JPH0525049Y2 - - Google Patents

Description

[Detailed explanation of the idea] Industrial applications The present invention relates to a digital signal reproducing device.

BACKGROUND ART AND PROBLEMS Conventionally, digital audio tape recorders as outlined below have been proposed. This is a tape recorder that uses a 22-channel fixed magnetic head (inductive thin film magnetic head) to record digital audio signals on a cassette tape and to play them back.

In such a tape recorder, each half of the width of the cassette tape is provided with 20 audio channels and first and second auxiliary channels, the 20 audio channels record digital audio signals, and the first auxiliary For example, a still image signal is recorded in the channel, and the second
A time code signal is recorded on the auxiliary channel.

Next, referring to FIG. 3, a recording circuit for recording a time code signal on this second auxiliary channel will be described.

Reference numeral 11 denotes a time code signal generator, which is composed of a time information signal generator and a shift register. Then, the time information signal from the time information signal generator is supplied to the shift register in parallel, and the serial digital output from the shift register is sent to the FM modulator 1.
2 and the fixed magnetic head for recording through the amplifier 13.
The signal is supplied to the H _R and recorded on the magnetic tape TP.

FIG. 4 shows a frame pattern of a time code signal (SMPTE time code signal is acceptable) to be recorded on the second auxiliary track. In FIG. 4, TCS indicates a frame of a time code signal. This frame TCS has a time length of 1/30 second, and includes, for example, a 16-bit frame synchronization signal bit.
SY, 28-bit relative time (hours, minutes, seconds, frame number) signal bit RTC, 28-bit absolute time (hour, minute, second, frame number) signal bit
ABTC, 59 control signal bits
CTL and 16-bit CRC code signal bit CRC
The total number of bits is 147 bits.

By the way, by recording such a time code signal on a magnetic tape with a lower recording density than a digital audio signal, it is possible to reproduce the time code signal even when the magnetic tape is run at a certain speed higher than the normal speed. It is done like this.

By doing this, when fast forwarding or reversing a magnetic tape (cassette tape), the time code signal can be played back while the magnetic tape is in weak contact with the fixed magnetic head for playback, so the audio data recorded on the magnetic tape can be played back. This enables quick random access.

However, when the contact pressure of the magnetic tape against the magnetic head decreases, the short wavelength characteristics of the reproduced signal deteriorate, and as shown in FIG. As the temperature increases, the degree of deterioration becomes more severe as shown by curve A→B→C. In addition, in Fig. 5, the horizontal axis is 1/λ
(where λ is the wavelength), and the vertical axis represents the reproduction peak-to-peak voltage, respectively.

As described above, when the short wavelength characteristics of the reproduction signal of the digital signal recorded on the magnetic tape deteriorate, inter-symbol interference increases, making it difficult to detect time data.

Purpose of the invention In view of the above points, the present invention provides a device for reproducing modulated digital signals recorded on a magnetic tape, in which the reproduction from the magnetic head when the magnetic tape is run at a higher speed than the steady speed. The present invention aims to compensate for the deterioration of the short wavelength characteristics of the signal and to provide a device that can reliably detect data from a reproduced modulated digital signal.

Summary of the Invention The digital signal reproducing device according to the present invention includes a magnetic head for reproducing a modulated digital signal recorded on a magnetic tape, and a high frequency enhancement filter to which the reproduced signal from the magnetic head is supplied. When the magnetic tape is run at a higher speed than the normal speed, the level of the reproduced signal from the magnetic head is enhanced by a high frequency enhancement filter.

According to the present invention, in an apparatus for reproducing a modulated digital signal recorded on a magnetic tape,
Data can be reliably detected from the reproduced modulated digital signal by compensating for the deterioration of the short wavelength characteristics of the reproduced signal from the magnetic head when the magnetic tape is run at a higher speed than the normal speed. can get things.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. As described with reference to FIGS. 3 and 4, the magnetic tape (cassette tape) TP carries digital audio signals on tracks with 20 channels in each half width, and still image signals and signals on the first and second auxiliary channels, respectively. An FM modulated time code signal is recorded. H _P is a fixed magnetic head for reproduction that reproduces the FM modulated time code signal recorded in this second auxiliary channel, and uses, for example, a magnetoresistive magnetic head.

A reproduced signal from the magnetic head H _P is supplied to a high frequency enhancement filter 2 via an amplifier 1 .

The high frequency enhancement filter 2 is composed of, for example, an inductor (coil) connected between input and output terminals 2a and 2b, and a parallel circuit of a capacitor 4 and a resistor 5 connected between the output terminal 2b and ground.

An example of the frequency characteristics of this filter 2 is shown as a curve a in FIG. If the running speed of the magnetic tape TP is approximately 4 to 5 cm/sec during normal operation and 50 times that speed during fast forwarding or rewinding, the frequency characteristic a of the filter 2 will be approximately 2 to 10 KHz as shown in Fig. 2. The constants of circuit elements 3 to 5 are selected so that the response is flat in band b and increases as the frequency increases in band c of 100 to 500 KHz.

The output of the filter 2 is then supplied to the data detection circuit 7 via the amplifier 6, and the output is FM
A time code signal is obtained by being supplied to a demodulator 8 and demodulated, and this time code signal is supplied to a data decoder 9 and sent to an output terminal 10.
Relative time and absolute time data are output.

According to the present invention, in an apparatus for reproducing a modulated digital signal recorded on a magnetic tape,
Data can be reliably detected from the reproduced modulated digital signal by compensating for the deterioration of the short wavelength characteristics of the reproduced signal from the magnetic head when the magnetic tape is run at a higher speed than the normal speed. can get things.

In addition to FM modulation, PM modulation is also possible as a modulation method for the modulated digital signal recorded on the magnetic tape, and these modulation methods are preferable because they allow self-clocking. However, various pulse code modulation schemes such as NRZI are also possible.

Note that the reproducing magnetic head may be a rotating magnetic head.

Effects of the Invention According to the present invention, in an apparatus for reproducing a modulated digital signal recorded on a magnetic tape,
Data can be reliably detected from the reproduced modulated digital signal by compensating for the deterioration of the short wavelength characteristics of the reproduced signal from the magnetic head when the magnetic tape is run at a higher speed than the normal speed. can get things.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a digital signal reproducing device according to the present invention, FIG. 2 is a curve diagram of frequency characteristics of the filter shown in FIG. 1, and FIG. A circuit diagram showing the time code signal recording circuit of a digital audio tape recorder. Figure 4 is a pattern diagram showing the format of the time code signal. Figure 5 is the relationship between the reciprocal of the recording wavelength and the reproduction peak-to-peak voltage. FIG. TP is a magnetic tape, _HP is a reproduction magnetic head, and 2 is a filter.

Claims (1)

[Scope of utility model registration request] It has a magnetic head for reproducing a modulated digital signal recorded on a magnetic tape, and a high frequency enhancement filter to which the reproduced signal from the magnetic head is supplied,
A digital signal reproducing device, wherein when the magnetic tape is run at a higher speed than a normal speed, the level of the reproduced signal from the magnetic head is increased by the high frequency enhancement filter.