JPS63205858A - Sound signal recording system - Google Patents

Abstract

PURPOSE:To enlarge a transmission capacity by encoding a pulse code modulated sound signal by means of a CIRC (Cross. Interleave. Reed. Solomon. Code) system, and further, quaternary-coding it and multiplexing it in the vertical fly back period of a video signal. CONSTITUTION:The video signal is supplied to a time division multiplex circuit 2 through a pre-emphasis circuit 1. On the other hand, a digital sound signal is supplied to a CIRC encoder 3, and a quaternary code circuit 4 divides an encoded an encoded data into every two bits, and a quaternary coded series is formed. The quaternary signal, which has an instantaneous level corresponding to a respective code, is supplied to the above mentioned time division multiplex circuit 2, and by multiplexing it to the vertical fly back period of the video signal, the data transmission capacity is enlarged, and at the same time, a burst error is sufficiently corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for multiplexing and recording an audio signal onto a video signal.

BACKGROUND ARTMUS compresses high-definition television signals to a bandwidth of approximately 8 MHz to enable transmission by broadcasting satellites.
E (Multiple 5ub-Nyquist S
A method called "allpling encoding" has been proposed. According to this MUSE system, it is also easy to record high-quality television signals onto a recording medium such as an optical video disc.

The bandwidth obtained by this MUSE method is approximately 8MHz.
The audio signal is encoded using a method used in satellite broadcasting to multiplex the audio signal onto a high-definition television signal (hereinafter referred to as the MUSE signal), and then compressed in the time axis, and then compressed for transmission using the 4-phase DPSK method. A method has been proposed in which RF multiplexing is performed in the vertical retrace period of a MUSE signal that has been subjected to RF signal conversion. In addition, when recording a MUSE signal on an optical video disc, a binary signal obtained by compressing the time axis of an audio signal encoded at a bit rate of 1.024 Mb/S is used in the vertical blanking period of the MUSE signal. A method of baseband multiplexing and recording has been proposed.

However, since the former method uses a signal format for satellite broadcasting, error correction can be performed well against random errors, but it cannot perform sufficient error correction against burst errors peculiar to discs. There is a drawback that there is no In addition, in the latter method, binary signals are multiplexed during baseband multiplexing, so the data transmission capacity is insufficient. The disadvantage is that it cannot be recorded.

SUMMARY OF THE INVENTION Therefore, the present invention provides an audio signal recording method that can sufficiently perform "burst error correction" and increase data transmission capacity sufficiently, thereby making it possible to record high-quality audio signals. It is to be.

The audio signal recording method according to the present invention converts PCM audio signals into CI RC (Cross Interleave).
The video signal is encoded using the Reed-8 olomon code (Reed-8 olomon code) method, and the resulting code is 4-valued to obtain a 4-value signal, which is baseband multiplexed and recorded during the vertical retrace period of the video signal.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, the MUSE signal is supplied to a pre-emphasis circuit 1, subjected to emphasis, and then supplied to a time division multiplex circuit 2.

On the other hand, depending on the predetermined clock frequency and quantization number, the A/D
The converted digital audio signal is sent to the CIRC encoder 3.
is supplied to. The CIRC encoder 3 is formed based on the CIRC method, which is an error correction encoding method used for digital audio discs. In the CIRC encoder 3, 24 symbols of data are treated as one block, interleaved and parity is added, and one block consisting of 32 symbols (one symbol is 8 bits) is formed. The data encoded by this CIRC encoder 3 is supplied to a 4-probability encoding circuit 4 and subjected to 4-probability encoding. That is, C.I.
The output data of the RC encoder 3 is divided into two bits and converted into a four-level code sequence. A Gray code is used as each code in this four-level code series, and even if an error occurs in an adjacent level during level identification, the number of bit errors will be 1 bit. In other words, as described later, 0
The 2-bit code of 0.01.11.10 corresponds sequentially to each of four different levels.

The encoded data is supplied to the time axis compression circuit 5 and subjected to time axis compression. Of the signal configuration of the MUSE signal, the number of lines that can be used for audio signal recording is approximately 68 lines in one frame (1125 lines).

Therefore, a compression ratio of 68/1125 is required. Note that the time axis compressor 5 does not necessarily need to be placed after the 4-probability encoding circuit 4, but may be placed before it. The output of the time axis compression circuit 5 is supplied to a 4-level circuit 6. 4
The leveling circuit 6 makes the four-level codes 0O101, 11, and 10 correspond to each level of level 0, level 1, level 2, and level 3, respectively. That is, as shown in FIG. 2, one sample value of the video signal has an 8-bit level (25 bits).
6 levels), whereas the audio signal uses only 70% of the range of the video signal. For example, the audio signal is designed to correspond to any one of 38 levels (level 0), 98 levels (level 1), 158 levels (level 2), and 218 levels (level 3) of the video signal.

When the level range of the audio signal is increased (approximately 100%), overshoot and undershoot occur due to the influence of pre-emphasis, and the frequency band of the recording signal is occupied more than necessary, which tends to cause distortion. On the other hand, if it is made smaller, the S/N ratio of the data deteriorates, and the influence of noise on the four-level discrimination increases. Therefore, as in the example, 7
It is preferable to use a range of about 0%.

The time division multiplexing circuit 2 time division multiplexes the 256-level video signal and the 4-level audio signal output from the pre-emphasis circuit 1. That is, the audio signal is transmitted to each of the 6th line to the 39th line within the vertical retrace period of the first field of the video signal and the 568th line to the 601st line of the second field, a total of 68 lines, as shown in FIG. It is inserted into the formed audio data section. The frequency of the sampling clock of the MUSE signal is 16.2 MHz, and the number of clocks per line is 480. In each line into which an audio signal is inserted, an HD signal exists in the first 12 clock periods. An interval of 464 clocks which is separated by a guard interval of two clocks from this HD signal interval is an audio data interval, and an interval of two clocks following the audio data interval is a guard interval. Guard sections of two clocks placed before and after the 464 clock are prepared to reduce the influence on the HD signal. Also, 46
The number of clocks of 4 clocks is taken into consideration so that the number of bytes in one line is 116 bytes, and 1 byte (8 bits) of data is not configured across different lines.

The output of the time division multiplexing circuit 2 is supplied to a transmission filter 7 composed of, for example, an FIR digital filter, and its frequency band is limited to a predetermined width.

In order to minimize code amount interference, the overall characteristic formed by the transmission filter 7 and the reception filter 24, which will be described later, is made to be a cosine roll-off characteristic. Increasing the roll-off rate α here widens the band and S/
N decreases. On the other hand, if it is made smaller, the configuration will become more complex in order to accurately realize that characteristic (steep characteristic). Therefore, it is preferable to set the roll-off rate α to about 0.3, for example.

The output of the transmission filter 7 is supplied to a D/A converter 8 and converted into an analog signal. The output of the D/A converter 8 is emphasized by a pre-emphasis circuit 9 and then supplied to an FM modulation circuit 10 . In the FM modulation circuit 10, a carrier wave of a predetermined frequency is frequency-modulated by the supplied signal. The output of this FM modulation circuit 10 is supplied to an E10 modulator (not shown) or the like via a limiter 11 and recorded on a video disc.

Since audio data is inserted as a four-value signal by the recording device described above, the audio data section of each line has one value.
This means that 2 bits of data can be inserted per clock, and 116 bytes of audio data can be multiplexed.

Here, in CIRC encoding, one block is formed of 32 bytes, so 3 blocks of data and 20 bytes of data are inserted into the audio data section per line, and the vertical retrace line An audio data block is recorded in each line in the period as shown in FIG. 4, and 245 blocks of audio data can be recorded in one entire frame. The data transmission capacity in this case is 1.8816 Mbps, which enables multiplexing of two channels of audio data sampled at 44.1 kHz and 16-bit linear quantized. Further, since the CIRC method having a means for converting burst errors into random errors by interleaving is adopted as the encoding method, it is possible to perform sufficient error correction of burst errors. FIG. 5 is a block diagram showing a part of a reproducing apparatus for reproducing information recorded on a video disc by the recording apparatus as described above. In the figure, an RF multiplied signal read from a video disc is supplied to an FM demodulation circuit 21 and frequency demodulated. In the demodulated output, the level of the component emphasized during recording is returned to the original level by the de-emphasis circuit 22.

The output of the de-emphasis circuit 22 is supplied to a reception filter 24 to have its band limited, and then converted into a digital signal by an A/D converter 25. This A/D
The output of the converter 25 is supplied to a time division separation circuit 26 where it is time division separated into a video signal and an audio signal. The video signal is supplied to a de-emphasis circuit 23, and the level of the component emphasized during recording is returned to the original level.

The output of this de-emphasis circuit 23 is supplied to a MUSE7' coder (not shown) or the like.

On the other hand, the audio signal is supplied to a four-level discrimination circuit 27, which of the four levels mentioned above is identified and converted into a four-valued symbol. The signal converted into a four-valued symbol is subjected to time-axis expansion by a time-axis expansion circuit 28, and then supplied to a four-valued combination encoding circuit 29, where the four-valued symbol is converted into a normal binary symbol. The output of this four-value set encoding circuit 29 is C
After being supplied to an IRC decoder and subjected to processing such as error detection and correction, it is supplied to an audio decoder (not shown) and the like.

The characteristics of the pre-emphasis circuit and the de-emphasis circuit 22 are set so that the emphasis of the audio signal is optimal. Since the frequency spectrum of the PCM audio signal has relatively many high frequency components, the amount of emphasis is set relatively shallow. Since the pre-emphasis circuit and the de-emphasis circuit 22 are constructed of analog circuits, their characteristics can be set relatively freely, and their constructions are not very complicated. In the case of the emphasis characteristic as shown in FIG. 6, for example, m-1,7, fo-IMHz is used.

On the other hand, the characteristics of the pre-emphasis circuit 1 and the de-emphasis circuit 23 are set so that the emphasis of the video signal is optimized. However, since the video signal is also emphasized by the pre-emphasis circuit 9 and the de-emphasis circuit 22, the overall characteristics of both are set to be optimal. Since the frequency spectrum of the video signal has relatively few high frequency components, the amount of emphasis is set relatively deep. Since shallow emphasis is performed by the pre-emphasis circuit 9 and the de-emphasis circuit 22, the emphasis of the pre-emphasis circuit 1 and the de-emphasis circuit 23 can be shallower than when the characteristics are set alone.

Therefore, although these are constructed from digital circuits, their scale can be made smaller than when the characteristics are set alone.

In the above embodiment, the pre-emphasis circuit and the de-emphasis circuit 23 are inserted into the video signal path, but the same effect can be obtained by inserting them into the audio signal path. It is also possible to provide a dedicated emphasis circuit for each path of the video signal and the audio signal.

Figure 7 shows the relationship (theoretical value) between the S/N ratio (horizontal axis) and symbol error rate (vertical axis) when audio signals are transmitted in binary, 4-value, 8-value, and 16-value format. There is. Here, the S/N ratio is the ratio between the peak-to-peak value of the data level and the effective value of noise, and the noise is Gaussian noise. As is clear from the figure, in order to achieve a symbol error rate of 1×10″4, an S/N ratio of 27 dB is required in the case of 4-values, and about 35 in the case of 8-values. It is possible to secure an S/N ratio of approximately 35 clB for the reproduced baseband signal from the
The symbol error rate also deteriorates due to factors such as jitter and code amount interference. It is also necessary to consider deterioration due to dropout, which is unique to disks. Therefore, it is difficult to record and reproduce data with eight or more values.

Since it is advantageous for signal processing to set the level to 2n values, it is preferable to set the level to 4 values as in the embodiment.

Effects of the Invention As detailed above, the audio signal recording method according to the present invention has P.
The CM audio signal is encoded using the CIRC method, and the resulting code is 4-valued. The resulting 4-value signal is multiplexed and recorded in the vertical blanking period of the video signal, so the number of bits per clock is low. 2, which increases the data transmission capacity.At the same time, since the encoding is performed using the CIRC method, which has means for converting burst errors into random errors by interleaving, it is possible to perform sufficient error correction of burst errors. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of recording signal levels, and FIGS. 3 and 4 are
FIG. 5 is a block diagram showing a device for reproducing the signal recorded by the device in FIG. 1. FIG. 6 is a diagram showing the emphasis characteristics. 7 are diagrams showing theoretical values of error rates.

Claims (2)

[Claims] (1) An audio signal recording method in which a PCM audio signal is multiplexed with a video signal and recorded on a recording medium, and the audio signal is
The obtained code is divided into two bits each to form a quaternary code sequence, and a quaternary signal having an instantaneous level corresponding to each code of the quaternary code sequence is converted into the video signal. An audio signal recording method characterized by multiplexing and recording during the vertical retrace period. (2) In a video signal in which one line is represented by 480 samples, the 4-value signal is a signal corresponding to each sample, and the 4-value signal is expressed as 464/4 within an interval of 1 line.
Claim 1, characterized in that the four-level signal corresponding to 245 blocks of codes obtained by the CIRC method is multiplexed in a vertical retrace period within one frame period so as to be inserted into 80 sections. Audio signal recording method described in section.