JP2009135709A - Infrared-ray receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared-ray receiving device that prevents noise outputted by suitably detecting noise occurring when receiving an external infrared-ray emitted from a plasma display or the like. <P>SOLUTION: A demodulation circuit 21 in an infrared-ray receiving device demodulates a sound signal from an infrared signal received from an infrared wireless microphone 3. An asymmetric-signal detection circuit 23 detects an asymmetric signal from the sound signal demodulated by the demodulation circuit 21. An output limiting circuit 25 limits output of the sound signal according to the detection result of the asymmetric signal by the asymmetric-signal detection circuit 23. The output limiting circuit 25 may mute sound output when the asymmetric signal is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an infrared receiver provided in an infrared wireless microphone system.

  2. Description of the Related Art Conventionally, an infrared wireless microphone system that includes an infrared wireless microphone and an infrared receiver and transmits an audio signal using infrared rays is known. The infrared wireless microphone system is advantageous when a plurality of systems are used simultaneously in a narrow range because interference can be avoided if there is a partition wall that does not allow infrared rays to pass through. Using such characteristics, the infrared wireless microphone system is conveniently used in, for example, karaoke facilities and conference facilities.

  FIG. 7 shows the configuration of an infrared wireless microphone system. In the infrared wireless microphone system 101 of FIG. 7, the infrared wireless microphone 103 is an infrared transmitter, and generates and transmits an infrared signal from input voice. An infrared signal is received by the infrared receiving device 107 via the infrared sensor 105, and the demodulation circuit 109 of the infrared receiving device 107 demodulates the infrared signal to generate an audio signal. The audio signal is amplified by the power amplifier 111 and output from the speaker 113.

  In such an infrared receiver 107 of the infrared wireless microphone system 101, measures against noise caused by external infrared rays emitted from other than the infrared wireless microphone 103 are required.

  A powerful noise source is a plasma display. As shown in FIG. 7, the infrared wireless microphone system 101 is often installed together with the plasma display 115 in karaoke facilities and conference facilities. When the infrared light emitted from the plasma display 115 interferes with the infrared signal of the infrared wireless microphone 103, noise is mixed in the audio signal demodulated by the infrared receiver 107, and this noise is output from the speaker 113. Conventionally, noise is prevented by adjusting the positional relationship between the plasma display 115 and the infrared receiving device 107, but it may not be perfect by itself.

Therefore, a technique for dealing with noise caused by a plasma display has been proposed (Patent Document 1). This prior art filters the demodulated audio signal to extract the signal component of the horizontal synchronization frequency of the plasma display. If the extracted signal component is greater than or equal to the threshold value, the audio output is attenuated or blocked. In this way, noise due to infrared rays of the plasma display is detected, and noise output is limited.
JP 2005-6261 A

  However, in the conventional infrared receiver, the signal component of the horizontal synchronization frequency of the plasma display is extracted by filtering the demodulated signal, and this extracted component is used as an index of noise, that is, indirect detection is performed. ing. Therefore, there is a problem that direct detection such as whether or not the demodulated signal waveform itself includes noise due to infrared rays of the plasma display cannot be performed, and therefore the reliability is inferior. On the other hand, it is considered that more reliable detection can be performed if a direct detection process focusing on the characteristics of noise caused by the plasma display in the demodulated signal waveform itself can be performed.

  In addition, since the conventional infrared receiver focuses on the horizontal synchronization frequency of the plasma display, it can only detect noise due to the infrared of the plasma display. Noise at other frequencies cannot be detected, and furthermore, non-periodic noise cannot be detected at all, and there is a problem that the detectable noise is greatly restricted.

  The present invention has been made in order to solve the conventional problems, and an object of the present invention is to suitably detect noise generated when external infrared rays emitted from a plasma display or the like are received, and output unnecessary noise. It is an object of the present invention to provide an infrared receiver capable of preventing the above-described problem.

  The infrared receiver of the present invention includes a demodulator that demodulates an audio signal from an infrared signal received from an infrared wireless microphone, an asymmetric signal detector that detects an asymmetric signal from the audio signal demodulated by the demodulator, and the asymmetric signal. An output limiting unit that limits the output of the audio signal according to the detection result of the asymmetric signal by the detection unit.

  With this configuration, an asymmetric signal is detected from the demodulated audio signal, and the audio output is limited according to the detection result. Focusing on the fact that the audio signal when receiving infrared rays from the plasma display is an asymmetric signal, unlike the normal audio signal that is a symmetric signal, this ensures that the noise of the plasma display is detected. Can do. In addition, if the noise has an asymmetric waveform, noise caused by infrared rays from other than the plasma display can be detected, and non-periodic noise that has been impossible in the past can also be detected. Thus, it is possible to suitably detect noise generated when external infrared rays emitted from a plasma display or the like are received, and to prevent unnecessary noise from being output.

  In the infrared receiving device of the present invention, the output limiting unit mutes the output of the sound when the asymmetric signal is detected. With this configuration, it is possible to prevent noise from being output from the speaker.

  In the infrared receiver of the present invention, the asymmetric signal detection unit detects the asymmetric signal based on a deviation of the audio signal with reference to an average level of the audio signal. With this configuration, it can be suitably detected that the audio signal is an asymmetric signal.

  The infrared receiver of the present invention includes an average level detection unit that detects an average level of the audio signal, a positive waveform level detection unit that detects a positive waveform level of the audio signal from the audio signal and the average level, A negative waveform level detection unit that detects a negative waveform level of the audio signal from the audio signal and the average level, and a bias level detection that detects an intermediate level between the positive waveform level and the negative waveform level as a bias level of the audio signal And an asymmetry determination unit that compares the bias level with the average level to determine whether or not the audio signal is an asymmetric signal.

  With this configuration, it can be suitably detected that the audio signal is an asymmetric signal. Conventionally, since it is assumed that the audio signal is a symmetric signal, it has not been considered to process the audio signal by dividing it into positive and negative as described above. The present invention can suitably detect noise by adopting an unprecedented configuration in which an audio signal is divided into positive and negative by paying attention to noise asymmetry.

  Another aspect of the present invention is an infrared noise detection device, which is provided in an infrared reception device that receives an infrared signal from an infrared wireless microphone, and is generated when the infrared signal is received from a device other than the infrared wireless microphone. An apparatus for detecting noise, wherein an asymmetric signal is detected as the noise from an audio signal demodulated from the infrared signal.

  Another aspect of the present invention is an infrared wireless microphone system, which includes an infrared wireless microphone that transmits an infrared signal generated from input sound, and an infrared receiver that receives the infrared signal from the infrared wireless microphone. The infrared receiver includes a demodulator that demodulates an audio signal from the infrared signal, an asymmetric signal detector that detects an asymmetric signal from the audio signal demodulated by the demodulator, and the asymmetric signal detected by the asymmetric signal detector An output limiting unit that limits the output of the audio signal according to a signal detection result.

  Another aspect of the present invention is an infrared reception processing method that receives an infrared signal from an infrared wireless microphone, demodulates an audio signal, detects an asymmetric signal from the demodulated audio signal, and detects the asymmetric signal. The output of the audio signal is limited according to the signal detection result.

  The present invention detects asymmetric signals from demodulated audio signals and provides a configuration that limits audio output according to the detection results, thereby reducing noise generated when external infrared rays emitted from a plasma display or the like are received. It is possible to provide an infrared receiving device having an effect that it can be suitably detected and output of unnecessary noise can be prevented.

  Hereinafter, an infrared receiver according to an embodiment of the present invention will be described with reference to the drawings.

  An infrared wireless microphone system including an infrared receiver according to an embodiment of the present invention is shown in FIG. In FIG. 1, an infrared wireless microphone system 1 includes an infrared wireless microphone 3 that is an infrared transmission device that generates and transmits an infrared signal from input sound, an infrared sensor 5 that detects infrared light, and an infrared wireless signal that passes through the infrared sensor 5. An infrared receiving device 7 that receives an infrared signal from the microphone 3 and demodulates the audio signal from the infrared signal, a power amplifier 9 that amplifies the audio signal demodulated by the infrared receiving device 7, and outputs the amplified audio signal And a speaker 11 to be provided. The wireless microphone system 1 is installed together with the plasma display 13.

  As shown in the figure, the infrared receiver 7 includes an asymmetric signal detection circuit 23 for detecting an asymmetric signal from the audio signal demodulated by the demodulation circuit 21 in addition to a demodulation circuit 21 for demodulating the audio signal from the infrared signal, and an asymmetric signal. An output limiting circuit 25 that limits the output of the audio signal according to the detection result of the asymmetric signal by the detection circuit 23 is provided. An asymmetric signal is a signal in which upper and lower (positive and negative) waveforms are asymmetric with respect to an average level. The asymmetric signal detection circuit 23 functions as an infrared noise detection device provided in the infrared reception device 7. The output limiting circuit 25 performs mute control on the audio output when an asymmetric signal is detected.

  FIG. 2A shows the waveform of a normal audio signal, and FIG. 2B shows the waveform when the infrared light emitted from the plasma display 13 is demodulated. The principle of noise detection according to the present invention will be described with reference to these drawings.

  As shown in FIG. 2A, the normal audio signal is generally a symmetric signal, that is, the positive waveform and the negative waveform are symmetric with respect to the average level (DC bias component). On the other hand, as shown in FIG. 2B, when the infrared rays from the plasma display 13 are demodulated, the demodulated signal becomes an asymmetric signal, that is, a bias occurs with respect to the average level (DC bias component), and the positive waveform And the negative waveform becomes asymmetric. In general, the demodulated signal is biased to the positive side. Since the infrared signal level of the plasma display 13 is large, when the infrared signal is received, the waveform of the demodulated signal is a waveform of a normal audio signal on the waveform of FIG.

  The reason why the infrared rays from the plasma display 13 have a vertically asymmetric waveform is as follows. That is, the audio signal is FM-modulated with the average level as the center frequency, and FM demodulated at the same frequency as the FM modulation by the demodulation circuit 21, so that the average level of the audio signal coincides with the audio signal before modulation. Vertical symmetry with respect to the average level is maintained. On the other hand, since the signal from the plasma display 13 is not intended, it becomes a signal whose frequency is biased upward or downward with respect to the frequency to be FM demodulated. As a result, when FM demodulated, it becomes a vertically asymmetric waveform deviating from the average level. .

  In the present embodiment, paying attention to the characteristics of infrared rays from the plasma display 13 described above, the asymmetric signal detection circuit 23 detects the presence or absence of infrared rays from the plasma display 13 by detecting an asymmetric signal from the audio signal.

  FIG. 3 shows the configuration of the infrared receiver 7, and particularly shows the detailed configuration of the asymmetric signal detection circuit 23. As illustrated, the asymmetric signal detection circuit 23 includes an average level detection circuit 31, a positive waveform level detection circuit 33, a negative waveform level detection circuit 35, a bias level detection circuit 37, and an asymmetric determination circuit 39.

  The audio signal demodulated from the demodulation circuit 21 is input to the average level detection circuit 31. The average level detection circuit 31 detects the average level (DC bias component) of the audio signal by performing an averaging process.

  The demodulated signal is input from the demodulation circuit 21 and the average level is input from the average level detection circuit 31 to the positive waveform level detection circuit 33. The positive waveform level detection circuit 33 detects the positive waveform level of the audio signal from the audio signal and the average level. The positive waveform level is an average level of a positive waveform (a waveform on the positive side (upper side) with respect to the average level). At this time, the positive waveform level detection circuit 33 first obtains a positive waveform by removing a signal smaller than the average level from the audio signal and extracting a signal equal to or higher than the average level. Then, the positive waveform level detection circuit 33 calculates the average level of the positive waveform by the averaging process.

  The negative waveform level detection circuit 35 also receives the demodulated signal from the demodulation circuit 21 and the average level from the average level detection circuit 31. The negative waveform level detection circuit 35 detects the negative waveform level of the audio signal from the audio signal and the average level. The negative waveform level is an average level of a negative waveform (a waveform on the negative side (lower side) with respect to the average level). At this time, the negative waveform level detection circuit 35 first removes a signal larger than the average level from the audio signal and extracts a signal below the average level to obtain a negative waveform. Then, the negative waveform level detection circuit 35 calculates the average level of the negative waveform by the averaging process.

  The bias level detection circuit 37 receives a positive waveform level from the positive waveform level detection circuit 33 and a negative waveform level from the negative waveform level detection circuit 35. The bias level detection circuit 37 detects an intermediate level between the positive waveform level and the negative waveform level as the bias level of the audio signal.

  The asymmetry determination circuit 39 receives the average level from the average level detection circuit 31 and the bias level from the bias level detection circuit 37. The asymmetric determination circuit 39 compares the bias level with the average level to determine whether or not the audio signal is an asymmetric signal. At this time, the asymmetric determination circuit 39 determines that the audio signal is an asymmetric signal if the bias level and the average level do not match and both levels are different. More specifically, in the asymmetry determination circuit 39, threshold values are set above and below the average level. If the bias level is a value between the upper and lower threshold values, it is determined that the audio signal is a symmetric signal. Otherwise, it is determined that the audio signal is an asymmetric signal.

  As illustrated, the asymmetric determination circuit 39 includes a positive threshold value setting circuit 41, a negative threshold value setting circuit 43, a positive comparator 45, a negative comparator 47, and an OR circuit 49.

  The positive threshold value setting circuit 41 sets a positive threshold value (a positive threshold value with respect to the average level). A positive threshold is set by adding a preset value to the average level. Similarly, the negative threshold value setting circuit 43 sets a negative threshold value (threshold value on the negative side with respect to the average level). A negative threshold is set by subtracting a preset value from the average level.

  The positive comparator 45 compares the bias level with the positive threshold value and outputs the comparison result to the OR circuit 49. The negative comparator 47 compares the bias level with the negative threshold value and outputs the comparison result to the OR circuit 49.

  The OR circuit 49 is configured to output a determination result as to whether or not the audio signal is an asymmetric signal to the output limiting circuit 25 based on inputs from the positive comparator 45 and the negative comparator 47. When the positive comparator 45 outputs a comparison result that the bias level is greater than the positive threshold value, or the negative comparator 47 outputs a comparison result that the bias level is less than the negative threshold value, the OR circuit 49 generates a voice signal. A signal indicating that the signal is an asymmetric signal is sent to the output limiting circuit 25. In response to this signal, the output limiting circuit 25 performs mute control. If the bias level is less than or equal to the positive threshold value and greater than or equal to the negative threshold value, the OR circuit 49 outputs a determination result that the audio signal is a symmetric signal to the output limiting circuit 25. In response to this signal, the output limiting circuit 25 outputs an audio signal without performing mute control.

  The configuration of the infrared receiving device 7 according to the present embodiment has been described above. Next, the operation of the infrared receiver 7 will be described with reference to FIG.

  When an infrared signal is received via the infrared sensor 5 (S1), the infrared signal is demodulated by the demodulation circuit 21 to obtain an audio signal A (S3). Then, the audio signal is averaged by the average level detection circuit 31, and the average level B is detected (S5).

  The positive waveform level detection circuit 33 detects a positive waveform by removing a signal smaller than the average level B from the audio signal A and extracting a signal equal to or higher than the average level B (S7). Furthermore, the positive waveform level detection circuit 33 detects the positive waveform level C (the average level of the positive waveform) by averaging the positive waveforms (S9).

  Further, the negative waveform level detection circuit 35 detects a negative waveform by removing signals greater than the average level B from the audio signal A and extracting signals below the average level B (S11). Further, the negative waveform level detection circuit 35 detects the negative waveform level D (average level of the negative waveform) by averaging the negative waveforms (S13).

  Next, the bias level detection circuit 37 calculates a bias level E by calculating the average of the positive waveform level C and the negative waveform level D (S15).

  On the other hand, the positive threshold value setting circuit 41 calculates a positive threshold value F by adding a predetermined offset value [OFFSET (+)] to the averaging level B (S17). Further, the negative threshold value setting circuit 43 calculates a negative threshold value G by subtracting a predetermined offset value [OFFSET (−)] from the averaging level B (S19).

  Then, the bias level E and the positive threshold value F are compared by the positive comparator 45, and it is determined whether or not the bias level E is larger than the positive threshold value (S21). Further, the negative comparator 47 compares the bias level E with the negative threshold value G, and determines whether or not the bias level E is smaller than the negative threshold value G (S23).

  If the comparison result of either S21 or S23 is YES, the audio signal is an asymmetric signal. Therefore, the audio mute control of the output limiting circuit 25 is turned on (S25). If the comparison result of both S21 and S23 is NO, the audio signal is a symmetric signal. In this case, the audio mute control of the output limiting circuit 25 is turned off (S25), and the audio is output (S27).

  5 and 6 show specific signal waveform processing examples. FIG. 5 is processing a normal audio signal, and FIG. 6 is processing a waveform demodulated from infrared rays of the plasma display. In the graph in the figure, the horizontal axis is time, and the vertical axis is the electric signal level.

  As shown in FIG. 5, a normal audio signal is generally symmetric with respect to an average level (bias). Therefore, the bias level (an intermediate value (middle point) between the positive waveform level and the negative waveform level) is close to the average level. As a result, the bias level becomes a value between the positive threshold value and the negative threshold value. In the figure, the positive threshold is set to a value that is a volt greater than the average level (average level + a [V]), and the negative threshold is set to a value that is b volts less than the average level (average level−b [ V]). Since the bias level is within the upper and lower threshold values, it is determined that the audio signal is a symmetric signal, the audio mute is turned off, and the audio is output from the speaker 11.

  On the other hand, as shown in FIG. 6, when the infrared rays from the plasma display are demodulated, the demodulated signal is asymmetric with respect to the average level. Therefore, the bias level is far from the average level, and as a result, the bias level is outside the range of the upper and lower threshold values. Generally, as shown in the figure, the demodulated signal is biased to the positive side, so the bias level is a value exceeding the positive threshold value. As a result, it is determined that the audio signal is an asymmetric signal, the audio mute is turned on, and the audio is not output from the speaker 11.

  The operation of the infrared receiving apparatus 7 according to the present embodiment has been described above. In the above description, infrared rays from a plasma display have been described exclusively as infrared rays that cause noise. However, the infrared receiving device 7 of the present embodiment can detect any noise having an asymmetric waveform, and therefore can also detect noise due to infrared rays from noise sources other than the plasma display. That is, since the signal component of the horizontal synchronization frequency of the plasma display is not detected as in the prior art, noise having a frequency different from the horizontal synchronization frequency of the plasma display can be detected, and therefore noise other than the plasma display can also be detected. Furthermore, since the frequency is not used as a detection index, it is possible to detect aperiodic noise (noise having no period) that was completely impossible with the prior art.

  The non-periodic noise source is, for example, a fluorescent lamp. Noise can be a problem when fluorescent lights and infrared sensors are close together. The signal obtained by demodulating the infrared rays from the fluorescent lamp has no periodicity but is an asymmetric signal, and can therefore be detected by the infrared receiving device 7 of the present embodiment.

  However, within the scope of the present invention, the infrared receiver of the present invention may be configured to detect noise from a noise source other than the plasma display, or may detect only noise from the plasma display. May be configured. These can be realized by optimizing the threshold value.

  The infrared receiver 7 according to the embodiment of the present invention has been described above. According to the present embodiment, an asymmetric signal is detected from the demodulated audio signal, and the audio output is limited according to the detection result. Focusing on the fact that the audio signal when receiving infrared rays from the plasma display is an asymmetric signal, unlike the normal audio signal that is a symmetric signal, this ensures that the noise of the plasma display is detected. Can do. In addition, if the noise has an asymmetric waveform, noise caused by infrared rays from other than the plasma display can be detected, and non-periodic noise that has been impossible in the past can also be detected. Thus, it is possible to suitably detect noise generated when external infrared rays emitted from a plasma display or the like are received, and to prevent unnecessary noise from being output.

  Further, according to the present embodiment, the sound output is muted when an asymmetric signal is detected. This can prevent noise from being output from the speaker.

  Further, according to the present embodiment, an asymmetric signal is detected based on the deviation of the audio signal with reference to the average level of the audio signal. As a result, it can be suitably detected that the audio signal is an asymmetric signal.

  Further, according to the present embodiment, the average level of the audio signal is detected, the positive waveform level of the audio signal is detected from the audio signal and the average level, and the negative waveform level of the audio signal is detected from the audio signal and the average level. The intermediate level between the positive waveform level and the negative waveform level is detected as the bias level of the audio signal, and it is determined whether the audio signal is an asymmetric signal by comparing the bias level with the average level. With such a configuration, it can be suitably detected that the audio signal is an asymmetric signal. Conventionally, since it is assumed that the audio signal is a symmetric signal, it has not been considered to process the audio signal by dividing it into positive and negative as described above. The present invention can suitably detect noise by adopting an unprecedented configuration in which an audio signal is divided into positive and negative by paying attention to noise asymmetry.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and it goes without saying that those skilled in the art can modify the above-described embodiments within the scope of the present invention.

  As described above, the infrared receiving apparatus according to the present invention has an effect that it is possible to suitably detect noise generated when external infrared light emitted from a plasma display or the like is received and to prevent unnecessary noise output. It is useful as an infrared wireless microphone system for karaoke facilities.

1 is a block diagram of an infrared wireless microphone system including an infrared receiver according to an embodiment of the present invention. (A) The figure which shows the waveform of a normal audio | voice signal (b) The figure which shows the waveform at the time of demodulating the infrared rays light-emitted from the plasma display Block diagram showing the configuration of the infrared receiver Diagram showing operation of infrared receiver The figure which shows the specific process example in the case of processing a normal audio signal The figure which shows the specific process example in the case of processing the signal demodulated from the infrared of a plasma display Diagram showing a conventional infrared wireless microphone system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Infrared wireless microphone system 3 Infrared wireless microphone 5 Infrared sensor 7 Infrared receiver 9 Power amplifier 11 Speaker 13 Plasma display 21 Demodulator 23 Asymmetric signal detector 25 Output limiting circuit 31 Average level detector 33 Positive waveform level detector 35 Negative waveform Level detection circuit 37 Bias level detection circuit 39 Asymmetric determination circuit

Claims (7)

A demodulator that demodulates the audio signal from the infrared signal received from the infrared wireless microphone;
An asymmetric signal detector for detecting an asymmetric signal from the audio signal demodulated by the demodulator;
An output limiting unit that limits the output of the audio signal according to the detection result of the asymmetric signal by the asymmetric signal detection unit;
An infrared receiver characterized by comprising:   The infrared receiving device according to claim 1, wherein the output limiting unit mutes an audio output when the asymmetric signal is detected.   The infrared receiver according to claim 1, wherein the asymmetric signal detection unit detects the asymmetric signal based on a bias of the audio signal with reference to an average level of the audio signal. An average level detector for detecting an average level of the audio signal;
A positive waveform level detector for detecting a positive waveform level of the audio signal from the audio signal and the average level;
A negative waveform level detector that detects a negative waveform level of the audio signal from the audio signal and the average level;
A bias level detector that detects an intermediate level between the positive waveform level and the negative waveform level as a bias level of the audio signal;
An asymmetric determination unit that compares the bias level with the average level to determine whether the audio signal is an asymmetric signal;
The infrared receiver according to claim 3, further comprising:   An infrared noise detection device for detecting noise generated when an infrared signal is received from a device other than the infrared wireless microphone, the infrared noise detection device being demodulated from the infrared signal. An infrared noise detection device, wherein an asymmetric signal is detected as the noise from an audio signal. An infrared wireless microphone that transmits an infrared signal generated from the input voice;
An infrared receiver for receiving the infrared signal from the infrared wireless microphone;
The infrared receiver is
A demodulator that demodulates an audio signal from the infrared signal;
An asymmetric signal detector for detecting an asymmetric signal from the audio signal demodulated by the demodulator;
An output limiting unit that limits the output of the audio signal according to the detection result of the asymmetric signal by the asymmetric signal detection unit;
An infrared wireless microphone system characterized by comprising: Receives infrared signal from infrared wireless microphone and demodulates audio signal,
Detecting an asymmetric signal from the demodulated audio signal;
An infrared reception processing method, wherein output of the audio signal is limited according to a detection result of the asymmetric signal.

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