Noise reduction apparatus, noise reduction method, and computer-readable recording medium

A noise reduction apparatus includes: an input device to which an electric signal is input from an external device; a signal processing circuit configured to perform predetermined signal processing on the electric signal input to the input device and output a generated signal to an external device; a switch configured to change over to either one of a connected state in which the input device and the signal processing circuit are electrically connected to each other and a disconnected state in which the input device and the signal processing circuit are electrically disconnected to each other; and a noise processing circuit configured to subtract a noise signal output from the signal processing circuit when the switch is in the disconnected state from the signal output from the signal processing circuit when the switch is in the connected state, and output a subtraction result.

BACKGROUND

1. Technical Field

The present disclosure relates to a noise reduction apparatus, a noise reduction method, and a computer-readable recording medium to reduce noise that occurs in a signal processing unit.

2. Related Art

There is a conventionally known technology of imaging devices, such as video cameras, to reduce noise due to a noise source near a microphone when stereo recording is conducted (see Japanese Laid-open Patent Publication No. 2006-67355). With this technology, out of first and second microphones, noise is reduced by subtracting a signal of a noise component obtained from the second microphone located near the noise source from a sound signal obtained from the first microphone located far from the noise source.

SUMMARY

In some embodiments, a noise reduction apparatus includes: an input device to which an electric signal is input from an external device; a signal processing circuit configured to perform predetermined signal processing on the electric signal input to the input device and output a generated signal to an external device; a switch that is provided between the input device and the signal processing circuit, the switch being configured to change over to either one of a connected state in which the input device and the signal processing circuit are electrically connected to each other and a disconnected state in which the input device and the signal processing circuit are electrically disconnected to each other; and a noise processing circuit configured to subtract a noise signal output from the signal processing circuit when the switch is in the disconnected state from the signal output from the signal processing circuit when the switch is in the connected state, and output a subtraction result.

In some embodiments, provided is a noise reduction method implemented by a noise reduction apparatus including: an input device to which an electric signal is input from an external device; a signal processing unit configured to perform predetermined signal processing on the electric signal input to the input device and output a generated signal to an external device; and a switch that is provided between the input device and the signal processing circuit, the switch being configured to change over to either one of a connected state in which the input device and the signal processing circuit are electrically connected to each other and a disconnected state in which the input device and the signal processing circuit are electrically disconnected to each other. The noise reduction method includes subtracting a noise signal output from the signal processing circuit when the switch is in the disconnected state from the signal output from the signal processing circuit when the switch is in the connected state, and outputting a subtraction result.

In some embodiments, provided is a non-transitory computer-readable recording medium with an executable program for a noise reduction apparatus stored thereon, the noise reduction apparatus including: an input device to which an electric signal is input from an external device; a signal processing unit configured to perform predetermined signal processing on the electric signal input to the input device and output a generated signal to an external device; and a switch that is provided between the input device and the signal processing circuit, the switch being configured to change over to either one of a connected state in which the input device and the signal processing circuit are electrically connected to each other and a disconnected state in which the input device and the signal processing circuit are electrically disconnected to each other. The program causes the noise reduction apparatus to execute: subtracting a noise signal output from the signal processing circuit when the switch is in the disconnected state from the signal output from the signal processing circuit when the switch is in the connected state, and outputting a subtraction result.

DETAILED DESCRIPTION

Aspects (hereinafter, referred to as “embodiments”) for carrying out the disclosure are explained below with reference to the drawings. Furthermore, the disclosure is not limited to the following embodiments. Moreover, in the drawings referred to in the following explanation, shapes, sizes, and positional relationships are schematically illustrated merely to understand the details of the disclosure. That is, the disclosure is not exclusively limited to the shapes, the sizes, and the positional relationships illustrated in the drawings.

First Embodiment

Noise Reduction Apparatus

FIG. 1is a block diagram that illustrates a functional configuration of a noise reduction apparatus according to a first embodiment of the disclosure. A noise reduction apparatus1illustrated inFIG. 1is used in any of the following: a sound recording and playing back device, such as an IC recorder, which acquires sound with for example a microphone, records it as sound data, and outputs the sound data from a speaker, or the like; a capturing device that is capable of recording image data generated by an imaging element, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), and displaying the image corresponding to the image data; and a headphone that plays back and outputs the sound data from an external device. The noise reduction apparatus1is an apparatus that removes self-noise that occurs in a codec circuit, an image processing circuit, or the like, which performs signal processing on sound data or image data. Here, the self-noise is the noise generated due to a voltage fluctuation when a device is started up or the noise peculiar to an electric circuit provided in the device even though no sound data or image data is input.

As illustrated inFIG. 1, the noise reduction apparatus1includes an input device10, a switch11, a signal processing unit12, a noise processing unit13, a memory I/F unit14, a recording medium15, a recording unit16, and a control unit17.

The input device10receives electric signals acquired by an external device. Specifically, the input device10receives analog or digital sound signals (electric signals) converted from the sound collected by a microphone, and analog or digital image signals (electric signals) generated by an imaging element such as CCD or CMOS. The input device10is configured as appropriate depending on the configuration of the noise reduction apparatus1. For example, when a portable recording medium is used to transfer sound signals or image signals with an external device, the input device10is configured as a reader device that has the recording medium removably attached thereto and that reads the recorded sound signal or image signal. Furthermore, when a server that records sound signals and image signals acquired by an external device is used, the input device10is configured as a communication device, or the like, capable of communicating with the server in both directions and, by performing data communication with the server, acquiring a sound signal or image signal. Furthermore, the input device10may be configured as an interface device, or the like, to which a sound signal or image signal is input from an external device via a cable.

The switch11is provided between the input device10and the signal processing unit12to change over to either one of the connected state in which the input device10and the signal processing unit12are electrically connected to each other and the disconnected state in which the input device10and the signal processing unit12are electrically disconnected to each other. The switch11changes over to either one of the connected state and the disconnected state under the control of the control unit17. The switch11is configured by using any of, for example, a mechanical switch such as a toggle switch or push switch, an analog semiconductor switch formed of an IC such as a MOS, and a mechanical relay switch formed of a MOS.

Under the control of the control unit17, the signal processing unit12executes predetermined signal processing on an electric signal, input via the input device10and the switch11, to generate an output signal and outputs the output signal to the noise processing unit13. Here, the predetermined signal processing is amplification processing, A/D conversion processing, gain adjustment processing, format conversion processing for conversion into a predetermined format, and the like, for electric signals. The signal processing unit12is configured by using DSP (Digital Signal Processing), FPGA (Field Programmable Gate Array), or the like.

Under the control of the control unit17, the noise processing unit13subtracts a noise signal output from the signal processing unit12when the state of the switch11is the disconnected state from a signal (output signal) output from the signal processing unit12when the state of the switch11is the connected state and then outputs it to the memory I/F unit14. The noise processing unit13is configured by using DSP, FPGA, or the like.

Under the control of the control unit17, the recording medium15records a signal (output signal) output from the noise processing unit13via the memory I/F unit14. The recording medium15is mounted to the noise reduction apparatus1in an attachable and detachable manner via the memory I/F unit14. The recording medium15is configured by using, for example, a memory card.

The recording unit16records various programs executed by the noise reduction apparatus1and various types of data executed by the noise reduction apparatus1. The recording unit16is configured by using a Flash memory, SDRAM (Synchronous Dynamic Random Access Memory), or the like. Furthermore, the recording unit16includes a program recording unit161that records a program executed by the noise reduction apparatus1.

The control unit17controls each unit included in the noise reduction apparatus1in an integrated manner. The control unit17is configured by using a CPU (Central Processing Unit), or the like. The control unit17controls the state of the switch11. Furthermore, the control unit17controls each of the signal processing unit12, the noise processing unit13, and the memory I/F unit14. Specifically, the control unit17changes the state of the switch11to any one of the connected state and the disconnected state. Furthermore, when the state of the switch11is the disconnected state and when there is no data from the input device10, the control unit17causes the signal processing unit12to output a signal (noise signal) to the noise processing unit13.

Process of the Noise Reduction Apparatus

Next, a process performed by the noise reduction apparatus1is explained.FIG. 2is a flowchart that illustrates the outline of the process performed by the noise reduction apparatus1.

As illustrated inFIG. 2, the control unit17first changes the state of the switch11to the disconnected state (Step S101) and causes the signal processing unit12to output a noise signal while in the disconnected state where the input device10and the signal processing unit12are disconnected to each other and in the state where no electric signal is input from the input device10to the signal processing unit12, whereby the noise processing unit13is caused to acquire a noise signal from the signal processing unit12(Step S102).

Then, the control unit17changes the state of the switch11to the connected state (Step S103) and, in the connected state where the input device10and the signal processing unit12are connected to each other, causes the signal processing unit12to execute signal processing on an electric signal input from the input device10and output an output signal, whereby the noise processing unit13is caused to acquire the output signal from the signal processing unit12(Step S104).

Then, the control unit17causes the noise processing unit13to subtract the noise signal output from the signal processing unit12in the disconnected state where the input device10and the signal processing unit12are disconnected to each other from the output signal output from the signal processing unit12in the connected state where the input device10and the signal processing unit12are connected to each other (Step S105). This makes it possible to reduce at least the noise signal included in the signal processing unit12from the output signal.

Then, the control unit17records a subtraction result, which is obtained after the noise processing unit13has removed the noise signal from the output signal, in the recording medium15via the memory I/F unit14(Step S106). After Step S106, the noise reduction apparatus1terminates this process.

According to the first embodiment of the disclosure described above, as the noise processing unit13subtracts a noise signal output from the signal processing unit12when the state of the switch11is the disconnected state from an output signal output from the signal processing unit12when the state of the switch11is the connected state and then outputs it, whereby it is possible to reduce the self-noise occurring in the noise reduction apparatus1from the output signal.

Furthermore, according to the first embodiment of the disclosure, the noise processing unit13may cause the recording unit16to record a noise signal output from the signal processing unit12when the state of the switch11is the disconnected state.

Second Embodiment

Next, a second embodiment of the disclosure is explained. According to the second embodiment, the noise reduction apparatus is applied to a sound recording device including a microphone. After the configuration of the sound recording device according to the second embodiment is explained below, a process performed by the sound recording device according to the second embodiment is explained. Furthermore, the same component as that in the noise reduction apparatus1according to the above-described first embodiment is attached with the same reference numeral, and a detailed explanation is omitted.

Configuration of the Sound Recording Device

FIG. 3is a block diagram that illustrates a functional configuration of the sound recording device according to the second embodiment of the disclosure. A sound recording device1A illustrated inFIG. 3is a device that collects sound, generates a sound signal (electric signal) based on the collected sound, and records it.

As illustrated inFIG. 3, the sound recording device1A includes a microphone21, an external input terminal22, the switch11, a sound processing unit23, an operating device24, a Flash memory25, an SDRAM26, the memory I/F unit14, the recording medium15, a driver27, a display unit28, a temperature detecting unit29, a bus30, and a control unit31.

The microphone21receives sound, converts it into an analog sound signal (electric signal), and outputs the sound signal to the sound processing unit23via the external input terminal22and the switch11. In the explanation according to the second embodiment, the microphone21is a directional microphone; however, this is not a limitation, and it may be a unidirectional microphone and, furthermore, a microphone with changeable directional characteristic may be used. Further, the microphone21may be a stereo microphone capable of collecting right and left sound. Moreover, according to the second embodiment, the microphone21functions as a first microphone.

The plug of an external microphone is inserted into the external input terminal22. The external input terminal22receives input of an analog sound signal (electric signal) converted from the sound by the external microphone and outputs the received sound signal to the sound processing unit23via the switch11. Furthermore, the microphone21is electrically connected to the external input terminal22. The external input terminal22electrically connects the external microphone and the switch11when the plug of the external microphone is inserted into the external input terminal22and electrically connects the microphone21and the switch11when the plug of the external microphone is not inserted into the external input terminal22. The external input terminal22is configured by using a microphone jack, or the like. Furthermore, according to the second embodiment, the external microphone functions as a second microphone.

FIG. 4is a cross-sectional view that schematically illustrates a configuration of the external input terminal22.

As illustrated inFIG. 4, the external input terminal22includes an insertion portion221, a first contact member222, a second contact member223, and a third contact member224.

The plug of the external microphone is inserted into the insertion portion221. A first end of the first contact member222is grounded (GND). When the plug of the external microphone is inserted into the insertion portion221, a second end222aof the first contact member222is brought into contact with it to be electrically connected. A first end of the second contact member223is electrically connected to the switch11via an undepicted circuit. When the plug of the external microphone is inserted into the insertion portion221, a second end223aof the second contact member223is brought into contact with it to be electrically connected. A first end224aof the third contact member224is electrically connected to the microphone21, a second end224bis electrically connected to the switch11, and when the plug of the external microphone is inserted into the insertion portion221, the second end224bis electrically disconnected from the switch11. Specifically, when the plug of the external microphone is inserted into the insertion portion221, the first end224aof the third contact member224is brought into contact with the plug of the external microphone so that the second end224bis separated from a terminal225, whereby the microphone21and the switch11are electrically disconnected. Furthermore, the configuration of the external input terminal22may be changed as appropriate to other than the shape illustrated inFIG. 4. Furthermore, although the microphone21is electrically connected to the switch11via the external input terminal22according to the second embodiment, this is not a limitation, and the microphone21and the switch11may have a direct electrical connection by omitting the configuration of the external input terminal22.

With reference back toFIG. 3, the configuration of the sound recording device1A is continuously explained.

Under the control of the control unit31, the sound processing unit23performs various types of signal processing on a sound signal (electric signal) input via the switch11. Under the control of the control unit31, the sound processing unit23records the sound signal (output signal), on which signal processing has been performed, in the recording medium15via the bus30and the memory I/F unit14. Specifically, under the control of the control unit31, the sound processing unit23converts a sound signal into sound data in a predetermined format on a frame-by-frame basis and temporarily records it in the SDRAM26. For example, under the control of the control unit31, the sound processing unit23continuously performs the operations for the above-described conversion into sound data and the recording of the sound data in the SDRAM26during recording and sequentially records the sound data, recorded in the SDRAM26, in the recording medium15in a FIFO (First In First Out) manner. The sound processing unit23is configured by using DSP, FPGA, or the like. The sound processing unit23includes a signal processing unit231and a noise processing unit232. Furthermore, according to the second embodiment, the sound processing unit23functions as a noise reduction apparatus.

Under the control of the control unit31, the signal processing unit231performs predetermined signal processing on a sound signal (electric signal) and outputs it to the noise processing unit232. The signal processing unit231includes at least an amplifier unit231a, an A/D converter231b, a filter unit231c, an equalizer231d, an ALC (Automatic Level Control) unit231e, and an ADC Vol unit231f.

Under the control of the control unit31, the amplifier unit231aamplifies the sound signal, input via the switch11, and outputs it to the A/D converter231b. The amplifier unit231ais configured by using an amplifier circuit such as an amplifier. Furthermore, according to the second embodiment, the amplifier unit231afunctions as an amplifying unit.

Under the control of the control unit31, the A/D converter231bconducts A/D conversion on the analog sound signal, input from the amplifier unit231a, to convert it into a digital sound signal (quantized data) and outputs the digital sound signal to the filter unit231c. The A/D converter231bis configured by using an A/D conversion circuit, or the like.

The filter unit231ccuts off an unnecessary frequency from the digital sound signal, input from the A/D converter231b, and outputs it to the equalizer231d. The filter unit231cis configured by using, for example, a low-pass filter circuit.

Under the control of the control unit31, the equalizer231dadjusts a specific frequency with regard to the digital sound signal input from the filter unit231cand outputs it to the ALC unit231e. The equalizer231dis configured by using various filters.

Under the control of the control unit31, the ALC unit231eautomatically controls the gain of the sound signal and outputs it to the ADC Vol unit231f. The ALC unit231eis configured by using an ALC circuit, or the like.

Under the control of the control unit31, the ADC Vol unit231famplifies the digital sound signal, input from the ALC unit231e, and outputs it to the noise processing unit232. The ADC Vol unit231fis configured by using an ADC Vol circuit, or the like.

Under the control of the control unit31, the noise processing unit232reduces noise included in the sound signal (output signal) input from the sound processing unit23. Under the control of the control unit31, the noise processing unit232records the sound signal with reduced noise in the SDRAM26via the bus30or in the recording medium15via the bus30and the memory I/F unit14. The noise processing unit232is provided after the signal processing unit231. The noise processing unit232includes a converter232a, a calculating unit232b, and a decoding unit232c.

Under the control of the control unit31, the converter232agenerates first amplitude information by conducting discrete Fourier transform (hereafter, simply referred to as “DFT process”) on a signal (noise signal) output from the signal processing unit231when the switch11sets the state between the external input terminal22and the signal processing unit231to the disconnected state. Specifically, the converter232agenerates the first amplitude information by performing the DFT process on a digital signal (noise signal) output from the signal processing unit231. Furthermore, under the control of the control unit31, the converter232arecords the first amplitude information in the Flash memory25or the SDRAM26via the bus30or records it in the recording medium15via the bus30and the memory I/F unit14. Furthermore, under the control of the control unit31, the converter232agenerates second amplitude information by conducting the DFT process on a digital sound signal output from the signal processing unit231when the switch11sets the state between the external input terminal22and the signal processing unit231to the connected state and outputs the second amplitude information to the calculating unit232b. Specifically, the converter232agenerates second phase information by conducting the DFT process on a digital sound signal output from the signal processing unit231and generates the second amplitude information based on the second phase information.

Under the control of the control unit31, the calculating unit232bcalculates the difference between the second amplitude information input from the converter232aand the first amplitude information recorded in the Flash memory25or the SDRAM26and outputs the difference to the decoding unit232c. Specifically, under the control of the control unit31, the calculating unit232bsubtracts the first amplitude information recorded in the SDRAM26from the second amplitude information input from the converter232aand outputs the subtraction result to the decoding unit232c.

Under the control of the control unit31, the decoding unit232cconducts inverse Fourier transform (hereafter, simply referred to as “IDFT process”) on the difference calculated by the calculating unit232bto generate a decoded sound signal (decoded signal) with noise reduced. Specifically, the decoding unit232cdecodes the signal based on the difference between the second amplitude information and the first amplitude information and the second phase information. Under the control of the control unit31, the decoding unit232crecords the decoded sound signal in the recording medium15via the bus30and the memory I/F unit14.

The operating device24receives input of signals for giving commands for various operations related to the sound recording device1A. The operating device24outputs received command signals to the control unit31via the bus30. For example, the operating device24receives input of a start signal for giving a command to the sound recording device1A so as to start recording, a termination signal for giving a command to terminate recording, a switch signal for changing over to any of modes (e.g., multiple recording modes) executable by the sound recording device1A, an adjustment signal for adjusting the gain of a sound signal, and the like. The operating device24is configured by using a button, arrow key, switch, touch panel, and the like. It is obvious that the operating device24may form a graphical user interface (GUI), or the like, by using a touch panel, a display monitor, and the like.

The Flash memory25includes: a program recording unit251that records a program executed by the sound recording device1A; and a noise-information recording unit252that records the noise information relating multiple sets of first amplitude information generated by the converter232aand the temperature detected by the temperature detecting unit29described later. Furthermore, the Flash memory25records various parameters, and the like, regarding the sound recording device1A.

FIG. 5is a diagram that schematically illustrates an example of the noise information recorded in the noise-information recording unit252. InFIG. 5, the horizontal axis indicates a temperature, the vertical axis indicates a noise level, and a curved line L1indicates the relation between the temperature and the noise level. As illustrated in the curved line L1ofFIG. 5, the noise-information recording unit252records the first amplitude information (noise level) for each temperature. Although the first amplitude information is related to every temperature in a continuous manner inFIG. 5, this is not a limitation, and the temperature detected by the temperature detecting unit29described later and the first amplitude information may be recorded by being related discretely.

With reference back toFIG. 3, the configuration of the sound recording device1A is continuously explained.

The SDRAM26temporarily records various types of information that is being processed by the sound recording device1A. Furthermore, the SDRAM26temporarily records the first amplitude information generated by the converter232a.

Under the control of the control unit31, the driver27controls the display mode of the display unit28. For example, under the control of the control unit31, the driver27causes the display unit28to present the gain with regard to a sound signal, the volume of a sound signal, the recording time of a sound signal, and the like.

The display unit28is configured by using a display panel such as liquid crystal or organic EL (Electro Luminescence), and it displays information input from the driver27.

The temperature detecting unit29detects the ambient temperature of the sound recording device1A. The temperature detecting unit29outputs a detection result to the control unit31via the bus30. The temperature detecting unit29is configured by using a temperature sensor, or the like.

The bus30is the transmission path that connects each component in the sound recording device1A, and it transmits various types of data generated inside the sound recording device1A to each component in the sound recording device1A.

The control unit31controls overall units included in the sound recording device1A. The control unit31is configured by using a general-purpose processor such as a CPU or a dedicated processor such as various arithmetic circuits performing a specific function, e.g., ASIC (Application Specific Integrated Circuit) or FPGA. When the control unit31is a general-purpose processor, it transmits commands, data, and the like, to each unit included in the sound recording device1A by reading various programs stored in the program recording unit251and controls the overall operation of the sound recording device1A in an integrated manner. Furthermore, when the control unit31is a dedicated processor, the processor may independently execute various processes, or the processor and the program recording unit251may execute various processes in cooperation or in combination by using various types of data, and the like, recorded in the program recording unit251. The control unit31includes a switch controller311, a determining unit312, and a noise controller313.

The switch controller311controls the state of the switch11. Specifically, the switch controller311changes the state of the switch11to the disconnected state before the sound recording device1A starts recording or after the sound recording device1A terminates recording. Furthermore, if a start signal is input from the operating device24, the switch controller311changes the state of the switch11to the connected state after a certain time period has elapsed.

The determining unit312determines whether the first amplitude information related to the current temperature detected by the temperature detecting unit29is recorded in the noise-information recording unit252of the Flash memory25.

In accordance with a determination result of the determining unit312, the noise controller313selects the first amplitude information used for a calculation operation by the calculating unit232bfrom the sets of first amplitude information recorded in the Flash memory25and outputs it to the calculating unit232b.

Process of the sound recording device Next, a process performed by the sound recording device1A is explained.FIG. 6is a flowchart that illustrates the outline of the process performed by the sound recording device1A.FIG. 7is a timing chart of the process performed by the sound recording device1A. InFIG. 7, from the upper end, (a) represents the timing of on/off operation of the operating device24, (b) represents the sound collection timing of the microphone21, (c) represents the reading timing of a sound signal, (d) represents the timing of the DFT process by the converter232a, (e) represents the timing of writing or reading the first amplitude information to or from the Flash memory25, (f) represents the timing of a difference calculation process by the calculating unit232b, (g) represents the timing of the IDFT process by the decoding unit232c, (h) represents the timing of the temperature detection by the temperature detecting unit29, (i) represents the determination timing by the determining unit312, and (j) represents the state of the switch11. Furthermore, inFIG. 7, the horizontal axis indicates a time.

As illustrated inFIG. 6, first, when the power button of the operating device24is operated and the sound recording device1A is started up, the control unit31makes various default settings regarding the sound recording device1A (Step S201). Here, the default settings include checking the presence or absence of a sound file recorded in the recording medium15, checking the remaining amount of battery, setting the time and date, and the like. In this case, the switch controller311changes the state of the switch11to the disconnected state.

Then, when a start signal is input due to an operation on the operating device24so that sound recording is started (Step S202: Yes), the control unit31causes the signal processing unit231to output a noise signal and causes the converter232ato load silent sound data (Step S203), causes the converter232ato perform the DFT process on a noise signal that is silent sound data input from the signal processing unit231(Step S204), and causes the temperature detecting unit29to detect the temperature (Step S205). Specifically, as illustrated inFIG. 7, when the recording button of the operating device24is operated and a start signal is input (time t1), the control unit31causes the signal processing unit231to output a noise signal and causes the converter232ato load silent sound data (time t2), causes the converter232ato perform the DFT process on the noise signal that is silent sound data input from the signal processing unit231(time t3), and causes the temperature detecting unit29to detect the temperature (the time t3).

FIG. 8is a diagram that schematically illustrates an example of silent sound data.FIG. 9is a diagram that schematically illustrates an example of the noise distribution of the silent sound data when the converter232aperforms the DFT process. InFIG. 8, the horizontal axis indicates time, the vertical axis indicates a noise level, and a wavelength D1indicates the noise signal that is silent sound data. InFIG. 9, the horizontal axis indicates a time, and the vertical axis indicates a frequency (Hz).

As illustrated inFIG. 8, when the recording button of the operating device24is operated, the control unit31causes the signal processing unit231to output a noise signal and causes the converter232ato load silent sound data (the wavelength D1) and, as illustrated inFIG. 9, causes the converter232ato perform the DFT process on the noise signal that is the silent sound data input from the signal processing unit231.

With reference back toFIG. 6, the process after Step S206is continuously explained.

At Step S206, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25. Specifically, as illustrated inFIG. 7, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(the time t3). When the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(Step S206: Yes), the sound recording device1A proceeds to Step S208described later. Conversely, when the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is not recorded in the Flash memory25(Step S206: No), the sound recording device1A proceeds to Step S207described later.

At Step S207, the control unit31records the first amplitude information generated by the converter232aand the temperature detected by the temperature detecting unit29in a related manner in the Flash memory25. Specifically, as illustrated inFIG. 7, the control unit31records the first amplitude information generated by the converter232aand the temperature detected by the temperature detecting unit29in a related manner in the Flash memory25(time t4). After Step S207, the sound recording device1A proceeds to Step S208described later.

Then, the switch controller311changes the state of the switch11to the connected state (Step S208). Specifically, as illustrated inFIG. 7, the switch controller311changes the state of the switch11to the connected state (the time t4).

Then, when a certain time period has elapsed (Step S209: Yes), the sound recording device1A proceeds to Step S210described later. Conversely, when the certain time period has not elapsed (Step S209: No), the sound recording device1A stands by until the certain time period has elapsed. Here, the reason for the standby until the certain time period (e.g., 0.5 seconds) has elapsed is to prevent the recording of noise that occurs when an electric current is applied after the sound recording device1A is started up.

At Step S210, the control unit31causes the signal processing unit231to start to record the sound signal from the microphone21. Specifically, as illustrated inFIG. 7, the control unit31causes the signal processing unit231to start to record the sound signal (time t5).

Then, the control unit31causes the converter232ato sequentially perform the DFT process on sound signals output from the signal processing unit231in sequence (Step S211). Specifically, as illustrated inFIG. 7, the control unit31causes the converter232ato perform the DFT process on a sound signal output from the signal processing unit231(the time t5).

Then, the control unit31causes the calculating unit232bto sequentially calculate the difference between the second amplitude information input from the converter232ain sequence and the first amplitude information recorded in the Flash memory25(Step S212). Specifically, as illustrated inFIG. 7, the control unit31causes the calculating unit232bto sequentially calculate the difference between the second amplitude information input from the converter232ain sequence and the first amplitude information recorded in the Flash memory25(time t6).

FIG. 10is a diagram that schematically illustrates an example of the noise distribution of a calculation result by the calculating unit232b. InFIG. 10, the horizontal axis indicates a time, and the vertical axis indicates a frequency (Hz). As illustrated inFIG. 10, the calculating unit232bsubtracts the first amplitude information from the second amplitude information input from the converter232a, thereby reducing a noise signal included in the second amplitude information.

After Step S212, the control unit31causes the decoding unit232cto sequentially perform the IDFT process on the difference input from the calculating unit232b(Step S213). Specifically, as illustrated inFIG. 7, the control unit31causes the decoding unit232cto sequentially perform the IDFT process on the difference input from the calculating unit232b(time t7).

FIG. 11is a diagram that schematically illustrates a sound signal having undergone the IDFT process by the decoding unit232c.FIG. 12illustrates data of a 1-kHz signal before noise removal.FIG. 13illustrates data of a 1-kHz signal after noise removal. InFIG. 11, the horizontal axis indicates a time, the vertical axis indicates a noise level, and a wavelength D2indicates a sound signal. InFIG. 12andFIG. 13, the horizontal axis indicates a frequency [Hz], and the vertical axis indicates a signal level [dBFS]. InFIG. 12, a wavelength L10indicates the 1-kHz signal before noise removal. Furthermore, inFIG. 13, a wavelength L11indicates the 1-kHz signal after noise removal.

As illustrated in the wavelength D2ofFIG. 11, the noise has been reduced in the sound signal having undergone the IDFT process by the decoding unit232c. Specifically, as illustrated inFIG. 12andFIG. 13, it is understood that noise has been removed with little effect on the level of the recorded sound (1 KHz). This allows a reduction in the self-noise that occurs in the sound recording device1A.

With reference back toFIG. 6, the process after Step S214is continuously explained.

At Step S214, the control unit31records the sound signal decoded by the decoding unit232cin the recording medium15via the memory I/F unit14.

Then, when the operating device24is operated and the recording of the sound recording device1A is stopped (Step S215: Yes), the sound recording device1A proceeds to Step S220described later. Specifically, as illustrated inFIG. 7, when the operating device24is operated, the recording of the sound recording device1A is stopped (time t11). Conversely, when the operating device24is not operated and the recording of the sound recording device1A is not stopped (Step S215: No), the sound recording device1A proceeds to Step S216described later.

At Step S216, when a certain time period has elapsed after the temperature detecting unit29detects the temperature (Step S216: Yes), the control unit31causes the temperature detecting unit29to detect the temperature (Step S217). Specifically, as illustrated inFIG. 7, the control unit31causes the temperature detecting unit29to detect the temperature (time t8).

Then, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(Step S218). Specifically, as illustrated inFIG. 7, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(time t9). When the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(Step S218: Yes), the sound recording device1A proceeds to Step S219described later. Conversely, when the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is not recorded in the Flash memory25(Step S218: No), the sound recording device1A proceeds to the above-described Step S211.

At Step S219, the noise controller313updates the first amplitude information used by the calculating unit232bto the first amplitude information related to the temperature detected by the temperature detecting unit29. Specifically, as illustrated inFIG. 7, the noise controller313updates the first amplitude information used by the calculating unit232bto the first amplitude information (R2) related to the temperature detected by the temperature detecting unit29. This allows the calculating unit232bto subtract the first amplitude information (R2) related to the current temperature from the second amplitude information generated by the converter232a. After Step S219, the sound recording device1A returns to the above-described Step S211and, until the recording is stopped, repeatedly performs the above-described Step S211to Step S219. In this case, as illustrated inFIG. 7, in the sound recording device1A, each time a certain time period has elapsed, the temperature detecting unit29detects the temperature (time t10), the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(the time t10) and, when the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25, the first amplitude information is applied to the calculating unit232b. Furthermore, when the above-described Step S211to Step S219are repeatedly performed, the sound processing unit23converts a sound signal into sound data in a predetermined format on a frame-by-frame basis, shifts frames such that the frames are overlapped with each other, and connects sets of sound data (e.g., sound data1, sound data2) in a smooth manner while executing the Overlap-add method for addition by applying a weight with a window function, thereby loading a sound signal with noise reduced.

At Step S216, the sound recording device1A returns to the above-described Step S211when a certain time period has not elapsed after the temperature detecting unit29detects the temperature (Step S216: No).

At Step S220, the switch controller311changes the state of the switch11to the disconnected state. Specifically, as illustrated inFIG. 7, the switch controller311changes the state of the switch11to the disconnected state (time t12).

Then, when a certain time period has elapsed (Step S221: Yes), the control unit31causes the temperature detecting unit29to detect the temperature (Step S222). Specifically, as illustrated inFIG. 7, the control unit31causes the temperature detecting unit29to detect the temperature (time t13). After Step S222, the sound recording device1A proceeds to Step S223described later. Conversely, when the certain time period has not elapsed (Step S221: No), the sound recording device1A stands by until the certain time period has elapsed.

Then, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(Step S223). Specifically, as illustrated inFIG. 7, the determining unit312determines whether the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(time t13). When the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is recorded in the Flash memory25(Step S223: Yes), the sound recording device1A terminates this process. Conversely, when the determining unit312determines that the first amplitude information identical to the data related to the temperature detected by the temperature detecting unit29is not recorded in the Flash memory25(Step S223: No), the sound recording device1A proceeds to Step S224described later.

At Step S224, the control unit31causes the signal processing unit231to output a noise signal and causes the converter232ato load silent sound data. Specifically, as illustrated inFIG. 7, the control unit31causes the signal processing unit231to output a noise signal and causes the converter232ato load silent sound data (time t14).

Then, the control unit31causes the converter232ato perform the DFT process on the noise signal that is the silent sound data input from the signal processing unit231(Step S225). Specifically, as illustrated inFIG. 7, the control unit31causes the converter232ato perform the DFT process on the noise signal that is the silent sound data input from the signal processing unit231(the time t14).

Then, the control unit31records the first amplitude information generated by the converter232aand the temperature detected by the temperature detecting unit29in a related manner in the Flash memory25(Step S226). After Step S226, the sound recording device1A terminates this process.

At Step S202, when the recording of sound is not started without inputting a start signal due to an operation on the operating device24(Step S202: No), the sound recording device1A proceeds to Step S227described later.

Then, when a certain time period has elapsed (Step S227: Yes), the sound recording device1A terminates this process. Conversely, when the certain time period has not elapsed (Step S227: No), the sound recording device1A returns to Step S202.

According to the above-described second embodiment of the disclosure, the noise processing unit232subtracts the noise signal output from the signal processing unit231when the state of the switch11is the disconnected state from the output signal output from the signal processing unit231when the state of the switch11is the connected state and outputs it, whereby it is possible to reduce self-noise occurring in the sound recording device1A from a sound signal.

Furthermore, according to the second embodiment of the disclosure, as the switch controller311sets the state of the switch11to the disconnected state, the noise processing unit232may acquire self-noise occurring in the sound recording device1A in a silent sound state; thus, the first amplitude information, which is noise, may be acquired with a simple configuration.

Furthermore, according to the second embodiment of the disclosure, as each of the sound recording devices1A is capable of acquiring the first amplitude information that is noise, self-noise may be reduced with high accuracy without preparing various types of data.

Furthermore, according to the second embodiment of the disclosure, the calculating unit232bcalculates the difference between the second amplitude information input from the converter232aand the first amplitude information, whereby self-noise occurring in the sound recording device1A may be reduced from a sound signal.

Furthermore, according to the second embodiment of the disclosure, as the temperature detected by the temperature detecting unit29and the first amplitude information generated by the converter232aare recorded in a related manner in the Flash memory25, the first amplitude information may be acquired for each temperature.

Furthermore, according to the second embodiment of the disclosure, the calculating unit232bacquires the first amplitude information related to the current temperature detected by the temperature detecting unit29from the Flash memory25and uses the acquired first amplitude information to calculate the difference between the second amplitude information and the first amplitude information, whereby it is possible to reduce noise in accordance with the usage environment of the sound recording device1A.

Furthermore, according to the second embodiment of the disclosure, when the determining unit312determines that the first amplitude information related to the current temperature detected by the temperature detecting unit29is not recorded in the Flash memory25, the Flash memory25records the current temperature detected by the temperature detecting unit29and the first amplitude information in a related manner, whereby the first amplitude information may be sequentially updated in accordance with the usage environment of the sound recording device1A.

Furthermore, according to the second embodiment of the disclosure, when the determining unit312determines that the first amplitude information related to the current temperature detected by the temperature detecting unit29is not recorded in the Flash memory25, the calculating unit232bmay calculate the difference between the second amplitude information and the first amplitude information by using the first amplitude information related to the temperature closest to the current temperature recorded in the Flash memory25. This makes it possible to reduce self-noise occurring in the sound recording device1A from a sound signal.

Furthermore, according to the second embodiment of the disclosure, the first amplitude information generated by the converter232aand the temperature detected by the temperature detecting unit29are recorded in a related manner in the Flash memory25; however, this is not a limitation and, for example, each of the recording modes executable by the sound recording device1A may be related to first amplitude information. For example, as illustrated inFIG. 14, the control unit31may relate first amplitude information (noise level M1, M2) generated by the converter232ato each of recording modes (e.g., mode A, mode B) of the sound recording device1A in accordance with a designation signal whose input has been received by the operating device24and record them in the Flash memory25. Thus, even when a different load is applied to the sound processing unit23depending on a different mode and a power fluctuation is different, noise may be reduced in an optimal way for each mode.

Furthermore, according to the second embodiment of the disclosure, the amplification factor of the amplifier unit231aand the first amplitude information generated by the converter232amay be recorded in a related manner in the Flash memory25. Specifically, as illustrated by a curved line L2inFIG. 15, the control unit31may record the amplification factor of the amplifier unit231aand the first amplitude information generated by the converter232ain a related manner in the Flash memory25. This allows a reduction in noise in an optimal way for each gain.

Furthermore, according to the second embodiment of the disclosure, the first amplitude information generated by the converter232a, the temperature detected by the temperature detecting unit29, the amplification factor of the amplifier unit231a, and multiple recording modes executable by the sound recording device1A may be recorded in a related manner in the Flash memory25. Specifically, as illustrated inFIG. 16, the control unit31records the first amplitude information generated by the converter232a, the temperature detected by the temperature detecting unit29, the amplification factor of the amplifier unit231a, and multiple modes executable by the sound recording device1A in a related manner in the Flash memory25. This allows a reduction in noise in accordance with various conditions.

Other Embodiments

Furthermore, the noise reduction apparatus according to the disclosure is applicable to digital still cameras, digital video cameras, mobile phones having a capturing function, tablet-type electronic devices having a capturing function, medical systems that generate image data for medical and industrial fields, captured by a headphone, endoscope, or microscope, and the like, as well as sound recording devices.

Furthermore, a program executed by the noise reduction apparatus according to the disclosure is provided by being recorded, in the form of file data that is installable and executable, in a recording medium readable by a computer, such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk), a USB medium, or a flash memory.

Furthermore, for explanations of the flowchart and the timing chart in this description, a sequential order of operations at the respective steps is indicated by using terms such as “first”, “next”, and “then”; however, the sequential order of an operation necessary to implement the disclosure is not uniquely defined by using those terms. That is, the order of operations in the flowchart and the timing chart described in this description may be changed to such a degree that there is no contradiction.

Furthermore, the disclosure is not limited to the above-described embodiment as it is, and at the embodiment phase, components may be modified and embodied without departing from the scope of the disclosure. Further, the components disclosed in the above-described embodiment may be combined as appropriate to form various disclosures. For example, some components may be deleted from the entire components described in the above-described embodiment. Furthermore, the components described in each embodiment may be combined as appropriate.

Furthermore, in the description and drawings, if a term is described together with a different term having a broader meaning or the same meaning at least once, it may be replaced with the different term in any part of the description or drawings. Thus, various modifications and applications are possible without departing from the scope of the disclosure.

Thus, the disclosure may include various embodiments not described here, and various design changes, and the like, may be made within the range of technical ideas specified in claims.

According to the disclosure, there is an advantage such that it is possible to reduce self-noise that occurs in a device.