JP2009246788A - Modulation apparatus, demodulation apparatus, information transfer system, modulation method ,and demodulation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulation apparatus which remarkably reduces noise through simple processing and reduces restrictions during communication. <P>SOLUTION: In an information transfer system, a component of an input audio signal Sa is eliminated by a modulation apparatus, a component in a partial frequency band of remaining frequency bands is frequency-shifted with a shift amount corresponding to encoded information relating to transmission information and superimposed on an eliminated frequency band, thereby emitting a modulation audio signal Se that has been modulated. In a demodulation apparatus, meanwhile, the frequency shift amount is recognized from the collected modulation audio signal Se and can be demodulated into encoded information. Consequently, even if the modulation audio signal Se emitted in information transfer is heard, a sense of incompatibility in hearing relating to modulation can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for transmitting code information superimposed on an audio signal.

As a communication method for transmitting code information wirelessly, in addition to communication using radio waves, a technique for superimposing encoded information by modulating a sound wave such as a musical sound has been studied. When the encoded information is superimposed by modulating the sound wave in this way, in order to communicate using a general speaker or microphone, it is necessary to use an acoustic wave in the audible range, but the encoded information is superimposed. Various studies have been made to prevent unpleasant noise from being mixed with the original musical tone due to the modulation (for example, Patent Document 1, Patent Document 2, and Patent Document 3).
JP 2007-104598 A JP 2006-251676 A JP 2006-195061 A

  Like the techniques disclosed in the above patent documents, noise generated during modulation has been reduced, but the amount of reduction is insufficient, the processing load is large, and there is a restriction on the communication position during communication. Etc. remained.

  The present invention has been made in view of the above-described circumstances, and can greatly reduce noise generated during modulation by simple processing, and has few restrictions during communication, a demodulator, and an information transmission system. An object of the present invention is to provide a modulation method and a demodulation method.

  In order to solve the above-described problems, the present invention provides an input unit that inputs an audio signal, an acquisition unit that acquires encoded information, and an audio signal input by the input unit that is less than a predetermined frequency. Extraction means for extracting an audio signal having a component of a part of the frequency band out of the frequency band, and the frequency band component of the audio signal extracted by the extraction means as the encoded information acquired by the acquisition means Frequency shift means for shifting to a high frequency band equal to or higher than the predetermined frequency by a corresponding shift amount, and superposition for superimposing the audio signal whose frequency band is shifted by the frequency shift means on the audio signal input by the input means And a modulation device.

  In another preferred aspect, the superimposing unit includes a removing unit that removes the high frequency band component of the audio signal input by the input unit.

  Moreover, in another preferable aspect, the apparatus further includes carrier generation means for generating a plurality of carrier signals having different frequencies, and the frequency shift means includes a carrier signal generated by the carrier generation means. The frequency band component of the audio signal is shifted by multiplying the audio signal extracted by the extraction unit by the carrier signal of the frequency selected according to the encoding information acquired by the acquisition unit. The frequency of the carrier signal generated by the carrier generation means is set such that the phase of the carrier signal before and after switching is matched when the carrier signal selected by the frequency shift means is switched. And

  In another preferred aspect, the superimposing unit includes a delay unit that performs a delay process of a preset delay time on the audio signal input by the input unit.

  Further, the present invention provides an input means for inputting an audio signal, a component of a part of the frequency band of the frequency band of the audio signal input by the input means, and a plurality of preset frequencies from the part of the frequency band. A detection unit that detects a correlation with each of components in a plurality of frequency bands in which the frequency of the shift amount is shifted, and selects one of the plurality of shift amounts according to a detection result; and the detection unit selects There is provided a demodulating device comprising encoding information generating means for generating encoded information encoded according to the shift amount.

  In another preferred aspect, the detection means includes a part of a frequency band less than a predetermined frequency and a frequency band equal to or higher than the predetermined frequency among the frequency bands of the audio signal input by the input means. The correlation is detected by the undulation of the amplitude of the audio signal generated by adding the two parts.

  The present invention is also characterized in that the modulation device described above, the demodulation device described above, the sound emission means for emitting the audio signal superimposed by the superimposition means of the modulation device, and the sound emission means. Sound pickup means for picking up an audio signal, the input means of the demodulator inputs the audio signal picked up by the sound pickup means, and the shift amount set in advance by the detection means of the demodulator is The information transmission system is characterized in that the frequency shift amount can be shifted by the frequency shift means of the modulation device.

  The present invention also provides an input process for inputting an audio signal, an acquisition process for acquiring encoded information, and a frequency band less than a predetermined frequency of the audio signal input in the input process. An extraction process of extracting an audio signal having a component of a frequency band of the part, and a frequency band component of the audio signal extracted in the extraction process with a shift amount corresponding to the encoded information acquired in the acquisition process A frequency shift process for shifting to a high frequency band above a predetermined frequency, and a superimposition process for superimposing an audio signal whose frequency band has been shifted in the frequency shift process on an audio signal input in the input process. A characteristic modulation method is provided.

  In addition, the present invention provides an input process for inputting an audio signal, a component of a part of the frequency band of the frequency band of the audio signal input in the input process, and a plurality of preset frequency bands Detecting a correlation with each of the components in the plurality of frequency bands in which the frequency of the shift amount is shifted, and selecting one of the plurality of shift amounts according to the detection result; and selecting in the detection step There is provided a demodulation method comprising: an encoded information generation process for generating encoded information encoded according to the shift amount.

  According to the present invention, it is possible to provide a modulation device, a demodulation device, an information transmission system, a modulation method, and a demodulation method that can greatly reduce noise generated during modulation by simple processing and that have less restrictions during communication. Can do.

  Hereinafter, an embodiment of the present invention will be described.

<Embodiment>
As shown in FIG. 1, the information transmission system 10 according to the embodiment of the present invention receives transmission information to be transmitted from an external device or the like, and receives an audio signal Sa from the external device or the like. Modulator 1 that outputs a signal modulated in accordance with transmission information (hereinafter referred to as modulated audio signal Se), speaker 2 that emits modulated audio signal Se output from modulator 1, and modulation emitted by speaker 2 A microphone 3 that picks up the audio signal Se and a demodulator 4 that receives transmission information by demodulating the modulated audio signal Se picked up by the microphone 3 are provided. Hereinafter, configurations of the modulation device 1 and the demodulation device 4 will be described in order.

  First, the configuration of the modulation device 1 will be described with reference to FIG. The configuration described below may be realized by hardware, or a CPU (Central Processing Unit) of a computer (not shown) may execute a control program to realize the functions described below.

  The LPF 110 is a low-pass filter that receives an audio signal Sa and attenuates a high frequency band equal to or higher than a preset cutoff frequency to remove and output a high frequency band component. As will be described later, a part of the high frequency band is a frequency band on which a modulated signal is superimposed. In this example, the cutoff frequency is set to 10 kHz. Hereinafter, the audio signal from which the high frequency band component output from the LPF 110 is removed is referred to as an audio signal Sb.

  The HPF 120 is a high-pass filter that receives the audio signal Sb from the LPF 110 and attenuates and outputs a low frequency band equal to or lower than a preset cutoff frequency. In this example, the cutoff frequency is set to 6 kHz. Therefore, the audio signal (hereinafter referred to as audio signal Sc) output from the HPF 120 is extracted as an audio signal having components in a frequency band of approximately 6 kHz to 10 kHz in the frequency band of the audio signal Sa.

  The encoder 130 receives the transmission information and outputs the encoded information obtained by encoding the transmission information to the switch 150. In this example, the encoded information is information obtained by encoding transmission information into 1-bit binary symbols of “0” and “1”. In this encoding, processing such as interleaving and addition of an error correction code may be performed. Here, the time per bit is a preset time, that is, encoding information having a predetermined bit rate is generated.

  The carrier frequency generator 140 includes a carrier frequency generator A141 and a carrier frequency generator B142, and performs sine wave carrier signals fa and fb having different preset frequencies by performing a table, function calculation, and the like, respectively. Is output to the switch 150. Then, the switch 150 acquires the encoded information output from the encoder 130, selects one of the input carrier signals fa and fb according to the encoded information, and switches and outputs it. In this example, when the symbol indicated by the encoding information is “0”, the carrier signal fa is output, and when the symbol is “1”, the carrier signal fb is output.

  Here, the phase of both the carrier signals fa and fb before and after switching coincide with each other so that a discontinuity in the output waveform from the switch 150 does not occur when the carrier signal fa and the carrier signal fb are switched. The frequency may be set to. Here, since the time per bit of the transmission code of the encoded information is determined, the switching timing is fixed to a time that is an integral multiple of that time. For example, assume that the time per bit is set as 88 samples when the sampling rate is 44.1 kHz.

  At this time, one cycle of the carrier signal fa is 11 samples (frequency is approximately 4 kHz, hereinafter omitted to be 4 kHz), and one cycle of the carrier signal fb is 8 samples (frequency is approximately 5.5 kHz, hereinafter omitted). 5.5 kHz), the carrier signal fa per bit is exactly 8 cycles, the carrier signal fb is exactly 11 cycles, and the phases match when switching, so that the continuity of the waveform can be maintained. FIG. 3 shows an output signal from the switch 150 when the carrier signals fa and fb set in this way are switched every 88 samples according to the encoding information “010101”.

  Since the frequency determined as described above is set in the carrier frequency generator A141 and the carrier frequency generator B142, the continuity of the waveform at the time of switching in the switch 150 can be maintained. As for the modulated audio signal Se output in this way, it is possible to suppress the possibility that noise is generated when the carrier signal fa, fb is switched in the switch 150, which is desirable in terms of hearing. In this example, it is assumed that 4 kHz is set as the frequency in the carrier frequency generator A141 and 5.5 kHz is set as the frequency in the carrier frequency generator B142. Therefore, the frequency of the carrier signal fa is 4 kHz, and the frequency of the carrier signal fb is 5.5 kHz.

  Multiplier 160 multiplies audio signal Sc output from HPF 120 by carrier signal fa or carrier signal fb output from switch 150. Thereby, the multiplier 160 shifts the component of the frequency band of the audio signal Sc to the upper frequency band by the frequency of the carrier signal to be multiplied, and also to the lower frequency band. Specifically, when multiplied by the carrier signal fa, the frequency of the carrier signal fa is 4 kHz, so the frequency band component of the audio signal Sc is from the frequency band of 6 kHz to 10 kHz to the frequency of 2 kHz to 6 kHz. Shift to two frequency bands, a band and a frequency band from 10 kHz to 14 kHz. On the other hand, when multiplied by the carrier signal fb, the frequency of the carrier signal fa is 5.5 kHz, so that the frequency band component of the audio signal Sc is 0.5 kHz to 4. kHz from the frequency band of 6 kHz to 10 kHz. Shift to two frequency bands, a frequency band of 5 kHz and a frequency band of 11.5 kHz to 15.5 kHz. Here, the frequency band shifted upward is set in the cutoff frequency, carrier frequency generator A141, and carrier frequency generator B142 set in the LPF 110 so as to be a frequency band from which components are removed in the LPF 110. Each frequency is determined.

  The HPF 170 is a high-pass filter that removes the lower frequency band component and passes only the upper frequency band component from the audio signal whose frequency band is shifted by the multiplier 160. Since only the lower frequency band component needs to be removed in this way, the cut-off frequency may be set between 6 kHz and 10 kHz, for example, 8 kHz. In this way, the lower frequency band component is removed, and an audio signal having only the frequency band component shifted upward (hereinafter referred to as audio signal Sd) is output.

  The delay circuit 180 performs a delay process for a preset delay time on the audio signal Sb output from the LPF 110 and outputs the result. This delay time is set as the same time as the processing time in the HPF 120, the multiplier 160, and the HPF 170. By delaying the audio signal Sb in this way, the process of shifting the above frequency is performed on the audio signal Sb and the difference in processing time until the audio signal Sd is output is adjusted, and the audio signal Sb and the audio signal Sd are adjusted. It can be assumed that there is no time lag.

  The adder 190 outputs a superimposed audio signal (hereinafter referred to as a modulated audio signal Se) by adding the audio signal Sb delayed in the delay circuit 180 and the audio signal Sd output from the HPF 170. The modulated audio signal Se output from the adder 190 in this manner is subjected to D / A conversion, amplification processing, and the like as necessary, and is output to the speaker 2. Then, the modulated audio signal Se is emitted from the speaker 2. The above is the description of the configuration of the modulation device 1.

  Next, the operation of the modulation device 1 will be described with reference to FIG. 4 showing the change in frequency distribution until the input audio signal Sa is emitted as the modulated audio signal Se.

  Assume that the audio signal Sa has a frequency distribution shown in FIG. Since the audio signal Sa has a frequency band component of 10 kHz or more removed by the LPF 110, the audio signal Sb output from the LPF 110 has a frequency distribution as shown in FIG. Next, since the audio signal Sb has components in the frequency band of 6 kHz or less removed by the HPF 120, the audio signal Sc output from the HPF 120 has a frequency band of 6 kHz to 10 kHz as shown in FIG. The frequency distribution has a component.

  The input transmission information is output as encoded information encoded by the encoder 130, and is output to the multiplier 160 while the carrier signal fa or the carrier signal fb is switched according to the content. As a result, the multiplier 160 shifts the frequency band component of 6 kHz to 10 kHz of the audio signal Sc up and down, and the HPF 170 removes the frequency band component shifted downward. The audio signal Sd output from the HPF 170 in this way has a frequency distribution as shown in FIG. Here, the audio signals Sd (0) and Sd (1) indicate the audio signal Sd whose frequency band components are shifted by the carrier signals fa and fb, respectively, and the frequency distribution indicated by the broken line is removed by the HPF 170. The frequency band components are shown.

  Since the audio signal Sd output from the HPF 170 in this way is added by the adder 190 with the audio signal Sb subjected to the delay processing in the delay circuit 180, the modulated audio signal Se output from the adder 190 is as shown in FIG. The frequency distribution is as shown in (e). Here, the modulated audio signals Se (0) and Se (1) indicate the modulated audio signals Se obtained by adding the audio signals Sd (0) and Sd (1) and the audio signal Sb, respectively. In this way, the input audio signal Sa is converted into the modulated audio signals Se (0) and Se (1) corresponding to the encoded information “0” and “1” output by the encoder 130. Will be modulated. That is, modulation is performed by shifting the component of the audio signal Sa in the frequency band from 6 kHz to 10 kHz to the high frequency band by a shift amount corresponding to “0” and “1” of the encoded information. The above is the description of the operation of the modulation device 1.

  Next, the configuration of the demodulation device 4 will be described with reference to FIG. The configuration described below may be realized by hardware, or a CPU of a computer (not shown) may execute a control program to realize the functions described below.

  The remodulator 410 receives the modulated audio signal Se collected by the microphone 3. The remodulator 410 has a configuration as shown in FIG. 6 and will be described below.

  The remodulator 410 includes BPFs 411, 412, and 413 and adders 414 and 415. The BPFs 411, 412, and 413 are band pass filters in which different center frequencies are preset. The BPFs 411, 412, and 413 receive the modulated audio signal Se, and output a signal obtained by removing frequency bands other than the frequency band near the center frequency set for each of the frequency bands of the modulated audio signal Se.

  In the BPF 411, any frequency (6.5 kHz in this example) in the frequency band (6 kHz to 10 kHz) of the audio signal Sc related to the modulation device 1 is set as the center frequency. The BPF 412 is set to a frequency obtained by adding the frequency of the carrier signal fa according to the modulation device 1 to the center frequency set in the BPF 411, that is, in this example, 10.5 kHz is set as the center frequency. Further, the BPF 413 is set to a frequency obtained by adding and shifting the frequency of the carrier signal fb related to the modulation device 1 to the center frequency set in the BPF 411, that is, in this example, 12 kHz is set as the center frequency. Note that the bandwidths of the BPFs 411, 412, and 413 may be set as appropriate, but they are preferably all the same bandwidth.

  The adder 414 adds the signals output from the BPFs 411 and 412 and outputs the added output signal Sf1. Thereby, the correlation of both signals can be detected. That is, the center frequencies set in the BPFs 411 and 412 are shifted by 4 kHz from the frequency of the carrier signal fa. Here, among the modulated audio signal Se, the modulated audio signal Se (0) corresponding to the encoded information “0” has its frequency band component from 6 kHz to 10 kHz shifted upward by 4 kHz as described above. It is superimposed on the frequency band from 10 kHz to 14 kHz. Therefore, while the modulated audio signal Se (0) is being input to the remodulator 410, the signal in the frequency band near 6.5 kHz of the modulated audio signal Se (0) and the vicinity of 10.5 kHz further 4 kHz above. Therefore, the output signal Sf1 obtained by adding these signals is a signal having a strong amplitude swell of 4 kHz.

  On the other hand, among the modulated audio signal Se, the modulated audio signal Se (1) corresponding to the encoded information “1” has its frequency band component from 6 kHz to 10 kHz shifted upward by 5.5 kHz as described above. In addition, it is superimposed on a frequency band from 11.5 kHz to 15.5 kHz. Therefore, while the modulated audio signal Se (1) is being input to the remodulator 410, the signal in the frequency band near 6.5 kHz of the modulated audio signal Se (1) and the vicinity of 10.5 kHz further 4 kHz above. Since the signal in the frequency band is not a relationship in which the frequency band is shifted (not 5.5 kHz) and does not have a strong correlation, the output signal Sf1 obtained by adding these signals does not have a strong amplitude swell. Signal.

  The adder 415 adds the signals output from the BPFs 411 and 413, and outputs the added output signal Sf2. The center frequencies set in the BPFs 411 and 413 are shifted by 5.5 kHz from the frequency of the carrier signal fb. Therefore, for the same reason as described above, while the modulated audio signal Se (0) is input to the remodulator 410, the output signal Sf2 is a signal that does not have strong amplitude undulations, while the modulated audio signal Se. While (0) is input to the remodulator 410, the output signal Sf2 is a signal having a strong amplitude swell of 5.5 kHz.

  FIG. 7 shows the output signals Sf1 and Sf2 output from the remodulator 410 in this way. In FIG. 7, the modulated audio signal Se input to the remodulator 410 has the encoding information corresponding to “01010101”, that is, the modulated audio signals Se (0) and Se (1) are alternately input. It is supposed to be. FIG. 7A shows the output signal Sf1, and FIG. 7B shows the output signal Sf2. The above is the description of the configuration of the remodulator 410.

  The carrier component detector 420 receives the output signals Sf1 and Sf2. The carrier component detector 420 detects a carrier frequency component from the undulation of the amplitude of the input output signals Sf1 and Sf2, and has a configuration as shown in FIG. Hereinafter, the configuration will be described.

  The carrier component detector 420 includes rectifiers 421 and 422 and BPFs 423 and 424. The rectifiers 421 and 422 receive the output signals Sf1 and Sf2, respectively, perform rectification by absolute value processing, square calculation, and the like, and output them to the BPFs 423 and 424.

  The BPFs 423 and 424 are band pass filters, and the center frequencies are preset as a frequency 4 kHz of the carrier signal fa and a frequency 5.5 kHz of the carrier frequency fb, respectively. Therefore, the output signals Sg1 and Sg2 output from the BPFs 423 and 424 are signals obtained by extracting the carrier frequency components of the output signals Sf1 and Sf2 (4 kHz for Sf1 and 5.5 kHz for Sf2). In this way, the carrier component detector 420 outputs the output signals Sg1 and Sg2 obtained by extracting the carrier frequency component from the output signals Sf1 and Sf2 input from the remodulator 410.

  FIG. 9 shows output signals Sg1 and Sg2 output from the carrier component detector 420 when the output signals Sf1 and Sf2 as shown in FIG. Here, FIG. 9A shows the output signal Sg1, and FIG. 9B shows the output signal Sg2. The above is the description of the configuration of the carrier component detector 420.

  The level detector 430 receives the output signals Sg1 and Sg2. The level detector 430 detects envelopes of the input output signals Sg1 and Sg2 and outputs them as level values, and has a configuration as shown in FIG. Hereinafter, the configuration will be described.

  The level detector 430 includes rectifiers 431 and 432 and LPFs 433 and 434. The rectifiers 431 and 432 receive the output signals Sg1 and Sg2, respectively, perform rectification by absolute value processing, square calculation, and the like, and output them to the LPFs 433 and 434. The LPFs 433 and 434 are low-pass filters in which a cutoff frequency is set in advance, smooth the signals input from the rectifiers 431 and 432, respectively, and output output signals Sh1 and Sh2 indicating level values. Since the cutoff frequency set in advance is intended for smoothing, it may be set to such an extent that transmission information encoded according to the time per bit of transmission code is not lost. As long as the level detector 430 can calculate a level value from an AC signal, other configurations such as a configuration based on peak detection and decay calculation may be used.

  FIG. 11 shows the output signals Sh1 and Sh2 output from the level detector 430 when the output signals Sg1 and Sg2 as shown in FIG. Here, the solid line indicates the output signal Sh1, and the broken line indicates the output signal Sh2. The above is the description of the configuration of the level detector 430.

  The adder 440 receives the output signals Sh1 and Sh2 and outputs an output signal Si indicating a difference between the output signal Sh1 and the output signal Sh2. FIG. 12 shows an output signal Si (broken line) output from the adder 440 when the output signals Sh1 and Sh2 as shown in FIG.

  The moving average calculator 450 receives the output signal Si and calculates a moving average of the output signal Si. The moving average calculator 450 is composed of, for example, an FIR (Finite Impulse Response) filter, and the filter tap length corresponds to the time per bit of the transmission code, and is configured to take an average in the front-rear direction from the center. . As a result, the output signal Si, which is the difference in the level value of the carrier frequency component, is averaged and output in the time per bit of the transmission code.

  The DC cut filter 460 receives the output signal Si averaged by the moving average calculator 450, and outputs the output signal Sj (see FIG. 12: one-dot chain line) from which a DC component or an unnecessary low-frequency fluctuation component close thereto is removed. Output. This is configured by, for example, a high-pass filter, and the cut-off frequency may be set so that encoded transmission information is not lost according to the time per bit of the transmission code.

  The positive / negative sign determiner 470 receives the output signal Sj. When the output signal Sj is positive, the output signal Sk has a level corresponding to “+1” and negative when it is “−1” (see FIG. 12: solid line). ) Is output.

  The decoder 480 receives the output signal Sk, and the time per one bit of the transmission code from the reference timing that is appropriately determined (in this example, the timing at which the level of the output signal Sk is first recognized). The cumulative addition is performed, and positive / negative is determined every time. If the result is positive, it is recognized that the code corresponding to the modulated audio signal Se is “0”, that is, the modulated audio signal Se (0) is received, and if the result is negative, the code corresponds to the modulated audio signal Se. It is recognized that the code is “1”, that is, the modulated audio signal Se (1) is received. That is, according to the detection result of the correlation of the signal in the remodulator 410, it is recognized whether the frequency band shift amount of the frequency band component of the audio signal Sc is 4 kHz or 5.5 kHz, and either one is selected. can do. As a result of selecting the shift amount in this way, the encoded information related to the transmission information transmitted from the modulation apparatus 1 is demodulated as encoded information indicating “01010101” as shown in FIG.

  Decoder 480 then outputs received information obtained by decoding the demodulated encoded information. In the modulation apparatus 1, when processing such as interleaving and error correction is performed, decoding according to the processing may be performed. The above is the description of the configuration of the demodulation device 4.

  As described above, in the information transmission system 10 according to the embodiment of the present invention, the high frequency band component of the input audio signal Sa is removed in the modulation device 1, and one of the remaining frequency bands is removed from the removed frequency band. It is possible to emit a modulated audio signal Se modulated by frequency-shifting and superimposing the frequency band components of the part with a shift amount corresponding to the encoded information related to the transmission information. On the other hand, the demodulator 4 can recognize the frequency shift amount from the collected modulated audio signal Se and demodulate it into encoded information. Therefore, even if the modulated audio signal Se that is emitted during the transmission of information is heard, the sense of incongruity associated with the modulation can be reduced. Further, if the input audio signal Sa does not originally contain a component in the high frequency band, an audibility improvement effect in which the frequency characteristic extends to the high frequency band can also be obtained by band expansion processing by modulation. Furthermore, by making the phases coincide when the carrier signals fa and fb are switched, it is possible to suppress the generation of noise at the time of switching.

  As mentioned above, although embodiment of this invention was described, this invention can be implemented in various aspects as follows.

<Modification 1>
The modulation processing of the modulation device 1 and the demodulation processing of the demodulation device 4 in the above-described embodiment may be performed by processing of another mode. For example, FFT (Fast Fourier transform) processing may be used. In this case, the modulation device 1 may be configured as shown in FIG. 14, and the demodulation device 4 may be configured as shown in FIG. Hereinafter, each structure is demonstrated in order.

  First, the modulation device 1 according to this modification will be described with reference to FIG. The FFT unit 1010 performs an FFT process on the input audio signal Sa and converts it to a frequency domain spectrum Sp. The encoder 1020 converts input transmission information into encoded information, similar to the encoder 130 in the embodiment.

  The duplication unit 1030 removes the components of the high frequency band of the spectrum Sp input from the FFT unit 1010, and shifts the frequency components of some of the remaining frequency bands by a shift amount corresponding to the encoded information. And superimposed on the removed high frequency band. For example, components in a frequency band of 10 kHz or more are removed, and components in a frequency band from 6 kHz to 10 kHz, which is a part of the remaining frequency band, are frequency-shifted and superimposed on a frequency band of 10 kHz or more. The amount of frequency shift at this time is +4 kHz when the input encoded information is “0”, and +5.5 kHz when it is “1”. Then, the spectrum Sq processed in this way is output.

  The inverse FFT unit 1040 performs inverse FFT processing on the spectrum Sq input from the duplication unit 1030, thereby converting the spectrum Sq into a modulated audio signal Se and outputting the modulated audio signal Se. Even with such a configuration, a modulated audio signal Se similar to that of the embodiment can be output. The above is description of the structure of the modulation apparatus 1 in this modification.

  Next, the demodulating device 4 according to this modification will be described with reference to FIG. The FFT unit 4010 receives the modulated audio signal Se, performs an FFT process, converts the signal into a frequency domain spectrum Sr, and outputs the spectrum Sr.

  The determination unit 4020 includes a spectrum in a frequency band of 6 kHz to 10 kHz (hereinafter referred to as spectrum A) and a spectrum in a frequency band of 10 kHz to 14 kHz (hereinafter referred to as spectrum B) of the spectrum Sr input from the FFT unit 4010 or A spectrum in the frequency band of 11.5 kHz to 15.5 kHz (hereinafter referred to as spectrum C) is compared to determine which of spectrum B and spectrum C has a spectrum shape close to spectrum A. This determination may be made from the correlation such as the similarity of the spectrum shape. Then, the output signal Sk corresponding to “+1” is output in the period determined as the spectrum B and “−1” is output in the period determined as the spectrum C. This output signal Sk is the same signal as the output signal Sk in the embodiment.

  Similar to the decoder 480 in the embodiment, the decoder 4030 demodulates the input output signal Sk into encoded information, and outputs reception information obtained by decoding the encoded information. The above is the description of the configuration of the demodulation device 4 in the present modification.

  In this way, the modulation apparatus 1 removes the high frequency band component of the input audio signal Sa, and encodes the transmission information with some of the remaining frequency band components in the removed frequency band. Any configuration may be used as long as the modulated audio signal Se modulated by frequency-shifting and superimposing with a shift amount corresponding to information can be emitted. The demodulating device 4 may have any configuration as long as it can recognize the frequency shift amount from the collected modulated audio signal Se and demodulate it into encoded information. It should be noted that both the modulation device 1 and the demodulation device 4 constitute not only the information transmission system 10 as the configuration of this modification, but also either the modulation device 1 or the demodulation device 4 is the configuration of this modification. The other may constitute the information transmission system 10 as a configuration of the embodiment.

<Modification 2>
In the above-described embodiment, a part of the remaining frequency band to be superimposed on the high frequency band is a frequency band between both cutoff frequencies by the combination of the LPF 110 and the HPF 120. Therefore, the upper limit frequency of the frequency band was the same frequency as the lower limit frequency of the high frequency band to be removed for superimposition, but a part of the remaining frequency band to be superimposed on the high frequency band This is not necessarily the case. For example, for a part of the remaining frequency band to be superimposed on the high frequency band, a component in the frequency band of 6 kHz to 9 kHz may be extracted using a BPF (band pass filter) or the like. . In this way, as long as it is a part of the remaining frequency band, any frequency band may be shifted and superimposed on the high frequency band. The bandwidth of the frequency band may be any bandwidth.

  Further, when there is no frequency band component to be superimposed in the frequency band of the input audio signal Sa, the LPF 110 is not used, and the frequency band component of a predetermined frequency or higher may not be removed. In this case, a component to be superimposed on a frequency band equal to or higher than a predetermined frequency may be extracted using the BPF as in the present modification.

<Modification 3>
In the above-described embodiment, the carrier frequency generator 140 has the two carrier frequency generators A141 and B142 having different carrier frequencies. However, the carrier frequency generator 140 has more carrier frequency generators. It may be. Then, the frequency of the carrier signal to be generated is made different, and each frequency is switched so that a discontinuity point does not occur in the output waveform from the switch 150 when the carrier signal is switched as described in the embodiment. It may be set so that the phases of both carrier signals fa and fb coincide with each other.

  In this way, the encoded information can be multi-valued in addition to the symbols “0” and “1”. If there are four carrier frequency generators, “00” “01” “10” "11" and 2 bits can be transmitted simultaneously.

  In this case, each configuration in the demodulator 4 may be changed in accordance with the number of carrier frequency generators (four in this example). Specifically, the remodulator 410 is provided with BPFs 412, 413, 414, and 415 (not shown) in which the frequency obtained by adding the frequency of each carrier signal to the center frequency set in the BPF 411 is set as the center frequency. Output signals Sf1, Sf2, Sf3, and Sf4 obtained by adding the output to the output of the BPF 411 are output. Then, the carrier component detector 420 and the level detector 430 process each output signal in the same manner as in the embodiment, and output signals Sh1, Sh2, Sh3, and Sh4 are output.

  Then, corresponding to the processing in the adder 440, moving average calculator 450, DC cut filter 460, positive / negative sign determiner 470, and decoder 480 in the embodiment, among the output signals Sh1, Sh2, Sh3, Sh4, the maximum What is necessary is to detect the output signal of the level. If the detected output signal is the output signal Sh1, the frequency shift amount in the modulation device 1 is selected as the shift amount of the center frequency set in the BPF 412 with respect to the center frequency set in the BPF 411. Can do. Therefore, during the detected period, the encoding information can be a symbol corresponding to the selected shift amount, for example, “00”. In this way, the bit rate of the encoded information output from the encoder 130 can be improved.

<Modification 4>
In the embodiment described above, communication of transmission information between the modulation device 1 and the demodulation device 4 is performed by emitting the modulated audio signal Se into the space, but the modulated audio signal Se is transmitted by wire. May be.

<Modification 5>
In the embodiment described above, communication of transmission information between the modulation device 1 and the demodulation device 4 is performed by emitting a modulated audio signal Se having a component in the audible frequency band into the space. A non-audible frequency band may be used. In this case, if the configuration of the speaker 2 can emit sound up to the frequency band of the non-audible range to be used, and the configuration of the microphone 3 can collect sound up to the frequency range of the non-audible range to be used. Good. In addition, each configuration of the modulation device 1 and the demodulation device 4 may be configured to process up to a non-audible frequency band to be used.

<Modification 6>
The control program executed by the modulation device 1 and the demodulation device 4 in the above-described embodiment is a computer such as a magnetic recording medium (magnetic tape, magnetic disk, etc.), an optical recording medium (optical disk, etc.), a magneto-optical recording medium, a semiconductor memory, etc. It may be provided in a state stored in a readable recording medium. In this case, a reading unit for reading these recording media may be provided. It is also possible to download via a network such as the Internet.

It is a block diagram which shows the structure of the information transmission system which concerns on embodiment. It is a block diagram which shows the structure of the modulation apparatus which concerns on embodiment. It is explanatory drawing which shows an example of the carrier signal output from the switch 150 which concerns on embodiment. It is explanatory drawing which shows the change of the frequency band of the audio signal which concerns on embodiment. It is a block diagram which shows the structure of the demodulation apparatus which concerns on embodiment. It is a block diagram which shows the structure of the remodulator which concerns on embodiment. It is explanatory drawing which shows an example of the output signal from the remodulator which concerns on embodiment. It is a block diagram which shows the structure of the carrier component detector which concerns on embodiment. It is explanatory drawing which shows an example of the output signal from the carrier component detector which concerns on embodiment. It is a block diagram which shows the structure of the level detector which concerns on embodiment. It is explanatory drawing which shows an example of the output signal from the level detector which concerns on embodiment. It is explanatory drawing which shows an example of the output signal from the adder which concerns on embodiment, a DC cut filter, and a positive / negative code determination device. It is explanatory drawing which shows an example of the encoding information which concerns on the decoder which concerns on embodiment. FIG. 10 is a block diagram illustrating a configuration of a modulation device according to modification example 1; FIG. 10 is a block diagram illustrating a configuration of a demodulation device according to Modification Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Modulator, 2 ... Speaker, 3 ... Microphone, 4 ... Demodulator, 10 ... Information transmission system, 110 ... LPF, 120, 170 ... HPF, 130 ... Encoder, 140 ... Carrier frequency generation part, 141, 142 DESCRIPTION OF SYMBOLS ... Carrier frequency generator, 150 ... Switch, 160 ... Multiplier, 180 ... Delay circuit, 190 ... Adder, 410 ... Remodulator, 411, 412, 413, 423, 424 ... BPF, 414, 415 ... Adder , 420 ... Carrier component detector, 421, 422, 431, 432 ... Rectifier, 430 ... Level detector, 433, 434 ... LPF, 440 ... Adder, 450 ... Moving average calculator, 460 ... DC cut filter, 470 ... Positive / negative sign determiner, 480... Decoder, 1010, 4010... FFT section, 1020... Encoder, 1030. ... inverse FFT unit, 4020 ... determining unit, 4030 ... decoder

Claims (9)

An input means for inputting an audio signal;
Obtaining means for obtaining encoded information;
Extraction means for extracting an audio signal having a component in a part of a frequency band out of a frequency band lower than a predetermined frequency of the audio signal input by the input means;
A frequency shift means for shifting the frequency band component of the audio signal extracted by the extraction means to a high frequency band equal to or higher than the predetermined frequency by a shift amount corresponding to the encoded information acquired by the acquisition means;
And a superimposing unit that superimposes the audio signal whose frequency band is shifted by the frequency shifting unit on the audio signal input by the input unit. The modulation apparatus according to claim 1, wherein the superimposing unit includes a removing unit that removes the high frequency band component of the audio signal input by the input unit. Further comprising carrier generating means for generating a plurality of carrier signals each having a frequency set differently,
The frequency shift means converts the carrier signal of the frequency selected according to the encoded information acquired by the acquisition means, out of the carrier signals generated by the carrier generation means, into the audio signal extracted by the extraction means. By multiplying the frequency band component of the audio signal,
The frequency of the carrier signal generated by the carrier generation means is set such that the phase of the carrier signal before and after switching is matched when the carrier signal selected by the frequency shift means is switched. The modulation device according to claim 1 or 2. The said superimposing means has a delay means which performs the delay process of the preset delay time with respect to the audio signal input by the said input means. The Claim 1 thru | or 3 characterized by the above-mentioned. Modulation device. An input means for inputting an audio signal;
A component of a frequency band of a part of the frequency band of the audio signal input by the input means, and a component of a plurality of frequency bands obtained by shifting the frequency of a plurality of shift amounts set in advance from the part of the frequency band. Detecting means for detecting a correlation with each of the plurality of shift amounts and selecting one of the plurality of shift amounts according to a detection result;
A demodulating apparatus comprising: encoded information generating means for generating encoded information encoded according to the shift amount selected by the detecting means. The detection means is generated by adding a part of a frequency band below a predetermined frequency and a part of a frequency band above the predetermined frequency among the frequency bands of the audio signal input by the input means. 6. The demodulator according to claim 5, wherein the correlation is detected based on the undulation of the amplitude of the audio signal. A modulation device according to any one of claims 1 to 4,
A demodulator according to claim 5 or 6,
Sound emitting means for emitting the audio signal superimposed by the superimposing means of the modulation device;
Sound collecting means for collecting the audio signal emitted by the sound emitting means;
The input means of the demodulator inputs the audio signal collected by the sound collection means,
The information transmission system characterized in that the shift amount preset in the detection means of the demodulation device is a frequency shift amount that can be shifted by the frequency shift means of the modulation device. An input process for inputting an audio signal;
An acquisition process of acquiring encoded information;
An extraction process of extracting an audio signal having a component of a part of a frequency band out of a frequency band less than a predetermined frequency of the audio signal input in the input process;
A frequency shift process for shifting the frequency band component of the audio signal extracted in the extraction process to a high frequency band equal to or higher than the predetermined frequency by a shift amount corresponding to the encoded information acquired in the acquisition process;
A modulation method comprising: a superimposition process of superimposing an audio signal whose frequency band is shifted in the frequency shift process on an audio signal input in the input process. An input process for inputting an audio signal;
A component of a part of the frequency band of the frequency band of the audio signal input in the input process, and a component of a plurality of frequency bands obtained by shifting the frequency of a plurality of shift amounts set in advance from the part of the frequency band. A detection process of detecting a correlation with each of the plurality of shift amounts according to a detection result;
A demodulating method comprising: an encoded information generating process for generating encoded information encoded according to the shift amount selected in the detecting process.

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