JPH0547131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to audio equipment, and particularly to an audio equipment suitable for being installed between a digital audio source and a DAT (digital audio tape device).

<Prior Art> Currently, digital audio recorders such as DATs cannot perform digital dubbing from compact disc players or digital audio sources that contain a copy prohibition code. For this reason, the audio signal is output in analog form from the audio source, inputted to the analog input terminal of the DAT via an amplifier, digitized by the DAT, and then recorded on tape.

Figure 3 is a conventional block diagram of a system when the audio source is a CD (compact disc), where 1 is a CD player, 2 is an amplifier, and 3 is a
DAT, the digital audio signal read from the CD is converted into an analog signal by a D/A converter (DAC) 1a, converted to a smooth analog signal by a low-pass filter 1b, and then passed through an amplifier 2.
Input to DAT3. In the DAT3, the analog audio signal output from the amplifier 3 is adjusted to an appropriate level for AD conversion by operating the volume 3a, and then passed through the low-pass filter 3b.
The high-frequency components of a predetermined frequency or higher (for example, 24KHz or higher if the DAT sampling frequency is 4KHz) are removed and the A/D converter (ADC) 3c
The signal is input to the computer, where it is AD converted to a digital signal and recorded on tape.

<Problems to be solved by the invention> However, in such conventional systems,
From CD player 1 to amplifier 2 and from amplifier 2
Because it is transmitted as an analog signal up to DAT3,
There are problems in that analog transmission distance becomes longer, transmission loss occurs, and sound quality deteriorates.

Furthermore, in conventional systems, the sound quality deteriorates because the signal passes through a low-pass filter twice, on the audio source side and on the DAT side, which causes phase distortion.

Furthermore, in conventional systems, the analog signal level is adjusted to an appropriate value using a volume on the DAT side, but if this level adjustment is not performed properly, sound quality will deteriorate. In other words, when the analog signal becomes overleveled, clipping occurs and distortion occurs.
If the level is too low, the bits cannot be used sufficiently, resulting in deterioration of sound quality.

From the above, it is an object of the present invention to shorten the distance for analog transmission, omit the volume for adjusting the level of analog signals, and further reduce the number of low-pass filters that pass through, thereby minimizing deterioration of sound quality. The goal is to provide audio equipment that can.

Another object of the present invention is that if the sampling clock frequency of an externally input digital audio signal matches the sampling clock frequency for DAT, the signal will be almost the same as the input digital audio signal even after AD/DA conversion. To provide an audio device that can record a digital signal without deterioration by inputting it to a DAT device.

<Means for Solving the Problems> According to the present invention, the above object is achieved when the digital input terminal into which the digital audio signal is input and the sampling frequency of the digital audio signal are set to DAT.
A digital input interface that determines whether the sampling frequency matches the sampling frequency of the digital audio signal and separates the sampling clock included in the digital audio signal, and a D/D converter that converts the digital audio signal input from the digital input interface into analog data. A converter, a low-pass filter that cuts high-frequency components included in the D/A converter output, and a low-pass filter output.
An A/D converter performs AD conversion to digital data using a predetermined sampling clock for the DAT, and converts the D/A converter output to digital data using a sampling clock separated by the digital interface, and the sampling frequency of the digital audio signal is A switching means for inputting the D/A converter output to the A/D converter when the sampling frequency matches the DAT sampling frequency, and inputting the low pass filter output to the A/D converter when the frequency does not match; This is accomplished by a digital output terminal that outputs a digital audio signal from.

<Function> The digital input interface determines whether the sampling frequency of the digital audio signal matches the sampling frequency for DAT, and
Separate the sampling clock included in the digital audio signal. The D/A converter converts the digital audio signal input from the digital input interface into an analog D/A converter, and the low-pass filter cuts out high-frequency components contained in the output of the D/A converter. The switching means switches the D/A when the sampling frequency of the digital audio signal matches the sampling frequency for DAT.
Input the converter output to the A/D converter, and if they do not match, input the low pass filter output to the A/D converter.
input into the converter. When the A/D converter receives a signal from a low-pass filter,
When the signal is input from the D/A converter, it is converted to digital using the sampling clock separated by the digital interface.
AD convert it and input it to the DAT device from the digital output terminal.

<Embodiment> FIG. 1 is a schematic block diagram of a system in which the present invention is applied to an amplifier.

11 is a CD player, 12 is an amplifier, 13 is
DAT, and in amplifier 12, 12a is D/
A converter, 12b is a low pass filter, 12
c is an A/D converter.

The amplifier 12 includes a D/A converter 12a, a low pass filter 12b, and an A/D converter 12.
Provide c. Then, a digital audio signal from the CD player 11 or the like is directly input to the D/A converter 12a in the amplifier, and the high-frequency components contained in the analog signal obtained from the D/A converter are cut by the low-pass filter 12b. The output is converted to digital by the A/D converter 12c, and the digital audio signal is input to the digital input terminal of the DAT and recorded on tape.

As a result, the analog signal portion is transferred from the D/A converter 12a in the amplifier 12 to the A/D converter 1.
2c, the analog signal level can be optimally adjusted with a fixed resistor without using a volume, and the number of low-pass filters to be passed through can be reduced.

FIG. 2 is a block diagram when the audio equipment according to the present invention is built into an amplifier.

12a converts digital audio signal to analog
D/A converter for DA conversion, 12b is D/A
A predetermined frequency included in the output of the converter 12a (for example, DAT sampling frequency of 48K)
12c is a low-pass filter that cuts out high frequency components (24KHz or higher), and 12c is for analog signals.
12d is an A/D converter that converts to digital at a predetermined sampling frequency for DAT; 12d is a digital input terminal into which a digital audio signal is input;
2e is a digital input interface for predetermined digital input interface processing; 12f;
is a digital filter, and 12g is the output of the low-pass filter 12b or D/A converter 12a as appropriate.
12h is a digital output interface,
12i is a digital output terminal, 12f is a sampling clock for DAT (frequency is 48KHz)
A clock generator 12k generates a sampling clock _P6 outputted from the digital input interface 12e and a sampling clock outputted from the clock generator 12j.
This is a switching circuit that switches _PD as appropriate and inputs it to the A/D converter 12c and the digital output interface 12h.

Digital audio signals from CD players, DAT devices, satellite broadcasting equipment, etc. are connected to digital input terminal 1.
2d via digital input interface 12
e, and then the digital filter 12f.
The signal is input to the D/A converter 12a via the D/A converter 12a.

Digital input interface 12e is PLL
It has a built-in circuit that separates the sampling clock P _S of a predetermined frequency included in the digital audio signal and inputs it to the digital filter 12f and the D/A converter 12. Furthermore, the digital input interface 12e checks whether the frequency of the sampling clock P _S is equal to the sampling clock frequency for DAT (for example, 48 KHz).
If they are equal, a high-level switching signal SWS is output, and the switching circuits 12g and 12k switch the connection state from the solid line position to the dotted line position shown in the figure.

The D/A converter 12a has a sampling frequency
The digital audio signal S _D is converted into an analog signal S _A based on the P _S , and the low-pass filter 12b cuts out high-frequency components contained in the D/A converter 12 b.

Now, the frequency of the sampling clock P _S of the externally input digital audio signal is 48KHz.
Otherwise, since the switching circuits 12g and 12k are in the connected state shown by the solid line in the figure, the A/D converter 12
c performs AD conversion on the analog signal input via the low-pass filter 12b. That is, A/D
The converter 12c is a clock generator 12j.
The low-pass filter output is converted into digital data in synchronization with the DAT sampling clock (48KHz) P _D generated from P D and is input to the digital output interface 12h. In addition, the A/D converter 12
Since c only needs to AD convert the analog signal output from the D/A converter 12a, the level can be adjusted and fixed using a resistor so that the analog signal can be optimally AD converted. As such, there is no need to adjust the volume level.

The digital output interface 12h outputs the input digital signal to the clock generator 12j.
DAT (not shown) is output from the digital output terminal 12i in synchronization with the sampling clock P _D generated from
input to the digital input terminal.

Note that the above is a case where the sampling clock frequency of the digital audio signal input to the digital input terminal 12d does not match the sampling clock frequency for the DAT, but if they match, a high level signal is output from the digital input interface 12e. The switching signal SWS is output and the switching circuit 1
2g and 12k are shown in the dotted line state. As a result,
D/A converter 12 to A/D converter 12c
The analog output of A is directly input, and the sampling clock P _S separated from the digital audio signal by the digital input interface 12e is input to the A/D converter 12c and the digital output interface 12h.

A/D converter 12c is D/A converter 1
The analog signal directly input from 2a is converted to digital in synchronization with the sampling clock (48KHz) P _S , and the converted digital signal is input to the digital output interface 12h. The digital signal obtained is input from the digital output terminal 12i to the digital input terminal of the DAT (not shown) in synchronization with the sampling lock _PS .

In this way, when the sampling lock frequency of an externally input digital audio signal (for example, a digital audio signal with a copy protection code) matches the sampling lock frequency for the DAT, the sampling clock included in the digital audio signal is By performing DA conversion and AD conversion in synchronization with _PS , it is possible to reproduce and output a digital signal that is almost the same as the input digital audio signal and has no deterioration.

Incidentally, although the above is a case in which the circuit configuration shown in FIG. 2 is provided in the amplifier, it is not necessarily necessary to provide it in the amplifier, and it may be provided in a selector device or the like.

<Effects of the Invention> According to the present invention, the analog signal portion can be made in a short distance from the D/A converter in the amplifier to the A/D converter, for example, and the analog signal portion can be made in a short distance from the D/A converter in the amplifier to the A/D converter. The signal level can be adjusted optimally, and the number of low-pass filters to be passed through can be reduced.
It is possible to minimize sound quality deterioration during AD conversion and DA conversion processing.

Furthermore, according to the present invention, when the sampling lock frequency of the externally input digital audio signal matches the sampling lock frequency for the DAT, the DAT uses a digital signal that is almost the same as the input digital audio signal and has no deterioration. It can be input into the device and recorded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a system in which the present invention is applied to an amplifier, FIG. 2 is a block diagram of an audio device of the present invention applied to an amplifier, and FIG. 3 is a block diagram of a conventional system. 11...CD player, 12...amplifier, 12
a...D/A converter, 12b...Low pass filter, 12c...A/D converter, 13...
DAT.

Claims (1)

[Claims] 1. Determine whether the sampling frequency of the digital audio signal matches the sampling frequency of the DAT and the sampling clock included in the digital audio signal. a digital input interface to separate; a D/A converter that converts the digital audio signal input from the digital input interface into an analog D/A converter; and a low-pass filter that cuts high-frequency components contained in the output of the D/A converter. an A/D converter that converts the output of the low-pass filter into a digital signal using a predetermined sampling clock for the DAT, and converts the output of the D/A converter into a digital signal using a sampling clock separated by the digital interface; and the digital audio signal. switching means for inputting the D/A converter output to the A/D converter when the sampling frequency matches the sampling frequency for the DAT, and inputting the low-pass filter output to the A/D converter when the sampling frequency does not match; An audio device characterized by having a digital output terminal that outputs a digital audio signal from an A/D converter.