JPH058508B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention records a video signal and a pulse code modulated (PCM) audio signal on a predetermined area of a magnetic tape, and an 8mm tape that plays back the recorded signal. Related to video tape recorders.

<Prior art> In conventional 8mm video tape recorders, audio signals are recorded with PCM modulation;
The sampling frequency of modulation is the horizontal synchronization frequency (H=
15.75kHz), that is, 31.5kHz, the frequency band of audio that can be recorded and played back is approximately 14kHz.
The recording area of PCM audio signals is narrow and the number of quantization is 8.
Since only 10 bits can be recorded,
Compress and convert the PCM audio signal to 8 bits and record it.
During playback, processing such as decompression to 10 bits is performed again, which degrades the acoustic characteristics and makes it impossible to record and play back high-quality audio signals.

<Object of the Invention> The present invention has been made in view of the above points, and is capable of operating in the standard mode as a normal 8 mm video tape recorder, and has an audio frequency band of 20 kHz. dynamite cleanse
8 which is capable of recording and reproducing only high-quality audio signals of 90 dB or more and without deterioration of acoustic characteristics (hereinafter referred to as high-fidelity PCM mode).
The purpose is to provide a millimeter videotape recorder.

<Structure of the Invention> In the present invention, in order to achieve the above-mentioned object, the encoding section includes an A/D conversion circuit that A/D converts the audio signal sampled by the sampling circuit in 16 bits;
PCM compressed to 8 bits in standard mode
The decoding section is provided with a selection means for selectively outputting the audio signal and, in the high-fidelity PCM mode, the 16-bit PCM audio signal on the A/D conversion circuit side. and selection means for selectively outputting a PCM audio signal expanded to 10 bits when in the standard mode and a 16 bits PCM audio signal when in the high-speed PCM mode to the D/A conversion circuit; , is equipped with a modulation/demodulation circuit that modulates or demodulates PCM audio signals during recording and playback, and each divided area formed by dividing the track on the magnetic tape into a plurality of parts.
A recording/reproducing means for recording and reproducing PCM audio signals is provided, and when in high-speed PCM mode,
Sampling is performed at a frequency of 44.1kHz, and the quantization number is
It is configured to record in 16 bits using the divided areas of the magnetic tape.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention.

The 8mm video tape recorder of this example is:
Basically, the input analog audio signal is
An encoding unit 1 that converts the PCM audio signal into a PCM audio signal, and a recording/reproducing unit 2 that records the PCM audio signal on a magnetic tape and plays back the recorded PCM audio signal.
, a decoding unit 3 that restores the reproduced PCM audio signal to an analog audio signal, and a control circuit 4 that outputs various timing signals and performs predetermined control such as distribution of the PCM audio signal. .

This 8mm video tape recorder is a regular 8mm video tape recorder.
Like a millimeter video tape recorder, it has two modes: a standard mode in which video signals and audio signals are recorded and reproduced, and the above-mentioned high-fidelity PCM mode in which high-fidelity PCM recording and reproduction of only audio signals is performed as described later. In order to switch between these two modes, the encoding unit 1 includes mode changeover switches S1 to S1.
S3, the decoding unit 3 includes a mode changeover switch S4.
~S6 and the recording/reproducing means 2 are each provided with a mode changeover switch S7, which changes the connection between two modes, the standard mode and the high-fidelity PCM mode, based on a changeover signal from the control circuit 4. These mode changeover switches S1~
Each movable contact a1 to a7 of S7 is an individual contact b1 to b
When it is on the 7 side, it is in high-speed PCM mode, and each movable contact a1 to a7 is connected to an individual contact c1 to c.
When it is on the 7 side, it is the standard mode for an 8 mm video tape recorder. Note that the encoding unit 1
The mode changeover switch S3 of the decoder 3 and the mode changeover switch S6 of the decoding section 3 each have a function as a selection means, as will be described later.

The encoding unit 1 includes analog noise reduction circuits 5 and 6 for both left and right channels (L, R) for the standard mode, and a 15kHz noise reduction circuit for the standard mode.
low-pass filters 7 and 8 and high-speed PCM
20kHz low pass filter for mode 9,1
0, a sampling circuit 11 that samples the analog audio signal at a predetermined sampling frequency, and a 16-bit A/D
A/D conversion circuit 12 that performs conversion and 10-bit PCM from A/D conversion circuit 12 in standard mode.
The compression conversion circuit 13 compresses and converts the audio signal to 8 bits, and in the standard mode, the PCM audio signal on the compression conversion circuit 13 side,
When in PCM mode, the A/D conversion circuit 12 side
The above-mentioned switch S3 is provided as a selection means for selectively outputting a PCM audio signal.

The recording/reproducing means 2 modulates the PCM audio signal distributed from the control circuit 4 by adding a code for error detection and correction, and also demodulates the reproduced signal from the magnetic tape to perform error detection and correction. ～No.
3RF modulation/demodulation circuits 14 to 16, amplifier 17, first to
Switches S8 and S for selectively switching the connection between the third RF modulation/demodulation circuits 14 to 16 and the amplifier 17
9, and magnetic head 1 for both left and right channels.
8, 19. This recording/reproducing means 2
In the high-fidelity PCM mode, the track on the magnetic tape is divided into a plurality of regions as described later, and a PCM audio signal is recorded in each divided area, and the recorded signal is reproduced.

Among the first to third RF modulation/demodulation circuits 14 to 16, only the first RF modulation/demodulation circuit 14 is used in the standard mode, and in the high frequency PCM mode, the first RF modulation/demodulation circuit 14 is used.
First to third RF modulation/demodulation circuits 14 to 16 are used. Switch S8 and switch S9 operate in each RF modulation/demodulation circuit 14 in the high-fidelity PCM mode.
This is a switch for selecting outputs from the RF modulation/demodulation circuits 14 to 16 at timings described later and applying them to the amplifier 17, as well as supplying reproduced signals from the amplifier 17 to the respective RF modulation/demodulation circuits 14 to 16.
Individual contacts b8, b9 to d9 and movable contacts a8, a9 corresponding to 16 are provided, respectively.

In the standard mode, the decoding unit 3 includes an expansion conversion circuit 20 that expands and converts the 8-bit PCM audio signal from the control circuit 4 into 10 bits and performs interpolation;
D/A conversion circuit 21 that performs D/A conversion with bits
, a switch S10 that separates the analog audio signal into left and right channel audio signals, and 15kHz low-pass filters 22 and 23 for the standard mode.
Similarly, analog noise reduction circuits 24 and 25 for standard mode and 20kHz low-pass filters 26 and 27 for high-speed PCM mode.
and in the standard mode, the expansion conversion circuit 20 side
The above-mentioned mode changeover switch S6 is provided as a selection means for selectively outputting the PCM audio signal and, in the high-fidelity PCM mode, the PCM audio signal that is not expanded or converted.

Next, the operation of the 8mm video tape recorder having the above configuration will be explained.

First, the operation in standard mode (VIDEO mode) as a normal 8 mm video tape recorder will be explained. Control circuit 4 corresponds to standard mode
Input VIDEO mode signal. By this,
From the control circuit 4, each mode selection switch S1 to S
A switching signal is applied to 7, and each movable contact a1 to a7 of each mode changeover switch S1 to S7 becomes the individual contact c1 to c7 side, and becomes the standard mode. When recording in this standard mode, the analog audio signals of both left and right channels pass through analog noise reduction circuits 5 and 6, are band-limited by 15kHz low-pass filters 7 and 8, and are passed through mode changeover switches S1 and S2. The signal is applied to the sampling circuit 11.

This sampling circuit 11 uses the sampling frequency of a normal 8mm video tape recorder, that is, 31.5kHz.
The sampled signal is sampled at a frequency of , and is provided to the A/D conversion circuit 12. The upper 10 bits of the PCM audio signal A/D converted by this A/D conversion circuit 12 are supplied to a compression conversion circuit 13 and compressed to 8 bits.
This compressed PCM audio signal is sent to the control circuit 4 via a mode changeover switch S3 as a selection means.
given to.

The PCM audio signal from this control circuit 4 is
The signal is applied only to the 1RF modulation/demodulation circuit 14, modulated with a code for error detection and correction of the PCM audio signal, and applied to the PCM input terminal of the amplifier 17 via switch S8. A video signal is input to this amplifier 17 via a mode changeover switch S7, and the video signal and the PCM audio signal are time-division multiplexed and recorded on a magnetic tape by magnetic heads 18 and 19.

The magnetic tape 30 is recorded in a video signal recording area V and a PCM audio signal recording area P, as shown in FIG. In addition,
In FIG. 2, subscripts n-1, n, and n+1 indicate each field. FIG. 5 shows the magnetic head 1
8 is a time chart showing the recording timing of a PCM audio signal according to No. 8, 19. 5A shows the head switching pulse, and FIGS. 5B and 5C show the recording timing of the PCM audio signal by the magnetic heads 18 and 19, respectively. In the high level period t1 of FIGS. Recording of the audio signal takes place.

On the other hand, during reproduction, each magnetic head 18, 1
The PCM audio signal played by switch S8
The signal is input to the first RF modulation/demodulation circuit 14 via. The first RF modulation/demodulation circuit 14 demodulates the signal, performs error correction, and provides the signal to the control circuit 4. The PCM audio signal from this control circuit 4 is sent to an expansion conversion circuit 20.
After being extended and converted to 10 bits, interpolation is performed, and the resultant signal is provided to the D/A conversion circuit 21 via a switch S6 serving as a selection means. In the D/A conversion circuit 21, only the upper 10 bits are used and converted into an analog audio signal, which is separated into left and right channels by a switch S10, and then sent to a 15kHz low-pass filter 22, 23 and an analog noise reduction circuit 24, 25 and is output as audio.

In this way, PCM audio is reproduced in the standard format of an ordinary 8mm video tape recorder.

Next, the operation of the high-fidelity PCM mode, which is a high-fidelity PCM recording and reproducing mode of audio signals, will be explained. A mode signal corresponding to the high-fidelity PCM mode is input to the control circuit 4. As a result, the control circuit 4 selects each mode changeover switch S1.
A switching signal is given to S7, and each movable contact a1 to a7 of each mode changeover switch S1 to S7 is switched to the individual contact b1 to b7 side, and the high frequency switch is switched to the individual contact b1 to b7 side.
It becomes PCM mode.

When recording in this high-fidelity PCM mode, the analog audio signals of both left and right channels are
The signal is applied to 20kHz low-pass filters 9 and 10 to limit the band. This band-limited analog audio signal is applied to the sampling circuit 11 via mode changeover switches S1 and S2.

In this sampling circuit 11, the signal is sampled at a sampling frequency of 44.1 kHz based on the timing signal from the control circuit 4, and is input to a 16-bit A/D conversion circuit 12. The 16-bit PCM audio signal A/D converted by the A/D conversion circuit 12 is applied to the control circuit 4 via the mode changeover switch 3 serving as selection means.

By the way, the standard format for 8mm video tape recorders stores 8-bit data in 1 field in 1050 words (NTSC) or 1250 words.
(CCIR) recording and playback is possible. Meanwhile, 44.1k
Audio data sampled at Hz consists of 8 bits for both left and right channels as 1 word.
2940words (NTSC) or 3528words (CCIR)
needs to be recorded and reproduced in one field. Therefore, if you have a standard format PCM circuit and three times the capacity of the PCM recording and playback area on magnetic tape, this 16-bit data sampled at 44.1kHz can be recorded on an 8mm video tape recorder. It will be possible to play it.

In view of this point, in the present invention, in the standard mode,
Although only the first RF modem circuit 14 was used,
In high-speed PCM mode, the first to third
The three RF modulation/demodulation circuits 14 to 16 are used, and the video signal recording area V of the magnetic tape 30 is also used to record and reproduce PCM audio signals.

In other words, the 16 bits given to the control circuit 4
The PCM audio signal is divided into upper and lower 8 bits and is applied to the first to third RF modulation/demodulation circuits 14 to 16, respectively. Each of these RF modulation/demodulation circuits 14 to 16
In this case, the same processing as in the standard format is performed. from the first to third RF modulation/demodulation circuits 14 to 16
The PCM audio signal is applied to the PCM input terminal or video signal input terminal of the amplifier 17 via switch S8 or switches S9 and S7, and is further recorded by magnetic heads 18 and 19.

FIG. 3 shows the recording pattern of the magnetic tape 30 at this time, and FIG. 6 shows the recording pattern of the magnetic head 1.
8 is a time chart showing the recording timing of a PCM audio signal according to No. 8, 19. 6A shows the head switching pulse, and FIGS. 6B and 6C show the recording timing of the PCM audio signal by the magnetic heads 18 and 19, respectively. During the high level period in FIGS. 6B and C, During period t1, the PCM audio signal from the first RF modulation/demodulation circuit 14 is recorded, and during period t2, the PCM audio signal from the second RF modulation/demodulation circuit 15 is recorded.
A PCM audio signal is recorded and the first
A PCM audio signal from the 3RF modulation/demodulation circuit 16 is recorded. That is, at this timing, the connection of the switch S8 or the switch S9 is switched. As shown in FIG. 3, among the areas in which the track of the magnetic tape 30 is divided into a plurality of areas (six in this embodiment), the PCM during periods t1, t2, and t3 are recorded in recording areas P ¹ , P ² , and P ³ , respectively. The audio signal will be recorded. In addition, in FIG. 3, the subscript n-
1, n, and n+1 indicate each field.

Also, Figures 3 and 6 show the case where recording is performed in the same direction as the standard playback direction, and the case where recording is performed in the opposite direction to the standard playback direction as shown in Figures 4 and 7. Auto-reverse is also possible.

On the other hand, during reproduction, each magnetic head 18, 1
The PCM audio signal played by switch S8
Alternatively, the first to third RF modulation/demodulation circuits 14 can be
~16 respectively. In the first to third RF modulation/demodulation circuits 14 to 16, standard format error correction is performed, and the signal is sent to the D/A converter 21 via the control circuit 4 and converted into an analog audio signal. The analog audio signal from the D/A converter 21 is separated into left and right channels by a switch S10, and then passed through a 20kHz low-pass filter 26, 2.
7, and is reproduced and output as audio via mode changeover switches S4 and S5.

In this way, it is possible to operate in the standard mode as an 8mm video tape recorder, and in the high-fidelity PCM mode, the video signal recording area of the magnetic tape is also used, the sampling frequency is set to 44.1kHz, and further, Quantization bit number 16
Since it uses bits, the audio band can be increased to 20kHz and the dynamic range can be increased to over 90dB.
Recording and playback of high-quality audio signals becomes possible.

<Effects of the Invention> As described above, according to the present invention, the encoding section has the following functions:
An A/D conversion circuit that converts the audio signal sampled by the sampling circuit into a 16-bit A/D converter, and a PCM audio signal compressed to 8 bits in standard mode.
In addition, when in high-speed PCM mode, the A/
A selection means for selectively outputting a 16-bit PCM audio signal on the D-conversion circuit side is provided, and the decoding section includes a 16-bit D/A conversion circuit and a 10-bit PCM audio signal in the standard mode.
A selection means is provided for selectively outputting a PCM audio signal expanded to bits, or a 16-bit PCM audio signal when in the high-fidelity PCM mode, to the D/A conversion circuit, and further for recording and outputting the PCM audio signal.
In addition to being equipped with a modulation/demodulation circuit that performs modulation or demodulation during playback, a recording/playback means for recording and playing back PCM audio signals is provided in each divided area formed by dividing the track on the magnetic tape into multiple parts.
In PCM mode, sampling is performed at a frequency of 44.1 kHz, the quantization number is set to 16 bits, and recording and playback are performed using the divided areas of the magnetic tape, so the audio band is set to 20 kHz and the dynamic range is set to 16 bits. This makes it possible to record and reproduce high-quality audio signals at 90 dB or more and with almost no deterioration in acoustic characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main part of an embodiment of the present invention, FIG. 2 is a schematic diagram showing the recording pattern of a standard mode magnetic tape, and FIGS. 3 and 4 are Hi-
A schematic diagram showing the magnetic tape recording pattern in FiPCM mode, Figure 5 is a time chart showing the recording timing in standard mode, Figures 6 and 7 are
This is a time chart showing the timing of recording in Hi-Fi PCM mode. 1... Encoding unit, 2... Recording/reproducing means, 3...
...Decoding unit, 4...Control circuit.

Claims (1)

[Claims] 1. A sampling circuit that samples an analog audio signal at a predetermined sampling frequency, an A/D conversion circuit that converts the output of the sampling circuit into a 16-bit A/D converter, and an A/D conversion circuit that samples the output of the A/D conversion circuit. The compression conversion circuit that compresses and converts the upper 10 bits into 8 bits, and the PCM audio signal on the compression conversion circuit side when in standard mode, and the PCM on the A/D conversion circuit side when in high-fidelity PCM mode.
An encoding unit having selection means for selectively outputting an audio signal, an expansion conversion circuit that expands and converts an 8-bit PCM audio signal to 10 bits, a 16-bit D/A conversion circuit, and an expansion conversion circuit side when in standard mode. of
PCM audio signals, or PCM audio signals that are not expanded or converted when in high-speed PCM mode.
It comprises a decoding section having a selection means for selectively outputting to the A conversion circuit, a plurality of modulation/demodulation circuits that modulates the PCM audio signal during recording and demodulates it during playback, and divides the track on the magnetic tape into a plurality of parts. Recording/playback of PCM audio signals in each divided area
reproducing means, outputting a timing signal of 31.5 kHz as a sampling frequency in the standard mode and 44.1 kHz in the high-fidelity PCM mode to the sampling circuit, and controlling the selection operation of both the selection means; An 8 mm video tape recorder comprising: a control circuit that distributes PCM audio signals to corresponding modulation/demodulation circuits of the recording/reproducing means in accordance with both of the modes.