JPH0578082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording device, and particularly to an offset four-phase differential PSK in a deep part of a magnetic layer of a magnetic tape.
(Offset Quaderature Differential Phase Shift
Keying: OQDPSK) or 4-phase differential PSK (QDPSK)
This invention relates to a magnetic recording device that records a digital audio signal modulated using a polyphase differential PSK modulation method such as the above, and records a video signal on the surface layer.

Prior Art FIG. 9 is a block system diagram showing a conventional magnetic recording device together with a reproducing system. In the same figure, input terminal 1
The color video signal input to the video signal processing circuit 2
After being converted into a frequency division multiplexed signal of, for example, a low frequency converted carrier color signal and a frequency modulated luminance signal, it is passed through a recording amplifier 3 and a switching circuit 4 to a magnetic tape 6 by rotary heads 5a and 5b.
recorded in

On the other hand, the left channel (Lch) and right channel (Rch) audio signals inputted to the input terminals 7 _L and 7 _R are converted into pulse code modulation (PCM) signals by the digital signal processing circuit 9, and After being multiplexed, it is modulated by an offset 4-phase PSK method by an OQPSK modulator 10, and is further modulated by a recording amplifier 11.
and the switching circuit 12, and are recorded on the magnetic tape 6 by the rotary heads 13a and 13b.

Here, on the audio track in which the OQPSK modulated digital audio signal is recorded in the deep layer of the magnetic layer of the magnetic tape 6 by the rotary heads 13a and 13b, the frequency is divided into the surface layer of the magnetic layer by the rotary heads 5a and 5b. Multiple video signals are recorded forming a video track.

During reproduction, the frequency division multiplexed video signal reproduced from the video track by the rotary heads 5a and 5b is supplied to the video signal processing circuit 15 through the switching circuit 4 and the reproduction amplifier 14, where the original reproduction is performed. After being returned to a color video signal, it is output to the output terminal 16.

On the other hand, the digital audio signals reproduced from the audio tracks by the rotary heads 13a and 13b are supplied to the digital signal processing circuit 20 through the switching circuit 12, the reproduction amplifier 17, the equalizer 18, and the OQPSK demodulator 19, respectively. After being converted to a reproduced PCM signal, the D/A converter 2
1, the signal is returned to the original analog audio signal, and as a result, the left channel reproduced audio signal and the right channel reproduced audio signal are outputted to the output terminals 22 _L and 22 _R separately and simultaneously.

As described above, the conventional apparatus shown in FIG. 9 is a rotary head type deep recording type VTR in which an OQPSK modulated digital audio signal is directly recorded in the deep part of the magnetic layer of the magnetic tape 6. This recording/reproducing device has already been published in the literature (for example, Arai et al.: “A STUDY ON THE
DIGITIZATION OF AUDIO SIGNALS FOR
VIDEO TAPERECORDER”，International
Conference on Acoustics, Speech, and
Signal Processing, p.29-33, 1986).

Problems to be Solved by the Invention However, since the above-mentioned conventional device directly records OQDPSK-modulated digital audio signals onto a magnetic tape, which is a non-linear transmission system, cross-modulation distortion occurs, and during playback, A noise spectrum that was absent during recording occurs in the low-frequency conversion carrier color signal band.

For this reason, there has been a problem in that the color S/N ratio is degraded by the noise spectrum in the reproduced signal when the video tracks are reproduced by the rotary heads 5a and 5b. In addition, the rotating head 13a,
There has been a problem in that the error rate of the reproduced digital audio signal deteriorates due to distortion due to tape nonlinearity in the reproduced signal when the audio track is reproduced by the 13b.

Furthermore, in order to perform OQPSK modulation on a digital audio signal and record and reproduce it, there is a problem in that a reference phase signal must also be recorded and reproduced at the same time.

The present invention was created in view of the above points,
It is an object of the present invention to provide a magnetic recording device that can reduce the noise spectrum and does not require recording a reference phase signal.

Means for Solving the Problems The magnetic recording apparatus of the present invention is a deep recording type magnetic recording apparatus that includes a modulation means for performing multiphase DPSK modulation or offset multiphase DPSK modulation, a bias superimposition circuit, and a recording means. It was established.

The recording means records the output signal of the bias superimposing circuit in the deep part of the magnetic layer of the magnetic tape by means of an audio rotary head having an azimuth angle different from that of the video rotary head.

Operation The digital audio signal generated by the modulation means and subjected to polyphase DPSK modulation or offset polyphase DPSK modulation is supplied to the bias superimposition circuit, where it is superimposed with a high frequency bias signal. The digital audio signal taken out from the bias superimposition circuit and superimposed with a high frequency bias signal is supplied to the audio rotary head by the recording means, thereby being recorded in the deep portion of the magnetic layer of the magnetic tape.

In this way, polyphase DPSK or offset polyphase
The digital audio signal modulated by DPSK is
Since it is recorded with a high frequency bias signal, linearity is improved. Furthermore, since a digital audio signal subjected to polyphase DPSK modulation or offset polyphase DPSK modulation can be demodulated without a reference phase signal, there is no need to record the reference signal phase.

Embodiment FIG. 1 is a block system diagram showing an embodiment of the apparatus of the present invention together with a regeneration system. In the same figure, dashed line A
The upper part is the magnetic recording device (recording system), and the part below A is the reproduction system.

To explain this embodiment, a color video signal of a standard color system enters the terminal 25 and is supplied to the video signal processing circuit 26 . The video signal processing circuit 26 separates a luminance signal and a carrier color signal by known means, generates a frequency-modulated luminance signal (FM luminance signal) obtained by frequency-modulating a carrier wave with this luminance signal, and The color signal is reduced-converted to generate a low-frequency-converted carrier color signal, and these two signals are frequency-division multiplexed to output a video signal for recording with a frequency spectrum as shown in FIG. 2A. In Figure 2 A,
I is an FM brightness signal whose carrier frequency band is 3.4MHz
~4.4MHz. is the low-pass conversion carrier color signal,
Its low-pass conversion color subcarrier frequency is approximately 629KHz.
The above recording video signal is supplied via a recording amplifier 27 to video rotary heads 28a and 28b. In addition, the video signal processing circuit 26 inputs the color video signal of the standard color method directly to the synchronization signal separation circuit 26.
Supply to 9. The synchronization signal separation circuit 29 separates the vertical synchronization signal and supplies it to a servo circuit 30, which will be described later.

Further, the left channel analog audio signal and the right channel analog audio signal inputted to the terminals 31a and 31b are filtered through reduction filters 32a and 32, respectively.
After unnecessary high-frequency components exceeding the audible frequency band are removed in step b, the sampling frequency is, for example, 47.952K.
Hz (=48KHz÷1.001) sample and hold circuits 33a, 33b to A/D converters 34a, 34
The signal is then linearly quantized to 16 bits and encoded into a PCM audio signal. The PCM audio signals of the left and right channels are supplied to an encoder 35.

The encoder 35 generates error detection and correction codes P and Q in the format shown in FIG. 3A from the even-numbered samples ES and the odd-numbered samples OS of one field period.

In Figure 3A, data DATA1, DATA2
For example, are samples ES and OS that have been subjected to time axis compression and interleaving, and each row of data in horizontal word units (one word is 8 bits).
Of DATA1 and DATA2 (8 x 50 bits each),
A predetermined operation is performed on each 10 words to generate 6 words of parity Q, which is repeated to obtain 8×30 (=8×6×5) bit parity Q for each row. In addition, the encoder 35 has eight columns in the vertical direction.
In other words, each row has 1 word (=8 bits) of data.
A predetermined operation is performed for every 32 words of DATA1, DATA2, and parity Q to generate parity P of 8×4 bits for each column of 4 words.

Next, the above data DATA1, DATA2 and parity P, Q are divided into 36 words for 8 columns,
Further, immediately before each of the 36 words, an 8-bit (1 word) synchronization signal SYNC, an identification signal ID, an address signal ADDR, and a block parity signal PARITY are added as shown in FIG. 3B, resulting in a total of 40 words. A data block is formed. Synchronous signal SYNC
indicates the start of each data block. Address signal ADDR indicates the order of each data block in one track of digital audio signals (ie, 130 data blocks). block parity signal
PARITY is an error detection signal obtained by PARITY=IDADDR. Here, it is an addition operator modulo 2.

130 data blocks in the data area shown in Figure 3C, data DATA1 and DATA2 shown in Figure 3A.
and parity P, Q are transmitted, but before that 4
A preamble for clock reproduction for a data block is added followed by a postampule for two data blocks.

In this way, the encoder 35 encodes a total of 136 data blocks (=43520 bits) as shown in FIG. 3C.
A digital audio signal with a signal format of 1 field period (=1/59.94 seconds) is generated.
Transmit with. Therefore, the transmission bit rate of the digital audio signal is 2.6086 (=136 x 320 x 59.94)
It becomes Mbps.

Note that the encoder 35 is field synchronized with the video signal to be recorded by the output signal of the servo circuit 30.

The offset four-phase differential PSK modulator (OQDPSK modulator) 36 includes a serial-to-parallel conversion circuit that converts this digital audio signal into serial to parallel and outputs it alternately as two code strings, and a serial-to-parallel conversion circuit that converts these two code strings into two code strings within one time slot from each other. Phase shifting means shifts the code by 1/2, and the two code strings from this phase shifting means are separately passed through two exclusive OR circuits, and then separately passed through two 1-time slot delay means. a code conversion circuit that generates and outputs two code strings that are separately converted into difference codes from the two exclusive OR circuits, and a code conversion circuit that receives these two difference codes as modulation signals. , a balanced modulation means that separately performs carrier suppression amplitude modulation on two carrier waves whose phases differ by 90 degrees from each other at a predetermined frequency _C , and two amplitude modulated waves from the balanced modulation means are synthesized.
It has a known configuration consisting of a synthesis circuit that outputs an OQDPSK-modulated digital audio signal.

The carrier wave frequency _C is selected to be approximately 2.00 MHz, which is 127 times the horizontal scanning frequency _H , as an example. Therefore, this OQDPSK modulator 36
The frequency spectrum of the output digital audio signal has a maximum level at the carrier frequency _C , and the transmission bit rate is 2.6086 Mbps, so
±n× _1.30MHz (=
2.6086MHz/2) becomes 0 at a distant frequency position,
This results in a well-known comb-like spectrum. however,
The above n is a natural number.

Therefore, the output digital audio signal of the OQDPSK modulator 36 is band-limited to remove unnecessary frequency components, and has a passband width centered around about 2.00 MHz that does not cause intersymbol interference. After being passed through a band filter 37 selected to be about 0.7 times the transmission bit rate and band-limited to a digital audio signal with a frequency spectrum as shown in FIG. , where a high frequency bias signal is superimposed.

The bias superimposition circuit 39 is a circuit that constitutes a main part of this embodiment, and has a configuration as shown in FIG. 4 or FIG. 5, for example. In Figures 4 and 5, the same components as in Figure 1 are given the same reference numerals.
In the figure, the same components as in FIG. 4 are given the same reference numerals.

The bias superimposition circuit 39 shown in FIG.
A high frequency bias signal of, for example, 7 MHz from the bias oscillator 46 is superimposed on the modulated digital audio signal, and this superimposed signal is outputted to the terminal 40 through the recording amplifier 47.

On the other hand, the bias superimposition circuit 39 shown in FIG.
The OQDPSK-modulated digital audio signal from the terminal 38 is taken out through a trap circuit consisting of a coil 50 and a capacitor 51, and then added and synthesized (superimposed) with a high frequency bias signal taken out from a bias oscillator 46 through a capacitor 52. , and then output to the terminal 40.

The circuit shown in FIG. 5 has a well-known circuit configuration for bias recording, and the trap circuit prevents the high frequency bias signal from being transmitted to the recording amplifier 47 side, and the capacitor 52 prevents the transmission of the digital audio signal to the bias oscillator 46 side. is prevented. The recording amplifier 47 of the bias superimposition circuit 39 shown in FIG. 5 is the bias superimposition circuit 3 shown in FIG.
An inexpensive recording amplifier can be used compared to the broadband, high-output, and expensive recording amplifier required for 9.

The above superimposed symbol taken out from the terminal 40 is
These are supplied to audio rotary heads 41a and 41b, respectively, in FIG. Audio rotary heads 41a and 4
1b is 180° to the rotating surface of the rotating cylinder (not shown)
They are mounted opposite to each other and are mounted at a certain angle ahead of the mounting positions of the image rotating heads 28a and 28b. Furthermore, the azimuth angles of the audio rotating heads 41a and 41b are +30° for one and -30° for the other, and the azimuth angles for the rotating heads 28a and 28b for video are +6° for one and -6° for the other. Selected.

The motor (not shown) that rotates the above-mentioned rotary cylinder rotates in phase synchronization with the vertical synchronization signal based on the output signal of the servo circuit 30 to which the vertical synchronization signal from the synchronization signal separation circuit 29 is supplied.

As a result, the audio rotary heads 41a, 41b
As a result, the digital audio signal is recorded with a high frequency bias into the deep part of the magnetic layer of the magnetic tape 43 which is running while being wound around the rotating cylinder over an angular range of more than 180 degrees to form an audio track.
Thereafter, a recording video signal is recorded on the surface layer of the magnetic layer on the audio track by the video rotary heads 28a, 28b to form a video track.

At the same time, the control head 42
The control pulse generated from the vertical synchronization signal taken out from the servo circuit 30 is recorded by forming a control track along the longitudinal direction of the magnetic tape.

Next, the operation of the reproducing system for the magnetic tape 43 recorded by the apparatus of this embodiment will be explained. The reproduced modulated digital audio signal is supplied to a preamplifier 55. At the same time, video signals alternately reproduced by the rotary heads 28a and 28b from the video track of the magnetic tape 43 are supplied to the switching amplifier 56. Further, control pulses reproduced by the control head 42 from the control track of the magnetic tape 43 are supplied to the servo circuit 30. Servo circuit 30
controls the rotating cylinder so that the regeneration control pulse is synchronized with the reference frequency signal.

The switching amplifier 56 has a rotary head 28a,
Each reproduced video signal 28b is amplified and switched to a continuous signal, and this signal is supplied to a video signal processing circuit 58 via a preamplifier 57. The video signal processing circuit 58 separates and extracts the FM luminance signal and the low frequency converted carrier color signal from the reproduced signal using known means, performs FM demodulation to obtain the luminance signal, and obtains the carrier color signal by frequency conversion. The carrier color signal is superimposed on the luminance signal and outputted from the terminal 59 as a reproduced color video signal of the standard color system.

On the other hand, the preamplifier 55 is connected to the rotary heads 41a, 4
The reproduced digital audio signals from each of the digital audio signals 2b are amplified and switched to a continuous signal and supplied to the band filter 60. The reproduced modulated digital audio signal with the frequency spectrum shown in FIG.
is supplied to the OQDPSK demodulator 61, where the known
The signal is OQDPSK demodulated into a digital audio signal and supplied to the decoder 62.

The configuration of the OQDPSK demodulator 61 is to convert the modulated digital audio signal into two signals having a phase difference of 90° from each other.
an arithmetic means for further multiplying both signals obtained by respectively adding and subtracting the two signals by multiplying the carrier waves of the multiplication means separately; and two zero-cross comparators for separately comparing the levels of the two signals from the multiplication means; After multiplying the output signals of these two zero-cross comparators, a control means controls the phase of the carrier wave by the signal multiplied by the output signal of the arithmetic means; A D flip-flop, a phase locked loop, a frequency divider, which obtains a demodulated digital audio signal by digitally processing two code strings corresponding to the difference code of
A configuration is known that includes a digital circuit such as an exclusive OR circuit.

A synchronizing signal generated from a pulse synchronized in phase with the rotation of the rotary cylinder is supplied from the servo circuit to the decoder 62 in order to determine the first reproduction position of the digital audio signal of each track. The decoder 62 performs processing such as error correction, time axis correction, time axis expansion, and deinterleaving on the reproduced digital audio signal, and combines each sample in the same order as in A/D conversion, and combines the samples in the same order as in the A/D conversion. The digital audio signal and the right channel digital audio signal are separated.

The digital audio signals of the left and right channels are converted into analog signals by D/A converters 63a and 63b, respectively, and then converted into D/A signals by degritch circuits 64a and 64b.
Noise components generated during A conversion are removed, and unnecessary high-frequency components exceeding the audible frequency band are removed by reduction filters 65a and 65b. As a result, the left channel and right channel analog audio signals are separately output to the terminals 66a and 66b, respectively.

Next, the noise pectrum reduction effect according to the present invention will be explained. Approximately 2.0MHz± as shown in Figure 6
An OQDPSK modulated digital audio signal with a frequency spectrum of 1.3 MHz is directly recorded on the deep part of the magnetic layer of the magnetic tape by an audio rotary head as in conventional equipment without superimposing a high frequency bias signal, and The frequency spectrum of the reproduced modulated digital audio signal when a recorded magnetic tape having a video signal recorded on the surface of the magnetic layer is reproduced by an audio rotary head is as shown in FIG. 7A.

In FIG. 7A, _sc is the color subcarrier frequency of the low-pass conversion carrier color signal, for example, 629KHz,
In the low frequency conversion carrier color signal band, as shown by the broken line V, a noise spectrum due to intermodulation distortion exists at a large level, and this occurs in the low frequency region where the azimuth loss effect is reduced. It also occurs in the reproduced video signal, and the color S/N
deteriorate. Further, such cross-modulation distortion occurs due to the nonlinearity of the tape, and the resulting distortion also degrades the error rate of the digital signal as described above.

On the other hand, when an OQDPSK-modulated digital audio signal having the frequency spectrum shown in FIG. is the seventh
As shown in Figure B, among the noise spectrum due to cross-modulation distortion in the low-pass conversion carrier color signal band surrounded by the broken line, the noise spectrum in the vicinity of the low-pass conversion color subcarrier frequency _sc is significantly reduced. Confirmed by experiment.

In addition, a digital audio signal with a frequency spectrum similar to that shown in Fig. 6 obtained by four-phase differential PSK modulation (QDPSK modulation) instead of OQDPSK modulation is directly deep-recorded without superimposing a high-frequency bias signal. The frequency spectrum when reproduced is as shown in Figure 8A, and the noise spectrum within the low-frequency conversion carrier color signal band surrounded by the broken line due to cross-modulation distortion is large, similar to the frequency spectrum in Figure 7A. Exist at the level.

On the other hand, when a high-frequency bias signal of, for example, 5.5 MHz is superimposed on the QDPSK-modulated digital audio signal for deep recording and then reproduced, the frequency spectrum becomes as shown in FIG. 8B. The noise spectrum within the low frequency conversion carrier color signal band surrounded by the broken line in Figure 8B is as shown in Figure 7B.
Similar to the frequency spectrum of the reduced converted color subcarrier frequency _sc , the noise spectrum near the reduced converted color subcarrier frequency sc is significantly reduced.

Therefore, the present invention applies not only to the OQDPSK modulated digital audio signal of the above embodiment, but also to
It can also be applied to QDPSK modulated digital audio signals. In addition, in Figures 7 and 8,
The high level component at 3.4MHz is due to crosstalk of the horizontal synchronization signal in the FM brightness signal. The high frequency noise spectrum can be reduced by a bandpass filter.

In addition to the above-mentioned OQDPSK and QDPSK modulation formats, the present invention also applies to 2-set and 8-phase offset DPSK modulation formats.
It can be similarly applied to modulated or DPSK modulated digital audio signals. Furthermore, in the embodiment, it has been explained that an NTSC color video signal is recorded as a predetermined signal format on the video track, but the present invention is capable of deep recording in which a PAL or SECAM format color video signal is recorded as a predetermined signal format. This method can be similarly applied to VTRs using this method.

Effects of the Invention As described above, according to the present invention, polyphase differential PSK
Alternatively, since the digital audio signal modulated by offset polyphase differential PSK is recorded in the deep part of the magnetic layer together with the high frequency bias signal, the low frequency conversion carrier color signal band is affected by cross modulation distortion due to linearity of the tape. OQDPSK can significantly reduce the noise spectrum in the reproduced signal that occurs in
Compared to a modulated digital audio signal, the transmission data rate can be reduced, and for the same transmission data rate, it can be transmitted in a narrow band by the amount of the reference phase signal, and the error rate of the reproduced digital audio signal can be improved. It has features such as being able to improve tape compatibility characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an embodiment of the apparatus of the present invention together with a reproduction system, FIG. 2 is a diagram showing an example of the frequency spectrum of the signals of each part of the block system shown in FIG. 1, and FIG. 1 Signal format diagram for explaining the operation of the encoder in the illustrated block system,
4 and 5 are block system diagrams showing each example of the bias superimposition circuit in the block system shown in FIG. 1, FIG. 6 is a diagram showing an example of the frequency spectrum of a signal recorded on an audio track, and FIG. Diagrams A and B are
A diagram showing a comparison of the frequency spectra of the reproduced signal when an OQDPSK-modulated digital audio signal is deeply recorded with a conventional device and the device of the present invention and reproduced. Figures 8A and B are QDPSK-modulated digital audio signals. A diagram showing a comparison of the frequency spectra of reproduced signals when a signal is deeply recorded by a conventional device and the device of the present invention and reproduced. FIG. 9 is a block system diagram showing an example of the conventional device together with the reproduction system. be. 25...Color video signal input terminal, 28a, 2
8b...Rotary head for video, 31a, 31b...
Analog audio signal input terminals, 34a, 34b...
A/D converter, 35... Encoder, 36...
OQDPSK modulator, 39... bias superimposition circuit,
41a, 4b...rotary head for audio, 43...magnetic tape, 45...addition circuit, 46...bias oscillator, 47...recording amplifier, 50...coil for trap circuit, 51...capacitor for trap circuit.

Claims (1)

[Scope of Claims] 1. An audio signal is recorded in the deep part of the magnetic layer of a magnetic tape by an audio rotary head, and on the surface part of the magnetic layer above the audio track formed thereby,
The audio rotary head is a magnetic recording device that records video signals by forming video tracks using video rotary heads with different azimuth angles, and is used to record digital audio signals that have been subjected to polyphase DPSK modulation or offset polyphase DPSK modulation. a bias superimposition circuit that superimposes a high-frequency bias signal on the output digital audio signal of the modulation means; a bias superimposition circuit that supplies the output signal of the bias superimposition circuit to the audio rotary head as the audio signal; 1. A magnetic recording device comprising a recording means for recording in a deep layer.