JPH0563650A - Voice optical space transmitter - Google Patents

Abstract

PURPOSE:To reduce the frequency of occurrence of a mute signal by inputting a transmission error detection signal from a decoder to a forward backward protection circuit and using an output signal as a mute signal. CONSTITUTION:An electric/optic conversion section 11 converts a digital audio signal into an optical signal, which radiates into space. Furthermore, an opto- electric conversion section 12 converts the received optical signal into an electric signal, Then the electric signal is inputted to a decoder 13 for digital audio format, decoded and the decoder 13 is used to detect a transmission error caused on a transmission line. The transmission error is detected by monitoring the code rule of a transmission code of the digital audio format of the decoder 13 or monitoring a parity bit in the digital audio format. A detected transmission error detection signal 14 is inputted to a forward/backward protection circuit 16 together with a frame synchronizing signal 15 and a mute signal 17 is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio / optical space transmission apparatus for digital audio signals using infrared light, which is mainly used in audio equipment.

[0002]

2. Description of the Related Art The structure and operation of a conventional audio optical transmission apparatus will be described with reference to the audio optical transmission apparatus for digital audio signals shown in FIG.

The device is a wired transmission using a fiber, and according to the figure, reference numeral 21 is an electro-optical conversion unit, which converts a digital audio signal into an optical signal and transmits the optical signal to the fiber 2.
Release into 2. A photoelectric conversion unit 23 converts the received optical signal into an electric signal. Next, this electric signal is input to the decoder 24 of the digital audio format to be decoded and a transmission error occurring on the transmission path is detected, and the detected transmission error signal is immediately muted signal 2
It is used as 5.

In the case of the audio / optical space transmission device, the same configuration is used, and the fiber 22 is not used, and only signal transmission is performed using space. As described above, there is a general tendency for the audio / optical space transmission apparatus to be configured with the configuration of the digital audio signal transmission apparatus using the conventional fiber.

[0005]

However, in the above-mentioned audio / optical space transmission apparatus, since the structure of the transmission apparatus using the fiber 22 is the basic, in the optical space transmission in which the transmission error occurs more often than the fiber. Since the transmission error detection signal is immediately changed to the mute signal, the phenomenon that the mute is frequently applied occurs. Eg 4
In the case of a 4.1 kHz sampling digital audio signal, assuming that the transmission error occurrence probability is 10 ⁻⁷ , mute is applied once every 1.7 seconds, resulting in unbearable speech. ..

The present invention solves such a conventional problem by reducing the frequency of muting to such an extent that there is no practical problem, transmitting voice in the optical space, and transmitting the optical space in the case of blocking the optical path. It is an object of the present invention to provide an audio / optical space transmission device that can surely mute a specific failure.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention puts a transmission error detection signal from a digital audio format decoder into a front / rear protection circuit and makes an output signal a mute signal. The frequency of mute signal generation is reduced.

[0008]

As described above, the transmission error detection signal from the digital audio format decoder is input to the front / rear protection circuit, and the output signal is set to the mute signal.
The frequency of mute signal generation is reduced to such an extent that it is not a practical problem, and muting is reliably performed when the optical path is cut off.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a voice / optical space transmission apparatus according to the present invention will be described with reference to FIGS. An electro-optical conversion unit 11 converts a digital audio signal into an optical signal and radiates it into space. Reference numeral 12 denotes a photoelectric conversion unit, which converts a received optical signal into an electric signal. Next, this electric signal is input to the decoder 13 of digital audio format for decoding and the decoder 13
Detects a transmission error that has occurred on the transmission path. The detection of the transmission error is performed by monitoring the code rule of the DMI code of the transmission code of the digital audio format of the decoder 13 or the parity bit in the digital audio format. The detected transmission error detection signal 14 is input to the front / rear protection circuit 16 together with the frame synchronization signal 15, and the mute signal 17 is output.

Details of the front / rear protection circuit 16 will be described with reference to FIG. The front / rear protection circuit 16 includes D flip-flops 31 to 34 and NAND gates 35 and 36.
The transmission error detection signal 14 is L and is sampled for each frame synchronization signal 15 when there is no error at all. When L continues for four consecutive times, the output of the NAND gate 35 becomes H, the output of 36 becomes L, and the mute signal 17 becomes L. Assuming that the state has shifted from this state to a state in which some error has started, for example, the transmission error detection signal 14 is H, L, H,
If it becomes L, the output of the NAND gate 35 becomes H, the output of 36 becomes H, and the latch circuit 37 holds the previous state. Therefore, the mute signal 17 is L (non-mute).
Becomes Next, assuming the case where the optical path is blocked, the transmission error detection signal 14 becomes H, H, H, H.
The output of the gate 35 becomes L, the output of 36 becomes H, the latch circuit is inverted, the mute signal 17 becomes H (mute), and the mute signal is output. In order to release the mute from this state, it is necessary to wait for the state in which the transmission error detection signal 14 is continuously L at least three times.

Therefore, the front-rear protection circuit 16 reduces the output of the transmission error detection signal, which is frequently generated in the audio-optical space transmission, to the mute signal without making it to the mute signal immediately. And a mute signal is surely generated in the case of a serious obstacle such as the interruption of the optical path.

The output frequency of the mute signal 17 based on the transmission error detection signal 14 can be changed by increasing or decreasing the number of D flip-flops. Therefore, the mute signal can be appropriately changed according to the data handled by the optical space transmission device. The output frequency can be selected.

[0013]

As is apparent from the above embodiments, the present invention inputs the error detection signal from the digital audio format decoder to the front / rear protection circuit and outputs the mute signal in the conventional audio / optical space transmission apparatus. As a result, even in the case of audio-optical spatial transmission using a spatial transmission line with many transmission errors, the frequency of mute signal output is reduced to a practical level, while muting is reliably performed when a serious failure such as an optical path cutoff occurs. It is possible to provide an audio / optical space transmission device with high practical value that can be used.

[Brief description of drawings]

FIG. 1 is a block diagram of an audio / optical space transmission apparatus according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a front / rear protection circuit, which is the main part of the same.

FIG. 3 is a block diagram of a conventional audio optical transmission device.

[Explanation of symbols]

 Reference Signs List 11 electro-optical conversion unit 12 opto-electric conversion unit 13 digital audio format decoder 14 transmission error detection signal 16 front-back protection circuit 17 mute signal

Claims (1)

[Claims] 1. An electro-optical conversion unit for radiating a digital audio format signal to space, an opto-electric conversion unit for receiving an optical signal transmitted in space and converting it into an electric signal, and detecting a transmission error, Audio-optical space consisting of a digital audio format decoder that outputs a transmission error detection signal, and a front / rear protection circuit that inputs this transmission error detection signal and outputs a mute signal that is less frequent in response to this transmission error detection signal Transmission equipment.