JPH04353675A - Digital data reproducer - Google Patents

Abstract

PURPOSE:To effectively utilize the error-correcting power of reproduced data in accordance with a reproduced state. CONSTITUTION:In a digital data reproducer for reproducing digital data recorded by a magnetic tape, the reproduced state of an error flag, etc., before the error correction of digital data reproduced from the magnetic tape is detected, and, from the detected reproduced state, correction circuits 15, 16, 17, 18 are selected while the greatest number of error corrections by erasure correction is controlled so that the error correction of reproduced data is conducted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital data reproducing apparatus suitable for application to a VTR which records and reproduces an audio signal recorded together with a video signal as digital data, for example.

0002

[Background Art] Digital data handled by a digital data reproducing device such as a digital VTR has a correction code added to the recorded data in advance, and based on this correction code, the reproducing device can perform error processing such as error detection and error correction. It's like this.

A product code of C1 parity and C2 parity is known as a data structure to which this correction code is added. An example of this product code is shown in FIG.
The data structure of 0 is the digital audio tape recorder (
DAT), which shows the data structure of one block, and C1 parity is added by calculating the data in the vertical direction of this one block, and C1 parity is added.
1 code, and C2 parity is added in the calculation of data in the horizontal direction, resulting in a C2 code with C2 parity added. In this way, a product code is constructed by adding parity twice both vertically and horizontally. Then, during playback, C1 code and C2 code
Using code theory based on code syndrome calculations, it is possible to determine whether an error has occurred in each code. This syndrome operation can be performed, for example, by adding the data that makes up each code, and when the calculated value becomes 0, it can be determined that there is no error in this code series, and when the calculated value does not become 0, it can be determined that there is no error in this code series. It can be determined that this is occurring.

[0004] Another known error correction method for product-encoded digital data is called erasure correction. This erasure correction is, for example, C1
By parity check and C2 parity check, C
After detecting the locations where errors occur in the 1 code and the C2 code, the error detection locations are corrected up to a predetermined number, and the correction is performed as shown below.

[0005] First, the C1 code and the C2 code are C1[4
2, 38, 5] and C2 [22, 18, 5] (i.e., the number of bits of C1 code is 42, the number of information is 38, the minimum distance is 5, and the number of bits of C2 code is 22, number of information 18, minimum distance 5), and up to 4 erasure corrections (4 error corrections) are possible.

[0006] Here, the syndromes are defined as s0 to s3,
If the error vectors are e1 to e4 and the error locations are x1 to x4, then the syndromes s0 to s3
is expressed by the following equation.

[0007]

[Math 1]

[0008]

[Math 2]

[0009]

[Math 3]

0010

[Math 4]

[0011] It can also be expressed as shown in the following equation.

0012

[Math 5]

[0013] Here, in the case of this formula [Equation 5], it can be transformed as shown in the following formula using Cramer's formula.

[Math 6]

[0014] However, xai=αai and α=(0,0,0,
0,0,0,1,0)

This value is the Galois field of GF(28). Therefore, from the formula [Equation 6], if the error locations x1 to x4 are known when decoding the C1 code, the C2 code can perform up to 4 error corrections (4 erasure corrections).

[0016]

[Problem to be Solved by the Invention] By the way, when the error rate is good, the error locations x1 to x4
becomes more probable, and by performing up to 4 erasure corrections, the interpolation probability is reduced and more probable reproduced data can be obtained. However, when the error rate is poor, the probability that error locations x1 to x4 are likely decreases, so it is dangerous to perform erasure correction at maximum capacity.

[0017] For this reason, when maximum erasure correction is performed, there is a high possibility that the reproduced data will be erroneously corrected depending on the reproduction state. For example, if the error correction capability is limited to two erasure corrections, the error correction capability is not effectively utilized when the reproduction condition is good.

An object of the present invention is to enable a digital data reproducing apparatus to effectively utilize the error correction capability of reproduced data depending on the reproduction state.

[0019]

[Means for Solving the Problems] The present invention provides a digital data reproducing device for reproducing digital data recorded on a magnetic tape, which detects error flags before error correction in digital data reproduced from the magnetic tape, and detects error flags in predetermined units. The maximum number of error corrections by erasure correction is controlled according to the number of error flags for each error flag, and errors in reproduced data are corrected.

Further, the present invention provides a digital data reproducing apparatus for reproducing digital data recorded on a magnetic tape, in which the maximum number of errors corrected by erasure correction is controlled according to the reproduction state of the magnetic tape, so that the reproduction data can be corrected. It is designed to perform error correction.

[0021]

[Operation] By doing this, appropriate erasure correction is performed according to the error occurrence state of the reproduced data and the reproduction state of the magnetic tape. The maximum error correction is performed, and the reproduced data is always well corrected.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. In this example, an example will be shown in which the present invention is applied to a VTR device of a system called 8 mm video, which records and reproduces digital audio signals in a time-sharing manner with video signals.

In FIG. 1, reference numeral 1 indicates a rotary head drum, and magnetic heads 2 and 3 are arranged on this rotary head drum 1 with an angular interval of 180° from each other. In this case, the rotary head drum 1 is rotated at a frame frequency by a servo circuit (not shown) in synchronization with the luminance signal of the recorded video signal.

A magnetic tape (not shown) is run diagonally at a constant speed over an angular range of just over 221 degrees with respect to the rotating peripheral surfaces of these magnetic heads 2 and 3, and
Video signals are recorded and played back within an angular range of 80°, approximately 3
Digital audio signals are recorded and played back within an angular range of 6 degrees. In this case, two types of magnetic tapes can be used for recording and reproducing with the magnetic heads 2 and 3 of this embodiment: metal-deposited tape (ME tape) and metal-coated tape (MP tape).

[0025] Here, the format of the digital audio signal recorded on the magnetic tape and played back by the VTR of this example will be explained. In 16-bit mode (one sample data is one
In the case of the 6-bit mode), each block has the data structure shown in FIG. In other words, one block consists of 44 symbols, and from the beginning they are: synchronization signal, block address, ID, parity (block address and I
D parity), one symbol is allocated to each
Recorded data such as audio data or C2 is recorded in the next 36 symbols.
Parity is assigned, and the last four symbols are assigned C1 parity. In this case, each symbol is composed of 8 bits, and when data processing is performed in the recording system circuit and the reproduction system circuit, it is processed as 8-bit parallel data. The data of this block configuration is made up of 22 blocks as one segment, and one frame is made up of 5 segments. Therefore, one frame is composed of 110 blocks. Then, the C2 parity mentioned above is 1
It is added to each segment to form a product code.

The structure of one frame is shown in FIG. 4, and the structure of one segment is shown in FIG. That is, of the 22 blocks constituting one segment, data such as voice is assigned to 36 predetermined symbols in 18 blocks (see FIG. 3), and C2 parity is assigned to 36 predetermined symbols in the remaining 4 blocks. Note that the data recording section in FIG. 5 has 38 symbols because two predetermined symbols of the header section are added to the above-mentioned 36 symbols. Then, data of this segment configuration is collected into five segments to form one frame of data shown in FIG. 4. For this one frame of data, C2 parity is assigned to 20 blocks out of 110 blocks. By configuring the recording data in this way, C1 parity functions as a correction code for data in each block, C2 parity functions as a correction code for data in each frame (between blocks), and by adding both parities, Constructed as a product code.

[0027] This data structure shows an example of the 16-bit mode; in this example, there is also a 12-bit mode (a mode in which one sample data is formed of 12 bits), and each Two types of recording modes are available for each bit mode: a standard mode in which recording and playback are performed at the standard tape speed, and a long-time mode in which recording and playback are performed at half the tape speed of this standard mode. . In this case, in the case of the same bit mode, the data structure is the same in the standard mode and the long time mode. Note that each of these modes can be selected regardless of whether a metal vapor-deposited tape or a metal-coated tape is used. However, the 8mm video system used in the VTR device of this example is capable of recording in 16-bit mode or 12-bit mode only in the recording mode that performs high-band recording, and cannot be used in recording modes that are not high-band recording. Sometimes, digital audio signals are recorded in an 8-bit mode (conventional mode) with lower recording density. In the case of this 8-bit mode, data recording and playback processing is performed in a different manner than in the 16-bit mode or 12-bit mode, and in this example, only the case of playback in the 16-bit mode or 12-bit mode will be explained. do. Further, in this example, still image data is recorded instead of audio data so that digital still image data can be recorded.

Returning to the configuration of FIG. 1 again, the reproduction signals of the magnetic heads 2 and 3 are supplied to the reproduction amplifiers 5 and 6 via the rotary transformer 4, and the outputs of the reproduction amplifiers 5 and 6 of the respective channels are Supplied to equalizers 7 and 8. Then, the outputs of the equalizers 7 and 8 of the respective channels are supplied to a changeover switch 9 for switching digital audio signals. When the magnetic heads 2 and 3 are located in an angular range of approximately 36° for reproducing the digital audio signal described above, this selector switch 9 selects and outputs the reproduced signal from the magnetic head 2 or 3 within this angular range. let Further, although not shown, another changeover switch selects and outputs a signal reproduced within an angular range of about 180° for reproducing the video signal, and supplies the signal to the video signal reproduction system circuit.

The reproduced signal output from the changeover switch 9 is supplied to a comparator 10 to be converted into binary data, and the output of the comparator 10 is supplied to a demodulation circuit 11. Then, the demodulated signal output from the demodulation circuit 11 is supplied to the C1 error correction circuit 12, and the C1
Perform code error correction. Then, the reproduced data corrected by this C1 error correction circuit 12 is transferred to a selector switch 13.
is supplied to the movable contact 13m. This changeover switch 13, whose switching is controlled by the system controller 30 of this VTR, supplies the reproduced data obtained at the first fixed contact 13a to the C2 error correction circuit 15, and the second
The reproduced data obtained at the fixed contact 13b is supplied to the movable contact 14m of the changeover switch 14. This changeover switch 14 is also controlled by the system controller 30, and supplies the reproduced data obtained at the first fixed contact 14a to the first erasure correction circuit 16 that performs 2 erasure correction + 1 error correction, Second fixed contact 14
The reproduced data obtained at point b is supplied to the second erasure correction circuit 17 that performs 3 erasure correction, and the reproduced data obtained at the third fixed contact 14c is supplied to the third erasure correction circuit 18 that performs 4 erasure correction. supply

In this case, in this example, the movable contact 1 of the changeover switch 13 is controlled by the system controller 30.
3m and the movable contact 14m of the changeover switch 14 are switched based on the error rate of the reproduced data. That is, when the error rate of the reproduced data is the best, the movable contact 13m of the changeover switch 13 is connected to the first fixed contact 13a, and the error is corrected by the C2 parity check in the C2 error correction circuit 15. Then, when the error rate worsens from this state, the changeover switch 13
The movable contact 13m of the changeover switch 14 is connected to the second fixed contact 13b, and the movable contact 14m of the changeover switch 14 is connected to the first fixed contact 14a.
6, a maximum of two erasure corrections and one error correction by C2 parity check are performed. Further, when the error rate worsens from this state, the movable contact 14m of the changeover switch 14 is connected to the second fixed contact 14b, and the second erasure correction circuit 17 performs up to three erasure corrections. Furthermore, when the error rate worsens from this state, the movable contact 14m of the changeover switch 14 is connected to the third fixed contact 14c, and the third erasure correction circuit 18 performs up to four erasure corrections.

Here, the error rate at which the changeover switches 13 and 14 are to be switched is determined based on the number of error flags (number of errors occurring before error correction) for each predetermined unit of reproduced data. This error flag is
This flag is set at a location where an error is detected in the C1 parity check in the C1 error correction circuit 12. The numerical value of the error flag that switches the changeover switches 13 and 14 is determined by the digital audio signal recording mode (16
bit mode, 12 bit mode, etc.), and also changes depending on the tape recording mode (standard mode or long time mode).
The numerical value of the error flag that switches between 3 and 14 is changed. In addition, the type of tape being played (
metal vaporized tape or metal coated tape)
The numerical value of the error flag used to switch the changeover switches 13 and 14 is changed.

In this case, in some recording modes, switching to the second erasure correction circuit 17 or the third erasure correction circuit 18 is prevented even when the number of error flags is the largest. That is, in the case of this example, as shown in Table 1 below, the correction process is determined for the case where the number of error flags is the largest and the error rate is the worst in each recording mode.

[0033]

[Table 1]

As shown in Table 1, the maximum correction process for each recording mode sometimes changes depending on whether the magnetic tape is a metal-deposited tape or a metal-coated tape.

Further, in this example, in addition to changing the recording mode by distinguishing between the standard mode and the long-time mode, the number of error flags to be changed by the changeover switches 13 and 14 is also changed by changing the playback mode. It is set as. The playback mode in this case is variable speed playback, in which in addition to the standard speed (1x speed playback), playback is performed at high speeds such as 2x speed playback, 3x playback, etc. (so-called fast forward playback, rewind playback) In some cases, the error rate value at which the changeover switches 13 and 14 are switched is changed for each playback mode prepared for this VTR. That is, in the case of this example, as shown in Table 2 below, the correction process is determined for the case where the number of error flags is the largest and the error rate is the worst in each reproduction mode.

[0036]

[Table 2]

In this way, each correction circuit 15,
The reproduced data corrected in steps 16, 17, and 18 is supplied to a deinterleaving circuit 19, and a deinterleaving process is performed to restore the data that was interleaved during recording. Then, the reproduced data deinterleaved by the deinterleave circuit 19 is supplied to an interpolation circuit 20 to perform interpolation processing for missing portions, and the interpolated reproduced data is supplied to the digital/analog converter 21. Then, this digital/analog converter 21 converts it into an analog signal, supplies the converted analog signal to a low-pass filter 22 to obtain a good analog audio signal, and supplies this analog audio signal to the audio signal output terminal 23. .

Note that the system controller 30 that controls the operation of the VTR in this example has information on the type of magnetic tape attached to the VTR (metal-deposited tape or metal-coated tape) determined by the tape type determination circuit 31. is provided. In addition, the recording mode information supply terminal 3
Information on the recording mode (standard mode or long time mode) of the signal being played back is supplied to the system controller 30 via the playback speed information supply terminal 33. Current tape playback mode (playback speed, i.e. 1x playback mode,
2x playback mode, etc.) is supplied.

Next, the operation when reproducing a digital audio signal with the reproducing apparatus configured as described above will be explained. The reproduced data demodulated by the demodulation circuit 11 is
C1 by C1 parity check in error correction circuit 12
Error correction of the code is performed, and an error flag is set at the location where the error occurs. Then, the system controller 30 determines the error rate of the reproduced data from the state of this error flag, and changes the changeover switches 13 and 14 based on the error rate determination result, tape type information, recording mode information, and playback status information. The switching is controlled to select the error correction method.

FIG. 2 shows a flowchart for selecting this error correction. First, the system controller selects the video tape (
An operation is performed to determine the type of magnetic tape (magnetic tape) based on information from the tape type determination circuit 31 (steps 101 and 102).
. When it is determined that the tape is a metal-deposited tape (ME tape), the recording mode is determined based on the information obtained from the recording mode information supply terminal 32 (step 103,
104). At this time, if it is determined that the recording mode is the conventional mode (8-bit mode), a corresponding error correction process is performed in a circuit for the 8-bit mode (not shown) (step 105).

Then, when the recording mode is not the conventional mode, it is determined whether it is the 12-bit mode or the 16-bit mode (step 106), and when it is determined that the recording mode is the 12-bit mode, up to 4 erasure corrections are performed (
Step 107). Also, when it is determined that the mode is 16 bits, the data recorded in the 16 bits mode is
It is determined whether the data is digital audio data or digital still image data (step 108), and if it is digital still image data, up to four erasure corrections are performed (step 107). When the data is digital audio data, it is determined whether the recording mode is standard mode (SP mode) or long-time mode (LP mode) (step 109), and if the recording mode is standard mode, up to 4 erasure corrections are performed. (Step 107). Furthermore, when in the long-time mode, the number of erasure corrections is limited to a maximum of three (step 110).

When it is determined in step 102 that the tape is a metal coated tape (MP tape), it is further determined whether or not this tape is compatible with the high band (step 11).
1) If high band is not supported, error correction processing for 8-bit mode is performed (step 105). In addition, when the high band is supported, the recording mode information supply terminal 32
The recording mode is determined based on the information obtained (steps 112 and 113). At this time, if it is determined that the recording mode is the conventional mode (8-bit mode), error correction processing for the 8-bit mode is performed (step 10).
5).

When the recording mode is not the conventional mode, it is determined whether it is the 12-bit mode or the 16-bit mode (step 114), and when it is determined that the recording mode is the 12-bit mode, the data recorded in the 12-bit mode is It is determined whether the data is digital audio data or digital still image data (step 115), and if it is digital still image data, up to four erasure corrections are performed (step 107). Further, when the data is digital audio data, the number of erasure corrections is limited to a maximum of three (step 110).

Further, when it is determined in step 114 that the mode is 16 bit mode, it is determined whether the data recorded in the 16 bit mode is digital audio data or digital still image data (step 116), and the data recorded in the 16 bit mode is determined as digital audio data or digital still image data. If it is data, up to four erasure corrections are performed (step 107). Also, when the data is digital audio data, it is determined whether the recording mode is the standard mode (SP mode) or the long time mode (LP mode) (step 117), and if the recording mode is the standard mode, the maximum
Even erasure correction is performed (step 107). Also, when in long-term mode, up to 2 erasure corrections +
The number of errors is limited to one error correction (step 118).

The processes shown in the flowchart of FIG. 2 are all for the case of normal speed playback (ie, 1x speed playback).

In this way, the system controller 3
By determining the maximum number of erasure corrections, 0, appropriate erasure correction is performed according to the mode, and a good audio signal is reproduced. Figure 6 is a diagram showing changes in reproduction fidelity probability due to differences in mode. Figure 6 shows recording in the standard 12-bit mode using metal evaporated tape (ME tape), which is the mode with the best characteristics. This compares the case of reproducing a signal recorded in the long-time mode, 16-bit mode, using metal-coated tape (MP tape), which is the mode with the worst characteristics. be.

[0047] When a signal recorded on a metal-deposited tape in standard mode is reproduced, the error rate of the reproduced signal is good, so error correction by C2 parity check, 2 erasure correction + 1 error correction, 3 erasure correction, Interpolation processing is performed when the playback condition deteriorates to the extent that it cannot be processed even with 4 erasure correction, and when this interpolation processing is no longer possible, muting processing is performed to stop audio output.

When a signal recorded on a metal-coated tape in long-time mode is reproduced, the error rate of the reproduced signal changes from a good state to error correction by C2 parity check, 2 erasure correction + 1 error correction (Fig. Characteristics indicated by a in 6), when the playback condition deteriorates to the extent that it cannot be processed by 2 erasure correction + 1 error correction, interpolation processing is performed, and when this interpolation processing is no longer possible, mute processing is performed to stop audio output. . Note that the characteristic indicated by b in FIG. 6 shows, for reference, the reproduction fidelity probability when erasure correction is not limited to 2 erasure corrections+1 error correction, but is processed up to 4 erasure corrections.

Comparing the reproduction fidelity probabilities of these two modes, it is found that when recording on a metal-deposited tape in the standard mode, the reproduction condition is relatively good, so even if erasure correction is performed to the maximum capacity, the reproduction fidelity probability remains low. is high, and good error processing corresponding to the error rate is always performed, making the most of the correction ability, and good audio reproduction is performed. When recording on metal-coated tape in long-time mode, the playback conditions are relatively poor, so when erasure correction is performed to its maximum capacity while the error rate of the playback signal is poor, erroneous corrections occur. The probability increases and the reproduction fidelity probability decreases (characteristic b in FIG. 6). In contrast, in this example, even if the error rate of the reproduced signal is poor, erasure correction is limited to 2 erasure corrections + 1 error correction, so erroneous corrections are prevented and the decline in reproduction fidelity probability is suppressed. ing. Therefore, even when reproducing a signal recorded on a metal-coated tape in a long-time mode, good error correction is performed without reducing the reproduction fidelity probability, and good audio reproduction is performed. Similarly, playback is limited to a maximum of 3 erasure corrections when recorded in 16-bit mode in long-term mode on metal-coated tape and in 12-bit mode in long-term mode on metal-coated tape. Although not shown, the reproduction fidelity probability is higher than in the case where up to 4 erasure corrections are processed, and good audio reproduction is performed.

FIG. 7 shows the relationship between each recording mode and the error rate. The linear recording density on the tape in each recording mode is different for the 12-bit mode and the 16-bit mode. They are the same, but the error rates are different. In other words, in descending order of error rate, they are standard mode for metal vaporized tape, standard mode for metal coated tape, long time mode for metal vaporized tape, and long time mode for metal coated tape, and this order is 12-bit mode. It can be seen that the characteristics are the same for the 16-bit mode and the case of 16-bit mode, and that the metal-deposited tape has better characteristics than the metal-coated tape, and the standard mode has better characteristics than the long-time mode.

[0051] In this way, the correction circuits 15,1
The reproduced data corrected by any one of 6, 17, and 18 is supplied to the audio signal output terminal 23 via the deinterleave 19, the interpolation circuit 20, the digital/analog converter 21, and the low-pass filter 22, and the error is corrected properly. A good audio signal is output.

Note that in this example, the maximum number of erasure corrections is limited by changing the reproduction mode, which is the reproduction state of the magnetic tape, so that good audio reproduction can be achieved from this point of view as well. That is, as shown in [Table 2],
The maximum number of erasure corrections when playing at double speed, such as 2x playback, 3x playback, etc., is limited, so as the playback speed increases and the probability of accurate audio data playback decreases, A margin is provided in the correction ability, a decrease in reproduction fidelity probability is suppressed, and relatively good audio can be reproduced even during double-speed reproduction.

The block structure (segment structure) of the data shown in the above embodiment is merely an example, and can be applied to data of other structures.

Further, in the above embodiment, an example was explained in which the present invention was applied to a digital audio signal reproducing circuit of a VTR device, but the present invention can also be applied to various other digital magnetic reproducing devices.

[0055]

[Effects of the Invention] According to the present invention, appropriate erasure correction can be performed in accordance with the number of error flags before error correction in digital data reproduced from a magnetic tape.
Maximum error correction is always performed to the extent that good error correction can be performed according to the playback state, and the playback data is always well corrected.

Further, according to the present invention, appropriate erasure correction is performed according to the reproduction state (playback mode) of the magnetic tape, and the maximum error correction is always possible according to the reproduction state. error correction is performed, and the reproduced data is always well corrected.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a reproduction system circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart diagram for explaining one embodiment.

FIG. 3 is an explanatory diagram showing a block configuration of data in one embodiment.

FIG. 4 is an explanatory diagram showing a frame structure of data in one embodiment.

FIG. 5 is an explanatory diagram showing a segment configuration of data in one embodiment.

FIG. 6 is an explanatory diagram showing the relationship between error rate and reproduction fidelity according to one embodiment.

FIG. 7 is an explanatory diagram showing the relationship between recording mode and error rate according to one embodiment.

[Explanation of symbols]

2, 3 Magnetic head 12 C1 error correction circuit 15 C2 error correction circuit 16 First erasure correction circuit 17 Second erasure correction circuit 18 Third erasure correction circuit 19 Deinterleave circuit 20 Interpolation circuit 21 Digital/analog converter 22 Low pass filter 23 Audio signal output terminal 30 System controller 31 Tape type discrimination circuit 32 Recording mode information supply terminal 33 Playback speed information supply terminal

Claims (2)

[Claims] Claim 1: A digital data reproducing device that reproduces digital data recorded on a magnetic tape, which detects error flags before error correction in digital data reproduced from the magnetic tape, and detects the number of error flags for each predetermined unit. A digital data reproducing device that corrects errors in reproduced data by controlling the maximum number of errors corrected by erasure correction. 2. In a digital data reproducing device that reproduces digital data recorded on a magnetic tape, the maximum number of error corrections by erasure correction is controlled according to the reproduction state of the magnetic tape, and error correction of the reproduced data is performed. A digital data reproducing device designed to perform the following functions.