JPH0756505Y2 - Audio signal switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention relates to an audio signal switching device, and more particularly to an audio signal switching device for automatically switching and outputting an analog signal from a cassette / tuner and a digital signal from a CD or DAT. Regarding the device.

(Prior Art) Conventionally, mutual switching among devices such as a CD, a cassette / tuner, and a DAT mounted on a vehicle has been performed by a configuration as shown in FIG. In other words, a CD or DAT that outputs a digital signal incorporates a D / A converter that converts the digital signal into an analog signal, and each device sends a mutual switching signal to another device when it is set to the play state. . The other device which has received this mutual switching signal stops its operation and outputs the analog signal from the device in the play state as it is.

For example, in FIG. 3, CD1 is set to the play state, and the mutual switching signal indicates that cassette / tuner 2 and DAT3
, The operation of the cassette / tuner 2 and DAT3 is stopped, and the analog signal from CD1 passes through the cassette / tuner 2 and DAT3 without any trouble and is output to the signal processing circuit side.

(Problems to be Solved by the Invention) As described above, in the conventional audio signal switching device,
A D / A converter is built in the CD1 or DAT3 that outputs a digital signal, and any one analog signal is output to the signal processing circuit side by the mutual switching signal using the analog signal as an output signal.

By the way, recently, there is an increasing demand for signal processing (for example, graphic equalizer processing) using digital signals from a CD or DAT as they are.

Then, by switching and selecting a device such as a CD / tuner that outputs both a digital signal and an analog signal, a device that outputs a digital signal such as a CD, a device that outputs an analog signal such as a cassette / tuner, etc. When used, the receiving side (signal processing side) cannot recognize whether the signal from the device selected by switching is a digital signal or an analog signal.

Therefore, conventionally, in the home audio device, when the user selects and switches the digital signal output device, the user also manually switches the digital signal input to the receiving side.

However, particularly in a vehicle-mounted audio device, it is not only a troublesome operation for the user to manually switch between the sending side and the receiving side, but also there is a problem in terms of safety of driving the vehicle.

Therefore, the object of the present invention is to include a digital signal and an analog signal in the output signal. When a digital signal is output, the digital signal is detected and the digital signal is automatically output. It is an object of the present invention to provide an audio signal switching device having a simple structure that can easily identify the digital signal.

(Means for Solving the Problems) In order to solve the above-mentioned problems, an audio signal switching device according to the present invention has an analog audio signal input terminal for inputting an analog audio signal and a digital audio signal input terminal for inputting a digital audio signal. Detecting means for detecting the presence of information peculiar to the digital signal from the digital audio signal at a predetermined time interval; and a digital audio signal in which the peculiar information is detected when the peculiar information is detected by the detecting means. And switching means for converting the analog audio signal into a digital audio signal by an A / D converter and outputting the analog audio signal when the specific information is not detected.

(Example) Next, this invention is demonstrated, referring drawings.

FIG. 1 is a block diagram showing an embodiment of an audio signal switching device according to the present invention.

In FIG. 1, digital signals SD1 and SD2 in EIAJ format are output from CD1 and DAT3, respectively. Also,
Similar to the conventional apparatus shown in FIG. 3, CD1 and DAT3 have built-in D / A converters and also output analog signals. Similar to FIG. 3, outputs of these analog signals are switched and controlled by a mutual switching signal generated by setting a play state of each device, and are supplied to the A / D converter 5.

Digital signals SD1 and SD2 from CD1 and DAT3 are input to two input terminals 41 and 42 of the demodulation circuit 4.

The microcomputer 7 receives the signals of the terminals 41 and 42 through the demodulation circuit 4 at a predetermined time interval in order to determine whether or not the digital signals are supplied to the two input terminals 41 and 42 of the demodulation circuit 4. To do.

Whether or not the digital signal is supplied can be determined by detecting the presence or absence of sampling frequency (FS) information in the EIAJ format digital signal. For example, the presence or absence of the sampling frequency can be determined by checking the C bit of the EIAJ format digital signal.

When the input terminal from which the sampling frequency information is detected (the input terminal to which the digital signal is supplied) is determined, the microcomputer 7 switches the switch built in the demodulation circuit 4 to switch the digital signal of the input terminal. To
The signal is output to a digital signal processing circuit (not shown) via the control of the switching circuit 6.

Similar to the conventional device shown in FIG. 1, the analog signal output based on the mutual switching signal is converted into a digital signal by the A / D converter 5, and when there is no digital signal input to the input terminal, the microcomputer 7 Is output via the control of the switching circuit 6 according to.

The specific operation of the embodiment shown in FIG. 1 will be described below.

Now, consider a case where the cassette / tuner 2 is selected and set to the play state. In this case, the analog signal from the cassette / tuner 2 is supplied to the switching circuit 6 as a signal converted into a digital signal by the A / D converter 5 by the mutual switching function as in the conventional device. At this time, since the CD1 and DAT3 are in the stopped (non-operating) state, the digital signal is input to the input terminals 41 and 42 of the demodulation circuit 4.
Not supplied to.

Therefore, since the microcomputer 7 does not detect the sampling frequency information of the digital signal, it outputs the digitally converted signal from the cassette / tuner 2 via the switching circuit 6.

In the above state, the microcomputer 7 switches and connects the input terminals 41 and 42 of the demodulation circuit 4 at fixed time intervals and waits for the arrival of a digital signal.

So, for example, if you set CD1 to play,
Sampling frequency information is detected in the signal from the input terminal 41, and the digital signal SD1 is output via the switching circuit 6.

After that, when DAT3 is set to the play state, input terminal 41
The sampling frequency information is not detected from the signal of, and the sampling frequency is detected from the signal to the input terminal 42,
Similarly, the digital signal SD2 is output.

Further, thereafter, when the cassette / tuner 2 is set to the play state, the sampling frequency information is not detected from the signals from the input terminals 41 and 42. Therefore, the switching circuit 6 is controlled from the cassette / tuner 2 by the control of the microcomputer 7. The digital signal corresponding to the analog signal of is output.

As described above, in the present invention, the type (analog / digital signal) of the input side signal can be discriminated from the receiving side (signal processing circuit side), and the digital signal priority use can be easily achieved. Source side (CD, cassette / tuner, DA
From the side of the device such as T), the connection is the same as the conventional connection, no special processing is required, and the configuration is simple.

In the embodiment shown in FIG. 1, the D / A converter is built in CD1 or DAT3 in relation to the conventional device shown in FIG. The analog signal from the signal set to the state
It is A / D converted and supplied to the switching circuit 6. But,
Analog signal from cassette / tuner 2 and CD1 or DAT
It goes without saying that the digital signal may be directly supplied to the switching circuit 6 without incorporating the D / A converter in 3.

FIG. 2 shows a flowchart showing a processing procedure for determining a signal to be selectively output by the switching circuit 6.

Now, when the cassette / tuner 2 is set to the play state and the CD1 and DAT3 are in the stopped state, the analog signal from the cassette / tuner 2 is converted into a digital signal by the A / D converter 5 and the switching circuit 6 Is being supplied to.

In this state, the microcomputer 7 controls whether or not sampling frequency information (FS information) is included in the input digital signals to the input terminals 41 and 42 of the demodulation circuit 4 at constant time intervals.

In step S1 of FIG. 2, it is determined whether sampling frequency information (FS information) of the digital signal SD1 is present,
If it is determined that the digital gin signal SD1 is present, the digital gin signal SD1 is selected and output via the switching circuit 6 (step S4).

If it is determined that the FS information of the digital signal SD1 does not exist, the presence or absence of the FS information of the digital signal SD2 is determined in step S2,
When it is determined that the analog signal is not present, the analog signal is output via the switching circuit 6 (step S3).

On the other hand, when it is determined that the FS information of the digital signal SD2 is present, the digital signal SD2 is output via the switching circuit 6 (step S5), and the FS of the digital signal SD2 is continued.
The presence or absence of information is determined (step S6).

When the FS information of the digital signal SD2 is detected in step S6, the process returns to step S5, and then the digital signal SD2 is detected.
Although SD2 is output, if it is determined that there is no FS information, the process returns to step S1 and the above-described process is repeated.

In the above embodiment, the sampling frequency (FS) information of the digital signal is detected by the processing of the microcomputer 7. However, if the presence or absence of the FS information corresponds to the logical levels "1" and "0" The same function can be achieved with a logic circuit configuration.

Further, it is obvious that the number of digital signals is not limited to two, and may be one or three or more. In the case of three or more digital signals, the sampling frequency information of each digital signal is searched at a fixed time interval, and the digital signal from which this information is detected is selected.

Further, the determination of the digital signal input may be made by detecting the locked state of the PLL circuit without depending on the sampling information, or by any other method. In short, it is possible to make a determination based on a signal having a characteristic form of a digital signal.

(Effect of the Invention) As described above, in the present invention, not only the analog signal is output by the conventional mutual switching signal, but also the presence or absence of the specific information indicating the digital signal such as the sampling frequency information of the digital signal is determined by the predetermined time. Since the digital signal is preferentially selected and output when this information is detected by judging at intervals, it is possible to smoothly perform the selective output of the analog signal and the digital signal with a simple structure.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an audio signal switching device according to the present invention, FIG. 2 is a flow chart showing the flow of signal switching output processing in the embodiment of FIG. 1, and FIG. 3 is a conventional audio signal. It is a block diagram which shows the structure of a switching device. 1 ... CD, 2 ... Cassette / tuner, 3 ... DAT, 4 ... Demodulation circuit, 5 ... A / D converter, 6 ... Switching circuit, 7 ... Microcomputer.

Claims (1)

[Scope of utility model registration request] 1. An analog audio signal input terminal for inputting an analog audio signal, a digital audio signal input terminal for inputting a digital audio signal, and the presence of information peculiar to the digital signal is detected from the digital audio signal at predetermined time intervals. And a digital audio signal in which the information specific to the previous term is detected when the information specific to the previous term is detected by the detecting means, and the analog audio signal is A / D when the information specific to the previous term is not detected. An audio signal switching device characterized by comprising switching means for converting to a digital audio signal by a converter and outputting the digital audio signal.