JPH0775106B2 - Digital audio tape recorder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a digital audio tape recorder.

[Prior Art] There are audio devices such as compact disc players (CD players), digital audio tape recorders (DAT), and satellite broadcast tuners (BS tuners) that can output audio signals in the form of digital signals. DAT
Has a digital in terminal and can record a digital audio signal from such a digital audio device.

By the way, the digital audio signal output from the CD player contains a copy prohibition code, and conventionally, it was not possible to supply the digital audio signal to the digital in terminal of the DAT for recording. for that reason,
Normally, the analog audio signal obtained at the line-out terminal of the CD player is supplied to the line-in terminal of the DAT for recording.

FIG. 5 is a system diagram showing an example thereof, in which 10 is a CD player and 20 is a DAT.

The audio signal reproduced by the CD player 10 is D /
While being converted into an analog signal by the A converter 11,
The band is limited by the low-pass filter 12 and guided to the line-out terminal 13. This line-out terminal 13
The analog audio signal output to is supplied to the line-in terminal 21 of the DAT 20.

The recording level of the audio signal supplied to the line-in terminal 21 is appropriately adjusted by the volume 22 and then band-limited by the low-pass filter 23. The band-limited audio signal is supplied to the A / D converter 24 and is subjected to A / D conversion processing at a predetermined sampling frequency. The digital audio signal output from the A / D converter 24 is supplied to a rotary magnetic head device (not shown) for digital recording.

Here, the low-pass filter 23 provided in the DAT 20 is
It is provided to remove the high frequency component so that aliasing distortion does not occur during conversion.

[Problems to be Solved by the Invention] By the way, when digitally recording an analog audio signal obtained from the CD player 10 as a source source as shown in FIG. , 23 need to be provided.

As a result, there is a drawback that the sound quality of the audio signal to be recorded in the DAT 20 deteriorates.

Therefore, the present invention proposes a digital audio tape recorder capable of high-fidelity digital recording.

[Means for Solving the Problem] The present invention provides a first recording system in which a digital signal supplied to a digital in terminal is subjected to signal processing by a signal processing circuit and recorded, and a digital in terminal. Convert the digital signal to analog signal with D / A converter,
This analog signal is band-limited by a single low-pass filter, then converted to a digital signal by an A / D converter, and the digital signal is processed by a signal processing circuit and recorded. A code detecting means for detecting a copy prohibition code from the digital signal supplied to the digital-in terminal, and when the code detecting means detects the copy permission, it is switched to the first recording system and the copy prohibition is detected. When it is performed, the second recording system is switched to.

[Operation] In the above configuration, when the copy-prohibited code is detected from the digital signal supplied to the digital in terminal, the digital signal supplied to the digital in terminal is converted into an analog signal by the D / A converter. , This analog signal is band limited by a single lowpass filter,
It is converted into a digital signal by the A / D converter, and this digital signal is processed by the signal processing circuit and recorded. Therefore, since it is only D / A converted and then passed through a single low-pass filter, deterioration of sound quality due to band limitation is reduced.

When a copy-prohibited code is detected from the digital signal supplied to the digital in terminal, the digital signal supplied to the digital in terminal is sent to the built-in D / A.
It is used after being converted into an analog signal with a converter, and is less susceptible to external noise than when using the analog signal supplied to the line-in terminal as in the past, and high quality digital recording. Is possible.

[Example] An example of the present invention will be described below with reference to FIG. FIG. 1 is a system diagram showing a main part of a digital audio tape recorder (DAT) 20.

In the figure, reference numeral 21 is a line-in terminal, and an analog signal supplied thereto is supplied to a fixed terminal on the side a of the changeover switch SW1 via a volume 22 and a low pass filter 23 for band limitation. The output signal of the changeover switch SW1 is supplied to the A / D converter 24 and converted into a digital signal, and then supplied to the fixed terminal on the a side of the changeover switch SW2. The output signal of the changeover switch SW2 is supplied to the signal processing circuit 25 and subjected to signal processing such as error correction. The output signal of the signal processing circuit 25 is supplied to the rotary magnetic head device 27 via the recording circuit 26 and recorded on the magnetic tape 28.

The digital signal passed through the signal processing circuit 25 is supplied to the fixed terminal on the side a of the changeover switch SW4, and
It is supplied to the modulation circuit 30 of the biphase mark and modulated, and then supplied to the digital out terminal 31.

Further, 41 is a digital in terminal, and the digital signal according to the format (EIAJ standard) of the digital audio interface supplied here is supplied to the biphase mark demodulation circuit 42 and demodulated. In this case, the digital signal is further supplied to the clock recovery circuit 43, and a sampling clock (in this example, in synchronization with the input digital signal generated by the clock recovery circuit 43).
44.1KHZ) is supplied to the demodulation circuit 42 and demodulated.

The output signal of the demodulation circuit 42 is supplied to the fixed terminal on the side b of the changeover switch SW2 and at the same time b of the changeover switch SW4 is supplied.
Side fixed terminal. The output signal of the changeover switch SW4 is supplied to the D / A converter 52, converted into an analog signal, and then band-limited by the low-pass filter 53. The output signal of the low-pass filter 53 is supplied to the line-out terminal 51 and also to the fixed terminal on the b side of the changeover switch SW1 via the fade-in / fade-out volume 54.

The sampling clock generated by the clock reproduction circuit 43 is supplied to the fixed terminal on the side a of the changeover switch SW3. The fixed terminals on the a side and the b side of the changeover switch SW3 are connected to each other via a connection switch SW5, and the sampling clock output from the changeover switch SW3 is D
It is supplied to the / A converter 52.

Further, 35 is a signal generating means, and the sampling clock generated by this signal generating means 35 is a changeover switch SW6.
Is supplied to the fixed terminal on the b side. This switch SW6
The fixed terminal on the a side of and its movable terminal are the connection switch SW.
7, and the fixed terminal on the side a is connected to the fixed terminal on the side b of the changeover switch SW3. The sampling clock output from the switch SW6 is A / D
It is supplied to the converter 24 and the signal processing circuit 25.

Also, 61 is a code detection circuit.
The digital signal supplied to the digital-in terminal is supplied to 61. The code detection circuit 61 detects the copy prohibition code contained in the digital signal. In the format of the digital audio interface, the copy prohibition code is contained in bit 2 of the channel status, the copy is prohibited at the low level “0”, and the copy is permitted at the high level “1”. When a digital signal is supplied to the digital-in terminal 41, the selector switches SW2, SW
4, SW6 and connection switch SW5 are controlled by the detection signal of the code detection circuit 61.

That is, when a digital signal is supplied to the digital-in terminal 41, the changeover switch SW1 is connected to the b side, the changeover switch SW3 is connected to the a side, and the connection switch SW7 is turned off. When the copy inhibition is detected, the changeover switch SW2 is connected to the side a, and the changeover switches SW4 and SW6 are connected.
Is connected to the b side, and the connection switch SW5 is turned off. On the other hand, when copy permission is detected, the changeover switch SW2 is connected to the b side, the changeover switches SW4 and SW6 are connected to the a side, and the connection switch SW5 is connected. Is turned on.

When an analog signal is supplied to the line-in terminal 21, the changeover switches SW1, SW2, SW4 are connected to the a side, the changeover switches SW3, SW6 are connected to the b side, and the connection switch SW5 is turned off. The switch SW7 is turned on.

In the above configuration, when a digital signal is supplied to the digital-in terminal 41 and the code detection circuit 61 detects copy inhibition, the changeover switches SW1 to SW4, SW
6, the connection switches SW5, SW7 are controlled as shown in FIG.

In this case, a signal is recorded or output via the following paths. For convenience of explanation, only the reference symbols are shown in the signal paths.

(1) 41 → 42 → SW4 → 52 → 53 → 54 → SW1 → 24 → SW2 → 25 → 26 → 27 As a result, the digital signal supplied to the digital in terminal 41 is once D / A converted, It is A / D converted again and recorded digitally.

(2) 41 → 42 → SW4 → 52 → 53 → 54 → SW1 → 24 → SW2 → 25 → 30 → 31 As a result, the digital signal supplied to the digital in terminal 41 is digitized again and the digital out terminal 31 Is output to.

(3) 41 → 42 → SW4 → 52 → 53 → 51 As a result, the digital signal supplied to the digital-in terminal 41 is analogized and output to the line-out terminal 51.

In such a signal processing path, the sampling clock generated by the clock recovery circuit 43 is supplied to the demodulation circuit 42. Similarly, the D / A converter 52 also has a clock recovery circuit 4
The sampling clock generated in 3 is supplied.

As a result, the digital signal is synchronized with the digital signal supplied to the digital-in terminal 41,
To be converted.

Further, the A / D converter 24 and the signal processing circuit 25 are supplied with a predetermined sampling clock generated by the signal generating means 35. This allows A / D according to the DAT format.
Conversion processing and signal processing are performed.

By thus providing the signal generating means 35 and the clock recovery circuit 43 which are independent of each other, the digital IN terminal 41
Even the digital signal supplied to the A / D converter can be subjected to D / A conversion and A / D conversion processing according to the respective signal formats.

Further, when the digital signal is supplied to the digital-in terminal 41 and the copy permission is detected by the code detection circuit 61, the changeover switches SW1 to SW4, SW6 and the connection switches are connected.
SW5 and SW7 are controlled as shown in FIG.

In this case, a signal is recorded or output via the following paths. For convenience of explanation, only the reference symbols are shown in the signal paths.

(1) 41 → 42 → SW2 → 25 → 26 → 27 As a result, the digital signal supplied to the digital-in terminal 41 is directly supplied to the signal processing circuit 25 through the demodulation circuit 42 and processed, and then the recording circuit. It is digitally recorded via 26.

(2) 41 → 42 → SW2 → 25 → 30 → 31 As a result, the signal supplied to the digital-in terminal 41 is output to the digital-out terminal 31 as a digital signal.

(3) 41 → 42 → SW2 → 25 → SW4 → 52 → 53 → 51 As a result, the digital signal supplied to the digital-in terminal 41 is analogized and output to the line-out terminal 51.

In such a signal processing path, the sampling clock generated by the clock recovery circuit 43 is supplied to the demodulation circuit 42 and the signal processing circuit 25. As a result, signal processing is performed in a state of being synchronized with the digital signal supplied to the digital-in terminal 41.

Further, the sampling clock generated by the clock recovery circuit is also supplied to the D / A converter 52. by this,
The digital signal is D / A converted in synchronization with the digital signal supplied to the digital-in terminal 41.

When an analog signal is supplied to the line-in terminal 21, the changeover switches SW1 to SW4, SW6, the connection switch SW5,
SW7 is controlled as shown in FIG.

In this case, a signal is recorded or output via the following paths. For convenience of explanation, only the reference symbols are shown in the signal paths.

(1) 21 → 22 → 23 → SW1 → 24 → SW2 → 25 → 26 → 27 As a result, the analog signal supplied to the line-in terminal 21 is digitized by the A / D converter 24 and then predetermined It is digitally recorded through signal processing.

(2) 21 → 22 → 23 → SW1 → 24 → SW2 → 25 → 30 → 31 As a result, the analog signal supplied to the line-in terminal 21 is digitized and output to the digital-out terminal 31.

(3) 21 → 22 → 23 → SW1 → 24 → SW2 → 25 → SW4 → 52 → 53 → 51 As a result, the analog signal supplied to the line-in terminal 21 is re-analogized and output to the line-out terminal 51. To be done.

In such a signal processing path, the sampling clock generated by the signal generating means 35 is supplied to the A / D converter 24, the signal processing circuit 25, and the D / A converter 52. As a result, A / D conversion processing, signal processing according to the DAT format,
D / A conversion processing is performed.

Thus, according to this example, when the copy-prohibited code is detected from the digital signal supplied to the digital-in terminal, the digital signal supplied to the digital-in terminal is converted into an analog signal by the D / A converter 52. The analog signal is converted and band-limited by the single low-pass filter 53, and then converted into a digital signal by the A / d converter 24.
This digital signal is processed by the signal processing circuit 25 and recorded. Therefore, since it is only D / A converted and then passed through a single low-pass filter 53, deterioration of sound quality due to band limitation can be reduced, and high-fidelity digital recording can be performed.

Further, according to this example, when the copy prohibition code is detected from the digital signal supplied to the digital in terminal, the digital signal supplied to the digital in terminal is converted into an analog signal by the built-in D / A converter 52. It is used after being converted, and is less susceptible to the influence of external noise as compared with the case of using an analog signal supplied to a line-in terminal as in the related art, and high-quality digital recording can be performed.

Further, according to this example, by adjusting the fade-in and fade-out volume to the maximum level, digital recording can be performed at an appropriate level.

Further, in the DAT, data processing is performed using a plurality of sampling locks which differ depending on the source source, so that the source source to be digitally recorded, for example, the digital signal reproduced from the CD player can be used as it is. .

As described above, according to the present invention, when the copy prohibition code is detected from the digital signal supplied to the digital in terminal, the digital signal supplied to the digital in terminal is D / A. It is converted to an analog signal by the converter, this analog signal is band-limited by a single low-pass filter, then converted to a digital signal by the A / D converter, and this digital signal is processed by the signal processing circuit and recorded. It Therefore, since only a single low-pass filter is passed after D / A conversion, deterioration of sound quality due to band limitation can be reduced, and high-fidelity digital recording can be performed.

When a copy-prohibited code is detected from the digital signal supplied to the digital in terminal, the digital signal supplied to the digital in terminal is sent to the built-in D / A.
It is used after being converted into an analog signal with a converter, and is less susceptible to external noise than when using the analog signal supplied to the line-in terminal as in the past, and high quality digital recording. It can be performed.

[Brief description of drawings]

FIG. 1 is a system diagram of a main part showing an embodiment of the present invention, and FIG.
4 to 4 are diagrams showing the signal recording path, and FIG. 5 is a system diagram of a main part for explaining the conventional example. 10 …… CD player 20 …… DAT 21 …… Line in terminal 24 …… A / D converter 25 …… Signal processing circuit 26 …… Recording circuit 27 …… Rotating magnetic head device 31 …… Digital out terminal 35 …… Signal generating means 41 …… Digital in terminal 42 …… Demodulation circuit 51 …… Line out terminal 52 …… D / A converter 53 …… Low pass filter 54 …… Fade-in / fade-out volume switches SW1 to SW4, SW6 …… Changeover switch SW5, SW7 …… Connection switch

Claims (1)

[Claims] 1. A first recording system in which a digital signal supplied to a digital in terminal is processed by a signal processing circuit and recorded, and a digital signal supplied to the digital in terminal.
The analog signal is converted by the D / A converter, this analog signal is band-limited by a single low-pass filter, then converted to a digital signal by the A / D converter, and this digital signal is processed by the signal processing circuit. A second recording system for recording the data, and code detecting means for detecting a copy prohibition code from the digital signal supplied to the digital in terminal. When the code detecting means detects the copy permission, A digital audio tape recorder characterized by being switched to the first recording system and being switched to the second recording system when copy inhibition is detected.