Signal processing system, signal processing method, and signal processing program

Abstract

The present invention provides a signal-processing system comprising: an adaptive decimation filter device having a decimation filter that outputs an output signal obtained by down-sampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter on the basis of the input signal characteristics; and a signal-processing device that performs signal processing according to the adjustment signal for the output signal of the decimation filter.

Description

[Technical Field]

[0001] The present invention relates to a signal processing system, a signal processing method, and a signal processing program. [Background technology]

[0002] Patent Document 1 discloses a scalable FIR (Finite Impulse Response) filter architecture. It states that this filter architecture is scalable to accommodate different complexities, and that the filter can be scaled up or down by adding or removing processing blocks from an existing configuration (column 3, lines 39-53).

[0003] Patent Document 2 discloses an active noise canceller that performs feedforward and feedback control (column 2, lines 6-20). The active noise canceller of Patent Document 2 minimizes latency by operating at an oversampling data rate (384 KHz) without using a decimation filter (column 2, lines 21-53).

[0004] Patent Document 3 discloses an ANC (active noise control) system 300. The ANC system 300 generates an anti-noise signal 324 from signals 316 and 338 detected by a sensor 314, which may be an accelerometer or vibration monitor configured to generate a signal based on engine noise, and a microphone 336 that detects sound waves in or near a target space 310 (column 5, line 25 to column 6, line 41).

[0005] Patent Document 4 states, "MFB (Motional Feedback) has long been known in the field of acoustics. MFB is a technology that detects the movement of the diaphragm in a speaker unit and applies negative feedback to the input audio signal, thereby controlling the movement of the diaphragm of the speaker unit and the input audio signal, for example, so that they move in the same way." (paragraph 0002), and also states, "In the present invention, for example, by switching the combination of feedback methods to be turned on, it is possible to select reproduced sounds that sound different depending on how MFB is applied. Furthermore, in response to this, the frequency characteristics of the reproduced sounds are corrected so that they are appropriate for the combination of feedback methods to be turned on. In other words, it is possible to provide optimal frequency characteristics for each combination of feedback methods to be turned on, and the quality of the reproduced sounds is maintained." (paragraph 0007). [Prior art document] [Patent Documents] [Patent Document 1] U.S. Patent No. 6,260,053 [Patent Document 2] U.S. Patent No. 9,082,392 [Patent Document 3] U.S. Patent No. 8,718,289 [Patent Document 4] Patent No. 5321263 Publication General Disclosure

[0006] A first aspect of the present invention provides a signal processing system that may include an adaptive decimation filter device having a decimation filter that outputs an output signal obtained by downsampling an input signal and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on characteristics of the input signal, and a signal processing device that performs signal processing on the output signal of the decimation filter in accordance with the adjustment signal.

[0007] The signal processing system may include an AD converter that converts an analog input signal into a digital input signal and supplies the digital input signal to the adaptive decimation filter device.

[0008] In any of the signal processing systems described above, the AD converter may convert an analog input signal containing a noise component into a digital input signal, and the signal processing device may adjust the phase of the output signal of the decimation filter in accordance with the adjustment signal and generate a noise canceling signal for reducing the noise component.

[0009] In any of the above signal processing systems, the signal processing device may include an adaptive filter section that performs filtering on the output signal of the decimation filter in accordance with the adjustment signal.

[0010] In any of the above signal processing systems, the adaptive filter section may select, in accordance with the adjustment signal, a filter that performs filtering to offset a change in delay time of the decimation filter that accompanies adjustment of the order.

[0011] In any of the above signal processing systems, the filter control unit may adjust the order of the decimation filter in accordance with the magnitude of a component to be inspected in the input signal, the component having at least a part of a frequency equal to or higher than the Nyquist frequency of the output signal of the decimation filter.

[0012] In any of the above signal processing systems, the filter control unit may set a first filter characteristic to the decimation filter when the magnitude of the component to be inspected is greater than a predetermined reference value, and may set a second filter characteristic, the order of which is smaller than that of the first filter characteristic, to the decimation filter when the magnitude of the component to be inspected is equal to or smaller than the reference value.

[0013] In any of the above signal processing systems, the filter control unit may set the second filter characteristic to the decimation filter when the magnitude of the component to be inspected is greater than a predetermined reference value, and may set the first filter characteristic, the order of which is greater than the second filter characteristic, to the decimation filter when the magnitude of the component to be inspected is equal to or less than the reference value.

[0014] In any of the above signal processing systems, the filter control unit may include a noise detection unit that detects signal levels of at least some frequencies equal to or higher than the Nyquist frequency in the input signal, and a filter characteristics determination unit that determines the order of a filter to be set in the decimation filter based on the signal levels detected by the noise detection unit.

[0015] In any of the signal processing systems described above, the filter control unit includes a noise detection unit that detects a signal level of at least a part of frequencies equal to or higher than the Nyquist frequency in the input signal, a signal detection unit that detects a signal level of at least a part of frequencies lower than the Nyquist frequency in the input signal, and a filter control unit that detects the signal level detected by the noise detection unit. signal The digital signal processing device may further include a filter characteristics determining section that determines the order of a filter to be set in the decimation filter based on the signal level detected by the detecting section.

[0016] In any of the above signal processing systems, the signal processing device may input the output signal of the decimation filter and the adjustment signal within an output cycle period of the signal processing device, perform signal processing according to the input output signal of the decimation filter and the adjustment signal, and output a signal generated by the signal processing.

[0017] A second aspect of the present invention provides a signal processing method, which may include: a decimation filter outputting an output signal obtained by downsampling an input signal; a filter control unit outputting an adjustment signal that adjusts the order of the decimation filter based on characteristics of the input signal; and a signal processing device performing signal processing on the output signal of the decimation filter in accordance with the adjustment signal.

[0018] In a third aspect of the present invention, there is provided a signal processing program executed by a computer. The signal processing program may cause a computer to function as an adaptive decimation filter device having a decimation filter that outputs an output signal obtained by downsampling an input signal and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on characteristics of the input signal, and as a signal processing device that performs signal processing on the output signal of the decimation filter in accordance with the adjustment signal.

[0019] The above summary of the invention does not list all of the features of the present invention, and subcombinations of these features may also be inventions. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows the configuration of a signal processing system 10 according to this embodiment. [Figure 2] 1 shows the configuration of an adaptive filter device 30 according to this embodiment. [Figure 3] 2 shows the configuration of a decimation filter 200 according to the present embodiment. [Figure 4] 1 shows an example of aliasing caused by downsampling. [Figure 5] 2 shows an example of the filter characteristics of the decimation filter 200 according to this embodiment. [Figure 6] 2 shows the configuration of a filter control section 210 according to the present embodiment. [Figure 7] 6 shows the configuration of a noise detection unit 620 according to this embodiment. [Figure 8] 2 shows an operation flow of the adaptive filter device 30 according to the present embodiment. [Figure 9] 6 shows the operation of the filter characteristic determination unit 660 according to this embodiment. [Figure 10] 1 shows the configuration of a noise detection unit 1020 according to a first modified example of this embodiment. [Figure 11] 11 shows the configuration of a filter control section 1110 according to a second modified example of this embodiment. [Figure 12] 11 shows the configuration of a signal detection unit 1140 according to a second modification of this embodiment. [Figure 13] 10 shows an operation flow of the adaptive filter device 30 according to a second modified example of the present embodiment. [Figure 14] 14 shows the configuration of a filter characteristic determination section 1460 according to a third modified example of this embodiment. [Figure 15] 15 shows the configuration of a filter characteristics determination section 1560 according to a fourth modified example of this embodiment. [Figure 16] 10 shows an example of hysteresis given to a filter code in a fourth modified example of the present embodiment. [Figure 17] 17 shows the configuration of a signal processing system 1700 according to a fifth modified example of this embodiment. [Figure 18] 18 shows the configuration of an adaptive decimation filter 1830 according to a sixth modification of this embodiment. [Figure 19] 18 shows the configuration of an aliasing noise detection unit 1810 according to a sixth modified example of this embodiment. [Figure 20] 19 shows the configuration of an aliasing noise level determination unit 1960 according to a sixth modified example of this embodiment. [Figure 21] 13 shows an example of filter / noise level information according to a sixth modified example of the present embodiment. [Figure 22] 13 shows the configuration of a signal processing system 2100 according to a seventh modification of this embodiment. [Figure 23] 13 shows a configuration of an adaptive decimation filter device 2130 according to a seventh modification of this embodiment. [Figure 24] 13 shows an example of a filter code according to a seventh modified example of the present embodiment. [Figure 25] 13 shows the configuration of an adaptive filter unit 2150 according to a seventh modification of this embodiment. [Figure 26] 13 shows an operation flow of a signal processing system 2100 according to a seventh modification of the present embodiment. [Figure 27] 27 shows the configuration of a signal processing system 2700 according to an eighth modification of this embodiment. [Figure 28]A first example of data to be encoded by the data encoder 2735 is shown. [Figure 29] A second example of data to be encoded by the data encoder 2735 is shown. [Figure 30] 27 shows a third example of data encoded by the data encoder 2735. [Figure 31] 13 shows the configuration of a signal processing system 3100 according to a ninth modification of this embodiment. [Figure 32] A first example of data to be encoded by the data encoder 3135 is shown. [Figure 33] 3 shows a second example of data encoded by the data encoder 3135. [Figure 34] A third example of data encoded by the data encoder 3135 is shown. [Figure 35] 16 shows the configuration of an ANC system 3500 according to a tenth modification of the present embodiment. [Figure 36] 16 shows the configuration of an MFB system 3600 according to an eleventh modification of the present embodiment. [Figure 37] 13 shows a modification of a signal processing system 2100 according to a seventh modification of the present embodiment. [Figure 38] 22 illustrates an example computer 2200 in which aspects of the present invention may be embodied, in whole or in part. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention as claimed. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0022] 1 shows the configuration of a signal processing system 10 according to this embodiment. The signal processing system 10 receives an analog signal, performs signal processing, and outputs the result of the signal processing. As an example, the signal processing system 10 is a noise canceller that receives an analog signal corresponding to noise reaching an audio listener or vibrations of a noise source, performs signal processing, and outputs a noise canceling signal for suppressing the noise. Alternatively, the signal processing system 10 may be a device that receives an analog signal and performs any signal processing.

[0023] The signal processing system 10 includes an AD (Analog-Digital) converter 20, an adaptive filter device 30, and a signal processing device 40. The AD converter 20 converts an analog input signal into a digital signal at each AD conversion period according to an AD conversion frequency. The AD converter 20 outputs the digitally converted input signal to the adaptive filter device 30 as a filter input signal.

[0024] The adaptive filter device 30 is connected to the AD converter 20. The adaptive filter device 30 receives a filter input signal, performs filtering, and outputs the result as a filter output signal. Here, the adaptive filter device 30 performs adaptive filtering that changes the characteristics of the filtering process in accordance with the characteristics of the filter input signal.

[0025] The signal processing device 40 is connected to the adaptive filter device 30. The signal processing device 40 receives a filter output signal from the adaptive filter device 30. The signal processing device 40 performs signal processing on the filter output signal and outputs the signal processing result. The signal processing device 40 may be a computer including a signal processing processor such as a DSP (Digital Signal Processor) or a microcontroller. The signal processing device 40 may also be a computer such as a PC (Personal Computer), a tablet computer, a smartphone, a workstation, a server computer, or a general-purpose computer, or may be a computer system in which multiple computers are connected. Such a computer system is also a computer in a broad sense. The signal processing device 40 performs signal processing on the filter output signal by executing a signal processing program on such a computer.

[0026] 2 shows the configuration of an adaptive filter device 30 according to this embodiment. The adaptive filter device 30 downsamples a filter input signal and outputs it as a filter output signal. For ease of explanation, the filter input signal will be abbreviated as the "input signal" and the filter output signal will be abbreviated as the "output signal" below. The adaptive filter device 30 includes a decimation filter 200 and a filter control unit 210.

[0027] The decimation filter 200 outputs an output signal obtained by downsampling an input signal. The filter control unit 210 changes the characteristics of the decimation filter 200 based on the characteristics of the input signal. More specifically, the filter control unit 210 determines the characteristics of the filter processing to be applied to the input signal based on the characteristics of the input signal, and outputs filter identification information that identifies the determined characteristics of the filter processing to the decimation filter 200. In this embodiment, the filter control unit 210 outputs a filter code that identifies, by code, the filter characteristics to be applied to the input signal, as an example of the filter identification information.

[0028] In this embodiment, the filter control unit 210 adjusts the order of the decimation filter 200 based on the characteristics of the input signal. As a result, the filter control unit 210 adjusts the filter characteristics (pass band, stop band, filter steepness determined by the pass band and stop band, attenuation of the stop band, etc.) of adjustment target components of the input signal that have at least some frequencies equal to or higher than the Nyquist frequency of the output signal in the decimation filter 200. Here, the decimation filter 200 may treat all frequencies of the input signal equal to or higher than the Nyquist frequency of the output signal as adjustment target components, or may treat only some frequencies as adjustment target components.

[0029] 3 shows the configuration of a decimation filter 200 according to this embodiment. The decimation filter 200 may be dedicated hardware implemented using a dedicated circuit, or may be implemented at least in part by executing a filter program on a computer. In this embodiment, the decimation filter 200 is, for example, an FIR (Finite Impulse Response) filter, but an IIR (Infinite Impulse Response) filter may also be used. The decimation filter 200 includes a plurality of delay elements 300-2 to 300-N (N is an integer equal to or greater than 2), a plurality of thinning elements 310-1 to 310-N, a plurality of multipliers 320-1 to 320-N, a plurality of adders 330-2 to 330-N, a filter coefficient storage unit 340, and a selector 350.

[0030] The plurality of delay elements 300-2 to 300-N (also referred to as delay elements 300) are connected in series in this order. The first delay element 300-2 receives an input signal every AD conversion cycle, delays it by one AD conversion cycle, and outputs it to the next delay element 300-3. Similarly, the delay elements 300-3 to 300-N delay the received input signal by one AD conversion cycle and outputs it to the delay element 300 in the next stage.

[0031] The plurality of decimation elements 310-1 to 310-N (also referred to as decimation elements 310) decimate the input signal from the AD converter 20 and the delayed input signals output by the respective delay elements 300-2 to 300-N by a factor of m. That is, the decimation element 310-1 decimates the input signal from the AD converter 20 and outputs the result. Each of the decimation elements 310-2 to 310-N decimates the delayed input signal from the corresponding delay element 300 among the delay elements 300-2 to 300-N and outputs the result. Here, each decimation element 310 decimates the input signal by outputting the received input signal every m AD conversion periods.

[0032] The plurality of multipliers 320-1 to 320-N (also referred to as multipliers 320) multiply each of the plurality of signals received from the plurality of thinning elements 310-1 to 310-N by each of the plurality of filter coefficients received from the filter coefficient storage unit 340. The plurality of adders 330-2 to 330-N supply the sum of the outputs of the plurality of multipliers 320-1 to 320-N to the selector 350. In addition, the plurality of adders 330-2 to 330-M (M is a positive integer smaller than N) supply the sum of the outputs of the plurality of multipliers 320-1 to 320-M to the selector 350.

[0033] The filter coefficient storage unit 340 supplies filter coefficients corresponding to the filter identification information (filter code) received from the filter control unit 210 to the multiple multipliers 320-1 to 320-N. In this embodiment, when the filter code instructs to set a first filter characteristic, the filter coefficient storage unit 340 supplies the multiple filter coefficients corresponding to the first filter characteristic to the multiple multipliers 320-1 to 320-N. When the filter code instructs to set a second filter characteristic, the filter coefficient storage unit 340 supplies the multiple filter coefficients corresponding to the second filter characteristic to the multiple multipliers 320-1 to 320-N.

[0034] The selector 350 changes the order of the decimation filter 200 in accordance with the filter identification information (filter code) received from the filter control unit 210. In this embodiment, the selector 350 selects the sum of the outputs of the multiple multipliers 320-1 to 320-N as the output signal in response to receiving a filter code instructing the setting of the first filter characteristic. Furthermore, the selector 350 selects the sum of the outputs of the multiple multipliers 320-1 to 320-M as the output signal in response to receiving a filter code instructing the setting of the second filter characteristic. In this way, the decimation filter 200 reduces the filter order in response to the setting of the second filter characteristic compared to when the first filter characteristic is set. Accordingly, the decimation filter 200 shortens the delay time in response to the setting of the second filter characteristic compared to when the first filter characteristic is set.

[0035] 4 shows an example of aliasing caused by downsampling. This figure shows aliasing that occurs in the output signal of decimation filter 200 using a graph with frequency on the horizontal axis and signal strength on the vertical axis.

[0036] In this diagram, "fs" indicates the frequency (sampling frequency) of the output signal output by the decimation filter 200. The frequency (AD conversion frequency) of the input signal supplied from the AD converter 20 to the decimation filter 200 is higher than the sampling frequency. The decimation filter 200 downsamples the input signal having the AD conversion frequency to lower the frequency and outputs it as an output signal having the sampling frequency. For example, in the case of noise cancellation, the AD conversion frequency may be approximately 200 KHz, and the sampling frequency fs may be approximately 2 KHz.

[0037] Since the sampling frequency of the output signal is fs, decimation filter 200 can, according to the sampling theorem, reproducibly output signal components below the Nyquist frequency fs / 2, which is half the sampling frequency fs of the input signal. However, if the input signal is simply decimated using a decimation filter, signal components above the Nyquist frequency fs / 2 (e.g., signal 400 in the figure) will be aliased back into the frequency domain below the Nyquist frequency fs / 2 due to aliasing and will be included in the output signal as aliasing (e.g., aliasing 410 in the figure).

[0038] Therefore, when downsampling an input signal, in addition to decimating the input signal, low-pass filtering is performed to remove or attenuate frequency components above a cutoff frequency in the input signal and pass frequency components below the cutoff frequency. This type of downsampling of an input signal is called "decimation." Here, this cutoff frequency is usually the Nyquist frequency, fs / 2, but it can also be a frequency lower than the Nyquist frequency, fs / 2.

[0039] Theoretically, decimation involves low-pass filtering an input signal at its frequency (i.e., the AD conversion frequency), and then reducing the frequency of the output signal to the sampling frequency by decimation. The decimation filter 200 shown in Fig. 3 is configured to perform equivalent conversion of such decimation processing using the Noble identity transformation so that decimation is performed first.

[0040] 5 shows an example of the filter characteristics of the decimation filter 200 according to this embodiment. The horizontal axis of this diagram shows the frequency obtained by normalizing the sampling frequency of the output signal to 1, and the vertical axis shows the signal amplification factor in decibels (dB).

[0041] The characteristics of the decimation filter 200 vary depending on the order of the decimation filter 200. When the first filter characteristic 500 is set, the decimation filter 200 has an order of N, whereas when the second filter characteristic 510 is set, the decimation filter 200 has an order of M, which is smaller than N. When the first filter characteristic 500 is set, the decimation filter 200 has a larger order and therefore a larger delay, but can attenuate more of the adjustment-targeted components of the input signal that are equal to or higher than the Nyquist frequency. When the second filter characteristic 510 is set, the decimation filter 200 has a smaller order and therefore a smaller delay, but can attenuate less of the adjustment-targeted components of the input signal that are equal to or higher than the Nyquist frequency, making it more likely that the adjustment-targeted components will remain in the output signal. Thus, there is a trade-off between the delay of the decimation filter 200 and the attenuation of the adjustment-targeted components.

[0042] Here, the "attenuation amount" of the adjustment target component in the input signal refers to the reciprocal of the gain of decimation filter 200 for the adjustment target component. First filter characteristic 500 in the figure has an attenuation amount of approximately 60 dB because the gain of the adjustment target component above the Nyquist frequency is approximately -60 dB. Second filter characteristic 510 has an attenuation amount of approximately 20 dB because the gain of the adjustment target component above the Nyquist frequency is approximately -20 dB. The attenuation amount of the adjustment target component may be the attenuation amount corresponding to the maximum gain within the frequency range that includes the adjustment target component, i.e., the minimum attenuation amount.

[0043] 6 shows the configuration of the filter control section 210 according to this embodiment. The filter control section 210 includes a noise detection section 620 and a filter characteristics determination section 660.

[0044] The noise detection unit 620 detects the signal level of at least some frequencies equal to or higher than the Nyquist frequency in the input signal. Here, the frequency components having at least some frequencies equal to or higher than the Nyquist frequency in the input signal detected by the noise detection unit 620 are referred to as the "test target component." As shown in FIG. 4, the test target component can become noise that is superimposed on the output signal due to aliasing after decimation by the decimation filter 200. The noise detection unit 620 outputs noise level information indicating the signal level (magnitude) of the test target component. In this embodiment, the noise detection unit 620 outputs, as an example of the noise level information, a level code obtained by normalizing the signal level of the test target component to a value between 0 and 1.

[0045] The filter characteristics determination unit 660 is connected to the noise detection unit 620 and receives a level code as an example of noise level information. The filter characteristics determination unit 660 determines the filter characteristics to be set in the decimation filter 200 based on the signal level of the component to be inspected detected by the noise detection unit 620. The filter characteristics determination unit 660 may adjust the order of the decimation filter 200 according to the signal level of the component to be inspected. The filter characteristics determination unit 660 outputs a filter code as an example of filter identification information according to the determined filter characteristics.

[0046] 7 shows the configuration of the noise detection unit 620 according to this embodiment. The noise detection unit 620 includes an HPF 730 and a noise level output unit 750. The high-pass filter (HPF) 730 attenuates signal components in the input signal that are in a frequency band below the Nyquist frequency of the output signal, and passes signal components in a frequency band equal to or higher than the Nyquist frequency of the output signal. That is, the HPF 730 according to this embodiment determines signal components in the frequency band equal to or higher than the Nyquist frequency of the output signal as components to be inspected, and passes the components to be inspected.

[0047] The noise level output section 750 outputs, as noise level information, the signal level of the signal output by the HPF 730. For example, the noise level output section 750 outputs a signal level corresponding to at least one of a peak value, an absolute value, an average value, an average value of peak values, or an average value of absolute values. Here, the noise level output section 750 may calculate, as the peak value or average value, the peak value or average value of the signal output by the HPF 730 over the most recent period of a predetermined length.

[0048] The frequency bands of the component to be inspected and the component to be adjusted may be determined appropriately depending on the application of the adaptive filter device 30. The frequency band of the component to be adjusted may be the same as the frequency band of the component to be inspected, may overlap only partially, or may be different. For example, the adaptive filter device 30 may set the component to be inspected as a signal component in a frequency band equal to or higher than the Nyquist frequency of the output signal, and set signal components in the same frequency band as the components to be adjusted. Furthermore, the adaptive filter device 30 may set a part of the component to be inspected as the component to be adjusted, or may set signal components in a wider frequency band including the component to be inspected as the component to be adjusted. For example, the adaptive filter device 30 may set the component to be inspected as the entire frequency band equal to or higher than the Nyquist frequency of the output signal, and set Zhou While the signal components are in the wavenumber band, only a portion of the frequency band equal to or higher than the Nyquist frequency of the output signal may be set as the adjustment target components.

[0049] 8 shows an operation flow of the adaptive filter device 30 according to this embodiment. In step S800, the adaptive filter device 30 acquires an input signal (filter input signal) from the AD converter 20. In S810, the noise detection unit 620 in the filter control unit 210 detects the signal level of at least some frequencies equal to or higher than the Nyquist frequency in the input signal. Here, the HPF 730 in the noise detection unit 620 may attenuate signal components in the input signal in a frequency band lower than the Nyquist frequency of the output signal, and the noise level output unit 750 in the noise detection unit 620 may output the signal level of the signal output by the HPF 730 as noise level information. In this way, the noise detection unit 620 can extract noise components equal to or higher than the Nyquist frequency that fold back into the frequency domain lower than the Nyquist frequency in the output signal and measure them as the noise level.

[0050] In S820, the filter characteristics determination unit 660 determines the filter characteristics to be set in the decimation filter 200 based on the signal level of the component to be inspected detected by the noise detection unit 620. The filter characteristics determination unit 660 may determine the filter characteristics so that the order of the decimation filter 200 is increased when the signal level of the component to be inspected is greater. In this way, the filter characteristics determination unit 660 maintains a greater amount of attenuation of the component to be adjusted by the decimation filter 200. Furthermore, the filter characteristics determination unit 660 may determine the filter characteristics so that the order of the decimation filter 200 is decreased when the signal level of the component to be inspected is smaller. In this way, the filter characteristics determination unit 660 can shorten the delay time of the decimation filter 200 in exchange for reducing the amount of attenuation of the component to be adjusted by the decimation filter 200.

[0051] The filter characteristics determination unit 660 may determine the filter characteristics in accordance with the magnitude of the signal level of the component to be inspected in the reverse order. inspectionWhen the signal level of the target component is higher, the filter characteristics are determined so that the order of the decimation filter 200 is reduced, thereby shortening the delay time of the decimation filter 200; inspection The delay time of the decimation filter 200 may be increased by determining the filter characteristics so that the order of the decimation filter 200 is increased when the signal level of the target component is smaller.

[0052] Here, the adjustment target component may be all frequency components equal to or greater than the Nyquist frequency. Alternatively, the adjustment target component may be signal components in a portion of the frequency band equal to or greater than the Nyquist frequency. For example, the adjustment target component may be signal components in a frequency band that aliases to a frequency band below the Nyquist frequency, where the influence of noise becomes significant (e.g., a frequency band from 2,000 Hz to 4,000 Hz, where human hearing is sensitive).

[0053] In S830, the filter characteristics determination unit 660 sets the determined filter characteristics in the decimation filter 200. This allows the filter characteristics determination unit 660 to adjust the order of the decimation filter 200 and the attenuation of the adjustment target component according to the signal level (noise level) of the test target component detected by the noise detection unit 620. When the level of noise aliasing at frequencies below the Nyquist frequency is high, the filter characteristics determination unit 660 increases the attenuation of the adjustment target component in the input signal to reduce the noise. When the level of noise aliasing at frequencies below the Nyquist frequency is low, the filter characteristics determination unit 660 decreases the attenuation of the adjustment target component in the input signal to reduce the noise attenuation and suppress the filter strength of the decimation filter 200. Note that the control by the filter characteristics determination unit 660 regarding the level of noise aliasing at frequencies below the Nyquist frequency can also reverse the relationship between the increase and decrease in attenuation and the magnitude of the noise level.

[0054] Here, the filter characteristics determination unit 660 may detect zero-crossing timings at which the filter input signal switches between positive and negative, and change the filter characteristics in accordance with the zero-crossing timings. Furthermore, the filter characteristics determination unit 660 may change the filter characteristics of the decimation filter 200 in stages from the current filter characteristics to target filter characteristics. This allows the filter characteristics determination unit 660 to suppress unnatural sounds that occur in audio signals, such as noise canceling signals, generated in accordance with the signal processing results of the output signal.

[0055] In S840, the adaptive filter device 30 downsamples the input signal using the decimation filter 200 whose filter characteristics have been set by the filter characteristics determination unit 660. When filter characteristics that increase the filter order are set, the decimation filter 200 increases the attenuation of the adjustment target component to achieve the target attenuation. When filter characteristics that decrease the filter order are set, the decimation filter 200 can reduce the attenuation of the adjustment target component within the target attenuation range.

[0056] 9 shows the operation of the filter characteristic determination unit 660 according to this embodiment. In this embodiment, the filter characteristic determination unit 660 in the filter control unit 210 determines the first filter characteristic ("Filter 1" in the figure) or the second filter characteristic ("Filter 2" in the figure) in accordance with the level code representing the noise level information output by the noise detection unit 620. ) The filter code that sets the filter coefficient is supplied to the decimation filter 200.

[0057] When the noise level (the signal level of the component to be inspected detected by the noise detector 620) is greater than a predetermined reference, the filter characteristic determination unit 660 sets the first filter characteristic in the decimation filter 200. In the example of this figure, when the noise level output by the noise detector 620 is greater than 0.5, the filter characteristic determination unit 660 supplies a filter code for setting the first filter characteristic with an attenuation amount of 60 dB (attenuated to 1 / 1000) of the component to be adjusted to the decimation filter 200. Thereby, the decimation filter 200 shown in FIG. 3 is set to the first filter characteristic by the filter coefficients stored in the filter coefficient storage unit 340, and the order becomes N.

[0058] On the other hand, when the noise level is below this reference, the filter characteristic determination unit 660 sets the second filter characteristic with an attenuation amount of the component to be adjusted smaller than the first filter characteristic in the decimation filter 200. In the example of this figure, when the noise level output by the noise detector 620 is smaller than 0.5, the filter characteristic determination unit 660 sets the second filter characteristic with an attenuation amount of 20 dB (attenuated to 1 / 10) of the component to be adjusted to the decimation filter 200. Thereby, the decimation filter 200 shown in FIG. 3 is set to the second filter characteristic by the filter coefficients stored in the filter coefficient storage unit 340, and the order becomes M (M < N). Note that the filter characteristic determination unit 660 may select the second filter characteristic with a smaller attenuation amount and a smaller delay amount when the noise level is greater than the reference value, contrary to the setting in FIG. 9, and select the first filter characteristic with a larger attenuation amount and a larger delay amount when the noise level is smaller than the reference value.

[0059] The adaptive filter device 30 described above can adjust the order of the decimation filter 200 and the attenuation of the adjustment target component by changing the filter characteristics of the decimation filter 200 in accordance with the signal level of the test target component, which indicates the noise level in the input signal. As a result, when the noise level is low, the adaptive filter device 30 can reduce the attenuation of the adjustment target component and reduce the delay of the decimation filter 200. In this case, the adaptive filter device 30 can supply the decimated input signal to the downstream signal processing device 40 more quickly, thereby ensuring a longer processing time for the signal processing device 40 in signal processing that requires real-time performance, such as noise canceling or distortion correction for speaker vibration.

[0060] Conversely, when the noise level is high, the adaptive filter device 30 can reduce the attenuation of the adjustment target component to reduce the delay of the decimation filter 200. In this case, when the noise level is high, the adaptive filter device 30 can supply the decimated input signal to the downstream signal processing device 40 more quickly, allowing the downstream signal processing device 40 sufficient processing time to generate a noise canceling signal with a phase difference of 180 degrees from the input. In this case, when the noise level is low, the supply of the decimated input signal to the downstream signal processing device 40 is delayed, resulting in a decrease in the noise canceling performance of the downstream signal processing device 40. Overall, the signal processing system 10 can reduce noise fluctuations caused by environmental changes by improving noise canceling performance when the noise level is high and decreasing noise canceling performance when the noise level is low.

[0061] The adaptive filter device 30 according to this embodiment adjusts the filter characteristics of the decimation filter 200 in two stages depending on the noise level. Alternatively, the filter characteristics of the decimation filter 200 may be adjusted in three or more stages depending on the noise level.

[0062] 10 shows the configuration of a noise detection unit 1020 according to a first modification of this embodiment. In this modification, the adaptive filter device 30 has a noise detection unit 1020 instead of the noise detection unit 620. The functions and configurations of the other blocks in the adaptive filter device 30 are the same as those shown in relation to FIGS. 1 to 9, and therefore, explanations will be omitted below except for the differences.

[0063] The noise detection unit 1020 includes a BPF 1030 and a noise level output unit 1050. The bandpass filter (BPF) 1030 attenuates signal components in the input signal other than those in a certain frequency band equal to or higher than the Nyquist frequency, and passes the signal components in this certain frequency band. That is, the BPF 1030 according to this embodiment determines signal components in a certain frequency band equal to or higher than the Nyquist frequency of the output signal as components to be inspected, and passes the components to be inspected.

[0064] The noise level output unit 1050 outputs, as noise level information, the signal level of the signal output by the BPF 1030. For example, the noise level output unit 1050 outputs a signal level corresponding to at least one of a peak value, an absolute value, an average value, an average value of peak values, or an average value of absolute values. Here, the noise level output unit 1050 may calculate, as the peak value or average value, the peak value or average value of the signal output by the BPF 1030 over the most recent period of a predetermined length.

[0065] In this modification, noise detection unit 1020 detects the noise level of only signal components in a certain frequency band among signal components in the input signal that are equal to or higher than the Nyquist frequency. This allows noise detection unit 1020 to adjust the filter characteristics of decimation filter 200 according to the noise level in a frequency band where the influence of noise becomes noticeable when the output signal is folded back below the Nyquist frequency (for example, a frequency band around 1 kHz where human hearing is sensitive).

[0066] The frequency bands of the test component and the adjustment component may be determined appropriately depending on the application of the adaptive filter device 30. The frequency band of the adjustment component may be the same as, partially overlap with, or different from the frequency band of the test component. For example, the adaptive filter device 30 may set the test component to signal components in only a portion of the frequency band equal to or higher than the Nyquist frequency of the output signal, and set signal components in the same frequency band as the adjustment target components. Alternatively, the adaptive filter device 30 may set a portion of the test component to signal components for adjustment, or signal components in a wider frequency band including the test component to signal components for adjustment. For example, the adaptive filter device 30 may set the test component to signal components in only a portion of the frequency band equal to or higher than the Nyquist frequency of the output signal, and set the entire frequency band equal to or higher than the Nyquist frequency of the output signal as the adjustment target components.

[0067] Fig. 11 shows the configuration of a filter control unit 1110 according to a second modified example of this embodiment. Filter control unit 1110 is a modified example of filter control unit 210 shown in relation to Fig. 6. In the following, explanations of blocks in filter control unit 1110 that have the same functions and configurations as filter control unit 210 will be omitted except for the differences.

[0068] The filter control section 1110 has a noise detection section 620, a signal detection section 1140, and a filter characteristics determination section 1160. The noise detection section 620 has the same function and configuration as the noise detection section 620 in FIG.

[0069] The signal detection unit 1140 detects, in the input signal, the original signal component that is to be subjected to signal processing by the signal processing device 40. More specifically, the signal detection unit 1140 detects the signal level of the signal component (hereinafter also referred to as the "main signal") of at least some frequencies that are lower than the Nyquist frequency in the input signal.

[0070] The filter characteristic determination unit 1160 is connected to the noise detection unit 620 and the signal detection unit 1140. The filter characteristic determination unit 1160 determines the filter characteristics to be set in the decimation filter 200 based on the signal level detected by the signal detection unit 1140 and the noise level detected by the noise detection unit 620.

[0071] 12 shows the configuration of a signal detection section 1140 according to a second modification of this embodiment. The signal detection section 1140 includes an LPF 1230 and a signal level output section 1250.

[0072] The LPF 1230 attenuates signal components of frequencies equal to or higher than the Nyquist frequency in the input signal and passes signal components of the output signal in a frequency band below the Nyquist frequency. That is, the LPF 1230 according to this embodiment regards signal components of the output signal in a frequency band below the Nyquist frequency as the main signal of the signal processing device 40 and passes the signal components of the main signal.

[0073] The signal level output unit 1250 is connected to the LPF 1230. The signal level output unit 1250 outputs a signal level corresponding to the input signal that has passed through the LPF 1230. The signal level output unit 1250 outputs a signal level code as an example of the signal level corresponding to at least one of the peak value, absolute value, average value, average value of the peak values, and average value of the absolute values ​​of the signal output by the LPF 1230.

[0074] Fig. 13 shows the operation flow of the adaptive filter device 30 according to the second modified example of this embodiment. Since the operation flow in this figure is a modified example of the operation flow shown in Fig. 8, a description thereof will be omitted hereinafter except for the differences.

[0075] S1300 and S1310 are the same as S800 and S810 in Fig. 8. In S1320, signal detection section 1140 in filter control section 1110 detects the signal level of at least some frequencies below the Nyquist frequency in the input signal.

[0076] In S1330, the filter characteristics determination unit 1160 determines the filter characteristics to be set in the decimation filter 200 based on the signal level detected by the signal detection unit 1140 and the noise level detected by the noise detection unit 620. When the signal level detected by the signal detection unit 1140 is higher than the noise level detected by the noise detection unit 620, the filter characteristics determination unit 1160 may determine the order of the decimation filter 200 and filter characteristics that reduce the amount of attenuation of the adjustment target component. For example, the filter characteristics determination unit 1160 may select the second filter characteristics when the ratio obtained by dividing the signal level detected by the signal detection unit 1140 by the noise level detected by the noise detection unit 620 is greater than a predetermined criterion, and may select the first filter characteristics when the ratio is equal to or less than this criterion. Alternatively, the filter characteristics determination unit 1160 may determine the order of the decimation filter 200 based on the noise level detected by the noise detection unit 620 from the signal level detected by the signal detection unit 1140. noise The second filter characteristic may be selected if the difference after subtracting the level is greater than a predetermined criterion, and the first filter characteristic may be selected if the difference is equal to or less than this criterion.

[0077] 8, the filter characteristic determination unit 1160 sets the determined filter characteristic to the decimation filter 200. At S1350, the adaptive filter device 30 downsamples the input signal using the decimation filter 200 whose filter characteristic has been set by the filter characteristic determination unit 1160, similar to S840 in FIG.

[0078] According to the adaptive filter device 30 of the second modification, the filter characteristics of the decimation filter 200 can be adjusted using the signal level of the signal component that is the target of signal processing by the signal processing device 40 (i.e., the signal level of the main signal) in addition to the signal level of the component to be inspected that is equal to or higher than the Nyquist frequency (i.e., the signal level of noise). If the main signal is sufficiently large, the adaptive filter device 30 reduces the order of the decimation filter 200, thereby reducing the attenuation of the component to be adjusted. Even if some aliasing noise occurs below the Nyquist frequency, a sufficient S / N ratio can be ensured in the region below the Nyquist frequency. Therefore, according to the adaptive filter device 30 of the second modification, if the signal component of the main signal is sufficiently large, the attenuation of the component to be adjusted can be reduced, thereby reducing the delay of the decimation filter 200.

[0079] From another perspective, a noise floor below the Nyquist frequency is originally superimposed on the input signal to the adaptive filter device 30. When the signal level output unit 1250 in the signal detection unit 1140 outputs a signal level corresponding to the average value or the average absolute value of the input signal that has passed through the LPF 1230, the signal detection unit 1140 outputs a signal level corresponding to the noise floor. Therefore, the filter characteristics determination unit 1160 can use a threshold value for the allowable amount of aliasing noise based on the magnitude of the noise floor as a criterion for selecting filter characteristics, thereby reducing the attenuation of the adjustment target component and the delay of the decimation filter 200 when the aliasing noise is sufficiently smaller than the noise floor contained in the main signal.

[0080] 14 shows the configuration of a filter characteristics determination unit 1460 according to a third modification of this embodiment. The filter characteristics determination unit 1460 is a modification of the filter characteristics determination unit 660 shown in relation to FIGS. 6 and 9, and therefore description thereof will be omitted hereinafter except for the differences. The filter characteristics determination unit 1460 determines the filter characteristics to be set in the decimation filter 200 based on the noise level detected by the noise detection unit 620. The filter characteristics determination unit 1460 according to this modification outputs a filter code as an example of filter identification information that specifies the filter characteristic to be set in the decimation filter 200 from among two or more filter characteristics, based on the noise level detected by the noise detection unit 620.

[0081] The filter characteristic determination unit 1460 includes a threshold storage unit 1470, a comparison unit 1480, and a decoding unit 1490. The threshold storage unit 1470 stores a plurality of thresholds 1 to X corresponding to boundary values ​​for each filter characteristic in a level code indicating the noise level detected by the noise detection unit 620. Here, X may be a value obtained by subtracting 1 from the number of settable filter characteristics. In this modification, as an example, threshold 1<threshold 2<...<threshold X.

[0082] The comparing unit 1480 is connected to the threshold storage unit 1470. The comparing unit 1480 has X comparators corresponding to each of the multiple thresholds 1 to X. Each comparator compares the level code with the corresponding threshold. In this modification, the xth comparator compares the level code with the xth threshold x, and outputs logic H (high) if the level code is greater than the threshold x, and outputs logic L (low) if the level code is equal to or less than the threshold x.

[0083] The decoding unit 1490 is connected to the comparing unit 1480. The decoding unit 1490 determines the value of a filter code that specifies the filter characteristics to be set in the decimation filter 200, according to the comparison results output by the multiple comparators in the comparing unit 1480. For example, if the first x-1th comparators in the comparing unit 1480 output logic H and the xth and subsequent comparators output logic L, the decoding unit 1490 outputs a filter code that specifies the xth filter characteristic because the level code exceeds threshold value x-1 and is equal to or less than threshold value x. The decoding unit 1490 may be realized by, for example, a priority encoder.

[0084] Here, the decoding unit 1490 outputs a filter code that specifies the order of decimation filter 200 and the filter characteristics that result in a greater amount of attenuation of the adjustment target component as the level code becomes larger (i.e., the noise level becomes larger). As a result, when the noise level is smaller, the decoding unit 1490 can set filter characteristics that result in a smaller amount of attenuation of the adjustment target component to decimation filter 200, and reduce the order of decimation filter 200. Furthermore, when the noise level is larger, the decoding unit 1490 can set filter characteristics that result in a greater order of decimation filter 200 and a greater amount of attenuation of the adjustment target component to decimation filter 200.

[0085] 15 shows the configuration of a filter characteristics determination unit 1560 according to a fourth modification of this embodiment. Since the filter characteristics determination unit 1560 is a modification of the filter characteristics determination unit 1460 shown in relation to FIG. 14, a description thereof will be omitted hereinafter except for the differences. The filter characteristics determination unit 1560 determines the filter characteristics to be set in the decimation filter 200 based on the noise level detected by the noise detection unit 620. The filter characteristics determination unit 1560 according to this modification outputs filter identification information that specifies the filter characteristic to be set in the decimation filter 200 from among two or more filter characteristics based on the noise level detected by the noise detection unit 620.

[0086] The filter characteristics determination unit 1560 according to this modification has hysteresis when switching between filter characteristics. The filter characteristics determination unit 1560 includes a threshold storage unit 1470, a comparison unit 1480, a decoding unit 1590, and a delay element 1595. The threshold storage unit 1470 and the comparison unit 1480 have the same functions and configurations as the threshold storage unit 1470 and the comparison unit 1480 in FIG. 14 .

[0087] The decoding unit 1590 is connected to the comparing unit 1480. The decoding unit 1590 determines the value of a filter code that specifies the filter characteristics to be set in the decimation filter 200, according to the comparison results output by the multiple comparators in the comparing unit 1480. The decoding unit 1590 outputs the comparison results by the comparing unit 1480 and its internal state, which includes the level code received via the comparing unit 1480, to a delay element 1595.

[0088] The delay element 1595 is connected to the decoding unit 1590. The delay element 1595 delays the internal state received from the decoding unit 1590 by one cycle and returns the delayed internal state to the decoding unit 1590. The decoding unit 1590 can provide hysteresis to the filter code switching by determining the value of the filter code using the previous state delayed by the delay element 1595. For example, the decoding unit 1590 may update the filter code and the delay element 1595 in accordance with the comparison results between the level code from the noise detection unit 620 and two thresholds having a difference of a hysteresis width, and the value indicating the current filter code held in the delay element 1595 at the timing when the comparison result of the comparison unit 1480 changes.

[0089] 16 shows an example of hysteresis applied to filter codes in the fourth modified example of this embodiment. In this figure, the horizontal axis represents the level code and the vertical axis represents the filter code, and the filter code determined by the decoding unit 1590 in accordance with the level code is shown.

[0090] In the example shown in the figure, the threshold storage unit 1470 stores two values, thresholds 0.4 and 0.5, with a hysteresis width of 0.1 (denoted as "hysteresis" in the figure) for the boundary between filter codes 1 and 2. The comparison unit 1480 includes two comparators for each filter code boundary and outputs a 2-bit signal representing the comparison result between the level code and each of the two thresholds. If the value held in the delay element 1595 indicates filter code 1, the decoding unit 1590 does not increase the filter code even when the level code increases and exceeds the threshold 0.4. However, when the level code further increases and exceeds the threshold 0.5, the decoding unit 1590 changes the filter code from 1 to 2. In response to this, the delay element 1595 updates the stored filter code from the value indicating filter code 1 to the value indicating filter code 2.

[0091] When the value held in the delay element 1595 is a value indicating filter code 2, the decoding unit 1590 does not decrease the filter code even when the level code decreases to a threshold of 0.5 or less, and changes the filter code from 2 to 1 when the level code further decreases to a threshold of 0.4 or less. In response to this, the delay element 1595 updates the filter code it stores from a value indicating filter code 2 to a value indicating filter code 1. When both the candidate value of the next filter code obtained by comparing the level code with the upper threshold for each boundary and the candidate value of the next filter code obtained by comparing the level code with the lower threshold for each boundary are different from the filter code held in the delay element 1595, the decoding unit 1590 may update the value of the filter code to the candidate value.

[0092] The filter characteristics determination unit 1560 described above can maintain hysteresis when switching the filter characteristics to be set in the decimation filter 200. This allows the filter characteristics determination unit 1560 to prevent the filter characteristics from switching frequently when, for example, the level code is fluctuating around a value close to the boundary of a certain threshold, thereby stabilizing the operation of the adaptive filter device 30.

[0093] 17 shows the configuration of a signal processing system 1700 according to a fifth modification of this embodiment. Since the signal processing system 1700 is a modification of the signal processing system 10 shown in relation to FIGS. 1 to 16, a description thereof will be omitted hereinafter except for the differences. In the signal processing system 1700, instead of determining the filter characteristics according to the input signal within the adaptive filter device 30, a signal processing device 1740 determines the filter characteristics.

[0094] The signal processing system 1700 includes an AD converter 20, an adaptive decimation filter device 1730, and a signal processing device 1740. The AD converter 20 has the same function and configuration as the AD converter 20 in FIG. 1. The adaptive decimation filter device 1730 includes a decimation filter 200 and a noise detection unit 620 in the filter control unit 210. The decimation filter 200 in this modification does not include a selector 350, and supplies filter coefficients included in filter parameters received from the signal processing device 1740 to each thinning element 310. In this modification, the noise detection unit 620 in the adaptive decimation filter device 1730 outputs a level code to the signal processing device 1740 as an example of noise level information indicating the signal level of the component to be inspected.

[0095] In addition to the signal processing of the signal processing device 40, the signal processing device 1740 implements the functions of the filter characteristics determination unit 660 in the filter control unit 210 and the selector 350 in the decimation filter 200. According to the signal processing system 1700 described above, the signal processing device 1740 performs the processes related to determining the filter characteristics according to the input signal and setting the filter characteristics, thereby simplifying the configuration of the adaptive decimation filter device 1730. Furthermore, by using a DSP or the like, the signal processing device 1740 can also determine the filter characteristics of the decimation filter 200 using the results of more advanced analysis processing, such as analyzing the input signal or output signal of the adaptive decimation filter device 1730 by subjecting it to a discrete Fourier transform (DFT).

[0096] 18 shows the configuration of an adaptive decimation filter 1830 according to a sixth modification of this embodiment. The adaptive decimation filter 1830 is a modification of the adaptive decimation filter device 1730 in the signal processing system 1700 shown in FIG. 17, and therefore, a description thereof will be omitted hereinafter except for the differences. The adaptive decimation filter device 1830 includes a decimation filter 200 and an aliasing noise detection unit 1810.

[0097] The decimation filter 200 may have the same functions and configuration as the decimation filter 200 shown in Fig. 3. In this modification, the decimation filter 200 receives a filter code as an example of a filter parameter, and is set to filter characteristics according to the filter code.

[0098] The aliasing noise detection unit 1810 receives an input signal and a filter code. The aliasing noise detection unit 1810 calculates the level of aliasing noise that occurs when the component to be inspected in the input signal is returned to a frequency lower than the Nyquist frequency after decimation by the decimation filter 200. In this modification, the aliasing noise detection unit 1810 calculates the level of aliasing noise that remains in the output signal when the decimation filter 200 is set to filter characteristics according to the filter code received from the signal processing device 1740. The aliasing noise detection unit 1810 calculates the level of aliasing noise that remains in the output signal when the decimation filter 200 is set to filter characteristics according to the filter code received from the signal processing device 1740. characteristics The filter / noise level information includes filter identification information such as a filter code for identifying the filter and noise level information indicating the level of aliasing noise, and outputs the information to the signal processing device 1740.

[0099] 19 shows the configuration of an aliasing noise detection unit 1810 according to a sixth modified example of this embodiment. The aliasing noise detection unit 1810 includes a noise detection unit 620 and an aliasing noise level determination unit 1960. The noise detection unit 620 may have the same function and configuration as the noise detection unit 620 shown in FIG.

[0100] The aliasing noise level determination unit 1960 is connected to the noise detection unit 620. The aliasing noise level determination unit 1960 receives a level code indicating the noise level detected by the noise detection unit 620 and a filter code received from the signal processing device 1740. The aliasing noise level determination unit 1960 calculates the level of aliasing noise that remains in the output signal when the signal level of the component to be inspected indicated by the level code is attenuated by the decimation filter 200 having filter characteristics corresponding to the filter code. The aliasing noise level determination unit 1960 outputs noise level information indicating the calculated level of aliasing noise to the signal processing device 1740 together with filter identification information such as the filter code.

[0101] 20 shows the configuration of the aliasing noise level determination unit 1960 according to the sixth modification of this embodiment. The aliasing noise level determination unit 1960 includes a decoding unit 2070 and a calculation unit 2080.

[0102] The decoding unit 2070 decodes the filter code and outputs the amount of aliasing noise attenuation of the decimation filter 200 for the filter characteristics corresponding to the filter code. For example, the decoding unit 2070 may hold a table that stores, for each possible value of the filter code, the amount of aliasing noise attenuation of the decimation filter 200 when the filter characteristics corresponding to the value of the filter code are set in the decimation filter 200, and output the amount of aliasing noise attenuation corresponding to the input filter code. Alternatively, when the decoding unit 2070 receives filter parameters including filter coefficients, it may calculate the amount of aliasing noise attenuation of the decimation filter 200 using the filter coefficients.

[0103] The calculation unit 2080 is connected to the decoding unit 2070. The calculation unit 2080 calculates the level of aliasing noise that remains in the output signal when aliasing noise of a magnitude indicated by the level code is attenuated by the aliasing noise attenuation amount received from the decoding unit 2070.

[0104] For example, when the level code is 0.5 and the aliasing noise attenuation is 1 / 10, the calculating unit 2080 calculates that the level of the aliasing noise remaining in the output signal is 0.05 (0.5 × 1 / 10). In this way, the calculating unit 2080 may calculate the level of the aliasing noise remaining in the output signal by multiplying the signal level of the test component indicated by the level code by the aliasing noise attenuation. Furthermore, when the unit of the level code and the aliasing noise attenuation is dB, the calculating unit 2080 may calculate the level of the aliasing noise remaining in the output signal by subtracting the dB value of the aliasing noise attenuation from the dB value of the level code.

[0105] The calculation unit 2080 outputs noise level information indicating the calculated level of aliasing noise together with filter identification information such as a filter code to the signal processing device 1740. Here, instead of directly outputting the level of aliasing noise as noise level information, the calculation unit 2080 may output noise level information indicating the result of comparing the level of aliasing noise with a threshold (for example, whether it is greater than the threshold), or noise level information obtained by quantizing the aliasing noise level.

[0106] 21 shows an example of filter / noise level information according to a sixth modification of this embodiment. In this modification, the filter / noise level information is represented by two bits, FN1 and FN0. FN1 indicates noise level information. The calculation unit 2080 sets FN1 to 0 when the aliasing noise level exceeds −100 dBFS, and sets FN1 to 1 when the aliasing noise level is −100 dBFS or less.

[0107] FN0 indicates filter identification information. The calculation unit 2080 sets FN0 to 0 in filter mode 1 that specifies filter 1, for example, and sets FN0 to 1 in filter mode 2 that specifies filter 2, for example. The delay amount (delay time) of the decimation filter 200 differs depending on the filter mode; in filter mode 1, the delay is four cycles of the sampling period (1 / fs) of the output signal, and in filter mode 2, the delay is six cycles of the sampling period of the output signal.

[0108] According to the adaptive decimation filter 1830 of this modification, the signal processing device 1740 can determine the filter characteristics according to the input signal, and the filter characteristics of the decimation filter 200 can be flexibly changed according to the application of the signal processing system 1700. 18 30 provides the signal processing device 1740 with filter / noise level information including noise level information indicating the level of aliasing noise remaining in the output signal, so that the signal processing device 1740 can appropriately determine the filter characteristics of the decimation filter 200 using the filter / noise level information even if it does not know the specific values ​​of the noise attenuation and delay for each filter characteristic that can be set in the decimation filter 200.

[0109] 22 shows the configuration of a signal processing system 2100 according to a seventh modification of this embodiment. For example, in real-time signal processing applications such as ANC (active noise control) or MFB (motional feedback), the signal processing system needs to keep the delay time from receiving an input signal to outputting a processed output signal within an acceptable range. The active noise canceller described in Patent Document 2 operates at a very high oversampling data rate of 384 kHz, while the target frequencies for noise cancellation are 1 kHz or less, thereby eliminating the use of a decimation filter and reducing the delay time.

[0110] However, the active noise canceller described in Patent Document 2 processes signals at a rate that is extremely high for the target frequency of the signal processing, which increases power consumption and requires a signal processing circuit capable of high-speed signal processing. Furthermore, if the operating frequency of the signal processing circuit is high, large switching noise is generated, which may interfere with the feedback path and feedforward path used for noise cancellation and degrade noise canceling performance.

[0111] The signal processing system 2100 according to this modification enables signal processing at a relatively low data rate by using an adaptive decimation filter device 2130 that can adjust the filter characteristics and delay time according to the characteristics of the input signal. The signal processing system 2100 then performs signal processing in the signal processing device 2140 that is adapted to the filter characteristics of the adaptive decimation filter device 2130, thereby adjusting the balance between decimation processing and signal processing and generating a more suitable signal processing output within the given delay time constraints.

[0112] 1 to 16, the signal processing system 2100 according to this modification is a modification of the signal processing system 10 shown in Figures 1 to 16, and therefore description thereof will be omitted hereinafter except for the differences. The signal processing system 2100 includes an AD converter 20, an adaptive decimation filter device 2130, and a signal processing device 2140. The AD converter 20 is the same as the AD converter 20 shown in Figure 1, and converts an analog input signal into a digital input signal and supplies it to the adaptive decimation filter device 2130.

[0113] The adaptive decimation filter device 2130 is a modified example of the adaptive filter device 30 shown in relation to FIGS. 1 to 16. The adaptive decimation filter device 2130 outputs a filter output signal (output signal) obtained by downsampling a filter input signal (input signal). Here, the adaptive decimation filter device 2130 performs adaptive decimation filtering to adjust the filter characteristics based on the characteristics of the input signal. The adaptive decimation filter device 2130 adjusts the filter characteristics by adjusting the order of the decimation filter 200 in the adaptive decimation filter device 2130 based on the characteristics of the input signal. The adaptive decimation filter device 2130 is configured by adding, to the adaptive filter device 30 of FIG. 1, a function to output a filter code to the signal processing device 2140 as an example of filter identification information for identifying the filter characteristics used by the adaptive decimation filter device 2130. Such filter identification information and filter codes are examples of adjustment signals that the adaptive decimation filter device 2130 uses to adjust the order of the decimation filter 200 .

[0114] The signal processing device 2140 is a modified example of the signal processing device 40 shown in Fig. 1. The signal processing device 2140 receives the output signal of the adaptive decimation filter device 2130 and filter identification information, which is an example of an adjustment signal, from the adaptive decimation filter device 2130. The signal processing device 2140 performs signal processing on the output signal of the adaptive decimation filter device 2130 in accordance with the adjustment signal, and outputs the signal processing result. The signal processing device 2140 includes an adaptive filter unit 2150. The adaptive filter unit 2150 performs filter processing on the output signal of the adaptive decimation filter device 2130 in accordance with the adjustment signal.

[0115] 23 shows the configuration of an adaptive decimation filter device 2130 according to a seventh modification of this embodiment. The adaptive decimation filter device 2130 is a modification of the adaptive filter device 30 shown in FIG. 2, and therefore description thereof will be omitted hereinafter except for the differences. The adaptive decimation filter device 2130 includes a decimation filter 200 that outputs an output signal obtained by downsampling an input signal, and a filter control unit 210 that adjusts the filter characteristics of the decimation filter 200 based on the characteristics of the input signal. The adaptive decimation filter device 2130 also supplies a filter code, which is output by the filter control unit 210 to the decimation filter 200 to adjust the filter characteristics, including the order of the decimation filter 200, to a signal processing device 2140.

[0116] FIG. 24 shows an example of a filter code according to a seventh modification of this embodiment. In this modification, the filter code is represented by two bits, FC1 and FC0. When the filter code (FC1, FC0) = (0, 0), the filter code specifies the filter characteristics of filter mode 1. With the filter characteristics of filter mode 1, the delay time is four cycles, which is the period (1 / fs) of the output signal of decimation filter 200. Similarly, when the filter code (FC1, FC0) = (0, 1), the filter code specifies the filter characteristics of filter mode 2, with a delay time of six cycles. When the filter code (FC1, FC0) = (1, 0), the filter code specifies the filter characteristics of filter mode 3, with a delay time of eight cycles. When the filter code (FC1, FC0) = (1, 1), the filter code specifies the filter characteristics of filter mode 4, with a delay time of ten cycles. Note that the filter delay time is longer when the filter order is large and shorter when the filter order is small.

[0117] 25 shows the configuration of an adaptive filter unit 2150 according to a seventh modification of this embodiment. The adaptive filter unit 2150 includes a plurality of filters 2500-1 to 2500-4 (also referred to as “filters 2500”) and a selection unit 2510.

[0118] Each of the multiple filters 2500 performs filtering on the output signal from the adaptive decimation filter device 2130 according to the intended use of the signal processing system 2100. For example, when the signal processing system 2100 is used for ANC, each filter 2500 receives an output signal obtained by downsampling an input signal and performs filtering to generate a noise canceling signal for removing noise contained in the output signal. The multiple filters 2500 may have different filter characteristics from each other.

[0119] The selection unit 2510 selects a filter 2500 to perform filtering from among the plurality of filters 2500, based on filter identification information (filter code) from the adaptive decimation filter device 2130. In the example shown in the figure, the selection unit 2510 switches to which of the plurality of filters 2500 the output signal from the adaptive decimation filter device 2130 is to be supplied, in accordance with the filter code from the adaptive decimation filter device 2130. Furthermore, the selection unit 2510 selects, from among the plurality of filters 2500, the output of the filter 2500 that has performed signal processing on the output signal from the adaptive decimation filter device 2130, as the output of the selection unit 2510.

[0120] Here, the adaptive filter unit 2150 may include one filter 2500 for each type of filter identification information. In this case, the selection unit 2510 can select one filter 2500 associated with the filter identification information from the adaptive decimation filter device 2130. Alternatively, the adaptive filter unit 2150 may include two or more filters 2500 for each type of filter identification information. In this case, the selection unit 2510 may select a filter 2500 to use from the two or more filters 2500 associated with the filter identification information from the adaptive decimation filter device 2130, depending on the operation mode set in the signal processing system 2100, the characteristics of the input signal, and other conditions.

[0121] Instead of the configuration described above, the adaptive filter unit 2150 may have a filter processing device that can change a set of filter parameters such as filter coefficients. In this case, the selection unit 2510 may switch the set of filter parameters to be set in the filter processing device in accordance with the filter identification information, thereby causing the filter processing device to operate as the filter 2500 in accordance with the filter identification information.

[0122] Fig. 26 shows the operation flow of a signal processing system 2100 according to a seventh modified example of this embodiment. The operation flow in this figure is a modified example of the operation flow shown in Fig. 8, and therefore, explanation will be omitted hereinafter except for the differences.

[0123] In S800, the AD converter 20 samples the analog input signal to convert it into a digital input signal. Steps S810 to S830 are the same as steps S810 to S830 in FIG. 8. In S840, the adaptive decimation filter device 2130 downsamples the input signal using the decimation filter 200, whose filter characteristics are determined based on the characteristics of the input signal. As described in relation to FIGS. 1 to 16, the decimation filter 200 may have different attenuation amounts of the components to be adjusted and different filter orders depending on the filter characteristics. The adaptive decimation filter device 2130 outputs the output signal of the decimation filter 200 and filter identification information that identifies the filter characteristics of the decimation filter 200 to the signal processing device 2140.

[0124] At S2650, the signal processing device 2140 performs signal processing on the output signal of the adaptive decimation filter device 2130 in accordance with the filter identification information, and outputs the result of the signal processing. The adaptive decimation filter device 2130 performs decimation processing suited to the characteristics of the input signal, and the delay time from when the adaptive decimation filter device 2130 receives the input signal to when it outputs the output signal varies depending on the type of decimation processing. In real-time signal processing, there is an upper limit to the delay time of the signal processing of the entire signal processing system 2100, and it is required to output a signal processing result with a predetermined phase relative to the input. Therefore, the signal processing device 2140 changes the type of signal processing in accordance with the type of decimation processing in the adaptive decimation filter device 2130.

[0125] When the adaptive decimation filter device 2130 adjusts the order of the decimation filter 200 based on the characteristics of the input signal, the signal processing device 2140 adjusts the phase of the output signal of the decimation filter 200 in accordance with the adjustment signal and performs the desired signal processing. To this end, the adaptive filter unit 2150 in the signal processing device 2140 may select, in accordance with the filter identification information, a filter 2500 that performs filter processing that offsets a change in the delay time of the decimation filter 200 that accompanies the adjustment of the order. In this way, when the delay time of the decimation filter 200 is long, the adaptive filter unit 2150 selects a filter 2500 with a shorter signal processing time, thereby keeping the overall delay time of the signal processing system 2100 below an upper limit. Furthermore, when the delay time of the decimation filter 200 is short, the adaptive filter unit 2150 selects a filter 2500 with a longer signal processing time but higher accuracy, thereby outputting a more accurate signal processing result while keeping the overall delay time of the signal processing system 2100 below an upper limit.

[0126] Furthermore, adaptive filter unit 2150 may select filter 2500 having a relatively short delay time even when decimation filter 200 has a shorter delay time. In this case, when decimation filter 200 has a short delay time, signal processing system 2100 can shorten the signal processing time of the entire signal processing system 2100 and generate an output that responds more quickly to an input to signal processing system 2100.

[0127] 37, the signal processing device 2140 may be equipped with an interpolation filter and a DA converter 6000. As described in relation to FIG. 22, since the target frequency for noise cancellation in an active noise canceller is, for example, 1 kHz or less, it is usually preferable for the signal processing device 2140 to perform signal processing at a relatively low data rate, for example, 2 kHz. On the other hand, a DA converter is required to operate at a relatively high data rate, for example, about 19 times the audible frequency band (384 kHz) or more in order to improve sound quality, and therefore a discrepancy occurs between the data rate of the signal processing circuit and the data rate of the DA converter. Therefore, when the signal processing circuit, such as the adaptive filter unit 2150, is operated at a relatively low data rate, the signal processing device 2140 needs to perform upsampling to convert the data rate of the signal processing circuit to a relatively high data rate. SumpAn interpolation filter is introduced to prevent image components due to ringing, but the delay time of this interpolation filter also depends on the setting of the interpolation filter. Therefore, a signal processing device 2140 according to a modification of the signal processing system 2100 shown in Fig. 37 sets the filter characteristics of the interpolation filter and the interpolation filter in the DA converter 6000 using the filter identification information output from the adaptive decimation filter device 2130. As a result, when the delay time of the decimation filter 200 is set to be shorter, the signal processing device 2140 can also set the delay time of the interpolation filter to be shorter in conjunction with this, and can also generate an output that responds more quickly to the input to the signal processing system 2100.

[0128] According to the signal processing system 2100 described above, the adaptive decimation filter device 2130 changes the filter characteristics of the decimation filter 200 in accordance with the characteristics of the input signal, and the signal processing device 2140 receives filter identification information and performs signal processing according to the filter characteristics of the decimation filter 200. This makes it possible for the signal processing system 2100 to optimize both the decimation processing and the signal processing so as to bring the output signal closer to a target value.

[0129] 27 shows the configuration of a signal processing system 2700 according to an eighth modification of this embodiment. Since the signal processing system 2700 is a modification of the signal processing system 10 shown in FIGS. 1 to 16 and the signal processing system 2100 shown in FIG. 22, a description thereof will be omitted hereinafter except for the differences. The signal processing system 2700 includes an AD converter 20, an adaptive decimation filter device 2130, a data encoder 2735, and a signal processing device 2740. The AD converter 20 is similar to the AD converter 20 shown in FIGS. 1 and 22, and converts an analog input signal into a digital input signal and supplies it to the adaptive decimation filter device 2130.

[0130] The adaptive decimation filter device 2130 is similar to the adaptive decimation filter device 2130 shown in Fig. 22. The adaptive decimation filter device 2130 outputs a filter output signal (output signal) obtained by downsampling a filter input signal (input signal). Here, the adaptive decimation filter device 2130 performs adaptive decimation filter processing that adjusts the filter characteristics based on the characteristics of the input signal.

[0131] The data encoder 2735 is connected to the adaptive decimation filter device 2130. The data encoder 2735 receives and encodes the output signal (filter output signal) and filter identification information from the adaptive decimation filter device 2130, thereby generating data to be sent to the signal processing device 2740.

[0132] The signal processing device 2740 is connected to the data encoder 2735. The signal processing device 2740 receives the data encoded by the data encoder 2735 and performs signal processing. In all other respects, the signal processing device 2740 is similar to the signal processing device 2140 shown in FIG.

[0133] 28 shows a first example of data encoded by the data encoder 2735. The sampling clock LRCK is a clock signal having the sampling frequency fs of the output signal of the adaptive decimation filter device 2130 and the output of the signal processing device 2740. The data transfer clock BICK is a clock used for data transfer from the data encoder 2735 to the signal processing device 2740, and has a clock period corresponding to one cycle of data transfer. In this embodiment, the sampling clock LRCK and the data transfer clock BICK are, by way of example, a channel clock LRCK and an audio serial data clock BICK used for audio applications. Alternatively, the sampling clock LRCK and the data transfer clock BICK may be a sampling clock and a data transfer clock for other applications.

[0134] In the example shown in the figure, the data transfer clock BICK has a frequency 192 times that of the sampling clock LRCK. By making the data transfer clock BICK higher than the sampling clock LRCK, the transfer delay of the data output by the data encoder 2735 can be further reduced.

[0135] The data encoder 2735 starts data transfer processing for one sampling period in response to a rising (or falling) edge of the sampling clock LRCK. In the data transfer processing, the data encoder 2735 outputs a data packet including the output signal of the adaptive decimation filter device 2130 (24 bits, bits 23 to 0 in this figure) and the filter code (two bits, FC1 to 0 in this figure), one bit at a time per period of the data transfer clock BICK. Here, in order to extend the time available for signal processing in the signal processing device 2740, the data encoder 2735 outputs data including the output signal of the decimation filter 200 and the filter code to the signal processing device 2740 in the first half of the output cycle period (one period of the sampling clock LRCK) of the signal processing device 2740. In the example of this figure, the data encoder 2735 starts data transfer immediately after the start of the sampling period and sequentially transmits bits 23 to 0 of the output signal and the filter code FC1 to 0, one bit at a time, in synchronization with the data transfer clock BICK.

[0136] Upon receiving the output signal from adaptive decimation filter device 2130 and data including a filter code via data encoder 2735, signal processing device 2740 starts signal processing corresponding to the sampling period. In the example shown in the figure, signal processing device 2740 performs signal processing within the sampling period in which the data packet is received, and outputs data resulting from the signal processing. That is, signal processing device 2740 inputs the output signal and filter identification information of decimation filter 200 within the output cycle period of signal processing device 2740, performs signal processing according to the input output signal of decimation filter 200 and filter identification information, and outputs a signal generated by the signal processing.

[0137] According to the data encoder 2735 described above, a data packet including the output signal of the adaptive decimation filter device 2130 and a filter code can be transmitted to the signal processing device 2740 using the data transfer clock BICK, which has a higher frequency than the sampling clock LRCK. This allows the signal processing device 2740 to perform some or all of the signal processing after receiving the data packet within the sampling period.

[0138] FIG. 29 shows a second example of data encoded by the data encoder 2735. In this figure, a signal processing system 2100 receives signals of multiple channels, performs signal processing, and outputs the signal processing results for the multiple channels. In the example shown in this figure, an AD converter 20 converts two-channel analog input signals into two-channel digital input signals. An adaptive decimation filter device 2130 outputs multiple-channel output signals by downsampling the multiple-channel input signals from the AD converter 20. Here, the adaptive decimation filter device 2130 performs adaptive decimation filter processing that adjusts the filter characteristics based on the characteristics of the input signals. The adaptive decimation filter device 2130 may set different filter characteristics in the decimation filter 200 for the multiple-channel input signals according to the characteristics of each input signal.

[0139] In the example shown in this figure, data encoder 2735 outputs data including the output signal of decimation filter 200 and filter code for each of the multiple channels in the same manner as in Figure 28. Data encoder 2735 outputs data packets for the multiple channels in parallel using data paths for the multiple channels. Upon receiving the data packets for each of the multiple channels, signal processing device 2740 performs signal processing for each of the multiple channels in the same manner as in Figure 28 and outputs the signal processing results for each of the multiple channels.

[0140] FIG. 30 shows a third example of data encoded by data encoder 2735. In this figure, as in FIG. 29, signal processing system 2100 receives signals from multiple channels, performs signal processing, and outputs the signal processing results for the multiple channels. In the example of this figure, data encoder 2735 has a data path shared by multiple channels, and multiplexes data packets for the multiple channels (data packets including the output signal of decimation filter 200 and filter codes) during a sampling period and outputs them to signal processing device 2740. Signal processing device 2740 may start signal processing for each channel each time it receives a data packet for that channel. Alternatively, signal processing device 2740 may start signal processing for the multiple channels after receiving data packets for all channels.

[0141] 27 to 30, when the clock of the output signal of the adaptive decimation filter device 2130 is the sampling clock LRCK, the adaptive decimation filter device 2130 has a delay from when it receives an input signal at a certain point in time until it outputs an output signal affected by that input signal, the delay is equal to the sampling period of the input signal before decimation multiplied by half the order of the decimation filter 200. Therefore, the delay time from when the adaptive decimation filter device 2130 receives an input signal until the signal processing device 2740 outputs the signal processing result is the sum of the number of signal processing cycles of the signal processing device 2140 × the sampling period × the sampling period of the input signal × half the order of the decimation filter 200.

[0142] 28 to 30, the signal processing device 2740 performs signal processing that reflects the output signal and filter code included in the data packet received in each sampling period, and outputs the signal processing result. That is, in the examples of Figures 28 to 30, the signal processing delay of the signal processing device 2740 is one sampling period, which is constant regardless of the filter characteristics of the decimation filter 200.

[0143] For example, in noise canceling, the signal processing system 2700 outputs a noise canceling signal so that a noise-canceling sound that is 180° out of phase with the noise sound reaches the target position in synchronization with the timing at which the noise sound reaches the target position. In such real-time signal processing, the signal processing device 2740 prevents the phase of a signal corresponding to the output signal of the signal processing system 2700 from changing when the signal reaches the target, even if the delay time of the signal processing system 2700 changes depending on the filter characteristics of the decimation filter 200. To achieve this, the signal processing device 2740 may vary the phase of the signals output by each filter 2500 so as to cancel out the phase change depending on the delay time or order of the decimation filter 200.

[0144] Figure 31 shows the configuration of a signal processing system 3100 according to a ninth modification of this embodiment. Since signal processing system 3100 is a modification of signal processing system 10 shown in Figures 1 to 16, signal processing system 2100 shown in Figure 22, and signal processing system 2700 shown in Figure 27, a description thereof will be omitted below except for the differences. In signal processing system 3100, data encoder 3135 corresponding to data encoder 2735 in Figure 27 encodes the output signal of adaptive decimation filter device 2130, but does not encode the filter code.

[0145] The signal processing system 3100 includes an AD converter 20, an adaptive decimation filter device 2130, a data encoder 3135, and a signal processing device 3140. The AD converter 20 and the adaptive decimation filter device 2130 are similar to the AD converter 20 and the adaptive decimation filter device 2130 shown in FIG.

[0146] The data encoder 3135 is connected to the adaptive decimation filter device 2130. The data encoder 3135 receives and encodes the output signal (filter output signal) from the adaptive decimation filter device 2130, thereby forming a signal processing device. 31 The data encoder 3135 does not encode the filter identification information (filter code) from the adaptive decimation filter device 2130.

[0147] Signal processing device 3140 is connected to adaptive decimation filter device 2130 and data encoder 3135. Signal processing device 3140 receives the data encoded by data encoder 3135 and the filter identification information output by adaptive decimation filter device 2130 and performs signal processing. In other respects, signal processing device 3140 is similar to signal processing device 2140 shown in Fig. 22 and signal processing device 2740 shown in Fig. 27.

[0148] Fig. 32 shows a first example of data encoded by the data encoder 3135. The example in this figure is a modified example of the data shown in Fig. 28, so a description will be omitted below except for the differences. In the example in this figure, the adaptive decimation filter device 2130 supplies a filter code to the signal processing device 3140 without going through the data encoder 3135 during a sampling period defined by the sampling clock LRCK.

[0149] The data encoder 3135 starts data transfer processing for one sampling period in response to the rising (or falling) of the sampling clock LRCK. In the data transfer processing, the data encoder 3135 outputs a data packet including the output signal of the adaptive decimation filter device 2130 (24 bits from bits 23 to 0 in this figure), one bit at a time per period of the data transfer clock BICK. Here, the data encoder 3135 is a signal processing device 31 In order to increase the time available for signal processing in 40, data transfer is performed in the first half of one cycle of the sampling clock LRCK. In the example shown in this figure, the data encoder 3135 starts data transfer immediately after the start of the sampling cycle, and transmits bits 23 to 0 of the output signal one bit at a time in this order in synchronization with the data transfer clock BICK.

[0150] The signal processing device 3140 receives the filter code from the adaptive decimation filter device 2130 and starts signal processing corresponding to the sampling period when it receives data including the output signal from the adaptive decimation filter device 2130 via the data encoder 3135. In the example shown in the figure, the signal processing device 3140 performs signal processing within the sampling period in which the data packet is received, and outputs data resulting from the signal processing.

[0151] FIG. 33 shows a second example of data encoded by the data encoder 3135. This example is a modification of the examples shown in FIGS. 29 and 32, and therefore will not be described further below except for the differences. In this figure, a signal processing system 3100 receives signals from multiple channels, performs signal processing, and outputs the signal processing results for the multiple channels. In this example, an AD converter 20 converts two-channel analog input signals into two-channel digital input signals. An adaptive decimation filter device 2130 downsamples the input signals from the AD converter 20 and outputs output signals from multiple channels. Here, the adaptive decimation filter device 2130 performs adaptive decimation filtering, adjusting the filter characteristics based on the characteristics of the input signals. The adaptive decimation filter device 2130 may set different filter characteristics for the decimation filter 200 for the input signals from multiple channels, depending on the characteristics of each input signal.

[0152] In the example shown in the figure, adaptive decimation filter device 2130 supplies filter codes for each of the multiple channels to signal processing device 3140 without going through data encoder 3135. Data encoder 3135 outputs data including the output signal of decimation filter 200 for each of the multiple channels in the same manner as in FIG. 32. In the example shown in the figure, data encoder 3135 outputs data packets for the multiple channels in parallel using data paths for the multiple channels. Upon receiving the filter codes and data packets for each of the multiple channels, signal processing device 3140 performs signal processing for each of the multiple channels in the same manner as in FIGS. 28 and 32, and outputs the signal processing results for each of the multiple channels.

[0153] FIG. 34 shows a third example of data encoded by data encoder 3135. Since the example shown in this figure is a modification of the examples shown in FIGS. 30 and 33, a description thereof will be omitted hereinafter except for the differences. In this figure, as in FIG. 33, signal processing system 3100 inputs signals of multiple channels, performs signal processing, and outputs the signal processing results for the multiple channels. In the example shown in this figure, data encoder 3135 has a data path shared by multiple channels, and multiplexes data packets for the multiple channels (data packets including the output signal of decimation filter 200) during a sampling period and outputs them to signal processing device 3140. Furthermore, adaptive decimation filter device 2130 shares a path for transmitting filter codes among multiple channels, multiplexes filter codes for the multiple channels during a sampling period, and outputs them to signal processing device 3140 without going through data encoder 3135.

[0154] FIG. 35 shows the configuration of an ANC system 3500 according to a tenth modification of this embodiment. The ANC system 3500 muffles noise at a specific target position. The ANC system 3500 uses both feedforward control and feedback control. The ANC system 3500 uses feedforward control to detect vibrations, etc. of a noise source, and generates an anti-noise sound that is out of phase with the noise before it reaches the target position, and transmits the anti-noise sound to the target position. The ANC system 3500 uses feedback control to detect noise at the target position, and generates an anti-noise sound that reduces the noise, and transmits the anti-noise sound to the target position.

[0155] The ANC system 3500 includes a sensor 3510, a signal processing system 2100a, a DA converter 3570, a speaker 3580, a microphone 3520, and a signal processing system 2100b. The sensor 3510, the signal processing system 2100a, the DA converter 3570, and the speaker 3580 are used for feedforward control. The microphone 3520, the signal processing system 2100b, the DA converter 3570, and the speaker 3580 are used for feedback control. The signal processing device 2140, the DA converter 3570, and the speaker 3580 included in the signal processing system 2100a and the signal processing system 2100b are shared by the feedforward control and the feedback control.

[0156] Sensor 3510 is installed near a noise source that generates noise, such as a vehicle engine or motor. Sensor 3510 may be a sensor that detects the movement of the noise source that causes the noise, such as an acceleration sensor or a rotation angle sensor, or may be a sensor that detects the noise generated by the noise source, such as a microphone. Sensor 3510 supplies an analog signal including the detected noise component to signal processing system 2100a.

[0157] Signal processing system 2100a is connected to sensor 3510. In this modification, signal processing system 2100a is signal processing system 2100 shown in FIG. 22. In place of signal processing system 2100a, ANC system 3500 may use signal processing system 10 of FIGS. 1 to 16, signal processing system 1700 of FIG. 17, signal processing system 2700 of FIG. 27, signal processing system 3100 of FIG. 31, or modifications thereof. Signal processing system 2100a includes an AD converter 20a corresponding to AD converter 20 of signal processing system 2100, an adaptive decimation filter device 2130a corresponding to adaptive decimation filter device 2130 of signal processing system 2100, and a signal processing device 2140 corresponding to signal processing device 2140 of signal processing system 2100.

[0158] The AD converter 20a converts an analog signal containing noise components into a digital signal and supplies it to the adaptive decimation filter device 2130a as a filter input signal (input signal). The adaptive decimation filter device 2130a outputs a filter output signal (output signal) obtained by downsampling the filter input signal (input signal). Here, the adaptive decimation filter device 2130a performs adaptive filtering to adjust the filter characteristics based on the characteristics of the input signal.

[0159] The signal processing device 2140 receives the output signal of the adaptive decimation filter device 2130a and filter identification information from the adaptive decimation filter device 2130a. The signal processing device 2140 adjusts the phase of the output signal of the decimation filter 200 in the adaptive decimation filter device 2130a in accordance with the filter identification information that identifies the filter characteristics of the decimation filter 200, and generates a noise canceling signal to reduce noise components. The signal processing device 2140 supplies a digital output including the generated noise canceling signal to the DA converter 3570.

[0160] The DA converter 3570 is connected to the signal processing device 2140. The DA converter 3570 converts the digital output, including the noise canceling signal, from the signal processing device 2140 into an analog output. The speaker 3580 is installed closer to the position to be silenced than the sensor 3510. The speaker 3580 is connected to the DA converter 3570. The speaker 3580 converts the analog output into sound, thereby generating an anti-noise sound corresponding to the noise canceling signal from the signal processing device 2140.

[0161] As a result, the ANC system 3500 can change the filter characteristics of the decimation filter 200 in accordance with the characteristics of the input signal including a noise component in feedforward control, and can adjust the order of the decimation filter 200 and the attenuation amount of the adjustment target component. Then, the ANC system 3500 can perform adaptive filter processing in accordance with the filter characteristics of the decimation filter 200 in the signal processing device 2140.

[0162] In feedforward control, the ANC system 3500 transmits an anti-noise sound of opposite phase and amplitude to the noise sound to the target position in accordance with the timing at which the noise sound reaches the target position from the noise source. To this end, the signal processing device 2140 performs signal processing according to the filter characteristics of the decimation filter 200, thereby changing the phase of the noise canceling signal in accordance with changes in the delay time of the decimation filter 200, and synchronizing the anti-noise sound with the noise sound at the target position.

[0163] Furthermore, by performing signal processing according to the filter characteristics of the decimation filter 200, the signal processing device 2140 can output a more accurate noise canceling signal by taking time for signal processing when the delay time of the decimation filter 200 is short, and can also use signal processing with a shorter processing time to avoid delaying the timing at which the anti-noise sound propagates to the target position when the delay time of the decimation filter 200 is long. This allows the ANC system 3500 to achieve suitable noise suppression in the entire decimation processing and noise canceling processing.

[0164] The microphone 3520 is provided near a target position where noise is to be silenced. The microphone 3520 detects noise at the target position and supplies an analog input signal containing the detected noise components to the signal processing system 2100b. Here, noise reaching the target position from a noise source is suppressed by feedforward control. Therefore, the microphone 3520 detects noise including residual noise due to feedforward control and environmental noise reaching the target position from sources other than noise sources near the sensor 3510.

[0165] Signal processing system 2100b is connected to microphone 3520. In this modification, signal processing system 2100b is signal processing system 2100 shown in FIG. 22. In place of signal processing system 2100b, ANC system 3500 may use signal processing system 10 of FIGS. 1 to 16, signal processing system 1700 of FIG. 17, signal processing system 2700 of FIG. 27, signal processing system 3100 of FIG. 31, or modifications thereof. Signal processing system 2100b includes an AD converter 20b corresponding to AD converter 20 of signal processing system 2100, an adaptive decimation filter device 2130b corresponding to adaptive decimation filter device 2130 of signal processing system 2100, and a signal processing device 2140 corresponding to signal processing device 2140 of signal processing system 2100.

[0166] The AD converter 20b converts an analog signal containing noise components into a digital signal and supplies it to the adaptive decimation filter device 2130b as a filter input signal (input signal). The adaptive decimation filter device 2130b outputs a filter output signal (output signal) obtained by downsampling the filter input signal (input signal). Here, the adaptive decimation filter device 2130b performs adaptive filtering to adjust the filter characteristics based on the characteristics of the input signal.

[0167] The signal processing device 2140 receives the output signal of the adaptive decimation filter device 2130b and filter identification information from the adaptive decimation filter device 2130b. The signal processing device 2140 adjusts the phase of the output signal of the decimation filter 200 in the adaptive decimation filter device 2130b in accordance with the filter identification information, and generates a noise canceling signal for reducing noise components. The signal processing device 2140 supplies a digital output including the generated noise canceling signal to the DA converter 3570.

[0168] In this modification, the signal processing device 2140 is shared by the feedforward control and the feedback control. The signal processing device 2140 may supply a digital output including a noise canceling signal obtained by superimposing a noise canceling signal generated by the feedforward control and a noise canceling signal generated by the feedback control to the DA converter 3570.

[0169] The DA converter 3570 converts the digital output, including the noise canceling signal, from the signal processing device 2140 into an analog output. The speaker 3580 converts the analog output into sound, thereby generating an anti-noise sound corresponding to the noise canceling signal from the signal processing device 2140.

[0170] As a result, the ANC system 3500 can change the filter characteristics of the decimation filter 200 in the signal processing system 2100b in feedback control according to the characteristics of the input signal including a noise component, and can adjust the order of the decimation filter 200 and the attenuation amount of the adjustment target component. Then, the ANC system 3500 can perform adaptive filter processing according to the filter characteristics of the decimation filter 200 in the signal processing device 2140.

[0171] In the feedback control described above, the ANC system 3500 detects noise, including residual noise, at a target position and transmits an anti-noise sound to the target position to reduce the noise. Ideally, the anti-noise sound is an anti-phase sound with the same amplitude as the noise. However, there is a propagation delay in the feedback loop from when the noise near the target position is detected to when the anti-noise sound is transmitted to the target position.

[0172] In this modification, the signal processing device 2140 performs signal processing according to the filter characteristics of the decimation filter 200, thereby performing adaptive filter processing according to changes in the delay time of the decimation filter 200. As a result, when the delay time of the decimation filter 200 is shorter, the signal processing device 2140 can maintain a smaller propagation delay in the entire feedback loop, widen the bandwidth of the feedback loop, and improve its ability to follow changes in environmental noise. Furthermore, when the delay time of the decimation filter 200 is shorter, the signal processing device 2140 can also take more time to perform signal processing and output a more accurate noise canceling signal. As a result, the ANC system 3500 can achieve suitable noise suppression in the entire decimation processing and noise canceling processing.

[0173] 36 shows the configuration of an MFB system 3600 according to an eleventh modification of this embodiment. The MFB system 3600 detects the movement of a diaphragm of a speaker device 3610 and applies feedback to an audio signal supplied to the speaker device 3610, thereby correcting the vibration of the diaphragm so that it moves in the same manner as the input audio signal. The MFB system 3600 includes a speaker device 3610, a signal processing system 2100, and a DA converter 3680.

[0174] The speaker device 3610 is a target of distortion correction by MFB. The speaker device 3610 generates sound by vibrating a diaphragm in response to an analog signal input from a DA converter 3680. The speaker device 3610 has a function of outputting a signal corresponding to the vibration of the diaphragm to the signal processing system 2100. For example, the speaker device 3610 generates a voltage corresponding to the movement of the diaphragm by converting a signal current flowing through the speaker body into a voltage using a shunt resistor, and outputs the voltage to the signal processing system 2100. The speaker device 3610 may detect the vibration of the diaphragm using a displacement sensor installed on the diaphragm.

[0175] The signal processing system 2100 is connected to a speaker device 3610. In this modification, the signal processing system 2100 is the signal processing system 2100 shown in Fig. 22. The MFB system 3600 may use the signal processing system 10 of Figs. 1 to 16, the signal processing system 1700 of Fig. 17, the signal processing system 2700 of Fig. 27, the signal processing system 3100 of Fig. 31, or modifications thereof, instead of the signal processing system 2100. The signal processing system 2100 includes an AD converter 20, an adaptive decimation filter device 2130, and a signal processing device 2140.

[0176] The AD converter 20 converts an analog signal corresponding to the vibration of the diaphragm into a digital signal and supplies it to the adaptive decimation filter device 2130 as a filter input signal (input signal). The adaptive decimation filter device 2130 outputs a filter output signal (output signal) obtained by downsampling the filter input signal (input signal). Here, the adaptive decimation filter device 2130 performs adaptive filtering to adjust the filter characteristics based on the characteristics of the input signal. The signal processing device 2140 is 2130 and filter identification information from the adaptive decimation filter device 2130. The signal processing device 2140 performs signal processing on the output signal of the decimation filter 200 in the adaptive decimation filter device 2130 in accordance with the filter identification information.

[0177] For example, the signal processing device 2140 performs adaptive filter processing on the output signal of the decimation filter 200 using the adaptive filter unit 2150, thereby reproducing an audio signal corresponding to the vibration of the diaphragm from a signal corresponding to the vibration. The audio signal reproduced in this manner is an audio signal that reflects the distortion of the vibration of the diaphragm. The signal processing device 2140 applies distortion correction to the audio signal from the audio source so as to reduce or minimize the error between the audio signal input from the audio source and the reproduced audio signal, and outputs the resulting audio signal to the DA converter 3680.

[0178] The DA converter 3680 is connected to the signal processing system 2100. The DA converter 3680 converts a digital signal, which is a distortion-corrected audio signal, into an analog signal and supplies the analog signal to the speaker device 3610. The speaker device 3610 vibrates a diaphragm using the distortion-corrected audio signal.

[0179] In this modification, the signal processing device 2140 performs signal processing according to the filter characteristics of the decimation filter 200, thereby enabling adaptive filter processing according to changes in the delay time of the decimation filter 200. As a result, when the delay time of the decimation filter 200 is shorter, the signal processing device 2140 can maintain a smaller propagation delay in the entire feedback loop, widening the bandwidth of the feedback loop and improving the ability to follow changes in the audio signal from the audio source. Furthermore, when the delay time of the decimation filter 200 is shorter, the signal processing device 2140 can also take more time to perform signal processing and perform more accurate distortion correction. As a result, the MFB system 3600 can achieve a suitable MFB in the entire decimation processing and noise canceling processing.

[0180] Various embodiments of the present invention may be described with reference to flowcharts and block diagrams, where the blocks may represent (1) stages of a process in which operations are performed or (2) sections of an apparatus responsible for performing the operations. Particular stages and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer-readable instructions stored on a computer-readable medium, and / or a processor provided with computer-readable instructions stored on a computer-readable medium. Dedicated circuitry may include digital and / or analog hardware circuitry, and may include integrated circuits (ICs) and / or discrete circuits. Programmable circuitry may include reconfigurable hardware circuitry, including logical AND, OR, XOR, NAND, NOR, and other logical operations, flip-flops, registers, memory elements such as field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), and the like.

[0181] A computer-readable medium may include any tangible device capable of storing instructions that are executed by an appropriate device, such that the computer-readable medium having instructions stored thereon comprises an article of manufacture containing instructions that can be executed to create means for performing the operations specified in the flowcharts or block diagrams. Examples of computer-readable media may include electronic, magnetic, optical, electromagnetic, and semiconductor storage media. More specific examples of computer-readable media may include floppy disks, diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), electrically erasable programmable read-only memory (EEPROM), static random access memory (SRAM), compact disc read-only memory (CD-ROM), digital versatile disc (DVD), Blu-ray disc, memory stick, integrated circuit card, and the like.

[0182] The computer readable instructions may include either assembler instructions, Instruction Set Architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state-setting data, or source or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as JAVA®, C++, Smalltalk®, etc., and conventional procedural programming languages ​​such as the “C” programming language or similar programming languages.

[0183] The computer-readable instructions may be provided to a processor or programmable circuitry of a programmable data processing apparatus, such as a general-purpose computer, special-purpose computer, or other computer, either locally or over a wide-area network (WAN) such as a local area network (LAN), the Internet, etc., which executes the computer-readable instructions to create means for performing the operations specified in the flowcharts or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, etc.

[0184] 38 illustrates an example of a computer 2200 in which aspects of the present invention may be embodied, in whole or in part. Programs installed on the computer 2200 may cause the computer 2200 to function as or perform operations associated with an apparatus or one or more sections of the apparatus according to embodiments of the present invention, and / or to perform a process or steps of a process according to embodiments of the present invention. Such programs may be executed by the CPU 2212 to cause the computer 2200 to perform specific operations associated with some or all of the blocks of the flowcharts and block diagrams described herein.

[0185] A computer 2200 according to this embodiment includes a CPU 2212, a RAM 2214, a graphics controller 2216, and a display device 2218, which are interconnected by a host controller 2210. The computer 2200 also includes input / output units such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card drive, which are connected to the host controller 2210 via an input / output controller 2220. The computer also includes legacy input / output units such as a ROM 2230 and a keyboard 2242, which are connected to the input / output controller 2220 via an input / output chip 2240.

[0186] The CPU 2212 operates according to programs stored in the ROM 2230 and RAM 2214, thereby controlling each unit. The graphics controller 2216 acquires image data generated by the CPU 2212 into a frame buffer or the like provided in the RAM 2214 or into the graphics controller 2216 itself, and causes the image data to be displayed on the display device 2218.

[0187] The communications interface 2222 communicates with other electronic devices via a network. The hard disk drive 2224 stores programs and data used by the CPU 2212 in the computer 2200. The DVD-ROM drive 2226 reads programs or data from the DVD-ROM 2201 and provides the programs or data to the hard disk drive 2224 via the RAM 2214. The IC card drive reads programs and data from an IC card and / or writes programs and data to an IC card.

[0188] The ROM 2230 stores therein a boot program or the like that is executed by the computer 2200 upon activation, and / or programs that depend on the hardware of the computer 2200. The input / output chip 2240 may also connect various input / output units to the input / output controller 2220 via a parallel port, a serial port, a keyboard port, a mouse port, etc.

[0189] The programs are provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The programs are read from the computer-readable medium, installed in the hard disk drive 2224, RAM 2214, or ROM 2230, which are also examples of computer-readable media, and executed by the CPU 2212. Information processing described in these programs is read by the computer 2200, and brings about cooperation between the programs and the various types of hardware resources described above. An apparatus or method may be configured by realizing information manipulation or processing in accordance with the use of the computer 2200.

[0190] For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 may execute a communication program loaded into the RAM 2214 and instruct the communication interface 2222 to perform communication processing based on the processing described in the communication program. Under the control of the CPU 2212, the communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in the RAM 2214, the hard disk drive 2224, the DVD-ROM 2201, or a recording medium such as an IC card, and transmits the read transmission data to the network, or writes reception data received from the network to a reception buffer processing area or the like provided on the recording medium.

[0191] The CPU 2212 may also cause all or a necessary portion of a file or database stored on an external recording medium such as the hard disk drive 2224, the DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. to be read into the RAM 2214, and perform various types of processing on the data on the RAM 2214. The CPU 2212 then writes back the processed data to the external recording medium.

[0192] Various types of information, such as various types of programs, data, tables, and databases, may be stored on the recording medium and may undergo information processing. The CPU 2212 may perform various types of processing on data read from the RAM 2214, including various types of operations, information processing, conditional judgment, conditional branching, unconditional branching, information search / replacement, etc., as described throughout this disclosure and specified by the instruction sequences of the programs, and write the results back to the RAM 2214. The CPU 2212 may also search for information in a file, database, etc. on the recording medium. For example, if multiple entries each having an attribute value of a first attribute associated with an attribute value of a second attribute are stored on the recording medium, the CPU 2212 may search for an entry that matches a condition specified by the attribute value of the first attribute from among the multiple entries, read the attribute value of the second attribute stored in the entry, and thereby obtain the attribute value of the second attribute associated with the first attribute that satisfies a predetermined condition.

[0193] The above-described programs or software modules may be stored in a computer-readable medium on or near the computer 2200. A recording medium such as a hard disk or RAM provided in a server system connected to a dedicated communication network or the Internet can also be used as a computer-readable medium, thereby providing the programs to the computer 2200 via the network.

[0194] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0195] It should be noted that the order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before," "prior to," etc., and that the processes can be performed in any order unless the output of a previous process is used in a subsequent process. Even if the operational flow in the claims, specifications, and drawings is described using "first," "next," etc. for convenience, this does not mean that the processes must be performed in this order. [Explanation of symbols]

[0196] 10 Signal Processing System 20 AD converter 20a~b AD converter 30 Adaptive filter device 40 Signal Processing Device 200 Decimation Filter 210 Filter control section 300-2~N delay element 310-1~N Thinning elements 320-1~N multiplier 330-2~N Adder 340 Filter coefficient storage unit 350 Selector 400 signals 410 Aliasing 500 1st filter characteristic 510 Second filter characteristic 620 Noise detection unit 660 Filter characteristic determination section 730 HPF 750 Noise Level Output Unit 1020 Noise detection unit 1030 BPF 1050 Noise level output section 1110 Filter control section 1140 Signal detection unit 1160 Filter characteristic determination section 1230 LPF 1250 signal level output section 1460 Filter characteristic determination section 1470 Threshold memory unit 1480 Comparison Section 1490 Decoder 1560 Filter characteristic determination section 1590 Decoder 1595 Delay Elements 1700 Signal Processing System 1730 Adaptive Decimation Filter Device 1740 Signal Processing Device 1810 Aliasing noise detector 1830 Adaptive Decimation Filter 1960 Aliasing noise level determination section 2070 Decoder 2080 Calculation Unit 2100 Signal Processing System 2100a~b Signal Processing System 2130 Adaptive Decimation Filter Device 2130a~b Adaptive decimation filter device 2140 Signal Processing Device 2150 Adaptive filter section 2500-1~4 Filter 2510 Selection Section 2700 Signal Processing System 2735 Data Encoder 2740 Signal Processing Device 3100 Signal Processing System 3135 Data Encoder 3140 Signal Processing Device 3500 ANC System 3510 Sensor 3520 Microphone 3570 DA converter 3580 Speaker 3600 MFB System 3610 Speaker equipment 3680 DA converter 6000 Interpolation filter and DA converter 2200 Computer 2201 DVD-ROM 2210 host controller 2212 CPU 2214 RAM 2216 Graphics Controller 2218 Display Device 2220 Input / Output Controller 2222 communication interface 2224 hard disk drive 2226 DVD-ROM drive 2230 ROM 2240 I / O chip 2242 keyboard

Claims

1. an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; an AD converter that converts an analog input signal into a digital input signal and supplies the digital input signal to the adaptive decimation filter device; Equipped with The AD converter converts the analog input signal including a noise component into a digital input signal; The signal processing device adjusts the phase of the output signal of the decimation filter in accordance with the adjustment signal, and generates a noise canceling signal for reducing the noise component. Signal processing system.

2. an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; Equipped with the signal processing device has an adaptive filter unit that performs filter processing on the output signal of the decimation filter in accordance with the adjustment signal; The adaptive filter unit selects a filter that performs the filtering process to offset a change in delay time of the decimation filter caused by the adjustment of the order, in accordance with the adjustment signal. Signal processing system.

3. an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; Equipped with The filter control unit a noise detection unit that detects, in the input signal, a signal level of at least a part of frequencies equal to or higher than the Nyquist frequency of the output signal of the decimation filter; a filter characteristic determination unit that determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit; Contains Signal processing system.

4. 4. The signal processing system according to claim 3, wherein the filter control unit sets a first filter characteristic to the decimation filter when the signal level detected by the noise detection unit is greater than a predetermined reference, and sets a second filter characteristic, the order of which is smaller than the first filter characteristic, to the decimation filter when the signal level detected by the noise detection unit is equal to or less than the reference.

5. 4. The signal processing system according to claim 3, wherein the filter control unit sets a second filter characteristic to the decimation filter when the signal level detected by the noise detection unit is greater than a predetermined reference, and sets a first filter characteristic, the order of which is greater than the second filter characteristic, to the decimation filter when the signal level detected by the noise detection unit is equal to or less than the reference.

6. an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; Equipped with The filter control unit a noise detection unit that detects, in the input signal, a signal level of at least a part of frequencies equal to or higher than the Nyquist frequency of the output signal of the decimation filter; a signal detection unit that detects a signal level of at least a part of frequencies in the input signal that are lower than the Nyquist frequency of the output signal of the decimation filter; a filter characteristic determination unit that determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit and the signal level detected by the signal detection unit; Contains Signal processing system.

7. 7. The signal processing system according to claim 1, wherein the signal processing device inputs the output signal of the decimation filter and the adjustment signal within an output cycle period of the signal processing device, performs the signal processing according to the input output signal of the decimation filter and the adjustment signal, and outputs a signal generated by the signal processing.

8. an AD converter converting an analog input signal including a noise component into a digital input signal; a decimation filter outputting an output signal obtained by downsampling the input signal; a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device performing signal processing on the output signal of the decimation filter in accordance with the adjustment signal; Including, The signal processing device adjusts the phase of the output signal of the decimation filter in accordance with the adjustment signal, and generates a noise canceling signal for reducing the noise component. Signal processing methods.

9. a decimation filter that outputs an output signal obtained by downsampling an input signal; a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device performing signal processing on the output signal of the decimation filter in accordance with the adjustment signal; Including, the signal processing device has an adaptive filter unit that performs filter processing on the output signal of the decimation filter in accordance with the adjustment signal; The adaptive filter unit selects a filter that performs the filtering process to offset a change in delay time of the decimation filter caused by the adjustment of the order, in accordance with the adjustment signal. Signal processing methods.

10. a decimation filter that outputs an output signal obtained by downsampling an input signal; a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device performing signal processing on the output signal of the decimation filter in accordance with the adjustment signal; Including, a noise detection unit of the filter control unit detects a signal level of at least a part of frequencies in the input signal that are equal to or higher than the Nyquist frequency of the output signal of the decimation filter; A filter characteristic determination unit of the filter control unit determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit. Signal processing methods.

11. a decimation filter that outputs an output signal obtained by downsampling an input signal; a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device performing signal processing on the output signal of the decimation filter in accordance with the adjustment signal; Including, a noise detection unit of the filter control unit detects a signal level of at least a part of frequencies in the input signal that are equal to or higher than the Nyquist frequency of the output signal of the decimation filter; a signal detection unit of the filter control unit detects a signal level of at least a part of frequencies in the input signal that are lower than the Nyquist frequency of the output signal of the decimation filter; A filter characteristic determination unit of the filter control unit determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit and the signal level detected by the signal detection unit. Signal processing methods.

12. The method is executed by a computer, causing the computer to: an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; an AD converter that converts an analog input signal into a digital input signal and supplies the digital input signal to the adaptive decimation filter device; and make it work, The AD converter converts the analog input signal including a noise component into a digital input signal; The signal processing device adjusts the phase of the output signal of the decimation filter in accordance with the adjustment signal, and generates a noise canceling signal for reducing the noise component. Signal processing program.

13. The method is executed by a computer, causing the computer to: an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; and make it work, the signal processing device has an adaptive filter unit that performs filter processing on the output signal of the decimation filter in accordance with the adjustment signal; The adaptive filter unit selects a filter that performs the filtering process to offset a change in delay time of the decimation filter caused by the adjustment of the order, in accordance with the adjustment signal. Signal processing program.

14. The method is executed by a computer, causing the computer to: an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; and make it work, The filter control unit a noise detection unit that detects, in the input signal, a signal level of at least a part of frequencies equal to or higher than the Nyquist frequency of the output signal of the decimation filter; a filter characteristic determination unit that determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit; Contains Signal processing program.

15. The method is executed by a computer, causing the computer to: an adaptive decimation filter device including a decimation filter that outputs an output signal obtained by downsampling an input signal, and a filter control unit that outputs an adjustment signal that adjusts the order of the decimation filter based on the characteristics of the input signal; a signal processing device that performs signal processing on an output signal of the decimation filter in accordance with the adjustment signal; and make it work, The filter control unit a noise detection unit that detects, in the input signal, a signal level of at least a part of frequencies equal to or higher than the Nyquist frequency of the output signal of the decimation filter; a signal detection unit that detects a signal level of at least a part of frequencies in the input signal that are lower than the Nyquist frequency of the output signal of the decimation filter; a filter characteristic determination unit that determines the order of a filter to be set in the decimation filter based on the signal level detected by the noise detection unit and the signal level detected by the signal detection unit; Contains Signal processing program.

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