JP3067309B2 - Noise removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise eliminator for removing noise from a transmitted digital signal.

[0002]

SUMMARY OF THE INVENTION The present invention detects the CN ratio of a received digital signal, and if the detected CN ratio is lower than a predetermined value, switches external synchronization to internal synchronization to change the frame synchronization pattern of the digital signal. By replacing the appropriate frame synchronization pattern, replacing the control code of the digital signal with the appropriate control code, and replacing the range bits of the digital signal with the fixed range bits, noise that causes a great audibility can be reduced. It was made.

[0003]

2. Description of the Related Art As a method of reducing errors in a digital signal, there is a method of adding an error code. As a method of ensuring synchronization, forward protection and backward protection techniques are known. However, the ability to correct or interpolate a signal is limited, and increasing signal errors become noise.

[0004] Noise generated in a digital audio signal of a satellite broadcast includes noise generated when the audio data itself is erroneous, loss of synchronization due to an incorrect frame synchronization pattern, and compression when a digital signal is transmitted after being compressed. And a noise generated by an error in a signal for controlling the receiver.

[0005] The former noise is relatively less disturbing in the sense of hearing, and the latter noise is more disturbing.

[0006]

SUMMARY OF THE INVENTION In the sound of a satellite broadcast, when the reception CN ratio is lowered and becomes lower than a threshold level,
The noise suddenly increases, and the noise makes it difficult to hear speech.

An object of the present invention is to provide a noise eliminator capable of solving the above-mentioned problems and reducing noise which is a great hindrance to hearing.

[0008]

In order to achieve such an object, the present invention provides an internal synchronization means for performing internal synchronization,
Frame synchronization pattern generation means for generating an appropriate frame synchronization pattern; control code storage means for storing an appropriate control code; range bit generation means for generating a fixed range bit; and a CN ratio of the received digital signal. Detecting means for detecting, and when the CN ratio detected by the detecting means is smaller than a predetermined value, internal synchronization is applied by the internal synchronization means in place of external synchronization, and the frame synchronization pattern of the digital signal is converted to the frame synchronization pattern generation means. , The control code of the digital signal is changed to an appropriate control code from the control code storage means, and the range bit of the digital signal is changed to a fixed range bit from the range bit generation means. Control means.

[0009]

According to the present invention, the CN of the received digital signal is
The ratio is detected by the detecting means, and the C is detected by the detecting means.
When the N ratio is smaller than a predetermined value, the switching control means performs internal synchronization by the internal synchronization means in place of the external synchronization, and changes the frame synchronization pattern of the digital signal to an appropriate frame synchronization pattern from the frame synchronization pattern generation means. The control code of the digital signal is replaced with an appropriate control code from the control code storage means, and the range bit of the digital signal is replaced with a fixed range bit from the range bit generation means.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

A satellite broadcast audio noise eliminator (hereinafter referred to as a noise eliminator) 20 and a BS tuner 17 according to one embodiment.
Are connected as shown in FIG. 2 and the BS tuner 17
The BS-IF signal input to the IF input terminal 16 is FM
The audio signal is demodulated.
8, and the digital data is demodulated. The demodulated data is input to the noise removing device 20 together with a clock synchronized with the data. When an error is detected by the error detection / correction unit 19 of the BS tuner 17, a detection signal indicating that the error has been detected is input to the noise removal device 20.

In FIG. 1, reference numeral 7 denotes a frame synchronization pattern generation unit for generating a frame synchronization pattern. Reference numeral 6 denotes a changeover switch for switching to either the data input terminal 1 or the frame synchronization pattern generator 7. Reference numeral 10 denotes a control code storage unit which stores a control code of an error-free voice when the CN ratio is good. Reference numeral 9 denotes a changeover switch, which switches to either the changeover switch 6 or the control code storage unit 10. A range bit generator 14 generates a fixed range bit. Reference numeral 13 denotes a changeover switch which switches to either the changeover switch 9 or the range bit generator 14.

Reference numeral 5 denotes a frame synchronization detection unit which detects a frame synchronization and outputs a synchronization signal indicating the head of the digital data string input to the data input terminal 1.

Reference numeral 12 denotes an intra-frame counter for counting the number of data in one frame. Reference numeral 4 denotes a CN ratio measuring device, which is an error detection signal input terminal 2 from the BS tuner 17.
The CN ratio is measured on the basis of the error signal input to.

Reference numeral 11 denotes a timing control unit which switches the changeover switches 6, 9, and 13 at appropriate timings based on inputs from the CN ratio measuring device 4 and the in-frame counter 12.

Next, the operation will be described.

The digital data string input to the data input terminal 1 is input to the changeover switch 6 and the frame synchronization detector 5. The frame synchronization detecting section 5 detects the frame synchronization and outputs a synchronization signal indicating the head of the digital data sequence. Then, the number of data in one frame is counted by the in-frame count 12, and the counted number is output to the timing control unit 11.

The CN ratio is measured by the CN ratio measuring device 4 based on the error detection signal input from the BS tuner 17 to the error detection signal input terminal 2. When the deterioration of the CN ratio is observed, a signal indicating that the CN ratio has deteriorated is output to the timing control unit 11.

When the CN ratio has not deteriorated, the changeover switches 6, 9, and 13 are as shown in FIG. That is, the changeover switch 6 is connected to the data input terminal 1
, The changeover switch 9 is set to the changeover switch 6 side,
The changeover switch 13 is set to the changeover switch 9 side. Therefore, the data input to the data input terminal 1 is output to the data output terminal 15 via the changeover switches 6, 9, and 13.

The changeover switch 8 is as shown in FIG. That is, the changeover switch 8 is switched to the frame synchronization detection unit 5 side. The intra-frame counter 12 has been reset by the synchronization signal output by the frame synchronization detection unit 5. That is, external synchronization is established.

When the CN ratio is deteriorated, the changeover switch 8 is almost switched to the intra-frame counter 12 side, that is, the internal synchronization is established, the self-reset is performed by the intra-frame counter 12, and the counting is performed. Therefore, the count of the intra-frame counter 12 is not reset by erroneous synchronization, and the timing when the CN ratio is good is maintained.

On the other hand, the changeover switch 6 is switched to the frame synchronization pattern generation section 7 by the timing control section 11 at the portion of the frame synchronization pattern in the data string input to the data input terminal 1, and is replaced with a correct synchronization pattern. . Thereafter, the changeover switch 6 is switched to the data input terminal 1 side. Further, the changeover switch 9 is a portion indicating the control code of the voice of the data string, and is switched to the control code storage unit 10 by the timing control unit 11 so that the error stored in the control code storage unit 10 when the CN ratio is good is stored. Replaced with no phonetic code. Thereafter, the changeover switch 9 is switched to the changeover switch 6 side. Further, the changeover switch 13 is a part of the range bit indicating the compression state of the data in the data string, and is switched to the range bit generation part 14 by the timing control part 11 and is replaced with a fixed range bit. Thereafter, the changeover switch 13 is switched to the changeover switch 9 side.

Therefore, data in which only the synchronization pattern, the control code, and the range bit are replaced is output from the data output terminal 15.

[0025] Because of this, out-of-synchronization due to an erroneous frame synchronization pattern, an error in a signal indicating a compression method when a digital signal is compressed and transmitted, and an error in a signal for controlling a receiver are considered. , Noise can be removed, and voice can be heard even at a low CN ratio.

In this embodiment, an example of satellite broadcasting has been described. However, the present invention can also be applied to a system that transmits digital signals other than satellite broadcasting.

[0027]

As described above, according to the present invention,
The CN ratio of the received digital signal is detected. If the detected CN ratio is lower than a predetermined value, the external synchronization is switched to the internal synchronization, the frame synchronization pattern of the digital signal is replaced with a proper frame synchronization pattern, and the digital synchronization is performed. Since the control code of the signal is replaced with an appropriate control code and the range bit of the digital signal is replaced with a fixed range bit, there is an effect that noise which causes a great disturbance in hearing can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a connection between a satellite broadcast audio noise elimination device 20 and a BS tuner 17;

[Explanation of symbols]

 Reference Signs List 4 CN ratio measuring device 5 Frame synchronization detection unit 6, 8, 9, 13 Changeover switch 7 Frame synchronization pattern generation unit 10 Control code storage unit 11 Timing control unit 12 In-frame counter 14 Range bit generation unit

Claims (1)

(57) [Claims] 1. An internal synchronization means for performing internal synchronization, a frame synchronization pattern generation means for generating an appropriate frame synchronization pattern, a control code storage means for storing an appropriate control code, and a range for generating a fixed range bit Bit generation means, detection means for detecting a CN ratio of the received digital signal, and when the CN ratio detected by the detection means is smaller than a predetermined value, internal synchronization is performed by the internal synchronization means in place of external synchronization, Replacing the frame synchronization pattern of the digital signal with an appropriate frame synchronization pattern from the frame synchronization pattern generation means, replacing the control code of the digital signal with an appropriate control code from the control code storage means, Switch to the fixed range bit from the range bit generator Noise elimination device being characterized in that a control means.