JP2016010048A - Audio signal adjustment circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio signal adjustment circuit which performs appropriate loudness correction corresponding to a sound volume setting value of a volume.SOLUTION: An output signal of a loudness element 50 is negatively fed back to a line amplifier 21. The loudness element has frequency characteristics corresponding to inverse characteristics of an iso-loudness curve. In output of the line amplifier 21, low-frequency and high-frequency levels are increased by negatively feeding back the output of the loudness element. In the output of the line amplifier, the low-frequency and high-frequency levels are increased as a feedback amount becomes large. A control section 5 sets a gain of an electronic volume 22 for loudness correction correspondingly to the sound volume setting value of the sound volume (a manipulator of a control section that is not illustrated). For example, in the case where the sound volume setting value of the sound volume becomes small, the control section increases the gain of the electronic volume for loudness correction, enlarges a feedback amount of the loudness element and enlarges a loudness correction amount.

Description

  The present invention relates to an audio signal adjustment circuit for adjusting the level of an audio signal.

  The sensitivity of human hearing varies with frequency. For example, when the volume is low, it is difficult to hear a low frequency component and a high frequency component. Such a characteristic is defined as an equal loudness curve in ISO 226: 2003.

  Therefore, in the conventional circuit, it has been proposed to perform loudness correction for raising the low frequency component and the high frequency component when the volume is low. For example, the loudness control circuit of Patent Document 1 uses a variable resistor with a tap so that the frequency characteristics change in conjunction with the volume setting value of the volume.

Japanese Utility Model Publication No. 63-25772

  In the loudness control circuit of Patent Document 1, the frequency characteristics do not change in conjunction with the volume setting value of the volume in the area below the center tap. Therefore, appropriate loudness correction cannot be performed in a medium to low volume region where the usage frequency is relatively high.

  In addition, some loudness correction amounts can be manually adjusted. However, since the amount of loudness correction is not linked to the volume setting, it is necessary to reset the volume every time the volume is changed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an audio signal adjustment circuit that performs appropriate loudness correction in conjunction with a volume setting value of a volume.

  The audio signal adjustment circuit of the present invention is connected to a volume setting reception unit that receives a volume setting value, an amplifier that receives an audio signal, a first gain adjustment circuit that adjusts the gain of the amplifier, and an output of the line amplifier. And a loudness processing unit having a predetermined frequency characteristic.

  The audio signal adjustment circuit includes: a second gain adjustment circuit for changing an input amount from the loudness processing unit to the amplifier, the output of the loudness processing unit being input to the line amplifier; and the volume setting receiving unit. And a controller that controls the first gain adjustment circuit and the second gain adjustment circuit, respectively, according to the received volume setting value.

  As described above, the audio signal adjustment circuit feeds back the output of the line amplifier via the loudness processing unit having a frequency characteristic corresponding to the equal loudness curve. Since the feedback amount is set to a gain corresponding to the volume setting value, appropriate loudness correction can be performed in conjunction with the volume setting value of the volume. Note that the first gain adjustment circuit and the second gain adjustment circuit only need to have a function of performing gain adjustment (a simple attenuator may be used). In a conventional circuit capable of varying the loudness correction amount, a variable resistor having a mechanical structure is used as a variable element, which is unsuitable for a general-purpose electronic volume circuit using a recent IC. However, the present invention can use a general-purpose electronic volume with an integrated ground terminal. Therefore, the audio signal adjustment circuit can be realized simply by connecting a microcomputer (control unit) to the general-purpose electronic volume (second gain adjustment circuit), and loudness correction linked to the volume setting value without much cost. It can be performed.

  The loudness processing unit can be realized by, for example, a bandpass filter using an RC circuit. For example, when the loudness processing unit has a frequency characteristic corresponding to the inverse characteristic of the equal loudness curve, the output of the loudness processing unit is negatively fed back to the amplifier.

  In addition, the audio signal adjustment circuit includes a first loudness correction amount receiving unit that receives a setting of the loudness correction amount, and the control unit responds to the setting of the loudness correction amount received by the first loudness correction amount receiving unit. The input amount from the loudness processing unit to the amplifier in the second gain adjustment circuit may be changed.

  The required loudness correction amount differs depending not only on the volume setting value but also on the rated output of the audio device, gain, speaker efficiency, or listening position. Therefore, the audio signal adjustment circuit preferably allows the first loudness correction amount receiving unit to manually change the loudness correction amount even with the same volume setting value.

  The audio signal adjustment circuit includes a second loudness correction amount receiving unit that receives a loudness correction amount strength setting with respect to a change in the volume setting value, and the control unit receives the second loudness correction amount receiving unit. It is preferable to control the gain change amount of the second gain adjustment circuit with respect to the gain change amount of the first gain adjustment circuit in accordance with the intensity setting of the loudness correction amount.

  In this configuration, the change in the loudness correction amount that is linked to the change in the volume setting value can be made gentle or steep by the second loudness correction amount receiving unit.

  Further, it is preferable that the control unit sets a gain that compensates for a change in volume by the loudness processing unit and the second gain adjustment circuit in the first gain adjustment circuit.

  When performing loudness correction, a change in volume on hearing can be suppressed by raising the low frequency component and the high frequency component. However, there is a case where the volume on hearing is increased by raising the low frequency component and the high frequency component. Therefore, the control unit sets a gain that compensates for the increase in audible volume due to loudness correction. For example, when the volume setting value is changed by -10 dB lower and the audible volume increases by 2 dB due to the loudness correction, the audible volume changes only by about -8 dB. In this case, when the control unit receives a sound volume setting value of −10 dB from the sound volume setting reception unit, the control unit sets the gain of the first gain adjustment circuit to −12 dB, so that an appropriate user desires while performing loudness correction. The volume can be changed.

  According to the present invention, appropriate loudness correction can be performed in conjunction with the volume setting value of the volume.

It is a block diagram which shows the structure of an audio signal processing apparatus. It is a circuit diagram which shows a volume adjustment circuit. It is a figure which shows an example of a frequency characteristic. It is a figure which shows the relationship between the change of a 1st loudness volume, and a loudness correction amount. It is a figure which shows the relationship between a volume and a loudness correction amount. It is a figure which shows the relationship between the change of a 2nd loudness volume, and a loudness correction amount. It is a figure which shows the relationship between the volume volume and loudness correction amount which concern on an application example.

  FIG. 1 is a block diagram showing the configuration of the audio signal processing apparatus according to the first embodiment. The audio signal processing device includes an input unit 1, a signal processing unit 2, and an output unit 3.

  The input unit 1 inputs an audio signal from the outside. The audio signal input to the input unit 1 is input to the signal processing unit 2. In this example, only one channel of the audio signal is shown as a representative, but it is actually preferable to provide the signal processing unit 2 for each channel and perform signal processing for each channel.

  The signal processing unit 2 corresponds to the audio signal adjustment circuit of the present invention. The signal processing unit 2 includes a control unit 5, a volume volume 10, a first loudness volume 11, a second loudness volume 12, a gain adjustment unit 15, and a loudness correction unit 16.

  The gain adjusting unit 15 adjusts the level of the audio signal input from the input unit 1. The level-adjusted audio signal is output to the output unit 3. The audio signal output from the output unit 3 is amplified by a power amplifier (not shown) or the like and output to the speaker.

  The loudness correction unit 16 inputs the audio signal whose level has been adjusted by the gain adjustment unit 15. The loudness correction unit 16 gives a predetermined frequency characteristic to the input audio signal. The audio signal to which the frequency characteristic is given is fed back to the gain adjusting unit 15.

  FIG. 2 is a diagram illustrating a configuration of a volume adjustment circuit including the gain adjustment unit 15 and the loudness correction unit 16. The gain adjustment unit 15 includes a main electronic volume 20, a line amplifier 21, and a feedback resistor 31.

  The main electronic volume 20 corresponds to the first gain adjustment circuit of the present invention, and adjusts the gain of the line amplifier 21. The main electronic volume 20 is connected to an input line (IN in the drawing), a non-inverting input terminal (+ in the drawing) of the line amplifier 21, and a ground line (GND in the drawing). Accordingly, the main electronic volume 20 can be a general-purpose electronic volume in which ground terminals are integrated. The main electronic volume 20 can be easily controlled by connecting the control unit 5 which is a microcomputer. The main electronic volume 20 is set by the control unit 5 to a gain corresponding to the volume setting value of the volume volume 10 (corresponding to the volume setting reception unit of the present invention).

  The line amplifier 21 corresponds to the amplifier of the present invention and is an amplifier circuit connected to the audio signal line. The output terminal of the line amplifier 21 is negatively fed back to the inverting input terminal (-in the figure) via the feedback resistor 31, and the audio signal is amplified. The output terminal of the line amplifier 21 is connected to the output line (OUT in the figure) and the loudness correction unit 16.

  The loudness correction unit 16 includes a loudness element 50, a loudness correction electronic volume 22, a buffer amplifier 23, and a feedback resistor 32.

  The loudness element 50 corresponds to the loudness processing unit of the present invention, and is a band-pass filter using an RC circuit. Here, the loudness element 50 is set with a time constant such that the low range and the high range are attenuated with a peak of 1 kHz. That is, the loudness element 50 has a frequency characteristic corresponding to the inverse characteristic of the equal loudness curve. However, the frequency characteristic of the loudness element 50 does not need to be completely matched with the inverse characteristic of the equal loudness curve. A characteristic in which the low range and the high range are attenuated and a level difference from the mid range is generated corresponds to “a frequency characteristic corresponding to an equal loudness curve”.

  The loudness correction electronic volume 22 corresponds to the second gain adjustment circuit of the present invention, and adjusts the gain of the circuit buffer amplifier 23. The loudness correcting electronic volume 22 is connected to the loudness element 50, the non-inverting input terminal of the buffer amplifier 23, and the ground line. Therefore, a general-purpose electronic volume with an integrated ground terminal can be used as the loudness correction electronic volume 22. The loudness correcting electronic volume 22 can be easily controlled by connecting the control unit 5 which is a microcomputer.

  The buffer amplifier 23 is an impedance adjustment circuit, and is an amplifier for preventing the signal on the gain adjustment unit 15 side from affecting the output side of the loudness correction unit 16. The output terminal of the buffer amplifier 23 is connected to the inverting input terminal of the line amplifier 21 via its own inverting input terminal and the feedback resistor 32.

  As a result, the output signal of the loudness element 50 is negatively fed back to the line amplifier 21. As described above, the loudness element 50 has a frequency characteristic corresponding to the inverse characteristic of the equal loudness curve. The output of the line amplifier 21 is increased in low and high frequency levels by negative feedback of the output of the loudness element 50. That is, the output of the line amplifier 21 has a frequency characteristic corresponding to the characteristic of the equal loudness curve, as the input amount (feedback amount) from the loudness element 50 to the line amplifier 21 increases, the level of the low and high frequencies increases. And loudness correction is performed.

  FIG. 3 is a diagram illustrating an example of frequency characteristics. The horizontal axis of the graph in the figure corresponds to the frequency, and the vertical axis corresponds to the gain. For example, when the feedback amount from the loudness element 50 is 0, the frequency characteristic of the audio signal output from the line amplifier 21 is completely flat (corresponding to a line indicated by 15 dB in the figure). On the other hand, as the amount of feedback from the loudness element 50 increases, the frequency characteristics of the line amplifier 21 cause a level difference between the mid-frequency component, the low-frequency component, and the high-frequency component. For example, when the feedback amount is the largest, the output of the line amplifier 21 has a level difference of about 20 dB from the low frequency component (10 Hz) with 1 kHz as a reference (−5 dB), and the high frequency component (10 kHz) and 10 dB. A level difference of about a degree is generated.

  Therefore, the loudness correction for raising the low-frequency component and the high-frequency component with respect to the mid-frequency component becomes stronger as the feedback amount of the loudness element 50 increases.

  The feedback amount of the loudness element 50 is set by adjusting the gain of the loudness correction electronic volume 22. The loudness correction electronic volume 22 is connected to the control unit 5, and the control unit 5 sets the gain according to the volume setting value of the volume volume 10.

  FIG. 4A is a diagram showing the relationship between the volume and the loudness correction amount. The horizontal axis of the graph shown in FIG. 4A corresponds to the volume setting value of the volume volume 10, and the vertical axis corresponds to the setting value of the first loudness volume 11. As shown by the black dots in FIG. 4A, for example, when the volume setting value of the volume volume 10 is reduced from 15 dB to 5 dB, the control unit 5 increases the gain of the loudness correction electronic volume 22 to increase the loudness element 50. Increase the feedback amount and perform loudness correction. Further, for example, when the volume setting value of the volume volume 10 is reduced to −5 dB, the control unit 5 further increases the gain of the loudness correction electronic volume 22, increases the feedback amount of the loudness element 50, and increases the loudness correction amount. Enlarge.

  However, if the feedback amount of the loudness element 50 is increased and the loudness correction amount is increased, the volume of the audibility increases by the amount by which the low-frequency component and the high-frequency component are lifted, and the volume change intended by the user cannot be obtained. There is a case. Therefore, the control unit 5 sets the main electronic volume 20 as a gain that compensates for the increase in the audible volume due to the loudness correction. For example, it is assumed that when the volume setting value of the volume volume 10 is changed by −10 dB from 15 dB to 5 dB, the audible volume increases by 2 dB by performing the loudness correction. In this case, the control unit 5 changes the gain of the main electronic volume 20 by −12 dB and sets it to 3 dB. Then, the volume change in the sense of hearing becomes -10 dB, and appropriate loudness correction can be performed while realizing the volume change intended by the user. However, even when the gain of the main electronic volume 20 is set to 3 dB (changes −12 dB), the volume setting value displayed on the display unit (not shown) such as an LED remains 5 dB (changes −10 dB). For the user to recognize as if the user has changed the sound volume setting value to the intended value.

  In this way, the control unit 5 sets the gain of the loudness correction electronic volume 22 in accordance with the volume setting value of the volume volume 10 and performs appropriate loudness correction in conjunction with the volume setting value of the volume volume 10. As a result, the user can operate the volume volume 10 to perform appropriate loudness correction according to the audible characteristics.

  4A shows an example in which the loudness correction amount is changed stepwise in accordance with the change in the volume setting value. However, the loudness correction amount is continuously changed in accordance with the change in the volume setting value. You may make it make it. When the loudness correction amount is changed stepwise, the relationship between the volume setting value and the loudness correction amount (gain of the loudness correction electronic volume 22) is stored as a table in a memory (not shown) of the control unit 5, for example. deep. The control unit 5 can set the gain of the loudness correction electronic volume 22 by reading the table with the volume setting value of the volume volume 10. In addition, when the loudness correction amount is continuously changed, a function indicating the relationship between the sound volume setting value and the loudness correction amount (gain of the loudness correction electronic volume 22) is defined, thereby calculating each time. An appropriate loudness correction amount (gain of the electronic volume 22 for loudness correction) can be set. For example, assuming that the relationship between the gain Ga of the main electronic volume 20 and the gain Gb of the loudness correction electronic volume 22 is Ga = 20−Gb, the loudness correction is performed when the gain Ga of the main electronic volume 20 is changed from 15 dB to 5 dB. The gain Gb of the electronic volume 22 is changed from 15 dB to 5 dB.

  Next, FIG. 4B is a diagram showing the relationship between the change in the first loudness volume 11 and the loudness correction amount. In the example of FIG. 4B, the loudness correction is performed at the same volume setting value by changing the loudness correction amount in conjunction with the first loudness volume 11 (corresponding to the first loudness correction amount receiving unit of the present invention). This is an aspect in which the amount can be changed manually. As shown by the black dots in FIG. 4B, the control unit 5 does not change the volume setting value of the volume volume 10, but if the setting value of the first loudness volume 11 increases, The gain is increased, the feedback amount of the loudness element 50 is increased, and the loudness correction amount is increased. The required loudness correction amount differs depending not only on the volume setting value but also on the rated output of the audio device, gain, speaker efficiency, or listening position. Therefore, in the example of FIG. 4B, the difference in the rated output of the audio device, the gain, the efficiency of the speaker, or the listening position is changed by changing the loudness correction amount in conjunction with the set value of the first loudness volume 11. I am trying to compensate. Also in the example of FIG. 4B, the control unit 5 sets the main electronic volume 20 for a gain that compensates for the increase in the audible volume due to the increased loudness correction. For example, if it is assumed that the loudness correction increases and the audible volume increases by 2 dB, the control unit 5 changes the gain of the main electronic volume 20 to -2 dB and sets it to 13 dB.

  In the example shown in FIG. 4B, when the volume setting value is very large or very small (for example, Max or Min), the loudness correction is performed even if the setting value of the first loudness volume 11 is changed. Although the amount does not change, as shown in FIG. 5, the loudness correction amount may be changed in conjunction with the change of the setting value of the first loudness volume 11 at any volume setting value.

  Next, FIGS. 6A and 6B are diagrams showing the relationship between the volume and the loudness correction amount when the second loudness volume 12 is changed. When the second loudness volume 12 (corresponding to the second loudness correction amount receiving unit of the present invention) changes, the control unit 5 loosens the change in the loudness correction amount that changes in conjunction with the volume volume 10, Or steep. For example, as shown in FIG. 6A, when the volume setting value of the volume volume 10 is changed from 15 dB to 5 dB, when the loudness correction amount changes in two steps, the setting value of the second loudness volume 12 is increased. When it is set (or made smaller), the loudness correction amount that changes in conjunction with the volume volume 10 is moderated, and the loudness correction amount is set to change by one step.

  As described above, the audio signal adjustment circuit of the present embodiment can make the change in the loudness correction amount that changes in conjunction with the volume volume 10 moderate or steep, depending on the user's preference.

  Next, FIG. 7 is a diagram illustrating a relationship between a volume and a loudness correction amount according to an application example. In this example, in a medium volume region where the usage frequency is relatively high, a change in the loudness correction amount with respect to a change in the setting value of the first loudness volume 11 is moderated, and a region near the maximum volume or the minimum volume where the usage frequency is relatively low. Then, the change of the loudness correction amount with respect to the change of the first loudness volume 11 is made abrupt. As a result, in a medium volume area where the usage frequency is relatively high, even if the first loudness volume 11 is moved greatly, the change in the loudness correction amount is small, so that fine adjustment is facilitated for the user, and operability is improved.

  In the circuit configuration of FIG. 3, the example in which the loudness element 50 has a frequency characteristic corresponding to the inverse characteristic of the equal loudness curve and is negatively fed back to the line amplifier 21 has been shown. It is possible to input to the positive phase side of the amplifier 21, or a circuit to input the input audio signal and the output of the loudness element 50 to the negative phase side of the line amplifier 21 using a negative phase amplifier. Even with these circuit configurations, loudness correction linked to the sound volume setting value can be performed.

DESCRIPTION OF SYMBOLS 1 ... Input part 2 ... Signal processing part 3 ... Output part 5 ... Control part 10 ... Volume volume 11 ... First loudness volume 12 ... Second loudness volume 15 ... Gain adjustment part 16 ... Loudness correction part 20 ... Main electronic volume 21 ... Line amplifier 22 ... Loudness correction electronic volume 23 ... Buffer amplifier 50 ... Loudness element

Claims (5)

A volume setting reception unit for receiving a volume setting value;
An amplifier to which an audio signal is input;
A first gain adjustment circuit for adjusting the gain of the amplifier;
A loudness processing unit connected to the output of the amplifier and having a predetermined frequency characteristic;
An audio signal conditioning circuit comprising:
The output of the loudness processing unit is input to the amplifier,
A second gain adjustment circuit for changing an input amount from the loudness processing unit to the amplifier;
A control unit for controlling each of the first gain adjustment circuit and the second gain adjustment circuit according to the volume setting value received by the volume setting reception unit;
An audio signal adjustment circuit comprising: The loudness processing unit has a frequency characteristic corresponding to an inverse characteristic of an equal loudness curve,
The audio signal adjustment circuit according to claim 1, wherein an output of the loudness processing unit is negatively fed back to the amplifier. A first loudness correction amount receiving unit for receiving a setting of the loudness correction amount;
The control unit changes an input amount from the loudness processing unit in the second gain adjustment circuit to the amplifier according to the setting of the loudness correction amount received by the first loudness correction amount receiving unit. The audio signal adjustment circuit according to claim 2. A second loudness correction amount receiving unit for receiving a loudness correction amount strength setting with respect to a change in the volume setting value;
The control unit sets a gain change amount of the second gain adjustment circuit with respect to a gain change amount of the first gain adjustment circuit according to the intensity setting of the loudness correction amount received by the second loudness correction amount reception unit. 4. The audio signal adjustment circuit according to claim 1, wherein the audio signal adjustment circuit is controlled.   5. The audio signal adjustment circuit according to claim 1, wherein the control unit sets, in the first gain adjustment circuit, a gain that compensates for a volume change by the loudness processing unit and the second gain adjustment circuit.

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