JPS6369073A - Muting circuit - Google Patents

Abstract

PURPOSE:To stabilize action by applying muting when errors exceeding a prescribed number is detected by a checking signal, and releasing the muting after a servo condition is decided and a stationary state is obtained. CONSTITUTION:A first counter 51 counts the number of errors at the 2-track unit of an interleave pair, and a first detecting circuit 52 sets an FF60 when the counted value comes to be a prescribed value. From this time, a muting signal 18a is outputted and a muting condition is obtained. A second counter 61 makes a resetting signal 17a generated by a clock generating circuit 17 into a resetting input, and a sample pulse SP2 to be generated when an ATF synchronizing detecting input. A second detecting circuit 62, when the counted value of the counter 61 comes to be the prescribed number, resets the FF60, releases the muting and makes stable the action.

Description

[Detailed Description of the Invention] [Industrial Application Field] This IJJ is a muting method that suppresses the reproduction of noise in the case of signal dropout, synchronization loss, etc. in, for example, a rotary head type digital audio tape recorder. It is related to circuits.

[Prior Art] The case of a rotary head type digital audio tape recorder (hereinafter referred to as rR-DATJ) and a signal recording pattern called "interleaved bare" will be described below as an example.

Figure 2 is a diagram showing the relationship between the magnetic tape and drum of R-DAT. In Figure 9, (101) is the drum, (8)
indicates a magnetic head with +azimuth, (9) indicates a magnetic head with -azimuth, and (104) indicates a magnetic tape.The magnetic tape (104) is wound around the drum (101) at 90 degrees, and the magnetic tape (104) is placed on the magnetic tape (104). Record and play back to form recording tracks diagonally.

FIG. 3 shows the track format of the magnetic tape (104), and the arrow (205) indicates the magnetic head (8).

The running direction of (9), arrow (20B) is the magnetic tape (10
4) running direction, (202) is a signal of one track recorded during the 90° period when the magnetic tape (104) and the head (8) or (9) are in contact with each other, (204) is audio data and error. A PCM area (203a) and (203b) indicates a PCM area in which a check signal for correction or detection is recorded, and an ATF area (203b) in which an ATF signal for tracking is recorded.

Figure 4 is a block circuit diagram centered on the signal processing of R-DAT, where (1) is an analog signal input terminal, (2) is a low-pass filter, and (3) is an analog-to-digital conversion circuit (
(hereinafter referred to as AD conversion circuit), (4) is a memory circuit,
(5) is an encoding circuit, (6) is a modulation circuit, (23) is A
TF signal addition circuit, (7) is a changeover switch, (lO) is a changeover switch, (11) is a demodulation circuit, (12) is a memory circuit, (13) is a decoding circuit, (24) is an AND gate,
(14) is a digital-to-analog conversion circuit (hereinafter referred to as a DA conversion circuit), (15) is a low-pass filter,
(16) is an output terminal, (17) is a clock generation circuit that generates the system clock, and includes a low-pass filter (2)', an AD conversion circuit (3), and a memory circuit (4).
, an encoding circuit (5), and a modulation circuit (6) constitute a recording system, which includes a demodulation circuit (11), a memory circuit (12), a decoding circuit (13), a DA conversion circuit (14), and a low-pass filter (15). A reproduction system signal processing section is configured.

Next, we will explain the operation, starting with the recording system. The analog signal to be recorded is input from the input terminal (+), high frequency components are removed by the low-pass filter (2), and then the digital signal (hereinafter referred to as
(referred to as samples) and stored in the memory in the memory circuit (4).

The encoding circuit (5) reads the samples stored in the memory, generates check signals for error correction and error detection in units of one track, and writes them into the memory. When encoding is completed, the samples for one track are The samples of
The signal is converted into a signal suitable for magnetic recording and reproduction, and the ATF signal is added to the signal by the ATF signal addition circuit (23).
The information is recorded on a magnetic tape by a magnetic head (8) or a magnetic head (9) via a changeover switch (7) that changes over every degree.

Figure 5 shows the data array of the PCM area (204), where (170) is the +azimuth track pattern recorded by the head (8), and (171) is the -azimuth track pattern recorded by the head (9). It is.

The two channels of audio data generated during one rotation of the drum (101) are separated into even and odd samples for each channel in the memory circuit (4). They are arranged diagonally as shown, and the audio data is configured to be completed in two tracks. Q is a check signal for error correction, and one track 9 is completed. With this configuration, all signals from one magnetic head are lost, or approximately 1/2 of tape 1↑J from the tape edge.
Even if a burst occurs, either an even or odd sample group for each channel remains, so continuous sample errors do not occur, and noise-free playback can be obtained by means of average value interpolation, etc. This is a powerful correction. ability is obtained.

FIG. 6 is a diagram showing the code structure of one track. This figure shows the +azimuth track (170) in FIG. 5, and the samples are doubly encoded with CI code and C2 code. CI is encoded vertically and C2 is encoded horizontally. P and Q indicate check signals of the CllCl code, respectively. What is encoded in this way is m in the vertical direction.
The samples and the 1,000-nick signal P constitute one block of data, and a synchronization signal is added to this to form one block of signals shown in FIG.
It is recorded as a signal in the PCM area (204) shown in FIG.

Next, the operation of the reproduction system shown in FIG. 4 will be explained. The time-compressed reproduction signals reproduced by the magnetic head (8) and the magnetic head (8) are alternately supplied to the demodulation circuit (11) via a changeover switch (10) that is switched every unit time, and are then sent to the demodulation circuit (11) before modulation. The signal is returned to the signal and stored in the memory in the memory circuit (12). The decoding circuit (13) sequentially reads out the reproduced signal from the memory, performs error correction on each track of the reproduced signal, decodes it, and writes it into the memory.The decoded samples in the memory are read out at regular time intervals. After being converted into an analog signal by the DA conversion circuit (14), high frequency components are removed by the next-stage low-pass filter (15), and the signal is output from the output terminal (16).

Note that the lock necessary for the above-mentioned recording system and reproduction system signal processing is supplied from the clock generation circuit (17).

(18) is a muting circuit that counts the error detection results performed in the decoding circuit (13), outputs a muting signal when there are many errors, and turns off the gate (24);
The signal input to the DA conversion circuit (14) is cut off.
(1!3) is the ATF regenerated by the ATF synchronization detection circuit.
The synchronization signal of the signal is detected and the timing for extracting the pilot signals of both adjacent tracks is generated. (20)
is an error generating circuit which generates a tracking error signal from the difference in crosstalk level between pilot signals of one adjacent track. (21) is a servo circuit that controls the capstan motor (22) so that the pilot signal levels from both adjacent tracks are equal.

Next, the operation of the tracking servo system will be explained.

FIG. 8 is a diagram for explaining the operation of the ATF synchronization detection circuit (IS), and is a sample showing a partial track pattern of the ATF area shown in FIG. 3 and the timing for extracting pilot signals from both adjacent tracks. Pulse SPI, S
This shows F3.

In the figure, (81) is an ATF synchronization signal, and (82) is an ATF synchronization signal.

(83) indicates the pilot signal, :5S2)
This example shows a case where a magnetic head (8) traces a rack.

When the magnetic head (8) reproduces the ATF synchronization signal (81), the ATF synchronization detection circuit (19) detects this synchronization signal (81).
) is detected to generate a sample pulse SPI for extracting the pilot signal (82) of the first track, and then the recording area length of the synchronization signal is searched and a predetermined length is detected.
A sample pulse SP2 is generated with a predetermined time delay from the detection point. In the error generation circuit (20), the first
Track SF3 extracts the pilot signal of the third track and generates an error signal between the two. Servo circuit (21
) is tracked by controlling the capstan motor (22) so that this error signal becomes zero.

Next, the operation of the muting circuit (18) will be explained. Conventionally, a method has been used in which a muting circuit of a device using an error detection or correction code counts the number of error blocks every unit time, and muting is applied when the number of error blocks is counted or more than a predetermined number.

Figure 9 shows such a conventional muting circuit (18)
FIG. 2 is a block circuit diagram showing an example in which the method is applied to an R-DAT.

The decoding circuit (13) calculates the syndrome of the C1 code added to each block in the correction process.

This syndrome S is Si2 when there is one error in l block, and S-0 when there is no error. A counter (51) counts error pulses (13a) in blocks that are output when S≠O. Detection circuit (
52) is the error pulse of the counter (51) ゛(1
When the count value of 3a) exceeds N (integer), a pulse is generated to activate the monomulti (53). Mono multi (5
The output (18a) of 3) is output from the output terminal (54) as a muting signal. The muting time is a constant time determined by the time constant of the monomulti (53). (50) is a counter (5
This is the input terminal for the reset clock of 1).

As mentioned above, the R-DAT is a two-track complete type and has a strong correction ability that can correct the average value even if the signal of one track is missing, so the detection circuit (52) detects it. It is preferable that the number of count values N be larger, since this will not reduce the correction ability. Here, N=n+6, T is the period TI of one rotation of the drum (101), and the error correction code can completely correct up to 6 blocks per track.

FIG. 10 shows an example of an error state when the +azimuth head (8) is clogged during normal reproduction, and all signals on the +azimuth track (170) become erroneous and cannot be corrected. On the other hand - adjustment rack (171),
Correctable errors occur in three blocks at the position of the X mark, but they are corrected by the error correction code, and no errors remain in the signal of the -azimuth track (171). In this case, the number of error blocks is n + 3 < N, so muting is not applied.

The signal of the +azimuth track (170) is subjected to average value correction and output as audio. This shows the effect of counting the number of errors in units of two tracks (period T+).

Figure 11(a) shows the reproduced signal in a steady state;
b) shows an example of a reproduction signal in a transient state before the servo reaches a steady state while the R-DAT moves from a stopped state to regeneration state 7B. It shows the part where the level drops and signal error occurs, and the 11th
Figure (C) shows the timing of the sample pulse SP2.

FIG. 12 shows a signal area in which an error occurs on the track pattern in this transient state, and the shaded area corresponds to the signal area, and the number of blocks is approximately n/4. Further, the X marks indicate correctable error positions in three blocks, as shown in FIG. 1O.

In this case, although the number of errors is similar to that at which muting operates, both tracks cannot be corrected, and errors remain in both even and odd samples on the Rch, resulting in continuous sample errors.

When R-DAT is in a stopped state, syndrome S is SF for both the previous block! Since it becomes O, muting is applied. Then, in the transient state when the playback mode is set,
When the state shown in FIG. 12 exceeds the muting time determined by the time constant of the monomulti (53), unpleasant noise is output.

[Problems to be Solved by the Invention] As described above, the conventional muting circuit has the problem that unpleasant noise is output when the servo is disturbed and the muting time is exceeded. .

This invention was made in order to solve the above-mentioned problems, and it provides a muting circuit that can reliably apply muting while the tracking servo is disturbed while making use of the correction ability using the check signal. The aim is to obtain the following.

[Means for Solving the Problems] The muting circuit according to the present invention is configured to detect error blocks when the number of error blocks detected from a reproduced signal of a predetermined number of tracks exceeds the error correction ability of the check signal, or a number close to the error correction capacity of the check signal. and a means for canceling muting after detecting a number of ATF synchronization signals indicating that tracking is in a normal state from playback signals of a predetermined number of tracks. It is.

[Function] The muting circuit of the present invention applies muting when it detects a number of errors exceeding or close to the error correction capability of the check signal, determines the servo status using the ATF synchronization signal, and determines whether the servo is disconnected. Since the muting is not canceled in the normal state and is canceled after the servo reaches a steady state, stable muting operation can be obtained.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

Figure 1 is a block circuit diagram of the muting circuit (18), in which (60) is a flip-flop, (51), (6
1) is the first. The second counter, (52) is the counter (5
The first detection circuit (62) outputs a pulse when the count value of 1) reaches N, and the count value of the counter (61) is 2M.
A second detection circuit outputs a pulse when (17
a) is a reset signal (5) that is generated by the clock generation circuit (17) and is output once during the signal reproduction period of the M track;
4) is an output terminal for a muting signal (18a).

Next, the operation of this embodiment will be explained.

The first counter (51) counts the number of errors in units of two tracks of the interleaved pair, and the first detection circuit (52)
sets the flip-flop (60) when the count value becomes N, and from this time on, the muting signal (18a)
is output and a muting state is entered. The second counter (61) receives the reset signal (17a) generated by the clock generation circuit (17) every M tracks as a reset input, and the ATF synchronization detection circuit (19)
Sample pulse SP generated when F synchronization signal is detected
2 is the count input. The second detection circuit (62) is
When the count value of the 20th counter (61) reaches 2M, a pulse is output to reset the flip-flop (60) and cancel muting. As shown in FIG. 3, there are two ATF signal regions per track, and two sample pulses SP2 are output per track.

In the transient state of FIG. 11(b), as shown in FIG. 11(c), only one sample pulse 5P2L is not output,
Since the count value of the second counter (61) is only M between M tracks, the meeting is not canceled, and the meeting is canceled only after a steady state continues for M tracks, so unpleasant noise is output. be prevented from being

Note that the first detection circuit (52) in the above embodiment outputs a pulse when it detects a count value that is greater than the number n of PCM blocks in one track, but it is configured to output a pulse when the count value is smaller than n. However, although the correction ability decreases somewhat, the effect in transient conditions remains the same.

Furthermore, although the sample pulse SP2 was used as the input to the second counter (61), the same effect can be obtained by using the sample pulse SPI.

Furthermore, although the second detection circuit (62) outputs a pulse when it detects 2M SF3s, the same effect can be obtained even if the value is slightly less than 2M.

Further, although the above embodiments have been described using R-DAT as an example, the present invention is not limited to this. Furthermore, in the above embodiment,
Although we have explained the case of a recording format in which error detection and correction is performed in units of two tracks of an interleaved pair, the recording format is not limited to this. It is clear that the present invention can be similarly applied to a format in which recording is performed on a recording track, and that similar effects can be obtained.

[Effects of the Invention] As described above, the muting circuit according to the present invention includes means for applying muting when a number of error blocks exceeding a predetermined number is detected from a reproduced signal of a predetermined number of tracks;
This device is equipped with means for canceling muting after detecting more than a predetermined number of ATF synchronization signals from the reproduced signal of a predetermined number of tracks, and muting is applied when the error correction capability is exceeded or approaches it, and the reproduced signal is Since the muting is not canceled while the servo is not being reproduced in a normal state, it is effective in preventing the generation of noise due to disturbances in the servo system.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a layout diagram showing the relationship between the magnetic tape and drum of R-DAT, FIG. 3 is a track pattern diagram showing the track format of an interleave pair, and FIG. FIG. 4 is a block diagram showing the configuration of the recording/reproducing system of R-DAT, FIG. 5 is a recording pattern diagram showing the data arrangement of the recording track, FIG. 6 is a configuration diagram of the error correction code on the recording track, and FIG. Figure 8 is a block diagram showing the signal configuration of the l block, Figure 8 is a timing diagram for explaining the operation of the ATFM period detection circuit, Figure 9 is a block diagram of a conventional muting circuit, and Figure 10 is one of the Figure 11 is a waveform diagram showing the relationship between the reproduced signal and sample pulse, and Figure 12 is a signal error when the servo is in a transient state. FIG. 3 is a pattern diagram showing an example of a region. (51),'(81)...Counter, (52),
(132)...Detection circuit, (60)...Flip-flop. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) From the audio signal, the check signal for error detection/correction, the ATF signal for tracking, and the reproduction signals of a predetermined number of tracks reproduced from the recording medium recorded on the recording tracks as one group, the check signal is detected. A means for applying muting when the number of error blocks exceeding the correction capability or a number of errors close to this is detected, and a means for applying muting after detecting an ATF synchronization signal exceeding the number indicating that tracking is in a normal state from the reproduced signal of a predetermined number of tracks. and a means for canceling muting. (2) The recording format of the audio signal on the recording medium is such that the audio signal, check signal, and ATF signal are recorded in an interleaved pair format on two recording tracks, and the two recording tracks are played back. 2. The muting circuit according to claim 1, wherein error detection and correction is performed on a signal-by-signal basis, and the number of error blocks at this time is counted and subjected to muting.