Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JP2010212887 An object of the present invention is to provide a signal correction device capable of preventing an excessive reduction in volume while preventing clipping of a digital signal. A coefficient calculating unit 102A obtains a coefficient p according to an input signal x [n], and according to the coefficient p, a coefficient for controlling the level of a signal in a digital level correcting unit 101A, and a characteristic correcting unit By the balance setting unit 102B determining the coefficient for changing the characteristic of the signal in 101B, the digital level correction unit 101A and the characteristic correction unit 101B can perform adaptive processing. [Selected figure] Figure 1 Signal characteristic change device [0001] The present invention relates to a signal correction apparatus that changes the characteristics of an input signal. [0002] Desired listening environment (for example, indoor transfer characteristic) by changing characteristics (for example, volume, frequency characteristic, phase characteristic, tonality) of an input signal (for example, audio signal, audio signal) using DSP (Digital Signal Processor) or the like Development of signal characteristic change devices for providing a head-related transfer function and a volume). [0003] 08-05-2019 1 As an example, there is an equalizer device, in which the level (for example, power and signal amplitude) can be adjusted for each frequency band. When changing the level of the digital signal, raising the level may cause the signal to clip beyond the maximum level of the digital signal system. [0004] For this reason, the equalizer device that raises the level of the digital signal performs level control to lower the level of the input signal over the entire frequency band, and amplifies the level by the amount reduced by processing the digital signal after performing analog conversion. ing. [0005] Also, conventionally, in order to prevent the deterioration of the S / N ratio caused by the level increase and decrease as described above, the level of the input digital signal is reduced so as not to clip based on the maximum value of the level change amount. (See, for example, Patent Document 1). However, in the past, since the level was lowered by a fixed amount, an excessive reduction in volume might occur depending on the input signal. Japanese Patent Application Laid-Open No. 2002-345075 [0006] In the conventional signal characteristic change apparatus, the level of the digital signal is lowered to prevent the digital signal from being clipped, but the level is lowered by a fixed amount, so an excessive volume reduction occurs. Was a problem. The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a signal correction device capable of preventing an excessive decrease in volume while 08-05-2019 2 preventing clipping of digital signals. [0007] In order to achieve the above object, the present invention is a signal characteristic change device for changing the characteristic of an input signal, comprising: level control means for controlling the level of the input signal; and the input signal controlled in level by the level control means. Coefficient control means for calculating the level control coefficient for adjusting the level control of the level control means and the characteristic change coefficient for adjusting the level control of the characteristic change means based on the characteristic change means for changing the characteristics of And to be configured. [0008] As described above, in the present invention, when changing the characteristics of the input signal, the level of the input signal is controlled based on the feature quantity of the input signal in the previous stage. Therefore, according to the present invention, since adaptive processing can be performed according to the input signal, it is possible to provide a signal characteristic change device capable of preventing clipping while suppressing excessive volume reduction of the digital signal. [0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First Example FIG. 1 shows the configuration of a signal characteristic change apparatus according to an embodiment of the present invention. The signal characteristic change device includes a signal correction unit 101 and a characteristic change unit 102. This signal characteristic change device is mounted on, for example, a voice communication device such as a mobile phone, an electronic device such as a portable audio player, which converts a digital voice signal into an analog signal and outputs it. [0010] 08-05-2019 3 For example, in the case of a voice communication device, the communication device provided at the front stage of this circuit establishes a communication link with the communication device of the other party, and enables two-way communication with the other party. The received data received by the wireless communication unit is input signal x [n] (n = 1, 2, 3,...) For each unit of processing time (one frame = N samples) determined in advance by a decoder (not shown). , N) are decoded into digital signals. [0011] The input signal x [n] may be an audio signal or an audio signal. In the following description, the input signal x [n] is an audio signal. The range of N may be an integer of 1 or more, for example, a frame size of N = 160 samples. In the case of an audio signal, N is mainly used to the power of 2 such as 1024, 512, 256, and so on. [0012] Also, although the input signal x [n] is a signal represented by 16 bits, it is not limited to this, and even if it is a signal represented by b bits (b = 1, 2, 3. It may be a floating point signal. Hereinafter, the same conditions apply to signals to be described later (for example, d [n] and y [n] in FIG. 1). [0013] Subsequently, the signal correction unit 101 and the characteristic change unit 102 will be described. The signal correction unit 101 receives an input signal x [n] and outputs an output signal y [n] (n = 1, 2, 3,..., N) in which the characteristics of the signal are changed. [0014] The signal correction unit 101 includes a digital level correction unit 101A and a characteristic correction unit 101B. The digital level correction unit 101A performs dynamic range control (DRC) of the input signal x [n] using a level control coefficient TH input from the characteristic 08-05-2019 4 change unit 102 described later to calculate the signal level (eg, amplitude, power). It controls and outputs the signal d [n]. Specifically, when the level of the input signal x [n] is larger than the level control coefficient TH, the level of the input signal x [n] is attenuated and output according to the level control coefficient TH. [0015] On the other hand, when the level of the input signal x [n] is smaller than the level control coefficient TH, the level of the input signal x [n] is output without being changed. By the control as described above, it is possible to suppress in advance only a signal that is likely to be clipped. The digital level correction unit 101A may be any device that controls the signal level, and may be an automatic volume adjustment (AGC). [0016] Characteristic correction unit 101B changes the frequency characteristic of signal d [n] using characteristic change coefficient G (ω) input from characteristic change unit 102 described later. As a result, for example, it is possible to compensate for a degraded frequency band such as a speaker for a mobile phone handset or a speaker for a mobile phone hands-free, or to provide a special effect such as an indoor transfer characteristic or head transfer function. A listening environment can be realized. [0017] Specifically, signal d [n] is converted to a frequency domain signal and then multiplied by characteristic change coefficient G (ω), and the result is converted to a time domain signal and output as output signal y [n]. Do. The output signal y [n] is converted into an analog signal by a digital analog converter (D / A converter) in a subsequent stage not shown, and is amplified and output from the speaker through the amplifier. The characteristic correction unit 101B may change the frequency characteristic without converting to the frequency domain. [0018] In the present embodiment, the signal correction unit 101 is described as controlling the signal level, but the signal correction unit 101 is not limited to the characteristics of a signal such as an 08-05-2019 5 audio signal or an audio signal (for example, volume, frequency characteristics, phase characteristics, tonality). The configuration is not limited to the above as long as it changes the [0019] Characteristic changing unit 102 receives input signal x [n] and has level control coefficient TH that prevents clipping while suppressing excessive volume reduction of the signal for each frame, and characteristic change coefficient G (ω) (ω = 1 , 2, 3 ...). Here, the level control coefficient TH is a parameter used by the digital level correction unit 101A for amplifying or attenuating the level (for example, amplitude, power) of the signal to obtain a desired volume setting. Here, when the input signal x [n] is a 16-bit audio signal, the level control coefficient TH is in the range of 0 to 2 <16-1>. [0020] On the other hand, the characteristic change coefficient G (ω) is a parameter for changing the frequency characteristic, which is used by the characteristic correction unit 101B. Although ω indicates a frequency bin number, it may be a grouped frequency band unit. The level control coefficient TH and the characteristic change coefficient G (ω) are output for each frame. Therefore, the signal correction unit 101 can perform adaptive processing in accordance with the input signal, and can prevent clipping while suppressing excessive volume reduction of the signal. [0021] The characteristic change unit 102 includes a coefficient calculation unit 102A, a balance setting unit 102B, a digital level adjustment unit 102C, and a characteristic adjustment unit 102D. Hereinafter, each configuration will be described. [0022] 08-05-2019 6 The coefficient calculation unit 102A receives the input signal x [n] and outputs, as a coefficient p, a threshold of the minimum necessary level control coefficient for preventing clipping. The coefficient p is a feature of the input signal x [n] for each frame (for example, spectrum power absolute value, spectrum power average value, spectrum power dispersion value, spectrum power standard deviation value, amplitude average, amplitude maximum value, zero crossing number, Amplitude variance, amplitude standard deviation, amplitude difference dispersion between samples, amplitude difference standard deviation between samples, etc.) and minimum threshold of level control coefficients to prevent clipping Calculated based on the equation of [0023] As a result, since the coefficient p can be obtained by adaptive processing in accordance with the input signal for each frame, it is possible to prevent a clip while suppressing an excessive volume reduction of the signal. A specific configuration example of the coefficient calculation unit 102A will be described in detail later. [0024] The balance setting unit 102B receives the coefficient p as an input and makes a condition judgment so that sound quality deterioration (for example, distortion due to level control, unnaturalness in volume due to automatic volume control, sense of noise, etc.) does not occur. The temporary level control coefficient THp and the temporary characteristic change coefficient Gp (ω) are output. [0025] Here, the condition determination is to compare the magnitude relation between a value (minimum level control coefficient α) preset as the minimum value of the level control coefficient TH and the coefficient p. The minimum level control coefficient α is set so that the sound quality deterioration due to the control of the signal level does not occur. By calculating the temporary level control coefficient THp and the temporary characteristic change coefficient Gp (ω) based on the comparison result of the minimum level control coefficient α and the coefficient p, the sound quality deterioration due to the level control is prevented while the sound volume is excessively reduced. You can prevent the clip while suppressing the 08-05-2019 7 [0026] The specific operation of the balance setting unit 102B will be described. The balance setting unit 102B compares the coefficient p with the minimum level control coefficient α, and if the coefficient p is larger than the minimum level control coefficient α (α <p), it means that no speech degradation due to level control occurs. Therefore, the coefficient p is output as the temporary level correction coefficient THp as it is, and the temporary characteristic change coefficient G1 (ω) one frame before is output as the temporary characteristic change coefficient Gp (ω). [0027] Here, the temporary characteristic change coefficient G1 (ω) one frame before is the temporary characteristic change coefficient Gp (ω) calculated one frame before the present. The temporary characteristic change coefficient G1 (ω) one frame before may be information in which the characteristic one frame before the present is changed, and for example, the characteristic change coefficient G (ω) calculated one frame before the current ) May be. [0028] On the other hand, if the coefficient p is smaller than the minimum level control coefficient α (α> p), this means that voice deterioration occurs due to level control, so the minimum level control coefficient α is used as the provisional level correction coefficient THp. Output. Further, the amplification level and the attenuation level of the temporary characteristic change coefficient G1 (ω) one frame before are suppressed as shown in equation (1), and are output as the temporary characteristic change coefficient Gp (ω). [0029] [0030] 08-05-2019 8 In Equation (1), β is a parameter for weighting the suppression of the amplification level and the attenuation level of the temporary characteristic change coefficient Gp (ω), and β ≦ 1. If the minimum level control coefficient α is much larger than the balance control coefficient p (α >> p), the amplification level and the attenuation level of the temporary characteristic change coefficient Gp (ω) are greatly suppressed, and the processing does not substantially change the characteristics It becomes. [0031] If the minimum level control coefficient α and the coefficient p have the same value, the correction coefficient THp and the correction coefficient Gp (ω) may be determined under any of the above conditions. [0032] FIG. 2 is a diagram illustrating an example of the provisional level control coefficient THp set by the balance setting unit 102B. If the coefficient p is larger than the minimum level control coefficient α (1) (α <p), the temporary level control coefficient THp is determined based on the coefficient p. Here, the provisional level control coefficient THp may be determined by the coefficient p, and may not be output as the coefficient p as it is. [0033] On the other hand, when the coefficient p is smaller than the minimum level control coefficient α (2) (α> p), the temporary level control coefficient THp is determined based on the minimum level control coefficient α. Here, the provisional level control coefficient THp may be determined by the minimum level control coefficient α, and may not be output as the minimum level control coefficient α as it is. [0034] 08-05-2019 9 FIG. 3 is a diagram illustrating an example of the temporary characteristic change coefficient Gp (ω) set by the balance setting unit 102B. If the coefficient p is larger than the minimum level control coefficient α (1) (α <p), the temporary characteristic change coefficient Gp (ω) is determined based on the temporary characteristic change coefficient G1 (ω) one frame before . [0035] Here, the temporary characteristic change coefficient Gp (ω) may be determined by the temporary characteristic change coefficient G1 (ω) one frame before, and is output as the temporary characteristic change coefficient G1 (ω) one frame before. It does not have to be. [0036] On the other hand, if the coefficient p is smaller than the minimum level control coefficient α (2) (α> p), the temporary characteristic change coefficient Gp (ω) is the amplification level of the temporary characteristic change coefficient G1 (ω) one frame earlier and Suppress and output the attenuation level. Here, the temporary characteristic change coefficient Gp (ω) is not limited to the equation (1) as long as the amplification level and the attenuation level of the temporary characteristic change coefficient G1 (ω) one frame before are suppressed. [0037] The digital level adjustment unit 102C receives the temporary level control coefficient THp as an input to suppress a transient influence between adjacent frames. Specifically, the digital level adjustment unit 102C performs smoothing processing (smoothing processing) between the frames adjacent to the temporary level control coefficient THp according to Equation (2), and uses the value obtained by the smoothing processing as the level control coefficient TH. It is output to the correction unit 101A. Specifically, for R frame and subsequent ones, level control coefficient TH obtained by smoothing temporary level control coefficient THp according to equation (2) to suppress transient influence between adjacent frames. Ask and output this. [0038] 08-05-2019 10 [0039] The digital level correction unit 101A outputs the level control coefficient TH0 from the start of the call to the R-th frame (R ≧ 1). TH0 is a level control coefficient TH set in advance in the digital level correction unit 101A before the start of a call. Further, in the equation (2), THR indicates the level control coefficient TH calculated before the R frame. However, THR should just be information which controls the signal level before R frame, for example, suppose that it may be temporary level control coefficient THp before R frame. [0040] Also, φRj and φp are smoothing coefficients, and the weighting for the smoothing process can be changed. The digital level adjustment unit 102C only needs to suppress the transient influence between adjacent frames, and is not limited to the above example. [0041] Characteristic adjustment unit 102D receives the temporary characteristic change coefficient Gp (ω), performs smoothing processing (smoothing processing) between adjacent frames, and outputs characteristic change coefficient G (ω) set in characteristic correction unit 101B. . Specifically, the characteristic change obtained by smoothing the temporary characteristic change coefficient Gp (ω) in accordance with the equation (3) in order to suppress a transient influence between adjacent frames for the R frame and subsequent ones. The coefficient G (ω) is obtained and output. [0042] [0043] 08-05-2019 11 Note that from the call start to the R-th frame (Rω1), the characteristic correction unit 101B outputs the characteristic change coefficient G0 (ω). G0 (ω) is a characteristic change coefficient G (ω) set in advance in the characteristic correction unit 101B before the start of a call. [0044] In Equation (3), the characteristic change coefficient GR (ω) indicates the characteristic change coefficient G (ω) calculated before R frames. However, the characteristic change coefficient GR (ω) may be information in which the characteristics of the signal before R frame are changed, and may be, for example, a temporary characteristic change coefficient Gp (ω) before R frame. [0045] Also, φRj and φp are smoothing coefficients, and the weighting for the smoothing process can be changed. This does not have to be the same as the smoothing coefficient of the digital level adjustment unit 102C. The characteristic adjustment unit 102D may suppress transient influence between adjacent frames, and is not limited to this. [0046] Next, FIG. 4 shows a configuration example of the coefficient calculation unit 102A. The coefficient calculation unit 102A includes a feature amount extraction unit 102A1 and a regression operation unit 102A2. Furthermore, the feature quantity extraction unit 102A1 includes the extraction unit 102A11 to the extraction unit 102A14. Hereinafter, each configuration will be described. [0047] The feature amount extraction unit 102A1 receives the input signal x [n] as the feature amount 08-05-2019 12 (for example, spectrum power absolute value, spectrum power average value, spectrum power dispersion value, spectrum power standard deviation value, amplitude average, maximum amplitude value, A plurality of zero cross numbers, amplitude variance, amplitude standard deviation, amplitude difference variance between samples, amplitude difference standard deviation between samples, etc. are extracted for each frame, and the feature quantities A (m) (m = 1, 2, 3,. S) Output (S ≧ 1). Here, the feature amount extraction unit 102A1 is described as extracting four feature amounts, but it may be one that extracts one or more feature amounts. [0048] Extracting section 102A11 takes input signal x [n] as input, converts the signal in the time domain into a signal in the frequency domain, calculates the spectrum power for each frequency bin, and maximizes the spectrum power among the number of frequency bins ω (Maximum spectrum power) is calculated and output as feature quantity A (1). The extraction unit 102A11 includes a frequency domain conversion unit 102A111, a power calculation unit 102A112, and a maximum power calculation unit 102A113. [0049] Frequency domain conversion section 102A 111 receives input signal x [n] as input, and performs operation such as FFT (Fast Fourier Transform) to convert input signal x [n] from a signal in the time domain to a signal X (ω) in the frequency domain. Convert and output. [0050] The frequency domain transform unit 102A 111 may perform discrete Fourier transform (DFT), discrete cosine transform (DCT), Walsh Hadamard transform (WHT), harlet transform (HT), or slant transform. It is also possible to substitute other orthogonal transform that transforms into a frequency domain represented by (SLT: Slant Transform) and Karhunen-Loeve Transform (KLT). [0051] Specifically, if the input signal x [n] (n = 1, 2, 3,..., N) is an input signal in the time domain of n samples, then if the order of the FFT is N, the signal in the frequency domain X (ω) (ω = 1, 2, 3..., N) will have N frequency bin numbers. 08-05-2019 13 Note that the signal of the previous frame may be overlapped with the signal to be subjected to FFT or zero-padded, the data length may be a power of 2, and the FFT order N may be a power of 2. [0052] Power calculator 102A112 receives frequency domain signal X (ω) as input, calculates spectrum power for each frequency bin, and outputs it as spectrum power pow (ω) (ω = 1, 2, 3,..., N) . The power calculation unit 102A112 calculates the spectral power of the input signal for each frequency bin according to Equation (4). [0053] [0054] However, the output of the power calculation unit 102A112 may be one that does not square X (ω). Also, as shown in the equation (5), the spectrum power may be calculated using the average spectrum power pow (ω) using signals from the current to the number of R frames before (R is an integer). [0055] [0056] By using the average spectral power in this manner, it is possible to suppress transient effects between adjacent frames. 08-05-2019 14 Here, Xi (ω) shown in the equation (5) is a frequency domain signal X (ω) i frames before (i = 1, 2, 3..., R) from the present. Also, as shown in equation (6), the spectral power pow (ω) may be weighted by multiplying it with the characteristic change coefficient G0 (ω). [0057] [0058] By weighting in this manner, a more ideal coefficient p can be calculated. In addition, what is necessary is just to calculate spectrum power from frequency domain signal X ((omega)), and it is not limited to the above structures. [0059] Maximum power calculation unit 102A113 receives spectral power pow (ω), detects maximum spectral power pow_MAX among all frequency bins, and outputs it as feature quantity A (1). Also, a value normalized by dividing the spectral power pow_MAX by the sum of all frequency bins according to the equation (7) may be output as the feature value A (1). [0060] [0061] In this equation (7), A (1) is 1 or less (A (1) ≦ 1), but if it is close to 1, it means that the spectral power is concentrated in a specific frequency bin. If the characteristic is changed so as to amplify a specific frequency bin, it can be determined in advance whether or not a clip occurs in the feature quantity A (1) of this equation (7). The maximum power calculation unit 102A 113 may calculate the spectrum power that is the maximum among all the frequency bins, and is not limited to the above example. 08-05-2019 15 [0062] Extraction section 102A12 takes input signal x [n] as input, converts the signal of time domain to a signal of frequency domain, calculates spectrum power for each frequency bin, and calculates its average value (average spectrum power) , And output it as feature quantity A (2). The extraction unit 102A12 includes a frequency domain conversion unit 102A111, a power calculation unit 102A112, and an average power calculation unit 102A121. [0063] Average power calculation unit 102A121 receives spectrum power pow (ω), detects an average value pow_AVG (average spectrum power) of spectrum power for each frequency bin, and outputs it as feature quantity A (2). Specifically, it is determined according to the number (8). [0064] [0065] The extraction unit 102A13 receives the input signal x [n], obtains the dispersion value of the amplitude, and outputs it as the feature value A (3). The extracting unit 102A13 includes an amplitude variance calculating unit 102A131. Amplitude dispersion calculation unit 102A131 receives input signal x [n], obtains the dispersion value of the amplitude, and outputs it as feature amount A (3). Specifically, it is determined according to equation (9). Here, mean in equation (9) is the average value of x (n). [0066] [0067] 08-05-2019 16 Extraction unit 102A14 receives input signal x [n], obtains the number of zero crossings, and outputs it as feature quantity A (4). The extraction unit 102A14 includes a zero cross number calculation unit 102A141. [0068] The zero cross number calculation unit 102A 141 receives the input signal x [n], counts the zero cross number (when x [n] = 0 and when the positive and negative of x [n] are inverted), Output as (4). The zero crossing number is used to determine voiced speech and unvoiced speech, so that it is possible to prevent clipping while suppressing excessive volume reduction of the signal separately for voiced speech and unvoiced speech. [0069] The regression operation unit 102A2 calculates the threshold value of the minimum necessary level control coefficient for preventing clipping from the feature amount. For example, with the feature amount A (m) (m = 1, 2, 3, 4) as an input, the coefficient p is calculated based on the equation of the square error minimum criterion pre-regression analysis such as equation (4). Output. [0070] [0071] Here, ζ (m) (m = 1, 2, 3, 4) in the equation (10) is a regression analysis of the threshold of the minimum level control coefficient necessary to prevent clipping and the feature amount A (m) It is a coefficient and can be set in advance. If the correlation between the threshold of the minimum necessary level control coefficient for preventing clipping and the feature amount A (m) is high, a more ideal coefficient p can be 08-05-2019 17 calculated. [0072] As described above, in the signal characteristic change device configured as described above, the coefficient calculation unit 102A determines the coefficient p according to the input signal x [n], and the balance setting unit 102B determines the digital level correction unit 101A from the coefficient p. The coefficient for controlling the level of the signal at the time T.sub.1 and the coefficient for changing the characteristic of the signal at the characteristic correction unit 101B are determined. Therefore, according to the signal characteristic change device of the above configuration, the digital level correction unit 101A and the characteristic correction unit 101B can perform adaptive processing in accordance with the coefficient p of the input signal x [n], thereby preventing clipping of the digital signal. However, excessive volume reduction can be prevented. [0073] Second Embodiment Next, a second embodiment according to the present invention will be described. FIG. 5 shows the configuration. In the following description, the same components as those in the first embodiment described above are denoted by the same reference numerals, and redundant description will be omitted as necessary to make the description clear. [0074] The characteristic changing unit 102 according to the second embodiment receives an output signal y [n] obtained by changing the characteristic of the signal in addition to the input signal x [n] as an input, and suppresses an excessive decrease in volume of the signal for each frame. However, the level control coefficient TH and the characteristic change coefficient G (ω) (ω = 1, 2, 3. The characteristic change unit 102 according to the second embodiment uses a coefficient calculation unit 102A 'instead of the coefficient calculation unit 102A used in the characteristic change unit 102 according to the first embodiment. [0075] 08-05-2019 18 The coefficient calculation unit 102A ′ receives the output signal y [n] obtained by changing the characteristic of the signal in addition to the input signal x [n], and uses the threshold of the minimum necessary level control coefficient for preventing clipping as the coefficient p. Output. As shown in FIG. 6, the coefficient calculation unit 102A 'includes a feature quantity extraction unit 102A'1 and a regression operation unit 102A'2. [0076] The feature quantity extraction unit 102A'1 includes the extraction unit 102A'11, the extraction unit 102A'12, the extraction unit 102A'13, and the extraction unit 102A'14, and the input signal x In addition to [n], an output signal y [n] in which the characteristics of the signal are changed is input, and a plurality of feature quantities are extracted for each frame, feature quantity A (m) and feature quantity B (m) (m = 1 , 2, 3, 4). [0077] Here, although four feature quantities are extracted by the feature quantity extraction unit 102A'1, the feature quantities include spectrum power absolute value, spectrum power average value, spectrum power dispersion value, spectrum power standard deviation value, and amplitude average One or more of an amplitude maximum value, a zero cross number, an amplitude dispersion, an amplitude standard deviation, an amplitude difference dispersion between samples, an amplitude difference standard deviation between samples, and the like may be calculated. [0078] The extraction unit 102A'11 receives the input signal x [n] and the output signal y [n] obtained by changing the characteristics of the signal, converts the signal in the time domain into a signal in the frequency domain, and converts the spectrum for each frequency bin The power is calculated, and the spectrum power (maximum spectrum power) that is the largest among the frequency bin numbers ω is output as the feature amount A (1) and the feature amount B (1). The extraction unit 102A'11 includes a frequency domain conversion unit 102A'111, a power calculation unit 102A'112, and a maximum power calculation unit 102A'113. [0079] 08-05-2019 19 The frequency domain transform unit 102A '111 receives an output signal y [n] obtained by changing the characteristic of the signal in addition to the input signal x [n] as an input and performs an operation such as FFT (Fast Fourier Transform) to obtain the input signal x [ n] is converted from the time domain signal to the frequency domain signal X (ω), and the output signal y [n] is converted from the time domain signal to the frequency domain signal Y (ω). [0080] The power calculator 102A'112 receives the frequency domain signal Y (ω) in addition to the frequency domain signal X (ω), calculates the spectral power for each frequency bin, and calculates the spectral powers xpow (ω) and ypow Output as ω) (ω = 1, 2, 3..., N). The power calculator 102A'112 calculates the spectral power of the signal for each frequency bin according to the equations (11) and (12). [0081] [0082] [0083] Maximum power calculation unit 102A '113 receives spectral powers xpow (ω) and ypow (ω), detects maximum spectral powers xpow_MAX and ypow_MAX among all frequency bins, respectively, and detects them as feature amount A (1) And the feature amount B (1). [0084] The extraction unit 102A'12 receives the input signal x [n] and the output signal y [n] obtained by changing the characteristics of the signal, converts the signal in the time domain into a signal in the frequency domain, and converts the spectrum for each frequency bin The power is calculated, the average value (average spectrum power) is calculated, and it is output as the feature amount A (2) and the feature amount B (2). 08-05-2019 20 The extraction unit 102A12 includes a frequency domain conversion unit 102A111, a power calculation unit 102A112, and an average power calculation unit 102A'121. [0085] Average power calculation unit 102A '121 receives spectrum powers xpow (ω) and ypow (ω), detects average values xpow_AVG and ypow_AVG (average spectrum power) of spectrum power for each frequency bin, and detects them as feature amount A Output as (2) and the feature amount B (2). Specifically, it is calculated according to the equations (13) and (14). [0086] [0087] [0088] The extraction unit 102A'13 receives the input signal x [n] and the output signal y [n] obtained by changing the characteristics of the signal as input, and obtains the dispersion value of the amplitude, and uses it to calculate the feature amount A (3) Output as B (3). The extracting unit 102A'13 includes an amplitude variance calculating unit 102A'131. Amplitude dispersion calculation unit 102A '131 receives output signal y [n] obtained by changing the characteristic of the signal in addition to input signal x [n], and obtains the dispersion value of the amplitude, and calculates it as feature amount A (3). And the feature amount B (3). [0089] 08-05-2019 21 Specifically, it is determined according to the following equations (15) and (16). Here, xmean in the following equation (15) is an average value of x [n], and ymean in the following equation (16) is an average value of y [n]. [0090] [0091] [0092] The extraction unit 102A'14 receives the output signal y [n] obtained by changing the characteristic of the signal in addition to the input signal x [n], obtains the number of zero crossings, and calculates the number of feature points A (4) and the feature amount Output as B (4). The extracting unit 102A'14 includes a zero crossing number calculating unit 102A'141. [0093] The zero cross number calculation unit 102A '141 receives the output signal y [n] obtained by changing the characteristic of the signal in addition to the input signal x [n], and receives the zero cross number (x [n] = 0, y [n] = In the case of 0, and when the positive and negative of x [n] and y [n] are inverted, the result is output as the feature amount A (4) and the feature amount B (4). The zero crossing number is used to determine voiced speech and unvoiced speech, so that it is possible to prevent clipping while suppressing excessive volume reduction of the signal separately for voiced speech and unvoiced speech. [0094] 08-05-2019 22 The regression operation unit 102A'2 receives the feature amount A (m) and the feature amount B (m) (m = 1, 2, 3, 4) as an input, and uses the equation of the square error minimum criterion which is regressed in advance. Based on the factor p is output. Specifically, it is expressed by equation (17). [0095] [0096] Here, ζ ′ (m) and ξ ′ (m) (m = 1, 2, 3..., S) in the equation (17) are threshold values and characteristics of minimum necessary level control coefficients for preventing clipping in advance It is the coefficient which carried out regression analysis of quantity A (m) and featurevalue B (m), and can be preset. Here, since the feature amount B (m) is a feature amount of the output signal obtained by changing the characteristics of the signal, it is easy to determine whether the signal is clipped. This means that the correlation with the threshold of the minimum level control coefficient that prevents clipping is higher, and the ideal coefficient p can be calculated. [0097] As described above, even with such a configuration, the same effect as that of the first embodiment can be obtained. Moreover, according to such a configuration, since the feature amount B (m) is used, it is easy to determine whether the signal is clipping. This makes it possible to calculate a more ideal coefficient p because the correlation with the threshold of the minimum level control coefficient that prevents clipping is high. That is, according to the coefficient p, the digital level correction unit 101A and the characteristic correction unit 101B can perform adaptive processing with high accuracy. Therefore, while the digital signal is effectively prevented from being clipped, excessive volume reduction is prevented. it can. 08-05-2019 23 [0098] Third Embodiment Next, a third embodiment according to the present invention will be described. FIG. 7 shows the configuration. In the following description, the same components as those in the above-described embodiment are denoted by the same reference numerals, and redundant description will be omitted as appropriate to simplify the description. [0099] As shown in FIG. 7, the signal correction unit 101 in the third embodiment includes an automatic volume correction unit 101C in addition to the digital level correction unit 101A and the characteristic correction unit 101B. In the following description, the automatic volume correction unit 101C is located downstream of the digital level correction unit 101A. However, the automatic volume correction unit 101C may be upstream of the digital level correction unit 101A or downstream of the characteristic correction unit 101B. [0100] Automatic volume correction unit 101C receives signal d [n], performs automatic volume control, and outputs it as signal z [n]. The volume that is automatically set is determined based on a volume control coefficient GAIN [n] (details will be described later) output from the characteristic change unit 102 described later. That is, the signal d [n] is amplified or attenuated by the volume control coefficient GAIN [n] to obtain an output signal z [n] (z [n] = GAIN [n] · d [n]). By doing this, it is possible to automatically adjust to an appropriate sound pressure (such as a sound pressure that human feels comfortable). [0101] The characteristic change unit 102 uses a coefficient calculation unit 102Aa instead of the coefficient calculation unit 102A used in the characteristic change unit 102 described in the above-described embodiment. Also, a balance setting unit 102Ba is used instead of the balance setting unit 102B. Furthermore, an automatic volume adjustment unit 102E is used. 08-05-2019 24 [0102] As shown in FIG. 8, the coefficient calculation unit 102Aa receives the input signal x [n], outputs the threshold of the minimum level control coefficient necessary to prevent clipping as the coefficient p1, and further performs automatic volume control. The coefficient is output as the coefficient p2. The coefficient calculation unit 102Aa includes a feature quantity extraction unit 102A and a regression operation unit 102A2a. [0103] The regression operation unit 102A2a receives the feature amount A (m) (m = 1, 2, 3, 4) as an input, and calculates the coefficient p1 and the coefficient p2 based on the equation of the square error minimum criterion which has been subjected to regression analysis in advance. Output. Specifically, the coefficients p1 and p2 are calculated by the equations (18) and (19). [0104] [0105] [0106] Here, ζa (m) (m = 1, 2, 3, 4) in the equation (18) represents the threshold value of the minimum level control coefficient required to prevent clipping in advance and the feature value A (m) It is an analyzed coefficient and can be set in advance. [0107] Further, ξa (m) (m = 1, 2, 3, 4) in the equation (19) is a coefficient obtained by regression analysis of the coefficient for automatically adjusting to the appropriate sound pressure in advance and the feature quantity A (m) And can be set in advance. If correlation between feature value A (m) and threshold value for minimum necessary level control coefficient to prevent clipping and coefficient for automatic adjustment to appropriate 08-05-2019 25 sound pressure is high, more ideal coefficient p1 and coefficient p2 are calculated can do. [0108] The balance setting unit 102Ba receives the coefficient p1 and the coefficient p2 and makes a condition judgment so that sound quality deterioration (for example, distortion due to level control, unnaturalness in volume due to automatic volume control, sense of noise, etc.) does not occur. The temporary level control coefficient THp, the temporary characteristic change coefficient Gp (ω), and the temporary sound volume control coefficient GAINp are output. [0109] Here, the provisional level control coefficient THp and the provisional characteristic change coefficient Gp (ω) are determined by the same processing as in the first embodiment according to the coefficient p1. The temporary volume control coefficient GAINp obtains an absolute value | GAINp1-p2 | of the difference between the temporary volume control coefficient GAINp1 and the coefficient p2 determined one frame earlier than the present, and is smaller than the upper limit value γ (| GAINP1-p2 | <γ ), The provisional volume control coefficient GAINp is output as the coefficient p2 as it is. [0110] On the other hand, when it is larger than the upper limit value γ (| GAINp1-p2 |> γ), the temporary volume control coefficient GAINp is limited and output to γ. Here, the upper limit value γ is a volume difference that does not cause a hearing problem, and is generally about 3 dB. However, the upper limit value γ is not limited to this. By performing such processing, it is possible to prevent the sound quality deterioration (unnaturalness of the volume due to the automatic volume control). 08-05-2019 26 [0111] Automatic volume adjustment unit 102E receives the temporary volume control coefficient GAINp, performs smoothing processing (smoothing processing) on a sample basis to suppress transient influence between adjacent frames, and is set in automatic volume correction unit 101C. Output the volume control coefficient GAIN [n]. Specifically, it is determined according to equation (20). [0112] [0113] Here, the volume control coefficient GAIN [n] can be calculated using the volume control coefficients GAIN [n−L] to GAIN [n−1] calculated up to S samples before the present. Also, φLj and φp are smoothing coefficients, and weighting for smoothing can be changed. It should be noted that this automatic volume adjustment unit 102E only needs to suppress transient effects between adjacent frames, and may use smoothing processing as shown in, for example, Japanese Patent Application Laid-Open No. P2007-93827. [0114] As mentioned above, even if it is such composition, the same effect as an example mentioned above is exhibited. Moreover, according to such a configuration, it is possible to automatically adjust to an appropriate sound pressure in addition to preventing an excessive decrease in sound volume while preventing clipping of the digital signal. [0115] The present invention is not limited to the above embodiment as it is, and at the implementation stage, the constituent elements can be modified and embodied without departing from the scope 08-05-2019 27 of the invention. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiment. Further, for example, a configuration in which some components are deleted from all the components shown in the embodiment is also conceivable. [0116] Furthermore, the components described in different embodiments may be combined as appropriate. For example, in the above embodiment, the characteristic change unit 102 is described as performing signal processing with a plurality of functional blocks as shown in FIG. It is possible to realize with one chip. [0117] In this case, the signal processing may be performed according to the flowchart shown in FIG. That is, after acquiring the input signal x [n] in step 2a, in step 2b, processing similar to the feature quantity extraction unit 102A1 is performed, and in step 2c, processing similar to the regression operation unit 102A2 is performed. Then, in step 2d, the same process as the balance setting unit 102B is performed, and in step 2e, the same process as the digital level adjustment unit 102C and the characteristic adjustment unit 102D is performed. [0118] It goes without saying that the present invention can be implemented in various ways without departing from the scope of the present invention. [0119] FIG. 1 is a circuit block diagram showing a configuration of a signal characteristic change device according to an embodiment of the present invention. FIG. 7 is a view showing an example of a provisional level control coefficient THp set by the balance setting unit of the signal characteristic change device according to the embodiment of the present invention. The figure showing an example of the temporary characteristic change 08-05-2019 28 coefficient Gp ((omega)) set by the balance setting part of the signal characteristic change apparatus concerning one Embodiment of this invention. The structural example of 102 A of coefficient calculation parts of the signal characteristic change apparatus concerning one Embodiment of this invention. The circuit block diagram which shows the structure of the signal characteristic change apparatus concerning the 2nd Embodiment of this invention. The structural example of coefficient calculation part 102A 'of the signal characteristic change apparatus concerning the 2nd Embodiment of this invention. The circuit block diagram which shows the structure of the signal characteristic change apparatus concerning the 3rd Embodiment of this invention. The structural example of the coefficient calculation part 102Aa of the signal characteristic change apparatus concerning the 3rd Embodiment of this invention. The flowchart for demonstrating the process of the signal correction apparatus concerning one Embodiment of this invention. [0120] 101 Signal correction unit 102 Characteristic change unit 101A Digital level correction unit 101B Characteristic correction unit 102A Coefficient calculation unit 102B Balance setting unit 102C Digital level adjustment unit 102D Characteristic adjustment unit 102A1 ... feature amount extraction unit 102A2 ... regression operation unit 102A2, 102A11 ... extraction 1 unit, 102A12 ... extraction 2 unit, 102A13 ... extraction 3 unit, 102A14 ... extraction 4 unit, 102A1S ... extraction S unit, 102A 111 ... frequency domain conversion unit 102A112 ... power calculation unit, 102A 113 ... maximum power calculation unit, 102A 121 ... average power calculation unit, 102A 131 ... amplitude dispersion calculation unit, 102A 141 ... zero crossing number calculation unit. 08-05-2019 29

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