JP2006174083A - Audio signal processing method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently correct a particular frequency band of an audio signal by a desired characteristic. <P>SOLUTION: When correction processing is applied to a received audio signal for the particular frequency band, an audio signal processing apparatus selectively applies first correction processing to the signal components of the signals with the particular frequency band and whose level is a prescribed level or below so as to increase an output level along a prescribed curve and applies second correction processing to almost all of the signal components of the signals with the particular frequency band so as to uniformly increase the output level respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an audio signal processing method and apparatus for performing characteristic correction when reproducing an audio signal, and more particularly to a technique suitable for application when using a high-fidelity speaker apparatus capable of high-quality reproduction.

  Conventionally, speakers having various configurations have been put to practical use as speaker devices for high-fidelity reproduction capable of high-quality reproduction. For example, there is a three-way speaker device in which a reproduction band of an audio signal is divided into three bands, a low band, a middle band, and a high band, and an individual speaker unit is prepared for each band. This three-way speaker device uses a speaker unit with good reproduction characteristics in each band as a speaker unit for each band, and can faithfully reproduce the input audio signal from low to high frequencies. In general, the reproduction characteristics are improved as compared with a so-called full-range speaker unit that outputs audio in all bands with a single speaker unit.

  Further, in addition to the configuration for improving the sound quality of the reproduction sound of the speaker device as in the three-way configuration or the two-way configuration, the characteristics of the audio signal itself supplied to the speaker device are also an amplifier that is an audio signal processing device. Corrections are made on the device side, and as a result, the characteristics of audio output from the speaker device are improved. 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 corrects the low and high frequencies that are heard when the volume is low, mainly by performing a correction process that increases the output level of the low and high frequencies compared to the mid range. Is.

Patent Document 1 describes an example of a reproduction configuration when performing loudness correction.
JP 2002-171589 A

  However, the loudness-controlled playback sound simply boosts the signal in a specific frequency band almost uniformly regardless of the level, so it cannot be said that the playback sound is faithful to the input audio signal in a strict sense. It has been desired to develop a speaker device that can reproduce signals faithfully. In other words, conventional loudness-controlled playback sounds are played back with an increase in sounds that are difficult to hear at low volumes, making it easier to hear low and high frequencies compared to playback sounds that are not loudness-controlled. However, it is possible to enhance signal components that do not need to be enhanced because signals in a specific frequency band are uniformly enhanced at both low and large levels. In some cases, this results in an unnatural playback sound.

  Here, the problem of the reproduced sound in the conventional speaker device will be described. As an example when the reproduced sound does not faithfully reproduce the input audio signal, there is a problem of a small amplitude signal. That is, for example, as shown in FIG. 6A, 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 that of the input signal S1 for a waveform having a relatively large amplitude, but the amplitude of the waveform of a relatively small amplitude is larger than that of the input signal S1. It tends to be smaller. This is because a speaker unit having a general diaphragm that can output a relatively loud sound has poor reproduction characteristics of a small volume signal with small amplitude, and linearity of input / output characteristics of a small volume signal ( This is because linearity is not ensured.

  Similarly, for example, as shown in FIG. 6B, the input audio signal S3 having a relatively large amplitude waveform and the input audio signal S4 having a relatively small amplitude waveform overlap each other in terms of time. An audio signal S5 obtained by synthesizing both signals S3 and S4 is output, and an output audio signal S6 having a waveform whose level is lower than the waveform of the synthesized signal S5 is output from the speaker. For example, such an output state may occur when sounds of various musical instruments are reproduced simultaneously as audio to be reproduced from a speaker, such as symphony.

  Further, for example, as shown in FIG. 6C, when the input audio signal S7 is an impulse signal in which the amplitude of a specific single frequency signal gradually decreases, the waveform of the output audio signal S8 from the speaker However, the follow-up property becomes worse as the level becomes lower.

  In any of the examples in FIG. 6, as an output from the speaker, the output level of a small volume signal having a small amplitude becomes smaller than the input signal level, and the linearity of the small signal cannot be maintained. When the state shown in FIG. 6 is subjected to frequency analysis, for example, the state shown in FIG. 7 is obtained. The example of FIG. 7 is an example in which the sensitivity of the fundamental wave f1 and harmonics f2 and f3, which are harmonics of the fundamental wave, is analyzed. The fundamental wave f1 having a high level is output as it is, but the harmonics f2 and f3 having a level lower than that of the fundamental wave have the output sensitivity indicated by the solid line that is lower than the original level indicated by the broken line. ing.

  FIG. 8 is a diagram showing output characteristics from a low range to a high range at a plurality of signal levels. FIG. 8A is an ideal characteristic, and FIG. 8B is an actual speaker output. It is the figure which showed the characteristic. As shown in FIG. 8A, in an ideal state, it is assumed that the four levels L1, L2, L3, and L4 have a flat characteristic from a low range to a high range at almost equal intervals. At this time, as the output characteristics of the actual speaker shown in FIG. 8 (b), for the levels L1, L2, and L3 with high output levels, the output characteristics almost equal to the ideal characteristics can be secured, but the lowest level. Regarding the characteristics of L4, the sensitivity α decreases from the originally required level by any sensitivity in the frequency band.

  FIG. 9 is an input / output characteristic diagram showing such a decrease in sensitivity as a characteristic of a specific frequency. As shown in FIG. 9, it is necessary to have a broken line characteristic x in which the output level increases linearly with an increase in the input signal level to the speaker. The level changes almost linearly, but below a specific level, the vibration of the diaphragm with respect to the input is poor and the output sensitivity to the input is a curve characteristic y.

  Specifically, for example, assuming that the maximum level of listening by a general speaker is 70 to 100 spl (sound pressure level), a signal that is −30 dB to −60 dB lower than the maximum level is correct with respect to the maximum level − This means that the sound volume is not reduced (not proportional) from 30 dB to -60 dB. If it is assumed that the output of the amplifier device is reduced by 50 spl from 100 spl, the sound volume should be around 50 spl, but in reality, for example, only 40 spl lower than 10 spl can be obtained. It will not be possible. In other words, the inventor's analysis revealed that the linearity was not accurately obtained, which was one of the major causes that a satisfactory sound quality could not be obtained.

  As one of the conventionally known processes for correcting such poor reproduction characteristics, for example, the above-described loudness control is performed, and the output levels of the low frequency range and high frequency range are set to the mid frequency range. There is a process to enhance compared to. As another process, for example, a device called a graphic equalizer is used to increase or attenuate the level for each of the divided frequency bands so that the listener has the desired playback sound quality. There is also a case to let you. When a graphic equalizer is used, it is possible to correct the signal components in the desired frequency band. However, when adjusting the gain, as with the loudness control, the same amount is applied to all signal components in the band. It will increase or decrease the level. The process of raising or lowering the level by the same amount for all signal components in such a band is effective when, for example, it is desired to make only the signal component in a specific band stand out. If this is necessary, the balance of the reproduced audio signal may be lost, which may be undesirable.

  The present invention has been made in view of the above points, and an object of the present invention is to make it possible to satisfactorily correct a specific frequency band of an audio signal under various reproduction conditions.

  According to the present invention, when correction processing is performed on a signal in a specific frequency band of an input audio signal, an output level is expressed by a predetermined curve with respect to a signal component equal to or lower than a predetermined level of the signal in the specific frequency band. A first correction process for increasing and a second correction process for increasing the output level substantially uniformly for almost all signal components of a signal in a specific frequency band are selectively performed. is there.

  By doing so, processing to increase only the level of a signal with a small amplitude below a predetermined level in the frequency band where the signal is to be emphasized, and processing to increase all levels within the frequency band where the signal is to be emphasized regardless of the signal level Can be selectively performed, and a desired correction state can be selected according to the reproduction sound quality desired at that time.

  According to the present invention, the process of increasing only the level of a signal having a small amplitude equal to or lower than a predetermined level in the frequency band in which the signal is to be emphasized, and the process of increasing all levels in the frequency band in which the signal is to be emphasized regardless of the signal level. Can be selectively performed, and a desired correction state can be selected according to the desired reproduction sound quality at that time, and when a correction such as emphasis of a specific band is desired for the input audio signal, It is possible to cope with any correction state where it is desired to correct only a small level signal in the band, and the operator can adjust to a desired sound quality.

  In this case, the predetermined level in the first correction processing is almost assured of the linearity of the output level with respect to the input signal above the specific level as the input / output characteristics of the speaker device that outputs the corrected audio signal, and below the specific level. Thus, the signal level can be satisfactorily corrected in accordance with the characteristics of the connected speaker device when the output level with respect to the input signal is a specific level.

  In addition, since the specific frequency band is variably set based on the operation input, the arbitrary frequency band can be satisfactorily corrected.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a system configuration example according to the present embodiment. In this example, an audio playback system is connected to a speaker device, and FIG. 1 is a diagram showing an example of the overall system configuration. In this example, the audio signal source 10 is connected to the amplifier device 20 via the graphic equalizer 100, and the audio signal source 10 reproduces an audio signal recorded (stored) on a medium such as a CD (disk) or a memory. Then, the reproduced and output audio signal is processed by the graphic equalizer 100, and then supplied to the amplifier device 20, where the amplifier device 20 performs processing to make an audio signal for driving the speaker device. Here, the graphic equalizer 100 of this example is a hybrid graphic equalizer in which a plurality of correction states can be set. A specific configuration and processing state of the hybrid graphic equalizer will be described later.

  In the case of this example, the audio signal output from the audio signal source 10 is a two-channel signal of a left channel audio signal and a right channel audio signal. 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. Note that the configuration of a graphic equalizer or the like to be described later shows only one system (one channel) signal processing configuration, but actually, the number of channels to be processed is prepared.

  The configuration of each of the speaker devices 30L and 30R will be described. Each speaker device 30L and 30R includes one speaker unit 31 as a speaker unit serving as a sound output unit that outputs audio. Each speaker unit 31 is a so-called full-range speaker unit having a frequency characteristic that is almost flat in the audible band and a characteristic that is output from a low frequency to a high frequency as viewed from the output frequency band. There is a relatively large speaker unit that is provided with a relatively large diaphragm and is capable of outputting a loud signal. As for the speaker unit 31, since the diaphragm is relatively large, the linearity (linearity) of the input / output characteristics of a large signal above a predetermined level is almost 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, the speaker unit having the characteristic y described with reference to FIG. 9 in the background art column is used. A speaker unit having such characteristics is general as a speaker.

  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, the amplifier device 20 that processes the audio signal supplied to the speaker devices 30L and 30R is provided in the preceding stage. The connected graphic equalizer 100 corrects signal characteristics.

  FIG. 2 is a diagram showing a configuration example when the graphic equalizer 100 of the present embodiment has an analog circuit configuration. The configuration will be described below. An audio signal input to the audio signal input terminal 101 is supplied to the gain equalizer 103 via the buffer amplifier 102.

  For example, the gain equalizer 103 divides an input audio signal into signal components of a plurality of preset frequency bands using a bandpass filter, and individually processes the signal for each of the divided bands. A gain for amplifying (or attenuating) is set so that signal enhancement or attenuation can be made almost uniform with respect to the signal in the band. The output of the signal processed in each band is synthesized and output. The amplification amount or attenuation amount in each band in the gain-type equalizer unit 103 can be individually set based on an operation of an operation unit (not shown), for example. Each band can be set to a state where no amplification or attenuation is performed.

  The signal processed by the gain equalizer 103 is supplied to the dynamic range equalizer 105. For example, the dynamic range type equalizer unit 105 divides an input audio signal into signal components of a plurality of preset frequency bands using a bandpass filter, and each divided band is equal to or lower than a predetermined level. It is constructed by connecting various circuit elements and analog circuit parts such as operational amplifiers so that the process of amplifying (or attenuating) the signal only to the signal component of the signal. A predetermined correction characteristic that is not a typical amplification is set. Details of the processing state in the dynamic range type equalizer unit 105 will be described later. The outputs of the signals processed in the respective bands are synthesized and output.

  The output of the dynamic range type equalizer unit 105 is supplied to the audio signal output terminal 107 via the buffer amplifier 106, and is supplied to a subsequent device (here, the amplifier device 20) connected to the output terminal 107.

  FIG. 3 is a diagram showing a configuration example when the graphic equalizer 100 of the present embodiment has a digital circuit configuration. The configuration will be described below. The audio signal input to the audio signal input terminal 111 is supplied to the gain equalizer unit 120 and the dynamic range equalizer unit 130 via the buffer amplifier 112.

  The gain-type equalizer unit 120 includes a plurality of gain-type equalizers 121, 122, 123,... 129 that are set to amplify (or attenuate) signal components in different set frequency bands mainly by digital arithmetic processing. It is connected in stages. Amplification or attenuation in each of the gain-type equalizers 121 to 129 is configured to be performed substantially uniformly on the signal in the band. The amount of amplification or attenuation in each of the gain equalizers 121 to 129 in each band can be individually set based on, for example, an operation of an operation unit (not shown). It is also possible to set a state where no amplification or attenuation is performed in each band.

  The dynamic range type equalizer unit 130 is a dynamic range type equalizer that amplifies or attenuates only a signal component of a predetermined level or less with a predetermined correction characteristic, mainly for a signal component in a different set frequency band by digital arithmetic processing. 131, 132, 133... 139 are connected in a plurality of stages. Amplification amounts or attenuation amounts in the dynamic range equalizers 131 to 139 in the respective bands can be individually set based on, for example, operation of an operation unit (not shown). It is also possible to set a state where no amplification or attenuation is performed in each band.

  For each of the gain equalizers 121 to 129 and the dynamic range equalizers 131 to 139 that perform signal processing mainly by digital arithmetic processing, for example, an integrated circuit for audio signals called a DSP (digital signal processor) is used. Can be assembled. The frequency bands handled by each of the gain equalizers 121 to 129 and the dynamic range equalizers 131 to 139 may be fixedly set to individual frequency bands. However, the frequency division may be performed by an arithmetic process using a digital filter or the like. In the configuration in which the frequency band to be extracted is changed, the frequency band to be extracted may be variably set by changing the coefficient set in the filter. The bandwidth of the frequency band to be extracted may be variable.

  The signals processed by each of the gain equalizers 121 to 129 and the dynamic range equalizers 131 to 139 are supplied to the synthesizing unit 113 and synthesized into one system signal, and the synthesized signal is converted into an audio signal via the buffer amplifier 114. The signal is supplied to the output terminal 115 and supplied to a subsequent device (here, the amplifier device 20) connected to the output terminal 115.

  In the configuration of FIG. 3, a digital / analog converter for digitizing an audio signal and an analog / digital converter for converting a digital signal into analog are omitted.

  Next, an example of processing in the hybrid graphic equalizer 100 of this example will be described. FIG. 4C is a diagram showing an example of the case where the hybrid graphic equalizer 100 of this example performs the amplification process by the gain equalizer and the characteristic correction process by the dynamic range equalizer at the same time. In FIG. 4, the horizontal axis indicates the frequency and the vertical axis indicates the signal level. Here, as shown in FIG. 4C, amplification is performed by the gain equalizer in the frequency band F1, and dynamic in the frequency band F2. Amplification (characteristic correction) is performed by a range equalizer.

  The amplification by the gain equalizer in the frequency band F1 is a conventional amplification process performed by the equalizer. As shown in FIG. 4A, the signal components at all levels in the band are almost uniform. An amplification process for increasing the level is performed. The level to be increased can be adjusted by adjusting the gain of the amplifier provided in the equalizer.

  With respect to the characteristic correction by the dynamic range equalizer in the frequency band F2, as shown in FIG. 4B, the input / output characteristics of the speaker are mainly poor with respect to small level signal components below a predetermined level in the band. Correction processing is performed to correct. That is, for the audio signal in the frequency band F2, the level is not changed for a large signal above a predetermined level, and the level is increased for a small signal below a predetermined level. The predetermined level is determined by, for example, input / output characteristics of the speaker unit 31 included in the connected speaker devices 30L and 30R. Here, the boundary between the range in which the linearity (linearity) of the input / output characteristics of the speaker unit is substantially maintained and the range in which the linearity of the input / output characteristics is not ensured substantially coincide with a predetermined level. In addition, the characteristic for increasing the level of a small signal below a predetermined level is such that the lower the level, the higher the rate of increase compared to the characteristic with the same input and output. The speaker unit works to correct the poor input / output characteristics of the speaker unit.

  Specifically, as shown in FIG. 9 described in the background section, the input / output characteristic of the speaker unit is a characteristic y indicated by a curve in which the linearity of the input / output characteristic is not secured below a predetermined level. Assuming that the audio signal is below a predetermined level in the frequency band F2, for example, as shown in FIG. 5, the characteristic y is set so that the input and output of the characteristic y are substantially reversed. Note that the characteristic a shown in FIG. 5 shows an ideal characteristic in which linearity of input and output is ensured for reference.

  However, the adjustment amount that becomes the characteristic b shown in FIG. 5 may be used as the reference adjustment amount, and the increase rate of the small signal may be adjusted from the reference adjustment amount so as to be increased or decreased by a user operation or the like. In addition, the value itself of the level (a predetermined level described above) serving as a boundary point for increasing the level of the small signal may be variably set.

  By performing such dynamic range correction processing, the badness of input / output linearity is corrected within the frequency band in which the correction is performed, and the characteristic is close to the ideal characteristic a. For example, the output characteristics from the connected speaker devices 30L and 30R are obtained by performing dynamic range correction processing as shown in FIG. 5 for high frequency bands and mid frequency bands where a relatively small level signal is easily heard. Will be good. In this case, since the reproduction level of a large level signal is not corrected (enhanced) at all in the corresponding frequency band F2, dynamic range correction can be performed for a desired frequency band without disturbing the overall reproduction balance.

  In this example, the processing shown in FIG. 4B as an equalizer for performing such dynamic range correction and the processing shown in FIG. 4A as a gain equalizer are simultaneously performed in an arbitrary frequency band. Therefore, it is possible to adjust the playback sound quality as desired. Specifically, equalizer processing that emphasizes an arbitrary frequency band as a whole and dynamic range correction processing that corrects speaker characteristics in an arbitrary frequency band are possible. For example, sound quality suitable for audio to be reproduced can be easily obtained. It becomes possible to set.

  In the example of FIG. 4, the gain correction and the dynamic range correction are performed in each of the bands F1 and F2, but the same correction is performed in each of a plurality of bands (or all bands). May be. Alternatively, any one of the corrections may not be performed at all.

  Further, gain correction and dynamic range correction may be simultaneously performed for one specific frequency band. In this way, correction of speaker characteristics in the band and enhancement of the band can be performed at the same time, and a wider variety of reproduction sound quality settings can be made.

  In the above-described embodiment, an installation example of the audio reproduction system has not been particularly described, but the present invention can be applied to various audio devices that require this type of signal processing. For example, by applying it to a so-called car stereo playback system mounted on a vehicle such as an automobile, it is possible to correct a low-level sound that is generally easily extinguished by noise in a playback environment where the influence of outside noise is large. It is possible and both the improvement of the reproduction sound quality and the adjustment to the desired sound quality can be performed by increasing the band to be emphasized as a whole.

  In the above-described embodiment, no specific example is shown as an example of dividing the frequency band for performing the correction processing, but various division examples known as graphic equalizers can be applied. For example, any of a case where the audible band is divided by a relatively small number of divisions of about 4 bands and a case where the audible band is divided into more than 10 bands may be used.

  In addition, instead of fixedly determining the divided band using a prepared filter, a configuration in which a frequency position and a frequency bandwidth of each band can be variably set and an arbitrary frequency band for performing correction processing may be set. .

  In the above-described embodiment, the graphic equalizer is prepared as the dedicated audio signal processing means (correction means) for performing the correction process and is connected between the audio signal source and the amplifier device. Various audio devices such as a signal source, an amplifier device, or a speaker device may be processed by incorporating correction means for performing the same correction processing.

  Alternatively, an arithmetic processing device such as a personal computer device is provided with a port capable of inputting / outputting audio signals, and a program for performing the same audio signal correction processing is installed in the arithmetic processing device so that the same audio signal is used in the arithmetic processing. An apparatus for performing the correction process may be realized.

  In the above-described embodiment, it is assumed that the present invention is applied to the two-channel audio reproduction system shown in FIG. 1, but it may be configured as a multi-channel audio reproduction system such as 5.1 channel.

It is a block diagram which shows the system configuration example by one embodiment of this invention. It is a block diagram which shows the example which comprised the graphic equalizer by one embodiment of this invention with the analog circuit. It is a block diagram which shows the example which comprised the graphic equalizer by one embodiment of this invention with the digital circuit. It is a characteristic view showing an example of correction characteristics according to an embodiment of the present invention. It is a characteristic view showing an example of characteristics in a corrected band according to an embodiment of the present invention. It is explanatory drawing which showed the example of the 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 the 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.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Audio signal source, 20 ... Amplifier apparatus, 30L, 30R ... Speaker apparatus, 31 ... Speaker unit, 100 ... Graphic equalizer, 101 ... Audio signal input terminal, 102 ... Buffer amplifier, 103 ... Gain type equalizer part, 105 ... Dynamic Range type equalizer unit 106 ... buffer amplifier 107 107 audio signal output terminal 111 ... audio signal input terminal 112 ... buffer amplifier 120 ... gain type equalizer unit 130 130 dynamic range type equalizer unit 113 113 synthesis unit 114 ... Buffer amplifier, 115 ... Audio signal output terminal

Claims (6)

In an audio signal processing method for performing correction processing on a signal in a specific frequency band of an input audio signal,
A first correction process for raising an output level with a predetermined curve for a signal component below a predetermined level of the signal in the specific frequency band, and for almost all signal components of the signal in the specific frequency band The second correction process for raising the output level almost uniformly is selectively performed,
An audio signal processing method, wherein an output level is not changed for a signal outside the specific frequency band. The audio signal processing method according to claim 1, wherein
The predetermined level in the first correction process is such that the linearity of the output level with respect to the input signal is almost ensured at a specified level or higher as the input / output characteristics of the speaker device that outputs the corrected audio signal, and below the specified level. An audio signal processing method, wherein the output signal level is a specific level when the output level with respect to the input signal is reduced. The audio signal processing method according to claim 1, wherein
The audio signal processing method, wherein the specific frequency band is variably set based on an operation input. In an audio signal processing apparatus that performs correction processing on a signal in a specific frequency band of an input audio signal,
First correction means for performing a correction process for raising an output level with a predetermined curve with respect to a signal component of a predetermined frequency band or less of the signal in the specific frequency band;
An audio signal processing apparatus comprising: a second correction unit that performs a correction process for increasing the output level substantially uniformly with respect to almost all signal components of the signal in the specific frequency band. The audio signal processing device according to claim 4, wherein
The predetermined level to be corrected by the first correcting means is almost the same as the input / output characteristic of the speaker device that outputs the corrected audio signal, and the linearity of the output level with respect to the input signal is almost secured above the specific level, and the specific level An audio signal processing apparatus characterized by having a specific level when the output level with respect to an input signal drops below a level. The audio signal processing device according to claim 4, wherein
An audio signal processing apparatus comprising: operating means for setting the specific frequency band processed by the first and second correcting means.

Images