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 JP2006174081 PROBLEM TO BE SOLVED: To improve reproduction characteristics of a small volume signal from a speaker. SOLUTION: In the case where the linearity of the output level to the input signal is substantially secured above the predetermined level and the output level to the input signal decreases below the predetermined level as the input / output characteristic of the connected speaker device, The correction processing to compensate for the decrease in the output level is performed on the signal component below the predetermined level of the input audio signal, and the gain to increase the signal component below the predetermined level at least in the low region is reduced. It was set higher than the other frequency bands by setting the gain above compensation. [Selected figure] Figure 2 Audio signal processing method and apparatus [0001] The present invention relates to an audio signal processing method and apparatus for performing characteristic correction in the case of reproducing an audio signal from a speaker apparatus, and is particularly suitable for use in a speaker apparatus for high fidelity reproduction capable of reproducing high sound quality. It relates to technology. [0002] Conventionally, various configurations have been put to practical use as speaker devices for high fidelity reproduction capable of high-quality sound reproduction. 08-05-2019 1 For example, there is a three-way speaker device in which a reproduction band of an audio signal is divided into three bands of low, middle, and high bands, and separate speaker units are prepared for each band. This 3-way speaker device can reproduce the input audio signal faithfully from the low band to the high band by using a speaker unit for each band that has good reproduction characteristics in each band. Generally, the reproduction characteristic is better than that of a so-called full range type speaker unit in which audio of all bands is output by one speaker unit. [0003] Further, in addition to the configuration for enhancing the reproduced sound of the speaker device such as the 3-way configuration and the 2-way configuration as described above, the characteristic of the audio signal itself supplied to the speaker device is It is also performed to correct on the device side to improve the characteristics of the audio output from the speaker device as a result. For example, an audio amplifier device that performs processing such as amplification of an audio signal that drives a speaker device may perform correction called loudness control. This loudness control performs correction processing that enhances the output level compared to the midrange part with the bass part and the trebleband part, and corrects that the low band and the high band are heard mainly when the volume is small. It is a thing. [0004] FIG. 11 shows an example of characteristics when the conventional loudness correction is performed. As shown in FIG. 11, the low band fL is lifted, and the high band fH is also lifted. [0005] Patent Document 1 describes an example of a reproduction configuration when loudness correction is performed. JP 2002-171589 A [0006] 08-05-2019 2 However, since the loudness-controlled playback sound simply boosts the signal of a specific frequency band almost uniformly regardless of the level, it is not strictly a reproduction that is faithful to the input audio signal, but rather the input audio. It has been desired to develop a speaker device capable of faithful reproduction to a signal. That is, since the conventional loudness-controlled reproduction sound is reproduced by enhancing the sound which is hard to hear when the volume is small, the bass and treble parts become easier to hear compared to the reproduction sound without the loudness control, and the sound quality to some extent As shown in FIG. 11, the signal component of a specific frequency band is uniformly enhanced at either a small level or a large level, so that signal components that need not be enhanced are improved. Also, the sound may be unnaturally reproduced as a result. [0007] Here, to explain the problem of the reproduced sound in the conventional speaker device, there is a problem of a small amplitude signal as an example in the case where the reproduced sound does not faithfully reproduce the input audio signal. That is, for example, as shown in FIG. 7A, it is assumed that an input audio signal S1 having a waveform in which a waveform having a relatively large amplitude and a waveform having a relatively small amplitude are continuous is input to the speaker. At this time, the waveform of the output audio signal S2 from the speaker is substantially the same as the input signal S1 for the waveform of relatively large amplitude, but the amplitude of the waveform of relatively small amplitude is higher than that of the input signal S1. It tends to be smaller. This is because a speaker unit having a general diaphragm capable of outputting a relatively loud sound has poor reproduction characteristics of a small volume signal with a small amplitude, and the linearity of the input / output characteristics of the small volume signal ( Linearity) is not ensured. [0008] Similarly, for example, as shown in FIG. 7B, the input audio signal S3 of a waveform of relatively large amplitude and the input audio signal S4 of a waveform of relatively small amplitude temporally overlap each other, so that The audio signal S5 obtained by combining the two signals S3 and S4 is output, but the output audio signal S6 having a waveform whose level is lower than the waveform of the combined signal S5 is output from the speaker. For example, when the sounds of various instruments are simultaneously reproduced as the audio to be reproduced from the speaker, such as symphony, such an output state may occur. 08-05-2019 3 [0009] Furthermore, for example, as shown in FIG. 7C, when there is an impulse signal in which the amplitude of the signal of a specific single frequency gradually decreases as the input audio signal S7, the waveform of the output audio signal S8 from the speaker Also, as the level decreases, the followability deteriorates. [0010] In any of the examples shown in FIG. 7, as the output from the speaker, the output level of the small volume signal having a small amplitude becomes smaller than the input signal level, and the linearity of the small signal is not maintained. When frequency analysis is performed on the state shown in FIG. 6, for example, the state shown in FIG. 8 is obtained. The example of FIG. 8 is an example in which the sensitivities of the fundamental wave f1 and the harmonics f2 and f3 that are harmonics of the fundamental wave are analyzed. The fundamental wave f1 with a high level is output as it is, but the harmonics f2 and f3 whose levels are smaller than the fundamental wave have output sensitivities shown by a solid line that is lower than the original level shown by a broken line. ing. [0011] FIG. 9 is a diagram showing output characteristics from low to high frequencies at multiple levels of signal levels. FIG. 9 (a) is an ideal characteristic, and FIG. 9 (b) is an actual speaker output. It is the figure which showed the characteristic. As shown in FIG. 9A, in an ideal state, it is assumed that the four levels L1, L2, L3, and L4 have flat characteristics from low frequency to high frequency at substantially equal intervals. At this time, as the output characteristics of the actual speaker shown in FIG. 9 (b), for the levels L1, L2 and L3 having high output levels, output characteristics substantially equivalent to the ideal characteristics can be secured, but the lowest level The characteristic of L4 is a level which is lowered in any frequency band by the sensitivity α from the originally necessary level. [0012] It is an input / output characteristic diagram of FIG. 10 that such a decrease in sensitivity is seen 08-05-2019 4 as a characteristic of a specific frequency. As shown in FIG. 10, the characteristic x of the broken line in which the output level increases linearly with the increase of the input signal level to the speaker has to be originally required. In this case, the level changes almost linearly, but below a specific level, the movement of the diaphragm with respect to the input is bad, and the output sensitivity to the input has a characteristic y of a curve that is very bad. [0013] Specifically, for example, assuming that the maximum level of listening by a general speaker is 70 to 100 spl (sound pressure level), a signal which is -30 dB to -60 dB lower than the maximum level is correct for the maximum level- It means that the volume lowered by 30 dB to -60 dB is not output (not proportional). Assuming that the volume of the output of the amplifier device is reduced by 50 spl from 100 spl, the volume at around 50 spl should be obtained originally, but in practice only 40 spl whose output is 10 spl lower is actually obtained, for example. It will not be possible. That is, it means that linearity can not be accurately obtained, and it has been found by analysis of the present inventor that it is one of the major causes for not obtaining satisfactory sound quality. [0014] By the way, as the reproduction characteristics of the audio signal from the speaker device, if the difference between the input and output levels of the characteristic y shown in FIG. 10 described above can be corrected, the linearity of the input and output characteristics can be improved in characteristics. Although it can, depending on the reproduction conditions, such correction alone may not be sufficient. [0015] The present invention has been made in view of the foregoing, and it is an object of the present invention to improve the reproduction characteristics of a small volume signal from a speaker. [0016] According to the present invention, the linearity of the output level with respect to the input signal is substantially secured above the predetermined level as the input / output characteristic of the connected speaker device, and the output level with respect to the input signal decreases below the predetermined level. The correction processing to compensate for the decrease in the output level is performed on the signal component below the predetermined level of the input audio signal, and the gain to increase the signal component below the predetermined level at 08-05-2019 5 least in the low region is reduced. It is set to gain more than the compensation, and is higher than other frequency bands. [0017] In this way, a signal with a relatively large amplitude above a predetermined level is not enhanced, and the difference between the input / output level of a relatively small level signal below a predetermined level resulting from the characteristics of the speaker device is corrected It is possible to enhance low-level low-level signals that may be audible and audible. [0018] According to the present invention, a signal with a relatively large amplitude above a predetermined level is not enhanced, and the difference between the input and output levels of a relatively small level signal below a predetermined level resulting from the characteristics of the speaker device is corrected. It is possible to enhance low-level low-level signals that may sound deficient in hearing, and to improve playback sound quality without disturbing the overall playback balance. [0019] In this case, as the correction processing, the gain for enhancing the signal component below the predetermined level in the high region is increased, and the gain in the middle region is set to the gain that compensates for the reduction in the speaker device. Even small level signals can be enhanced well. [0020] In addition, a correction state in which only the decrease in output is compensated substantially uniformly in almost all frequency bands output by the speaker device, and a correction state in which the gain in excess of the reduction in a specific frequency band is set are selected. By being able to set to, it is possible to select the state in which only the correction based on the characteristics of the speaker device is performed and the state in which the low frequency range is enhanced. [0021] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 6. 08-05-2019 6 FIG. 1 is a diagram showing an example of a system configuration according to the present embodiment. The present embodiment is an audio reproduction system connected with a speaker device, and FIG. 1 is a diagram showing an example of the entire system configuration. In this example, the audio signal source 10 is connected to the amplifier device 20, and the audio signal source 10 reproduces an audio signal recorded (stored) in a medium such as a CD (disc) or memory, and reproduces the audio signal. The audio signal to be output is supplied to the amplifier device 20, and the amplifier device 20 performs processing to convert the audio signal into an audio signal for driving the speaker device. The amplifier device 20 includes the operation unit 20a, and can adjust the processing state of the audio signal by the user operation of the operation unit 20a. [0022] In the case of this example, as audio signal processing in the amplifier device 20, correction processing (dynamic range control processing to be described later) based on input / output characteristics of the connected speaker device can be performed. In addition, loudness control processing can be performed. The on / off of each correction process can be set by the user operation of the operation unit 20a, for example. The details of the specific correction process in these amplifier devices 20 will be described later. [0023] 08-05-2019 7 Here, the audio signal output from the audio signal source 10 is a signal of two channels of an audio signal for the left channel and an audio signal for the right channel. The left channel audio signal output from the amplifier device 20 is supplied to the left channel speaker device 30L for output, and the right channel audio signal is supplied to the right channel speaker device 30R for output. [0024] The configuration of each of the speaker devices 30L and 30R will be described. Each of the speaker devices 30L and 30R includes one speaker unit 31 (FIG. 2) as a speaker unit as sound output means for outputting audio. Each of the speaker units 31 is a so-called full-franking type speaker unit having a characteristic that is substantially flat in the audible band as a characteristic seen from the output frequency band and that is outputted from low to high frequencies There is a relatively large diaphragm and a relatively large speaker unit capable of outputting a high volume signal. As for the speaker unit 31, since the diaphragm is relatively large, the linearity (linearity) of the input / output characteristics of large signals above a predetermined level is substantially maintained, and the linearity of the input / output characteristics is not secured below the predetermined level. The output signal level is inferior to the input signal level. That is, in the column of background art, the speaker unit having the characteristic y described with reference to FIG. 10 is used. A speaker unit having such characteristics is general as a speaker. [0025] In this example, in the audio reproduction system to which the speaker devices 30L and 30R using the speaker unit 31 having such characteristics are connected, at the amplifier device 20 side that processes the audio signal supplied to the speaker devices 30L and 30R, Signal characteristic correction is performed. [0026] FIG. 2 is a diagram showing a configuration for characteristic correction in the amplifier device 20 of the present example, and shows a connection configuration up to the speaker unit 31 constituting the speaker devices 30L and 30R. 08-05-2019 8 As shown in FIG. 2, an audio signal obtained at the audio signal input terminal 21 of the amplifier device is supplied to an analog / digital converter 41 to be converted into a digital audio signal, and the converted digital audio signal is Signal processor 42 is supplied. In this example, this DSP 42 is used as a means for correcting audio signal characteristics. The correction state of the DSP 42 is controlled by the control unit 44. The control state of the control unit 44 is set according to the operation status of the operation unit 20a. Further, the control unit 44 is connected with a memory 45 for storing data necessary for control, so that data on the correction state in the DSP 42 is also stored. [0027] As correction processing in the DSP 42, for example, signal components of all frequency bands in digital operation processing are divided into signal components above a predetermined level and signal components below a predetermined level, and nothing about signal components above a predetermined level Do not perform correction processing. Then, for signal components less than the predetermined level, correction processing is performed such that the increase rate becomes higher as the output level becomes lower than the input level. Details of this correction process will be described later. [0028] Then, the signal component above the predetermined level not subjected to the correction process and the signal component below the predetermined level subjected to the correction process are synthesized, and the synthesized signal is supplied to the digital / analog converter 43 to be an analog audio signal. Convert. [0029] The converted analog audio signal is supplied to the amplifier 24, amplified for driving the speaker, and the amplified audio signal is supplied to the speaker unit 31 in the speaker devices 30L and 30R to output the audio signal (release Sound). [0030] Here, to describe audio signal correction processing in the amplifier device 20 of this example, so-called dynamic range control processing can be performed to correct the badness of the input / output characteristics of the speaker unit 31 and the dynamic range control processing In addition to the above, the loudness control process can be performed. 08-05-2019 9 [0031] That is, the setting example of the audio signal correction processing state based on the operation by the operation unit 20a of the amplifier device 20 of this example will be described with reference to the flowchart of FIG. As a state, it is determined whether the dynamic range control is set to ON (step ST11). In this determination, when the dynamic range control is set to OFF, the control unit 44 does not execute the correction process regarding the dynamic range control in the DSP 42 (step ST15). [0032] If it is determined in step ST11 that the dynamic range control is on, it is further determined whether the loudness control is set to on (step ST12). If the loudness control is set to OFF by this determination, the control unit 44 executes only the dynamic range control processing as the correction processing in the DSP 42 (step ST13). When the loudness control is set to ON, the control unit 44 executes the dynamic range control process in the state where the loudness correction is performed as the correction process in the DSP 42 (step ST14). [0033] Next, specific processing states of the dynamic range control processing selectively executed in this manner and the dynamic range control processing in the state where the loudness correction is performed will be described. First, dynamic range control processing in a state where loudness correction is not performed will be described. In this dynamic range control processing, as a speaker unit included in the speaker apparatus connected to the system of this embodiment, the linearity of the input / output characteristics of large signals above a predetermined level is substantially maintained, and the input / output below the predetermined level The linearity of 08-05-2019 10 the characteristic is not ensured, and the characteristic is that the output signal level is inferior to the input signal level. [0034] FIG. 4 is a diagram showing an example of the characteristic corrected by the dynamic range control process in the DSP 42. As shown in FIG. In FIG. 4, a characteristic a indicated by a broken line is a characteristic in which the linearity is linearly proportional to the increase and decrease of the input level and the increase and decrease of the output level, and is shown for reference. The characteristic b shown by the solid line is an example of the characteristic corrected by the DSP 42 of this example. [0035] As indicated by the characteristic b, the correction characteristic of the DSP 42 according to this embodiment is a characteristic having linearity such that the increase and decrease of the input level and the increase and decrease of the output level are linearly proportional in a range above a predetermined level. (Ie, the input level and the output level are made equal). And in the range below the predetermined level, the characteristic indicated by the curve where the increase rate becomes high compared to the linear input / output characteristic a as the level is lower with respect to the input level It is made to become. [0036] Here, with respect to the level position where the curve and the straight line of the characteristic b change, the range of the level in which the linearity (linearity) of the input / output characteristic is substantially maintained as the characteristic of the connected speaker unit 31, and the input / output characteristic It is made to substantially coincide with the level of the change point (that is, the above-mentioned predetermined level) with the range of the level at which the linearity of the above is not secured. Specifically, when the peak level of the audio signal is 0 dB, for example, when the range in which the linearity of the input / output characteristics of the speaker unit 31 is secured is from 0 dB to -25 dB, -25 dB is set to a predetermined level Then, the signal characteristic is not changed from 0 dB to about -25 dB, and the curve of the characteristic b is set to about -25 dB or less. In addition, the characteristics for determining the shape of the curve of the characteristic b curve are also set to characteristics in 08-05-2019 11 which the input and output characteristics of the input and output characteristics of the speaker unit as shown in FIG. 10 are substantially reversed. [0037] Although the characteristic b shown in FIG. 4 shows the characteristic at a specific frequency, in the case of this example, substantially the same characteristic is obtained in all the audible bands that can be reproduced by the speaker unit 31. It is made to have it. [0038] Therefore, when the audio reproduction system of this example shown in FIG. 1 is installed, it is possible to substantially linearly correct the badness of the input / output characteristics of the speaker devices 31L and 31R connected to the system. The characteristic (characteristic b in FIG. 4) is set by the operation of the operation unit 20a. Information of the set characteristic is stored, for example, in the memory 45 in the amplifier device 20, and thereafter correction is performed with the set characteristic unless reset is performed. [0039] FIG. 5 is a diagram showing a state in which an audio signal is output from the speaker devices 30L and 30R by correction with such characteristics as an output characteristic from low to high in multiple signal levels. FIG. 5A is a view showing the output characteristics (that is, the output characteristics not corrected) which the speaker devices 30L and 30R of this example have. FIG. 5A is the same as the speaker characteristic shown in FIG. 9B as the background art. That is, as shown in FIG. 5A, for the levels L1, L2 and L3 having high output levels, an output characteristic substantially equivalent to the ideal characteristic can be secured, but for the output characteristic at the lowest level L4, The level is lowered in any frequency band by the sensitivity α from the originally necessary level. [0040] 08-05-2019 12 Here, as the output characteristics of the signal input to the amplifier device 20 by performing the correction in the characteristic b shown in FIG. 4 in all the frequency bands by the correction in the amplifier device 20, for example, FIG. As shown in), the output level does not change with the input level for high levels L1, L2 and L3, but for the output characteristics of the lowest level L4, the sensitivity increases from the original level by the sensitivity β, in any frequency band Level. Here, the increased sensitivity β is set so as to substantially compensate for the sensitivity α which is lowered by the speaker devices 30L and 30R. [0041] With the characteristics as described above, audio signals processed by the amplifier device 20 are output from the speaker devices 30L and 30R, whereby the characteristics of the audio output from the speaker devices 30L and 30R are as shown in FIG. As shown, the four levels L1, L2, L3, and L4 have flat characteristics from low frequency to high frequency at substantially equal intervals, and are substantially equal to the ideal characteristics shown in FIG. 9A. Is a good characteristic that matches regardless of the level in all frequency bands. [0042] Although the correction characteristics described above with reference to FIGS. 4 and 5 have been described for the case where only the dynamic range control processing is performed, as described above, the loudness control function is used as the correction processing in the DSP 42 of this example. It is also possible to perform attached dynamic range control processing. FIG. 6 is a diagram showing the dynamic range control processing state with the loudness control function in this example. [0043] Before describing the dynamic range control process with the loudness control function in this example, to begin with, general loudness control which is conventionally known will be described again with reference to FIG. The control performs correction for lifting the low band fL regardless of the level, and performs correction for lifting the high band fH regardless of the level. [0044] 08-05-2019 13 On the other hand, FIG. 6 shows the dynamic range control processing state with the loudness control function of this example. FIG. 6A is a graph showing the output characteristics of the signal input to the amplifier device 20. There is no change in the input level for the levels L1 and L2 with high output levels, but the output characteristics of the lowest level L4 Is an elevated level by at least the sensitivity β from the original level. Here, the point where the increased lowest sensitivity β substantially compensates for the decreased sensitivity α in the speaker devices 30L and 30R is the same as the dynamic range control processing without the loudness control function. [0045] Then, the sensitivity β is increased only in the substantially middle range of the frequency band that the speaker devices 30L and 30R can reproduce, and for the low band and the high band, a gain higher than the sensitivity β is set. To enhance the low and high frequencies that are insufficient for hearing. However, it is different from the conventional loudness control in that the gain enhancement here is performed only for signals of small amplitude (small volume) below a predetermined level mainly enhanced by the dynamic range control processing. [0046] That is, as can be seen by looking closely at each of the levels L1, L2, L3 and L4 in FIG. 6A, the level L1 and L2 with high output levels have no change with the input level, and the output characteristics of the lowest level L4 As for the characteristic of (3), the correction of the sensitivity β and the loudness correction are performed at the same time, and the characteristic of drawing a curve in which the sensitivity of the low band and the high band is increased. In the case of this example, the curve state on the low band side and the curve state on the high band side are set individually and are not the same. In addition, with regard to level L3 between level L2 and level L4, only the low range and high range enhanced by the loudness correction are slightly higher, and as the level becomes higher, the degree of loudness correction becomes weaker Can be seen. For example, the level L3 shown in FIG. 6A is a level near the abovementioned predetermined level, which is a change point between the range in which the abovedescribed dynamic range control processing is performed and the range in which the input and output linearly change. Do. 08-05-2019 14 [0047] By performing correction in this manner, as input / output characteristics of audio signals output from the speaker devices 30L and 30R, for example, as shown in FIG. 6B, for levels L1 and L2 having high output levels, There is no change with the input level, and for the output characteristics of low level L4, only the low and high regions enhanced by the loudness correction are high, and compared with FIG. 6A, to correct the speaker characteristics. It is lowered by the increased sensitivity β. As for the level L3, only the low range and high range enhanced by loudness correction are slightly higher. [0048] By performing dynamic range control with such loudness control function, for the large-level signal component of the audio signal to be reproduced, the overall reproduction balance can be achieved with almost no change in the reproduction level at any frequency band. With good condition maintained, only low-frequency and high-frequency signal components lacking in auditory sense can be enhanced only for low-level signals, and auditory characteristic correction can be performed well. Moreover, since the poor input / output for the low level signal possessed by the speaker device is corrected by the dynamic range control correction, as an input / output characteristic of the overall reproduced audio signal excluding the portion lifted by the loudness control Is a characteristic with linearity, and can perform very good audio signal reproduction. [0049] And since it can set also about dynamic range control which does not make such a loudness amendment add, a user can choose a desired amendment state, for example, it becomes possible to choose an amendment state suitable for music to be reproduced. The gain for raising the low level signal by the loudness correction may be variably set. [0050] Note that the reproduction system of this embodiment is applicable to various audio reproduction systems, and in the example shown in FIG. 1, the audio signal source 10, the amplifier device 20, and the speaker devices 30L and 30R are separately configured. It may be 08-05-2019 15 an integrated system (apparatus). Alternatively, a correction means for correcting the characteristics of the single speaker device may be incorporated in a single speaker device, and may be connected to an amplifier device having no correction processing function. Alternatively, the same correction may be applied to the audio signal itself output from the audio signal source 10. [0051] Also, for example, the audio reproduction system of this example may be applied to a so-called reproduction system for car stereos mounted on a vehicle such as a car. By applying to such a reproduction system for car stereo, for example, in a reproduction environment where the influence of external noise is large, it becomes easy to hear a small level sound which is generally easily scraped by noise, and the sound quality is improved. In particular, by combining the loudness correction as described above, it is possible to clearly hear low-level and high-level lowlevel signals that are particularly difficult to hear, and the clarity of the reproduced sound can be effectively improved. [0052] In the above-described embodiment, as the dynamic range control correction with the loudness control function, the low band and the high band in the entire reproduction band are performed. However, for example, the loudness correction is performed only to the low band The loudness correction may be performed only for the low frequency area by performing correction such that the middle frequency range and the high frequency range are increased by the sensitivity β shown in FIG. 6A, for example. [0053] Further, although the application to the system for 2-channel audio reproduction shown in FIG. 1 is assumed in the embodiment described above, it may be configured as a system for multichannel audio reproduction such as 5.1 channel. [0054] It is a block diagram showing an example of system composition by one embodiment of the present invention. 08-05-2019 16 It is a block diagram showing an example of composition by a 1 embodiment of the present invention. It is a flowchart which shows the example of a correction process by one embodiment of this invention. FIG. 6 is a characteristic diagram showing an example of correction characteristics according to an embodiment of the present invention. It is the characteristic view which showed the example (example without loudness correction ¦ amendment) of the correction ¦ amendment state by one embodiment of this invention by the output sensitivity for every frequency. It is the characteristic view which showed the example (example with loudness correction ¦ amendment) of the correction ¦ amendment state by one embodiment of this invention by the output sensitivity for every frequency. It is explanatory drawing which showed the example of an output waveform of the conventional speaker. It is explanatory drawing which showed the example of the signal level of the conventional speaker. It is explanatory drawing which showed the output characteristic example (a) of an ideal speaker, and the output characteristic example (b) of the conventional speaker. It is explanatory drawing which showed the example of the input-output characteristic of the conventional speaker. It is a characteristic view showing an example of a characteristic of conventional loudness correction. Explanation of sign [0055] DESCRIPTION OF SYMBOLS 10 Audio signal source 20 Amplifier device 20a Operation part 21 Audio signal input terminal 24 Amplifier 30L, 30R Speaker device 31 Speaker unit 41 Analog / digital converter 42 DSP (Digital signal processor) 43: digital / analog converter 44: control unit 45: memory 08-05-2019 17
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