JPS5821325B2 - Drop Out - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a playback device capable of compensating for dropouts that occur when a playback output is obtained from a recording medium in which an analog information signal is converted into a digital signal and recorded. More specifically, the present invention relates to a playback device that easily compensates for dropouts during recording and playback of multiple channels.

Dropouts (reduction in playback output) often occur due to dust, scratches, deformation, etc. in the recording medium, such as magnetic tape.

Such dropouts become a problem when signals are digitally recorded (PCM recorded) on a recording medium.

Dropout compensation during PCM (Pulse Code Modulation) recording and playback generally includes a sub-record that is used when a dropout occurs in addition to the main record, and the dropout during playback is compensated for by the playback output of the sub-record. This is done by compensating for

According to such a method, dropout can be almost completely compensated for.

However, in PCM recording, tracks and heads must be provided according to the number of bits, and if both the main recording and the sub recording are to be recorded and reproduced using PCM, the number of tracks and heads will be considerable.

Therefore, a method has been proposed in which the main recording is performed using PCM, but the secondary recording for compensation is recorded in analog.

In this way, it is possible to simplify the secondary recording system.

However, in the case of multi-channel recording and playback such as 2-channel (stereo) or 4-channel, if the information signal of each channel is recorded in PCM and the analog information signal of each channel is sub-recorded for dropout compensation, the number of tracks will increase. As equipment increases and becomes more complex,
If a dropout occurs in a certain channel, it is necessary to send out a compensating analog signal corresponding to this channel, which makes the circuit configuration extremely complicated.

The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a playback device that can easily compensate for dropouts in multi-channel digital recording and playback.

To achieve the above object, the present invention is directed to converting a plurality of audio analog signals into digital signals and recording them independently or multiplexed in an audio multi-channel stereo recording and reproducing system such as 2-channel or 4-channel stereo. the synthesized analog signal obtained by synthesizing two or more audio analog signals of the plurality of audio analog signals while reproducing the digital signal from a recording medium on which the synthesized analog signal is recorded. a plurality of digital-to-analog converters that convert the plurality of digital signals obtained based on the reproduction output of the reproduction device into analog signals, respectively; and the plurality of digital signals obtained from the reproduction device. A dropout detection circuit for detecting a dropout in the playback output of the digital-to-analog converter, and a dropout detection circuit for detecting a dropout of the playback output, and a dropout detection circuit for detecting a dropout of the playback output, and a dropout detection circuit for detecting a dropout of the playback output, and a dropout detection circuit for detecting a dropout of the playback output, and a dropout detection circuit for detecting a dropout of the playback output of the digital This invention relates to an audio multi-channel reproduction device characterized by comprising a plurality of dropout compensation gate circuits that output a synthesized analog signal obtained from the reproduction device in place of the output signal of the analog converter. be.

If configured as described above, even in multi-channel playback,
It becomes possible to compensate for dropout with a simple configuration.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a VTR type recording device for producing magnetic tape capable of compensating for dropouts.

In this figure, 1 and 2 are first and second input terminals, which input analog information signals such as audio to the first channel (for example, the stereo left channel) and the second channel (for example, the stereo left channel). This is a terminal for inputting signals separately from the right channel.

3 and 4 are low-pass filters that remove high frequency noise signals from the first and second input signals.

5 and 6 are sample and hold circuits for digital conversion.

Reference numerals 7 and 8 are analog-to-digital converters, which are circuits that convert analog input signals of each channel into digital signals.

9 is a memory, and an analog/digital converter 7゜8
temporarily store the output signal of and convert it into a series of signals;
This circuit multiplexes the channel signal and the second channel signal.

Reference numeral 10 denotes an FM modulation circuit, which performs FM modulation on a digital signal.

11 and 12 are recording amplifiers, which are circuits that amplify the FM modulated wave to a recording level.

13 and 14 are switches which are switched corresponding to the recording state and the reproduction state.

Reference numerals 15 and 16 are recording heads that record FM-modulated digital signals onto the magnetic tape 17.

Since this embodiment uses a helical scan method, two heads scan one track.

Therefore, the row tracks are scanned alternately by both heads 15 and 16.

Line amplifiers 18 and 19 amplify the analog signals of the first and second channels.

20 is a mixing circuit which combines the analog signal of the first channel and the analog signal of the second channel.

For example, stereo left and right signals may be combined to form a single channel signal.

A recording amplifier 21 amplifies the analog signal synthesized by the mixing circuit 20 to a recording level.

22 is a switch that can be switched depending on the recording state or the reproducing state.

Reference numeral 23 denotes a magnetic head for recording a composite analog signal of the first channel and the second channel on the analog recording track of the magnetic tape 17.

In the above-mentioned recording device, the analog information signal or
channel component (left signal) and the second channel component (left signal)
If the signal is divided into two parts (right signal) and applied to the first input terminal 1 and the second input terminal 2, the high frequency is cut by the low-pass filters 3 and 4, and then sent to the sample and hold circuits 5 and 6. , the sample is held here.

Thereafter, each signal is converted into a digital signal by analog-to-digital converters 7 and 8 and sent to a memory 9.

The digital signal read out from the memory 9 based on the timing signal is FM modulated by the FM modulation circuit 10, and then
The data is sent to magnetic heads 15 and 16 and digitally recorded on magnetic tape 17.

The digital signals recorded on the magnetic tape 17 correspond to the analog information signals applied to the first and second input terminals 1 and 2.

On the magnetic tape 17, in addition to the above-mentioned main recording using digital signals, sub-recording using analog signals is also performed.

Sub-recording is performed by combining the analog signals of the first and second channels obtained from the input terminals 1 and 2 in the mixing circuit 20 and supplying the resultant to the magnetic head 23.

As a result, a digital recording in which a first channel signal and a second channel signal based on an analog information signal are multiplexed on the raw magnetic tape 11, and a first channel signal substantially equal to the analog information signal and a second channel signal based on the analog information signal are recorded. A composite analog signal with two channels of contradictory signals is recorded.

FIG. 3 shows an example of the track format for the above-mentioned recording, where A indicates a main track for PCM recording and B indicates a sub-track for analog recording.

In this example, recording was performed using a helical scan type VTR, so the track format would be as shown in Figure 3, or if recording was performed using a fixed head type VTR, the track format would be as shown in Figure 3.
The trunk configuration is as shown in the figure.

FIG. 2 shows a VTR type playback device.

The magnetic heads 15, 16, 23 shown in FIG. 2 are the same as the magnetic heads shown in FIG.
．． By switching 22 to the reproduction side, reproduction output can be obtained.

Regenerative amplifiers 24 and 25 amplify the head output.

Reference numeral 26 is a gate circuit, which is a switching circuit that receives switching pulses from line 26a and alternately outputs the outputs of the two heads 15 and 16.

A limiter 27 limits the amplitude of the reproduced output.

28 is an FM demodulator, 29 is a waveform shaping circuit, and 30 is a skew and jitter correction circuit.

In short, the structure from the magnetic heads 15 and 16 to the correction circuit 30 is the same as that of a general VTR.

Reference numeral 31 denotes a memory that stores multiplexed digital signals and reads out the stored contents in a predetermined format based on the clock pulse applied from the line 31a, thereby reading out the digital signals of the first channel. This is for separating and reading out two channels of digital signals.

32 and 33 are digital-to-analog converters, which are circuits that convert digital signals of each channel obtained from the memory 31 into analog signals.

34 and 35' are gate circuits for long-term dropout compensation, which consist of gates that transmit the output of the digital-to-analog converters 32 and 33, and gates that transmit compensation analog signals when a dropout occurs. .

36 and 37 are short-time dropout compensation circuits that, when a short-term dropout occurs, continue to send the output immediately before the dropout occurs.

38 and 39 are low-pass filters that remove high-frequency noise signals from the analog signals of the first and second channels.

40 is a first channel output terminal (left channel output terminal), and 41 is a second channel output terminal (right channel output terminal).

42 is a preamplifier, and 43 is a line amplifier, which amplifies the compensation reproduction analog output obtained from the magnetic head 23 and sends it to gate circuits 34 and 35.

44 is a limiter, which is a circuit that limits the amplitude of the FM signal obtained from the gate circuit 26.

Reference numeral 45 denotes a dropout detection circuit, which detects the occurrence of dropout and generates a signal corresponding to the period during which dropout occurs.

46 detects whether the dropout time width is equal to or greater than a predetermined value (100 μsec' in this embodiment);
When the time is shorter than 100 μsec, an output signal is sent to the line 47, and when the time is longer than 100 μsec, the output signal is stopped being sent to the line 47, and a dropout detection output is sent to the next stage waveform shaping circuit.

Line 47 is connected to control compensation circuit 36,37.

The waveform shaping circuit 48 is a circuit that forms a signal for controlling the gate circuits 34 and 35 based on a dropout detection output of 100 μsec or more.

The operation of the reproducing apparatus shown in FIG. 2 will be described next.

For reproduction, a magnetic tape 17 recorded with the recording apparatus shown in FIG. 1 is used.

That is, the analog information signals of the first and second channels are respectively converted into digital signals and digitally recorded, and the analog information signals of the first channel and the analog information signal of the second channel are combined. A magnetic tape 17 on which analog information signals are recorded is used.

When the magnetic tape 17 is mounted on a reproducing apparatus having a VTR configuration and run, a reproduced output can be obtained from the magnetic heads 15 and 16.

Since the magnetic heads 15 and 16 are rotating heads arranged at an interval of about 180 degrees, the magnetic heads 15 (!1-16) alternately obtain reproduction output from the magnetic tape 17 running on the head drum.

Magnetic head 15. :16. The digital playback output obtained from: is processed by the gate circuit 26 so that there is no overlap, resulting in a series of playback outputs.

The output of the gate circuit 36 is I as in a general VTR.
J mitter 27, FM demodulator 28, waveform shaping circuit 29,
The signal is processed by the correction circuit 30 and the like, and becomes a demodulated digital reproduction output.

At the same time, the reproduced output obtained from the gate circuit 26 is sent to a dropout detection circuit 45 via a limiter 44.

The FM demodulated multiplexed digital playback output is sent to the memory 31 and temporarily stored there.

The digital playback output is read out from the memory 31 in a state where it is separated into a first channel and a second channel based on the clock pulse, and a digital-to-analog converter 32 for the first channel and a digital-to-analog converter for the second channel are read out. Send to 33.

As a result, the first analog reproduction output corresponding to the analog input signal supplied to the input terminal 1 in FIG. 1 is obtained from the converter 32, and the first analog reproduction output corresponding to the analog input signal supplied to the input terminal 2 in FIG. A second analog reproduction output corresponding to the input signal is obtained.

In a state where dropout is not detected, no control signals are applied to the gate circuits 34, 35 and the compensation circuits 36, 37, so the outputs of the converters 32, 33 are transmitted to the gate circuits 34, 35 and the compensation circuits. 36, 37 and low pass filters 38, 39 and are sent to output terminals 40, 41, respectively.

This allows output of two channels (for example, a left channel and a right channel for stereo reproduction) to be obtained.

If a dropout is detected by the detection circuit 45 during playback as described above, the detection signal first appears on the line 47 via the time width detection circuit 46, and the dropout detection signal is sent to the dropout compensation circuits 36 and 37. Granted.

The dropout compensation circuits 36 and 37 have an analog playback output holding circuit configuration, and during the period when the detection signal is applied from the line 47, they hold the analog playback output immediately before the dropout occurs and send out that output. Let's go.

For example, if a dropout occurs from time t1 to time 12 as shown in FIG. 5, the analog reproduction output at tI is held until t2 and is used as the output.

If the dropout time is less than 100 μsec, the compensation as described above is not provided, or the dropout is less than 100 μsec.
When it exceeds μsec, this is detected by the time width detection circuit 746, and the output of the dropout detection circuit 45 is no longer sent to the line 47, but is sent to the waveform shaping circuit 48 instead.

As a result, instead of eliminating the compensation function of the compensation circuits 36 and 37, the gate circuits 34 and 35 are controlled, and the compensating analog playback output obtained from the analog playback head 23 is outputted via the gate circuits 34 and 35. Output terminal 40.4
Sent to 1.

At this time, the main reproduction output transmission circuit based on the digital reproduction output is cut off.

Since exactly the same compensating analog playback output is obtained from the output terminals 40 and 41, it is not a stereo output.

However, since it contains almost the same information content as the stereo output, it does not feel like something different, and it functions satisfactorily as compensation for dropouts.

When the dropout disappears and the output is no longer generated from the detection circuit 45, the gate circuits 34 and 35 return to their original state, and the main playback output converted from digital to analog is sent to the output terminals 40 and 41 again, resulting in stereo output. can get.

If dropout occurs only for a short period of time, less than 100 μsec, only the compensation circuits 36 and 37 will operate, and the gate circuits 34 and 35 will not operate.

As is clear from the explanation so far, in this device, even in multi-channel recording and reproduction, the number of recording and reproduction channels for dropout compensation is made smaller than the number of main recording and reproduction channels. The configuration is simple.

In addition, in this embodiment, the main recording and reproduction is performed by multiplexing, so the number of tracks and heads in PCM recording is reduced, making effective use of magnetic tape and reducing the equipment cost. The configuration has been simplified.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment and can be further modified.

For example, the main digital recording may be performed without multiplexing.

Also, if the number of main recording/playback channels is extremely large,
The number of channels for secondary analog recording may be one or more.

Further, in the embodiment, dropout is detected at the output stage of the gate circuit 26, but it may be detected at a location other than this.

In addition, in the embodiment, the time width detection circuit 46 and the compensation circuits 36, 3γ are provided to compensate for short-term dropouts, or these circuits are not provided, and when a dropout is detected, the head 23 is immediately activated. The analog reproduction output may be sent to the output terminals 40, 41.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a recording device according to an embodiment of the present invention, Fig. 2 is a block diagram of a reproducing device, Fig. 3 is a plan view showing the track form on a magnetic tape, and Fig. 4 is a fixed head system. FIG. 5 is a plan view showing the trunk form on the magnetic tape at the time of recording, and a waveform diagram showing the state of drop compensation. Note that in the symbols l used in the drawings, 1 is the first input terminal, 2 is the second input terminal, 15.16 is the head, 1
γ is a magnetic tape, 23 is a head, 31 is a memory, 32.
33 is a digital-to-analog converter, 34.35 is a gate circuit for long-term dropout compensation, 36.37 is a short-time dropout compensation circuit, 40.41 is an output terminal, 45
4 is a dropout detection circuit, 46 is a time width detection circuit, and 4 is a dropout detection circuit.
7 is a line.

Claims (1)

[Claims] 1. A plurality of audio analog signals in an audio multi-channel stereo recording and reproducing system are converted into digital signals and recorded, and two of the plurality of audio analog signals are converted into digital signals and recorded.
a playback device that plays back the synthesized analog signal at the same time as playing back the digital signal from a recording medium on which a synthesized analog signal obtained by synthesizing two or more audio analog signals; and a playback output of the playback device. a plurality of digital-to-analog converters for converting the plurality of digital signals obtained based on the digital signal into analog signals, respectively; a dropout detection circuit for detecting a dropout in the reproduction output of the plurality of digital signals obtained from the reproduction device; , provided at each of the output stages of the plurality of digital-to-analog converters, and only when a dropout is detected by the dropout detection circuit, a signal obtained from the playback device in place of the output signal of the digital-to-analog converter. 1. An audio multi-channel playback device comprising: a plurality of dropout compensation gate circuits for outputting the synthesized analog signal.