JPH06111484A - Digital signal recorder - Google Patents

Abstract

(57) [Summary] [Construction] A digital video signal is divided into blocks of 8 × 8 pixels, DCT is performed by the DCT circuit 13 in block units, and DCT coefficient data obtained by this DCT is quantized by a quantization circuit 14. The device is a device that performs the quantization value from the quantization circuit 14 in units of 2 bits consisting of extension bits and information bits, and the maximum number of connected "0" is 6 for any combination of the quantization values. Variable length coding circuit 15 for coding according to the following conversion table, and NRZI for NRZI modulating the coded code.
The modulation circuit 17 is provided. [Effect] There is no need for correlation, and high-density recording can be performed at a high data rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal recording apparatus for obtaining a recording signal on a recording medium by subjecting an input digital signal to orthogonal transformation and quantization and then recording modulation.

[0002]

2. Description of the Related Art As a digital modulation method suitable for a tape head system such as a digital video tape recorder or a digital audio tape recorder as an example of a digital signal recording apparatus, many methods have been proposed and put into practical use until now. . That is, the digital VTR
In a digital signal recording device such as a digital audio tape recorder or the like, which uses a wound magnetic head that cannot reproduce a direct current component in principle, a digital signal such as a digital video signal or a digital audio signal is encoded with a small direct current component. It is converted into and recorded. The conversion methods are roughly classified into the following three types.

The first conversion method is, for example, so-called M ² modulation, 8-10 conversion, 8-14 conversion, etc.
There is a method of limiting the number of code change points. Further, as the second conversion method, there is a method that utilizes the correlation of images or the like, such as so-called 8-8 conversion. Further, as a third conversion method, a so-called scrambled NRZ is used.
There is a method of randomizing the code such as (non-return-to-zero).

[0004]

In the first conversion method, the maximum magnetization reversal interval is uniquely determined, and in terms of suppressing the DC component, the second and third conversion methods are used. It is superior to However, the detection window width becomes narrower (clock frequency becomes higher), which is extremely disadvantageous in high bit rate recording. For example, in the high definition (HD) digital VTR currently commercialized, 14
Recording (8-8 conversion) of 8 Mbps / 1 CH is performed, and if this is M ² modulated, the clock is about 300 M.
Hz (the detection window width is 3.33 ns), which cannot be handled by a general element.

In addition, the second conversion method has a drawback that it cannot be used when images (data) have no correlation, for example, in the case of bit rate reduction image data.

Further, the third conversion method is a basic method of digital recording and is excellent in terms of the detection window width and the minimum magnetization reversal interval, but it has a stochastic element in terms of suppressing the DC component. For example, the maximum magnetization reversal interval is not uniquely determined.

Therefore, the present invention need not be correlated,
Another object of the present invention is to provide a digital signal recording apparatus using a modulation method suitable for high data rate and high density recording.

[0008]

DISCLOSURE OF THE INVENTION A digital signal recording apparatus of the present invention has been proposed in order to achieve the above-mentioned object. For example, an input digital signal such as a video signal is subjected to discrete cosine transform (DCT) or the like. A digital signal recording device in which orthogonal transformation (DCT) is performed by the orthogonal transformation means, and coefficient data obtained by the orthogonal transformation in the orthogonal transformation means is quantized by the quantization means, and the quantized value is an extension bit and an information bit. NRZI (non-return-to-zero identifier) is used to encode the coded coded by the coding means according to a conversion table having 2 bits as one unit.
NRZI modulating means for modulating the ical length) is provided, and the output from the NRZI modulating means is used as a recording signal to a recording medium.

Here, the conversion table of the encoding means is
For any combination of quantized values, the table is made up of combinations of codes in which the maximum number of "0" s connected is 6 or less.

The digital signal recording apparatus of the present invention is also provided with a quantization width limiting means for limiting the quantization width of the quantization means in accordance with the output of the encoding means.

That is, in the recording modulation method applied to the digital signal recording apparatus of the present invention, 1-byte data is converted into data having different occurrence frequencies of "1" and "0" (for example, data according to so-called B2 code). Then, when the NRZI modulation in which the polarity of the converted data is inverted with a code ("1" or "0") with a high frequency of occurrence is performed, a run length (Tmax) can be limited by a digital recording modulation method. is there.

[0012]

According to the digital signal recording apparatus of the present invention, for any combination of quantization values, the quantization value is calculated in accordance with the conversion table consisting of the combination of codes in which the maximum number of "0" s connected is 6 or less. Since the encoding is performed, the maximum magnetization reversal interval never exceeds 6.

[0013]

Embodiments of the digital signal recording apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a digital signal recording apparatus according to an embodiment of the present invention. Recently, it has been attempted to compress or transmit or record digital image data, and in this embodiment, as an example, a discrete cosine transform (DCT) is used for orthogonal transform, and the DCT coefficient data is compressed. Is taken as an example.

That is, in the digital signal recording apparatus of the present embodiment shown in FIG. 1, for example, a digital video signal is divided into blocks of 8 × 8 pixels, and the DCT circuit 13 performs discrete cosine transform (DCT) for each block, A digital signal recording device for quantizing DCT coefficient data obtained by this DCT in a quantizing circuit 14, wherein the quantized value from the quantizing circuit 14 has 2 bits consisting of extension bits and information bits as one unit. Variable length coding circuit 15 for coding according to the conversion table, and NR for NRZI modulating the code coded by the variable length coding circuit 15
ZI modulation circuit 17 is provided, and the NRZI modulation circuit 17 is provided.
Is used as a recording signal to the recording medium.

Here, the conversion table of the variable length coding circuit 15 is made up of a combination of codes in which the maximum number of "0" s connected is 6 or less for any combination of quantized values. ing.

First, prior to a detailed description of the digital signal recording apparatus of the present embodiment shown in FIG. 1, the modulation method used in the apparatus of the present embodiment will be described.

As the variable length coding, a so-called B2 code as shown in Table 1 of Table 1 is known.
In this table (1), d in the table is "0" or "1".
And 0 * n indicates a succession of n “0” s.

[0019]

[Table 1]

When applied to the case where the DCT coefficient data is quantized as in this embodiment, the B2 code has a maximum quantization value of DCT coefficient data of ± 127, and a maximum run length of "0". 63, which is a code obtained by adding EOB (end of block) indicating the end of the DCT block, and the maximum code length is 14 bits. In addition, the B2 code uses 2 bits (denoted as XY) as a pair, X as an extension bit, and Y as an information bit.
The code is extended by 2 bits until X = 0. However, only the code having the maximum code length of 14 bits is treated as the last X as an information bit.

Further, in the B2 code, since the positions of the extension bits and the information bits are clear, they will not be confused with each other. Also, if the extension bits are wrong, one code is wrongly two or two codes are wrongly one. However, as long as the EOB is correctly detected, the error cannot be propagated to the next DCT block. Absent.

Here, looking at the code in the above table (1), it can be seen that the probability of occurrence of "1" in the extension bit is very high. Therefore, by combining the data encoded by the B2 code and the NRZI modulation, it is possible to obtain a recording modulation method in which the run length is limited and the detection window width and the shortest inversion interval which are advantages of the NRZ system are preserved. There is a nature.

However, in the case of encoding with the table of Table (1), the run length cannot be limited (when the source data is continuous at -1). Of course, if the code "00" is not used, this can be prevented, and the maximum magnetization reversal interval (Tmax) in this case becomes 4. However, discarding the 2-bit variable length code is not preferable from the viewpoint of coding gain.

Therefore, in this embodiment, the following changes are made to the conversion table of Table (1).

That is, as a first modification, the variable length codes of -1 and 0 * 1 are exchanged in the conversion table of Table (1). As a result, Tmax becomes 6.

As a second modification, variable length codes of 1 and 0 * 2 are exchanged in the conversion table of Table (1). As a result, Tmax becomes 5. Note that 0 * 1 and 0 * 2 are not continuous.

Further, as a third modification, in the conversion table of Table (1), the code of which the end of the variable length code is "000" is assigned to the source code of 0 * 3 to 0 * 63. As a result, Tmax becomes 3. Note that 0 * n and 0 * 1 or 0 * 2 are not continuous. However, there are 63 variable length codes in Table (1) that end in “000”. However, as mentioned above, 0 * 1 and 0 * 2 are "00",
Since "01" is assigned, there are two more. In this embodiment, use of this code is prohibited. Even if the use is prohibited in this way, there is no problem in discarding this code because the 14-bit code is redundant.

By properly mapping the B2 code and the source code as described above and subjecting the code string to NRZI modulation, it becomes possible to obtain a recording signal capable of limiting the maximum magnetization reversal interval (Tmax).

The above-mentioned digital recording modulation method applied to the apparatus of this embodiment has the following features.

First, as a first feature, the present invention can be applied to a bit rate reduced image signal (a signal having no correlation). The second feature is that the detection window width is wide, which is very advantageous for recording a high data rate such as a high definition video signal (the clock frequency is the same as the data rate). The third feature is that the minimum magnetization reversal interval does not become narrow (same as the data rate). The fourth feature is that the maximum magnetization reversal interval is limited (Tmax3).

That is, comparing the modulation method applied to the apparatus of this embodiment with the conventional modulation method, Table (2) in Table 2
And the modulation method in this embodiment is Tma.
It can be seen that the combination of x, Tmin, and the detection window width is superior to the conventional recording modulation method.

[0032]

[Table 2]

From the above, by using the recording modulation method of this embodiment, the advantages of NRZ (NRZI) recording can be preserved as they are, and a recording code with a limited maximum magnetization reversal interval can be obtained. Therefore, by using this recording modulation method, it becomes possible to realize a high density, high data rate digital signal recording device (for example, VTR).

Next, returning to FIG. 1, details of the digital signal recording apparatus (VTR for performing bit rate reduction) of this embodiment to which the above-described recording modulation method is applied will be described.

In FIG. 1, the analog input video signal supplied to the input terminal 10 is A / D (analog / analog).
The digital) conversion circuit 11 quantizes the signal with an appropriate number of bits (e.g., 8 bits) and a sampling frequency to convert the signal into a digital signal. The A / D conversion circuit 1
The digital signal from 1 is sent to a blocking circuit 12 for forming the DCT block. As shown in FIG. 2, in the block circuit 12, the time series of the digital signal is continuously output from adjacent 8 horizontal pixels and 8 vertical pixels in one field by using, for example, a memory. Convert (block) as described.

For example, 6 of data (8 × 8) as shown in FIG. 3 which is time-series converted by the blocking circuit 12 is used.
The four samples are sent to the DCT circuit 13 that performs two-dimensional DCT. By performing the two-dimensional DCT in the DCT circuit 13, the 64 sample data of the block is decomposed into a two-dimensional spatial frequency component as shown in FIG. 4, for example. These frequency components are determined in order of, for example, higher statistical energy, and are scanned and output in the determined order (from low frequency components to high frequency components) by so-called zigzag scanning shown in FIG. 5, for example. It

The data DCTed by the DCT circuit 13 is sent to the next quantization circuit 14. The quantization circuit 14 performs quantization (requantization) with different weighting for each frequency component. Specifically, the low frequency component is densely quantized, and the high frequency component is roughly quantized (divided by a predetermined constant).

That is, the quantization circuit 14 shown in FIG.
As shown in A of the above, for the DCT output from the low frequency component to the high frequency component obtained by the zigzag scanning in the DCT circuit 13, a large constant is obtained from the low frequency component to the high frequency component. Processing is performed so as to perform division and obtain the result (quantized output).

The quantized output of the quantization circuit 14 is sent to the variable length coding circuit 15. The variable length coding circuit 15 reduces the data amount by performing variable length coding using the conversion table obtained by partially changing the B2 code of the present embodiment described above. That is, a general image signal originally has a low level of high frequency components, and since the quantizing circuit 14 performs division by a large constant, the probability that "0" data continues is high. Therefore, the continuous "0" data is 1
If it is represented by one code (that is, run length coding), the data amount can be further reduced.

Further, the apparatus of the present embodiment is provided with a quantization limiting circuit 18 as a quantization width limiting means for limiting the quantization width in the quantization circuit 14 according to the output of the variable length coding circuit 15. Is also provided.

That is, when the image signal is encoded by the variable length code, the amount of generated data usually changes depending on the pattern. However, the VT as in the device of this embodiment
Since R requires editing in units of one field or one frame, it is necessary to make the data amount constant below this unit. Therefore, the quantization limiting circuit 18
Changes the weighting constant in the quantizing circuit 14 to control (make constant) the amount of generated data.

Specifically, for example, 1 of video data
To realize / 4 compression, it is necessary to convert video data of 64 samples (1 DCT block of 8 bits) into data of 16 samples (1 DCT block of 8 videos). The quantization limiting circuit 18 of the present embodiment counts the data after variable-length coding in nDCT blocks (n = 100) and determines whether the number of bits is larger or smaller than n × 16 × 8 bits (reference value). The quantization width (divisor of division) of the quantization circuit (division circuit) 14 is switched.

In the apparatus of this embodiment, the generated data amount can be substantially matched with the target value by thus feeding back the quantization circuit 14 through the quantization limiting circuit 18. In this case,
It is necessary to record the control information (divisor) of the quantization width in the quantization limiting circuit 18 as an ID together with the recording signal.

Next, an error correction code addition circuit 16 adds an error correction code to the data from the variable length coding circuit 15 in units of one field or one frame, and at the same time, an appropriate number of samples is used. A sync block is constructed.

I from the error correction code adding circuit 16
The data sequence to which D and SYNC are added is sent to the NRZI modulation circuit 17 that performs the NRZI modulation in this embodiment as described above. The NRZI modulating circuit 17 performs the above-described processing of the present embodiment on the variable length coded data portion of the data sequence from the error correction code adding circuit 16 to generate a recording bit sequence with a limited Tmax. obtain.

The above error collection code is T
Although the max is not limited, this data is at most about 10% of the recorded data, so this is not a big problem. Of course, it is possible to limit Tmax by subjecting this data to, for example, 8-10 conversion.

The recording bit sequence from the NRZI modulating circuit 17 is sent as a recording signal to be sent to the recording medium via the output terminal 19 to a later stage structure such as a recording amplifier and a recording head (not shown).

Next, the configuration of a reproducing apparatus corresponding to the digital signal recording apparatus of the present embodiment shown in FIG. 1 described above is shown in FIG.
Shown in.

In FIG. 7, the reproduced data reproduced from the recording medium by a reproducing head, a reproducing amplifier, etc., which are not shown, is transmitted through a terminal 39 to the NRZI demodulation circuit 37.
Sent to. In the NRZI demodulation circuit 37, N of FIG.
NRZI demodulation corresponding to the modulation in the RZI modulation circuit 19 is performed.

The output of the NRZI demodulation circuit 39 is passed through a TBC (time base correction) circuit 38 which corrects the time axis so that the time axis of the reproduced signal matches the reference signal.
It is sent to the inverse conversion circuit 35 through the error correction circuit 36 that performs error correction. In the inverse conversion circuit 35,
Inverse conversion of the variable length code of the variable length coding circuit 15 of FIG. 1 is performed.

The output of the inverse conversion circuit 35 is sent to the inverse quantization circuit 34 which performs the inverse quantization corresponding to the quantization in the quantization circuit 14 of FIG. That is, the inverse quantization circuit 3
In 4, a process of multiplying by a divided number is performed as an operation reverse to the division in the quantization circuit 14 of FIG.
By passing through the inverse quantization circuit 34, a restored value (DCT block) approximate to the original value can be obtained.

Each frequency component of the DCT block obtained by the inverse quantization circuit 34 in this way is the inverse DCT circuit 33.
Is converted into an 8 × 8 two-dimensional image signal as shown in FIG. The 8 × 8 pixels from the inverse DCT circuit 33 are sent to an inverse blocking circuit 32 which is composed of a memory or the like and solves the 8 × 8 block.
2 is converted into a normal television signal time series. After that, it is converted into an analog signal by the D / A conversion circuit 31 which performs digital / analog conversion, and then output from the output terminal 30 as an output video signal.

[0053]

As described above, in the digital signal recording apparatus of the present invention, 2 bits consisting of extension bits and information bits are set as one unit, and "0" is set for any combination of quantization values. The quantized value is coded according to a conversion table composed of a combination of codes whose maximum number of connections is 6 or less, and the coded code is NRZI
Since the signal is modulated and used as a recording signal on the recording medium, there is no need for correlation, and high-density recording can be performed at a high data rate.

Further, in the digital signal recording apparatus of the present invention, since the quantization width is limited according to the encoded output, the amount of generated data can be made constant.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a digital signal recording apparatus of an embodiment of the present invention.

FIG. 2 is a diagram for explaining blocking.

FIG. 3 is a diagram showing an 8 × 8 original pixel.

FIG. 4 is a diagram showing each frequency component after DCT.

FIG. 5 is a diagram for explaining zigzag scanning.

FIG. 6 is a diagram for explaining division and multiplication during quantization and inverse quantization.

FIG. 7 is a diagram showing a schematic configuration of a reproducing apparatus corresponding to the digital signal recording apparatus of the embodiment of the present invention.

FIG. 8 is a diagram showing 8 × 8 restored pixels.

[Explanation of symbols]

 11 ... A / D conversion circuit 12 ... Blocking circuit 13 ... DCT circuit 14 ... Quantization circuit 15 ... Variable length coding circuit 16 ... Error correction Code addition circuit 17 ... NRZI modulation circuit 18 ... Quantization limiting circuit 31 ... D / A conversion circuit 32 ... Deblocking circuit 33 ... Inverse DCT circuit 34 ... Inverse quantization circuit 35 Inverse conversion circuit 36 Error correction circuit 37 NRZI demodulation circuit 38 TBC circuit

Claims (3)

[Claims] 1. A digital signal recording device in which an input digital signal is orthogonally transformed by an orthogonal transformation means, and coefficient data obtained by the orthogonal transformation by the orthogonal transformation means is quantized by a quantization means. Coding means for coding in accordance with a conversion table in which 2 bits consisting of bits and information bits are used as one unit, and NRZI modulating means for NRZI modulating the code coded by the coding means are provided. A digital signal recording device characterized in that the output of the recording medium is a recording signal to a recording medium. 2. The conversion table of the encoding means is a table composed of code combinations in which the maximum number of connected 0s is 6 or less for any combination of quantized values. Item 1. A digital signal recording device according to item 1. 3. A digital signal recording apparatus according to claim 1, further comprising: quantization width limiting means for limiting the quantization width of the quantization means according to the output of the encoding means.