delay circuit 105, which delays the signal to be recorded in the conventional circuit and makes the sum of the delay time and the time required for signal processing equal to the tape running time, is changed to ( As shown in equation 1), since the delay time is set slightly longer than the delay time in the conventional case, the positions of the synchronization marks S on the recording track during overdubbing are all behind the positions of the synchronization marks S on the playback track. . Therefore, as shown in FIG. 10b, the reference playback phase at this time does not depend on the synchronization mark detection signal of the overdubbed track, and is the same as that created only from the synchronization marks of the playback track that has not been overdubbed. become. Therefore, even if overdubbing is repeated, a reference reproduction phase can be obtained without being affected by overdubbing, a stable reproduction servo system can be achieved, and code blocks can be reliably reconstructed.

In the above embodiment, a case has been described in which the signal recording position of the overdubbed track is recorded a little later than the playback signal position of the already recorded track, but in contrast to this, the signal recording position of the overdubbed track is When recording is performed a little ahead of the playback signal position of the track that has already been recorded, the reference phase reproducing circuit detects the synchronization mark detection signal that is detected the latest among the synchronization mark detection signals obtained from multiple tracks. A similar effect can be obtained by configuring the reference reproduction phase.

Further, in the above embodiment, a one-shot multivibrator was used to create the reference reproduction phase from the output of the synchronization mark detection circuit, but any circuit having the same function as this may be used.

Furthermore, the number of tracks on a magnetic tape is not limited to 10, and the number of channels and the number of tracks may not match.

As described above, according to the present invention, the reference phase of tape running is reproduced using a plurality of outputs of the synchronization mark detection circuit provided in each track, and the signal to be recorded is delayed by a predetermined time during overdubbing. Since the information is recorded after recording, the information can be reproduced accurately even if an error occurs in the synchronization mark or if a positional shift occurs between tracks due to repeated overdubbing.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the recording format of a multi-track PCM recording/playback device, Fig. 2 is a diagram explaining a method of adding redundant tracks, Fig. 3 is a diagram showing code blocks, and Fig. 4 is a diagram showing a conventional multi-track PCM recording/playback device.
A block diagram of the PCM recording/playback device. Figure 5 shows the tracks re-recorded by overdubbing. Figure 6 shows the recording format of multiple tracks. Figure 7 shows the deviation of the tracks after overdubbing. Diagram showing the reference reproduction phase, No. 8
The figure is a circuit diagram of a reference phase reproducing circuit according to an embodiment of the present invention, FIG. 9 is a time chart of each part of FIG. 8, and FIG. 10 is a track and reference reproduction recorded by overdubbing operation according to the above embodiment. It is a figure showing a phase. 811-818...Synchronization mark detection circuit, 20
1... Time axis correction circuit, 807... Reference phase regeneration circuit, 804... Phase comparator, 105... Delay circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Audio signals of a single or multiple channels are converted into digital signals and recorded on multiple tracks in the longitudinal direction of the tape, and synchronization marks are provided on the audio information signals of each track for synchronizing data during playback. In a PCM recording/playback device that constructs a frame by periodically adding frames at the same position in the width direction of the tape, playback is performed using multiple synchronization mark detection circuits that detect the synchronization marks of each track and the output of these synchronization mark detection circuits. A time axis correction circuit that outputs data at a predetermined timing without time axis fluctuation, a plurality of one shot multivibrators that generate one shot pulses of negative polarity using synchronization mark detection of each track as a trigger, and the plurality of one shot pulses. It consists of a single AND circuit that takes the logical product of the outputs of the multivibrators, and processes the synchronization mark detection signals obtained from the multiple tracks detected by the synchronization mark detection circuit according to a predetermined rule, thereby adjusting the tape running state at a constant speed. a reference phase regeneration circuit that creates a reference regeneration phase that serves as a reference for maintaining the reference regeneration phase, and a phase comparator that compares the reference regeneration phase with a reference phase created by a clock oscillator and applies its output to the capstan motor. , a delay circuit that delays a predetermined time so that when recording and reproducing are performed simultaneously, the signal to be recorded is always recorded at a position later than or ahead of the signal corresponding to the signal on the reproduction track, and the above-mentioned reference phase is created. A PCM recording and reproducing apparatus characterized in that, as a rule, the first synchronization mark detection signal detected from among the synchronization mark detection signals obtained from a plurality of tracks is set as a reference reproduction phase. 2 The above predetermined time T _d is the average value of the tape running time from the playback head to the recording head, T ₁ is the signal processing time from the playback head to the recording head, T _p is the maximum value of the variation in the tape running time, or When the predetermined time longer than the effective value is ΔT ₁ , T _d = T ₁ − T _p + ΔT ₁ or
The PCM recording and reproducing apparatus according to claim 1, characterized in that T _d =T ₁ -T _p -ΔT ₁ .