JP2006174084A - Audio signal processing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED To finely improve a reproduction characteristic of a low volume signal from a speaker according to a reproduction state.
When a correction process is performed to output an input audio signal from a speaker device having a predetermined input / output characteristic, the predetermined input / output characteristic of the speaker device is output as an input signal at a predetermined level or higher. When the linearity of the level is almost secured and the output level with respect to the input signal decreases below the predetermined level, the output level is reduced for the signal component of the input audio signal below the predetermined level. In addition to performing correction processing, the correction processing state that compensates for the decrease in the output level is variably set according to the adjustment state of the volume output from the speaker device.
[Selection] Figure 2

Description

  The present invention relates to an audio signal processing method and apparatus for performing characteristic correction when an audio signal is reproduced from a speaker device, and is particularly suitable when applied to a speaker device for high-fidelity reproduction capable of high-quality reproduction. Regarding technology.

  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.

  By the way, the curve state of the curve of the characteristic y shown in FIG. 9 described above is an example. Actually, a specific curve of the characteristic y depends on characteristics of individual speaker devices, reproduction conditions, and the like. The state will change.

  The present invention has been made in view of this point, and an object thereof is to finely improve the reproduction characteristics of a low-volume signal from a speaker depending on the reproduction state.

  The present invention is a case where correction processing for outputting an input audio signal from a speaker device having a predetermined input / output characteristic is performed, and the predetermined input / output characteristic of the speaker device is output to an input signal at a predetermined level or more. When the linearity of the level is almost secured and the output level with respect to the input signal decreases below the predetermined level, the output level is reduced for the signal component of the input audio signal below the predetermined level. In addition to performing correction processing, the correction processing state for compensating for the decrease in the output level is variably set in accordance with the adjustment state of the volume output from the speaker device.

  As a result, the audio signal output from the speaker device can be corrected appropriately so that the input / output characteristics are substantially linear in accordance with the characteristics of the speaker apparatus while being adjusted according to the playback volume. To be done.

  According to the present invention, the audio signal output from the speaker device is appropriately corrected so that the input / output characteristics are substantially linear in accordance with the characteristics of the speaker device while being adjusted according to the reproduction volume. Thus, it is possible to improve the playback sound quality according to the playback volume at that time.

  In this case, as the volume adjustment state, when the volume is larger than the predetermined volume, the correction process is not performed, the correction process is performed when the volume is equal to or lower than the predetermined volume, and the volume is set below the predetermined volume. Since the correction amount is variably set in at least a plurality of stages, good correction suitable for each volume can be performed.

  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, and the audio signal source 10 reproduces an audio signal recorded (stored) on a medium such as a CD (disc) or a memory, and reproduces it. The output audio signal is supplied to the amplifier device 20, and the amplifier device 20 performs processing to convert the audio signal to drive the speaker device. The amplifier device 20 includes an operation unit 20a, and is configured to be able to adjust the processing state of the audio signal by a user operation of the operation unit 20a. For example, the operation unit 20a includes a volume adjusting volume. Details of a specific configuration and processing state in the amplifier device 20 will be described later.

  Here, 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.

  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 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 device 30 using the speaker unit 31 having such characteristics is connected, the signal characteristic correction is performed on the amplifier device 20 side that processes the audio signal supplied to the speaker device 30. Is to do.

  FIG. 2 is a diagram showing a configuration for correcting characteristics in the amplifier device 20 of this example, and shows a connection configuration up to the speaker unit 31 constituting the speaker devices 30L and 30R. As shown in FIG. 2, the 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 converted into a DSP (digital signal). -A signal processor 42 is supplied. In this example, the DSP 42 is used as a means for correcting audio signal characteristics. The correction state in the DSP 42 is controlled by the control unit 44. The control state in the control unit 44 is set according to the operation status in the operation unit 20a. The control unit 44 is connected to a memory 45 for storing data necessary for control, and stores data about a correction state in the DSP 42.

  As the correction processing in the DSP 42, for example, signal components in all frequency bands are divided into signal components of a predetermined level or higher and signal components of a predetermined level or lower for digital signal processing. Does not perform correction processing. For signal components that are less than a predetermined level, correction processing is performed as necessary so that the output level with respect to the input level is higher as the level is lower. Such audio signal correction is referred to herein as dynamic range correction processing. Here, in this example, this correction processing state is changed in accordance with the volume adjustment state in the operation unit 20a.

  Then, a signal component of a predetermined level or higher that has not been subjected to correction processing and a signal component of lower than a predetermined level that have been subjected to correction processing if necessary are combined, and the combined signal is supplied to the digital / analog converter 43 to provide analog audio. Convert to signal.

  The converted analog audio signal is supplied to the amplifier 24 to be amplified for driving the speaker, and the amplified audio signal is supplied to the speaker unit 31 in the speaker devices 30L and 30R for each channel. Is output (sounds emitted).

  Next, a processing example in which the dynamic range correction processing state of the audio signal is set in accordance with the volume setting state in the amplifier device 20 of this example will be described with reference to the flowchart of FIG. As shown in FIG. 3, when the control unit 44 sets the dynamic range correction processing state, it first determines the current volume (volume) setting state (step ST11). As the determination of the volume here, for example, the volume range that can be set by the amplifier device is divided into three ranges, and it is determined which of the three ranges of low volume, medium volume, and high volume. Then, it is determined which of the three ranges is determined (step ST12).

  If it is determined that the volume is low, the dynamic range correction amount is set to a large value (step ST13). If it is determined that the volume is medium, the dynamic range correction amount is set to a small value (step ST14). If it is determined that the volume is high, no dynamic range correction is set (step ST15). The setting state of the correction amount shown in this flowchart is updated every time the volume adjustment of the amplifier device is performed, for example.

  Next, a specific correction example of dynamic range correction in which the correction amount is set in this way will be described. FIG. 4 is a diagram showing an example of characteristics corrected by the DSP 42 in relation to input and output. Although FIG. 4 shows the characteristic at a specific frequency, as will be described later, the characteristic correction processing of this example does not depend on the frequency and basically corrects at any frequency within the audible band. In FIG. 4, a characteristic a indicated by a broken line has a linearity in which the increase and decrease of the input level and the increase and decrease of the output level are linearly proportional, and is shown for reference. Characteristics b and c indicated by solid lines are characteristics corrected by the DSP 42 of this example. The characteristic b is an example when the correction amount is set to a large value, and the characteristic c is an example when the correction amount is set to a small value. Here, as shown in FIG. The state is different.

  As shown by these characteristics b and c, the correction characteristics of the DSP 42 of this example are characteristics in which linearity in which the increase / decrease in the input level and the increase / decrease in the output level are linearly proportional within a predetermined level or more (that is, (That is, a characteristic that substantially matches the characteristic a) (that is, the input level and the output level are made equal). In a range below a predetermined level, the output level is lower than the input level, and the characteristic indicated by a curve that does not have linearity such that the rate of increase is higher than the linear input / output characteristic a as the level is lower. It is supposed to be.

  Here, with respect to the level positions where the curves and straight lines of the characteristics b and c change, the range of levels in which the linearity (linearity) of the input / output characteristics as the characteristics of the connected speaker units 31 is substantially maintained, It is made to substantially coincide with the level of the change point (that is, the above-mentioned predetermined level) with the level range in which the linearity of the input / output characteristics is not ensured. Specifically, when the peak level of the audio signal is set to 0 dB, for example, when the range in which the linearity of the input / output characteristics of the speaker unit 31 is ensured is from 0 dB to −25 dB, −25 dB is set to a predetermined level. The signal characteristic is not changed from 0 dB to approximately −25 dB, and is set so that the curves of the characteristics b and c are approximately −25 dB or less. Further, the characteristic that determines the shape of the curve of the characteristic b is also set to a characteristic in which the input and output of the input / output characteristics of the speaker unit are substantially reversed as shown in FIG. The curve is set to a curve that is weaker than the curve indicating the correction characteristic of the characteristic b (that is, a characteristic that is a curve that takes approximately between the linear ideal characteristic a and the characteristic b).

  The characteristics b and c shown in FIG. 4 indicate characteristics at a specific frequency. In this example, the characteristics b and c are almost the same in all audible bands that can be reproduced by the speaker unit 31. It has characteristics. In FIG. 4, the position (level) at which the curve of the characteristic b starts and the position at which the curve of the characteristic c start are set to substantially the same position. However, the level at which the curve of the characteristic c starts is A level lower than the starting level may be set.

  FIG. 5 shows a state in which an audio signal is output from the speaker devices 30L and 30R by the correction with such correction characteristics as output characteristics from a low range to a high range at a plurality of signal levels. FIG. FIG. 5 shows an example in which the correction characteristic b of FIG. 4 is set, and FIG. 5A shows the output characteristic (that is, the uncorrected output characteristic) of the speaker devices 30L and 30R of this example. It is a figure. FIG. 5A is the same as the speaker characteristic shown in FIG. 8B as the background art. That is, as shown in FIG. 5 (a), for the levels L1, L2, and L3 with high output levels, output characteristics almost equal to the ideal characteristics are secured, but for the output characteristics with the lowest level L4, It is a level that is lowered in any frequency band by the sensitivity α from the originally required level.

  Here, as the output characteristic of the signal input to the amplifier device 20 is obtained by performing correction in the frequency band shown in FIG. 4 in all frequency bands by correction in the amplifier device 20, FIG. As shown in FIG. 4, the output levels of the high output levels L1, L2, and L3 are not different from the input level, but the output characteristic of the lowest level L4 is increased from the original level by the sensitivity β in any frequency band. It is a level. Here, the increased sensitivity β is a level that substantially compensates for the sensitivity α that decreases in the speaker devices 30L and 30R.

  FIG. 5C shows the characteristics of the audio output from the speaker devices 30L and 30R by outputting the audio signal processed by the amplifier device 20 from the speaker devices 30L and 30R with such characteristics. As shown in the figure, the four levels L1, L2, L3, and L4 are flat at almost equal intervals from low to high, and are almost equal to the ideal characteristics shown in FIG. 8A. Is a good characteristic that matches regardless of the level in all frequency bands.

  Here, such correction characteristics are set when reproduction is performed at a relatively small volume. When the medium volume is set, correction processing slightly weaker than this is performed as shown in FIG. The state is set. However, in the case of medium volume, since the overall reproduction level is higher than that in the case of low volume, the same effect can be obtained even if a weak correction amount is set. In addition, the dynamic range correction process is not performed at all when the volume is high. However, when the volume is high, a small level signal component included in the audio signal component is also reproduced at a relatively high volume. Therefore, the input / output characteristics of the small level signal are not so much deteriorated, and as a result, it is reproduced well without correction.

  Therefore, according to the audio reproduction system of this example, the audio signal reproduced from the audio signal source 10 can be output from the speaker devices 30L and 30R with high sound quality at any volume. Such reproduction characteristics are completely different from the process of enhancing a signal in a specific frequency band, such as the conventionally known loudness control, regardless of the level, and faithfully reproduces the input audio signal. It is a characteristic.

  In addition, in the case of this example, the correction amount of the dynamic range is changed corresponding to the reproduction volume at that time, so that an appropriate correction corresponding to the reproduction volume at that time can be performed.

  In the example described so far, the two-stage correction characteristics b and c shown in FIG. 4 are prepared in advance, but more correction characteristics are prepared in advance, and the volume setting amount is set from among them. You may make it selectable according to it. Alternatively, the correction amount may be continuously changed, and the correction amount may be continuously changed according to the set value of the volume.

  Furthermore, in the above-described example, the dynamic range correction is not performed when the volume is high. However, the dynamic range correction with a small correction amount may be performed when the volume is high.

  In the description so far, only the sound volume is set as a factor for setting the correction amount. For example, the average level (or peak level) of the audio signal to be corrected is determined, and the level of the determined input audio signal and the sound volume are determined. From the adjustment state, a correction amount most suitable for correcting the output state of the connected speaker device may be set.

  In addition, the reproduction system of this example can be applied to various audio reproduction systems. 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. An integrated system (apparatus) may be used. Or it is good also as a structure which can be connected to the amplifier apparatus which does not have a correction process function by incorporating the correction | amendment means which correct | amends the characteristic of the speaker apparatus in the inside of a single speaker apparatus. Alternatively, the same correction may be applied to the audio signal itself output from the audio signal source 10.

  In the above-described embodiment, the correction processing is performed by digital arithmetic processing using a DSP. However, the correction circuit may be configured by analog circuit components.

  In addition, for example, by applying the audio playback system of this example to a so-called car stereo playback system mounted on a vehicle such as an automobile, in general in a playback environment where the influence of noise outside the vehicle is large, the audio playback system is easily extinguished by noise. Sound of level becomes easy to hear and sound quality improves.

  Further, in the above-described embodiment, it is assumed that the present invention is applied to the system for reproducing 2-channel audio shown in FIG. 1, but it may be configured as a system for reproducing multi-channel audio 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 structural example by one embodiment of this invention. It is a flowchart which shows the example of a correction process by one embodiment of this invention. It is a characteristic view showing an example of correction characteristics according to an embodiment of the present invention. It is the characteristic view which showed the output sensitivity for every frequency which showed the example of the correction | amendment state by one embodiment of this 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, 20a ... Operation part, 21 ... Audio signal input terminal, 24 ... Amplifier, 30L, 30R ... Speaker apparatus, 31 ... Speaker unit, 41 ... Analog / digital converter, 42 ... DSP (Digital signal processor) 43 ... Digital / analog converter 44 ... Control unit 45 ... Memory

Claims (4)

An audio signal processing method for performing correction processing for outputting an input audio signal from a speaker device having predetermined input / output characteristics,
Audio signal processing method in the case where the predetermined input / output characteristics of the speaker device are characteristics in which linearity of an output level with respect to an input signal is substantially secured above a predetermined level and the output level with respect to the input signal is reduced below the predetermined level. In
A correction process for compensating for a decrease in the output level is performed on the signal component of the input audio signal substantially below the predetermined level, and
An audio signal processing method, wherein a correction processing state that compensates for a decrease in the output level is variably set in accordance with an adjustment state of a volume output from the speaker device. The audio signal processing method according to claim 1, wherein
When the volume adjustment state is a large volume exceeding a predetermined volume, the correction process is not performed, the correction process is performed when the volume is equal to or lower than the predetermined volume, and further according to a volume setting amount equal to or lower than the predetermined volume. An audio signal processing method characterized in that the correction amount is variably set in at least a plurality of stages. An audio signal processing device that performs correction processing for outputting an input audio signal from a speaker device having predetermined input / output characteristics,
Audio signal processing apparatus in which linearity of output level with respect to input signal is almost ensured as predetermined input / output characteristics of said speaker device, and output level with respect to input signal decreases below said predetermined level In
Volume adjusting means for setting an output volume from the speaker device;
Correction means for performing a correction process to compensate for a decrease in the output level for a signal component substantially equal to or lower than the predetermined level of the input audio signal;
An audio signal processing apparatus comprising: control means for variably setting a correction processing state that compensates for a decrease in the output level in the correction means in accordance with an adjustment state in the volume adjusting means. The audio signal processing apparatus according to claim 3, wherein
The control means does not perform the correction process when the volume adjustment state by the volume adjustment means is a loud volume exceeding a predetermined volume, and performs the correction process when the volume is lower than the predetermined volume. Further, the audio signal processing apparatus is characterized in that the correction amount is variably set in at least a plurality of stages according to the volume setting amount equal to or less than the predetermined volume.

Images