JP3555735B2 - Synchronization method between digital audio signal and digital video signal - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for synchronizing a digital audio signal and a digital video signal in an apparatus for reproducing a digital audio signal and a digital video signal.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, digital video tape recorders (hereinafter referred to as digital VTRs) that record video and audio signals using digital signals have been developed. FIG. 7 shows a recording format of such a digital VTR on a tape. In the figure, a margin is provided at both ends of the track, and an ITI area for reliably performing after-recording, an audio area for recording an audio signal, and a video area for recording a video signal are provided from the recording start end side inside the margin. , A sub-code area for recording subsidiary data. Note that an inter-block gap (IBG) is provided between each area to secure the area. Such tracks are collected for 10 tracks and recorded as information for one frame (525/60 system).
[0003]
Next, details of signals recorded in each of the above areas will be described.
(1) ITI Area As shown in the enlarged portion of FIG. 7, the ITI area is composed of a 1400-bit preamble, 1830-bit SSA (Start-Sync Block Area), 90-bit TIA (Track Information Area), and 280 bits. It consists of a postamble.
[0004]
Here, the preamble has a function such as a run-in of the PLL at the time of reproduction, and the postamble has a role to gain a margin. The SSA and TIA are configured in units of 30-bit block data, and a predetermined SYNC pattern (ITI-SYNC) is recorded in the first 10 bits of each block data.
[0005]
In the 20-bit portion following the SYNC pattern, the SYNC block number (0 to 60) is mainly recorded in the SSA, and the 3-bit APT information (APT2 to APT0) is mainly recorded in the TIA. An SP / LP flag to be identified and a PF flag indicating a reference frame of the servo system are recorded. APT is ID data that defines a data structure on a track, and takes a value “000” in the digital VTR of the conventional example.
[0006]
From the above description, since a large number of sync blocks with a short code length are recorded at fixed positions on the magnetic tape in the ITI area, for example, the position at which the 61st SYNC pattern of SSA is detected from the reproduced data is tracked. By using as a reference for defining the above-mentioned post-recording position, the position to be rewritten at the time of post-recording can be specified with high accuracy, and good post-recording can be performed.
[0007]
(2) Audio Area The audio area has a preamble and a postamble before and after the audio area as shown in the enlarged portion of FIG. 7, and the preamble is used for a run-up for pulling in the PLL and for detecting the audio SYNC block before. Of pre-SYNC. The postamble includes a post SYNC for confirming the end of the audio area, and a guard area for protecting the audio area during video data dubbing.
[0008]
Audio data recorded in the area sandwiched between the amble areas is generated as follows. First, an audio signal for one track to be recorded is subjected to A / D conversion and shuffling, then framing is performed, and parity is further added. FIG. 8 shows a format to which parity is added by performing framing. In the figure, 5-byte audio accompanying data (hereinafter referred to as “AAUX data”) is added to the beginning of 72-byte audio data to form 77-byte data per block, and these are vertically stacked into 9 blocks for framing. Then, an 8-bit horizontal parity C1 and a vertical parity C2 corresponding to five blocks are added thereto. The digital signal of 1,080 × (25/24) = 10,500 bits obtained by subjecting the signal of 90 × (9 + 5) × 8 = 1,080 bits obtained in this way to 24-25 conversion is one track shown in FIG. Is recorded in the audio section inside.
[0009]
(3) Video Area The video area has the same preamble and postamble as the audio area as shown in the enlarged part of FIG. However, it differs from that of the audio area in that the guard area is formed longer. Video data is formed between a preamble and a postamble.
[0010]
(4) Subcode area The subcode area is an area provided mainly for recording information for high-speed search, and is formed so as to be sandwiched between a preamble and a postamble before and after. However, a pre-SYNC and a post-SYNC are not provided unlike the audio area and the video area.
The SYNC blocks constituting the audio area, the video area, and the subcode area described above are subjected to the 24/25 conversion in recording modulation (recording is performed by converting every 24 bits of a recording signal into 25 bits). Since the code is subjected to a recording modulation scheme in which a tracking control pilot frequency component is added to the code, the recording data amount in each area has the number of bits as shown in FIG.
[0011]
(5) Structure and Type of Pack As described above, in the digital VTR, an AAUX area of an audio area on a tape is used as an area for recording accompanying data, and the unit is a pack having a fixed length of 5 bytes. Be composed. Of these 5 bytes, the first byte (PC0) is an item indicating the content of the data. For example, “AUX SOURCE” and “AUX SOURCE CONTROL” in FIG. 9 are represented.
[0012]
“AAUX SOURCE” is used to record accompanying data relating to audio. That is, as shown in the figure, a flag (LF) indicating whether the audio sample frequency is locked with the video signal, the number of audio samples per frame (AF SIZE), the number of audio channels (CH), each audio Information on channel stereo / monaural mode (PA and AUDIO MODE), information on television system (50/60 and STYPE), presence / absence of emphasis (EF), time constant of emphasis (TC), sample frequency (SMP) , Quantization information (QU) is recorded.
[0013]
“AUX SOURCE CONTROL” is SCMS data (the upper bits indicate the presence or absence of a copyright, and the lower bits indicate whether or not the original tape), copy source data (which indicates whether the signal is an analog signal source), copy generation. Data, cipher (encryption) type data (CP), cipher data (CI), a flag (REC ST) indicating whether or not a recording start frame, a flag (REC END) indicating whether or not a recording last frame, original recording / after-recording Recording mode data (REC MODE) such as recording / insert recording, a flag (DRF) indicating a direction, reproduction speed data, and a genre category of recording contents are recorded.
[0014]
By the way, in a digital VTR, an audio signal is recorded together with a video signal. At this time, a field frequency in a 525/60 video signal is 59.94 Hz. On the other hand, the sampling frequency of the audio signal is set to 48 kHz, 44.1 kHz or the like. Therefore, the relationship between the cycle of one video frame and the sampling frequency of the audio signal does not have an integer ratio.
[0015]
Therefore, in the audio signal, the relationship between the average video frame and the sampling frequency of the audio signal is defined by a combination including an integer number of samples. For example, when the sampling frequency of the audio signal is 48 kHz, a combination of 1601 samples, 1602 samples, and 1600 samples of the audio signal per video frame is used.
[0016]
An audio signal is recorded on ten tracks on which data for one video frame is recorded, but may have a different number of samples for each video frame. Therefore, it is necessary to record information on the number of samples of the audio signal in one video frame. This information is recorded in “AF SIZE” in “AUX SOURCE”.
[0017]
Then, this “AF SIZE” is read at the time of reproduction, and is used, for example, as a clue for a phase control loop (hereinafter, referred to as PLL) in an audio reproduction circuit. That is, since the audio signal must be in phase with the video frame, it is necessary to change the frequency of the reproduction clock by this “AF SIZE”.
[0018]
[Problems to be solved by the invention]
However, in the above-described conventional example, when acquisition of "AF SIZE" information indicating the number of samples of the audio signal fails, or when accurate information cannot be obtained, the phase of the audio signal and the video frame become out of phase. was there.
[0019]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention provides an audio signal of an audio signal included in a predetermined period of the video signal in order to synchronize the digitized audio signal and the video signal. When reproducing a medium in which a signal indicating the number of samples is recorded together with a video signal and an audio signal of the predetermined period, a signal indicating the predetermined period generated from a reference clock of the reproduced video signal; And a digital audio signal and a digital video signal, wherein a clock frequency of the reproduced video signal or the reproduced audio signal is changed according to a result of the comparison. Wherein the signal indicating the number of audio samples is transmitted during the predetermined period. A value determined by majority decision is selected from the data of the number of audio samples inserted a plurality of times, and no signal indicating the number of audio samples included in the predetermined period is obtained. In this case, a signal indicating the number of audio samples of the audio signal included in the period before the predetermined period is substituted, or a value calculated from the sampling frequency of the audio signal and the frame frequency of the video signal is substituted. A method for synchronizing a digital audio signal and a digital video signal is provided.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of a method for synchronizing a digital audio signal and a digital video signal according to the present invention will be described with reference to the drawings.
The signal reproduction system of the digital VTR has, for example, a configuration as shown in FIG. In the figure, a reproduced signal obtained from a magnetic tape (not shown) by a magnetic head 1 is supplied to an equalizer 3 after being amplified by a preamplifier 2. Then, the signal subjected to the equalization processing by the equalizer 3 is further supplied to a digital signal detection circuit 4, where digital signals corresponding to logical values "1" and "0" are obtained. This digital signal is supplied to the digital signal processing circuit 5, and the AF SIZE extracting / analyzing means 6 extracts and analyzes "AF SIZE".
[0021]
The AF SIZE extracting / analyzing means 6 extracts "AF SIZE" in "AUX SOURCE" and analyzes the data to obtain the number of audio signal samples in one frame (hereinafter referred to as audio sample number). The data of the obtained number of audio samples is stored in the memory 7 and the first latch circuit 8. Note that the memory 7 stores data of the number of audio samples in “AF SIZE” over a plurality of past frames and prepares for a case where this data cannot be obtained. On the other hand, the first latch circuit 8 stores data on the number of audio samples of the current frame.
[0022]
The switch 19 is normally on the b side, but is switched to the a side when data on the number of audio samples in the current frame cannot be obtained, or when an error occurs even if data on the number of audio samples in the current frame can be obtained. .
[0023]
Next, some examples of processing steps by the arithmetic circuit 9 will be described. The arithmetic circuit 9 determines a substitute value of the data when the data of the number of audio samples is not obtained, or when there is an error even if the data of the number of audio samples can be obtained. In particular,
An average value of the data of a plurality of audio samples over a certain period of time stored in the memory 7 is obtained, and the average value is used as a substitute value.
[0024]
From the data of a plurality of audio samples over a certain period in the past stored in the memory 7, the average value of the remaining data excluding the data having an erroneous value and the data having a value exceeding a predetermined value is calculated. And use it as a substitute value.
[0025]
From the data of a plurality of audio samples over a certain period in the past stored in the memory 7, the data of the same maximum value is obtained. In this case, when the data of the same value with the largest number is the same, the substitute value is obtained by a method such as adopting data later in time or adopting a value close to the data of the preset value.
[0026]
Comparing a data pattern of a plurality of audio samples over a predetermined period in the past with a plurality of preset data patterns, and examining which of the plurality of preset data patterns the past data pattern corresponds to; A substitute value that is predicted by this is calculated.
For example, arithmetic processing such as
[0027]
On the other hand, a one-frame periodic pulse (frame pulse) is created by the frequency divider 11 from the video signal clock output from the video signal clock generator 10.
The counter 13 counts the VCO output from the VCO 16 for the audio signal clock, and counts the count value for one frame up to the second latch circuit 12 by the edge of the frame pulse output from the frequency divider 11. To save. Then, the counter 13 is reset.
[0028]
Next, when the switch 19 is on the a side, the comparison circuit 14 compares the content stored in the second latch circuit 12 with the substitute value obtained by the arithmetic circuit 9, and the switch 19 is on the b side. In some cases, the contents stored in the second latch circuit 12 and the contents stored in the first latch circuit 8 are compared. For example, this comparison is performed once per frame, immediately after the edge of the frame pulse arrives.
[0029]
The DC level adjustment circuit 15 uses a preset value as the DC data when the power is turned on, converts the data to a DC level via a D / A converter (not shown), and applies the converted data as a control voltage for the VCO 16.
Next, as shown in FIG. 2, when the count value of the counter 13 is larger than a value desired by the data of the number of audio samples according to the comparison result by the comparison circuit 14, the control voltage is reduced in a direction to lower the output frequency of the VCO 16. To change the DC data, the DC data stored in the memory 20 in the DC level adjustment circuit 15 is changed by the third latch circuit 21. When the count value of the counter 13 is smaller than a value desired by the data of the number of audio samples according to the comparison result by the comparison circuit 14, a DC level adjustment circuit is used to change the control voltage in a direction to increase the output frequency of the VCO 16. The DC data stored in the memory 20 in the memory 15 is changed by the third latch circuit 21.
[0030]
Specifically, when the content of the first latch circuit 8 is smaller than the content of the second latch circuit 12, a negative value is input to the DC level adjustment circuit 15, and the content of the first latch circuit 8 is changed to the second value. , A positive value is input to the DC level adjustment circuit 15. The input positive value or negative value is input to the addition circuit 22 and added to the content stored in the third latch circuit 21. Then, the data is again stored in the third latch circuit 21, subjected to D / A conversion via the memory 20, and then output as a DC output.
[0031]
The digital video signal digitally processed by the digital processing circuit 5 is D / A converted by the video D / A conversion circuit 17 using the video signal clock from the video signal clock generator 10, and the digital audio signal is output from the VCO 16. D / A conversion is performed by the audio D / A converter 18 using the audio signal clock. Then, it is output as a normal video signal and audio signal.
[0032]
Next, a second embodiment of the present invention will be described with reference to FIG. According to the figure, the data of the number of audio samples in one frame obtained by the AFSIZE extraction / analysis circuit 6 is sequentially stored from the first area to the n-th area in the memory 7 for each frame. Note that the frame after being stored in the n-th area is stored again by returning to the first area and rewriting the previous data.
[0033]
When data of the number of audio samples is not obtained even during one frame period due to an error such as recording and reproduction, the data corresponds to a memory area of the memory 7 in which the data of the number of audio samples is to be stored. The missing marker positioned at the address is set to “1” (the missing marker is “0” when the address is normal). Thereby, it is possible to indicate that the data of the number of audio samples of the frame with the missing marker set to “1” is missing.
[0034]
The data of the number of audio samples in the current frame is Xk, the data of the number of audio samples in the immediately preceding frame is Xk-1, and the data of the number of audio samples in the next frame is Xk + 1. When the data Xk is missing, one of the comparison circuit 14 the result of the arithmetic processing by the arithmetic processing circuit 9 to give me row using the data before and after stored in the memory 7 as a substitute value of data X k Should be input.
[0036]
Also, Xk-2 audio sample number data of the two previous frame, the number of audio samples of the data of the two subsequent frames as Xk + 2, one before and one of the frame in conjunction with the above-described processing the number of audio samples of the data frame after, than audio sample number of data of the two before and after the two frame importance performs calculation by adding weights may be as a substitute value of data X k .
[0039]
Further, when the data Xk of the number of audio samples of the current frame is missing, the data of the number of audio samples of the immediately preceding frame from the data Xk −2 of the number of the previous audio samples is calculated using only the past data. the variation of the data X k-1 calculated in, may predict the value of X k by performing the calculation to be added to X k-1.
[0042]
Next, a processing method when a plurality of errors occur in adjacent frames will be described. Consider a total of five frames including the current frame and two frames before and after the current frame. When only the data Xk of the number of audio samples of the current frame among these five frames is missing, the data of the number of audio samples of the frame immediately before and after the frame concerned is replaced with the data of the audio sample number of two frames before and after the frame. The value obtained by the arithmetic processing in which weighting is added to the data and the arithmetic processing is performed as the substitute value of the data of Xk.
[0043]
When the data Xk + 2 of the number of audio samples of the next two frames is missing in addition to Xk, the value of Xk is calculated using the data of Xk−1 and Xk + 1 .
[0044]
Further, when the data Xk + 1 of the number of audio samples of the next frame is missing in addition to Xk, the data XK-1 of the number of audio samples of the previous frame and the data XK + 2 of the number of audio samples of the next frame are also missing. To obtain the substitute values of the data of X k and X k + 1 . That is, when data is lost over a continuous frame, the calculation is performed using the data before and after that.
[0047]
Additionally, the following two methods are considered when _{X k + 1, X k +} 2 is also missing, in addition to _{X k.}
Assuming that data of the same number of audio samples as X _k-2 , X _k-1 , X _k , X _{k + 1} , and X _{k + 2} continues, the data of X _k-1 is converted to X _k , X _{k + 1} , and X _{k + 2.} Used as a substitute for.
A standard value, for example, when the audio sample frequency is 48 kHz and the frame frequency is 30 Hz, a value of 48 k / 30 = 1600 is used as a substitute value for X _k , X _{k + 1} , and X _{k + 2} .
[0048]
The data of the plurality of audio samples provided with the substitute values in this manner is stored in the corresponding area in the memory 7, and at the same time, the missing marker is rewritten to “0” indicating that there is no missing.
When the tape is not being played back, a preset value or a standard value relating to the audio sample frequency of the tape played back immediately beforehand is stored in an area for storing the data of the number of audio samples in the memory 7. And the state of the missing marker at that time is “0”.
[0049]
By performing the above processing, even if there is a missing “AF SIZE” data in a certain frame, the value of the data of the number of audio samples is complemented by the substitute value. It is possible to use the data complemented by the substitute value in the determination of. That is, since the missing data of the previous frame has already been complemented, it will not be lost in the subsequent processing. Therefore, as shown in FIG. 4, when two frames before and after the frame are combined and a total of five frames are considered, four combinations may be considered.
[0050]
FIG. 5 and FIG. 6 are diagrams showing modified examples of the digital VTR signal reproduction system according to the first and second embodiments of the present invention, in which the operation place is changed. In FIG. 5, the contents of the second latch circuit 12 and the contents of the AF SIZE extraction / analysis circuit are compared first, and the result is stored in the memory 7, and when there is data loss, the arithmetic processing by the arithmetic circuit 9 is performed. ing.
In FIG. 6, the memory 7, the arithmetic circuit 9, and the switch 19 are provided in the DC level adjustment circuit 15 to perform processing.
[0051]
In each of the embodiments described above, the data of the number of audio samples is described as being recorded once for each frame. However, the data may be recorded a plurality of times in one frame. In this case, information on the data of the number of audio samples obtained in one frame period during reproduction is stored in a plurality of areas in the memory, and a probable value is selected from each data by majority decision or the like.
[0052]
【The invention's effect】
As described above, according to the method for synchronizing the digital audio signal and the digital video signal according to the present invention, the data of the audio sampling number existing in the “AF SIZE” of the frame is complemented by the data of the previous and subsequent frames. Therefore, even when the acquisition of “AF SIZE” information indicating the number of samples of the audio signal fails or when accurate information cannot be obtained, the phase of the audio signal and the video frame can be accurately matched. This has the effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing a reproduction system of a digital VTR to which a method for synchronizing a digital audio signal and a digital video signal according to a first embodiment of the present invention is applied.
FIG. 2 is a diagram showing a configuration of a DC level adjustment circuit of a digital VTR to which the present invention has been applied.
FIG. 3 is a diagram showing a reproduction system of a digital VTR to which a method for synchronizing a digital audio signal and a digital video signal according to a second embodiment of the present invention is applied.
FIG. 4 is a diagram illustrating a missing pattern when five frames of data are used.
FIG. 5 is a diagram showing a modified example of a reproduction system of a digital VTR to which a method for synchronizing a digital audio signal and a digital video signal according to the present invention is applied.
FIG. 6 is a diagram showing a modified example of a reproduction system of a digital VTR to which a method for synchronizing a digital audio signal and a digital video signal according to the present invention is applied.
FIG. 7 is a diagram showing a recording format of one track of a digital VTR.
FIG. 8 is a diagram showing a structure of an audio frame format.
FIG. 9 is a diagram showing an AAUX SOURCE pack and an AAUX SOURCE CONTROL pack.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 magnetic head 2 preamplifier 3 equalizer 4 digital signal detection circuit 5 digital signal processing circuit 6 AF size extraction / analysis circuit 7 memory 8 first latch circuit 9 arithmetic circuit 10 video signal clock generator 11 frequency divider 12 second latch Circuit 13 Counter 14 Comparison circuit 15 DC level adjustment circuit 16 VCO
17 Video D / A conversion circuit 18 Audio D / A conversion circuit 19 Switch

Claims (1)

In order to synchronize the digitized audio signal and the video signal, a signal indicating the number of audio samples of the audio signal included in a predetermined period of the video signal was recorded together with the video signal and the audio signal of the predetermined period. When reproducing the medium, a signal indicating the predetermined period generated from the reference clock of the reproduced video signal is compared with a signal indicating the number of audio samples included in the predetermined period, and according to the comparison result, A method of synchronizing a digital audio signal and a digital video signal, characterized by changing a clock frequency of the reproduced video signal or the reproduced audio signal.
The signal indicating the number of audio samples is inserted a plurality of times in the predetermined period, and a value determined by majority decision is selected from among the data of the number of audio samples inserted a plurality of times,
Whether a signal indicating the number of audio samples contained in the predetermined period of time when not obtained even one is replaced by a signal indicating the number of audio samples before the audio signal included in the period of the predetermined time period, or the audio A method for synchronizing a digital audio signal and a digital video signal, wherein a value calculated from a sampling frequency of a signal and a frame frequency of the video signal is substituted.

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