JPH05198091A - Level control circuit - Google Patents

Abstract

PURPOSE:To prevent a sound from being distorted or becoming small even when an audio signal which has different characteristics like a microphone input and a line input is supplied. CONSTITUTION:An attenuator 83 adjusts the level of an input signal and a feedback unit 70 calculates a control value for the level adjustment of this attenuator 83 from the output level from the attenuator 83. Here, the attenuator 83 adjusts the level of the signal by corresponding to the characteristics of the signal, obtained by the switching of a changeover switch 81 switched according to plural input signals, according to the control value calculated by the feedback unit 70.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level control circuit for controlling the level of an audio signal or the like.

[0002]

2. Description of the Related Art Conventionally, when an audio signal is recorded on a magnetic tape by a tape recorder or the like, the recording signal level for the magnetic tape is optimized by controlling the level of the input audio signal. In this case, generally, the input signal is supplied to the recording system via an AGC (auto gain control) circuit, and by this configuration, level control is performed so that an optimum recording current flows to the magnetic head of the recording system. I'm trying to do it.

[0003]

By the way, in the case of recording sound with a tape recorder, for example, there are generally many kinds of sound sources to be recorded and their characteristics are also diverse. On the other hand, the conventional AGC circuit used in the tape recorder performs AGC having the same characteristics for input audio signals having various different characteristics as described above, for example. For this reason, it is difficult to record all types of sound with high quality in conventional AGC recording such as a tape recorder. That is, in the above-mentioned conventional tape recorder that performs AGC recording, for example, when a piano performance is recorded by a microphone (recording a microphone input) and when music from a record or the like is recorded (recording a line input). Although the characteristics of the supplied sound are completely different, since the AGC with the same characteristics as above is performed, for example, the sound of a recorded piano is distorted, or the volume of recorded music from a record or the like. Often becomes smaller and less powerful.

Therefore, the present invention has been proposed in view of the above situation, and the sound is distorted even when a plurality of audio signals having different properties such as a microphone input and a line input are supplied. It is an object of the present invention to provide a level control circuit that does not become smaller or smaller.

[0005]

The level control circuit of the present invention has been proposed in order to achieve the above-mentioned object, and it has a switching means for switching a plurality of input signals and a signal level of the input signals. Variable gain means for adjusting,
Control value setting means for calculating a control value for adjusting the signal level in the variable gain means based on the output level of the variable gain means, and the control value setting means is switched by the switching means. The control value corresponding to the signal is calculated.

More specifically, the level control circuit of the present invention prepares two AGC characteristics (parameters), for example, for a microphone and for a line, and uses them for a microphone input and line input changeover switch or a microphone input terminal, for example. The attached line / microphone automatic switch is used to switch the characteristics (parameters) of the AGC. That is, in general, a microphone input is often supplied with a signal having a wide dynamic range like the sound of the outside world, and
In the line input, for example, a signal (processed signal) that is compressed so that the dynamic range of a record, FM broadcast, TV broadcast or the like is narrowed is often supplied. In this way, in the case of the above microphone input, since an audio signal having a wide dynamic range and a wide variety is input, the above A
As a characteristic of GC, compression of volume and followability are generally required. Further, in the case of the above line input, since the signal is processed as described above, the AGC characteristics are required to have level stability and force retention. Therefore, in the level control circuit of the present invention, the difference in the characteristics of these signals is used to switch the characteristics of the AGC to enable later high-quality recording in the tape recorder.

[0007]

According to the level control circuit of the present invention, the control value setting means determines the control value for the variable gain means in accordance with the signal switched by the switching means for switching a plurality of input signals, that is, the nature of the input signal. Therefore, the variable gain means can adjust the level according to the property of the input signal.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the level control circuit according to the embodiment of the present invention includes a changeover switch 81 as a changeover means for changing over a plurality of input audio signals having different characteristics such as microphone input and line input. , And an attenuator 83 which is a variable gain means for adjusting the signal level of the input audio signal which is switched by the changeover switch 81 and supplied through the input terminal 91.

Further, the level control circuit of the present embodiment, together with the above-mentioned configuration, is feedback value which is control value setting means for calculating a control value for signal level adjustment in the attenuator 83 based on the output level of the attenuator 83. The feedback unit 70 has a unit 70, and the feedback unit 70 calculates a control value corresponding to the signal switched by the change-over switch 81 to calculate the control value.
3 is output.

That is, in the level control circuit of this embodiment shown in FIG. 1, the line input terminal 80 is connected to the switched terminal a of the changeover switch 81, and the microphone input terminal 82 is the switched terminal of the changeover switch 81. It is connected to b. The microphone input terminal 82 outputs a switching control signal according to the insertion of a microphone terminal, and the switching control signal is sent to the switching switch 81. Therefore, in the configuration of this embodiment, the switched terminal b is selected when the microphone terminal is inserted into the microphone input terminal 82, and the switched terminal b is selected when the microphone terminal is inserted into the microphone input terminal 82. The terminal a is selected so that automatic switching is performed.

The output of the changeover switch 81 is the terminal 91.
Is sent to the attenuator 83 via the and is adjusted in level. The output of the attenuator 83 is sent to the feedback unit 70 after being level-detected by a level detection circuit 5 described later that detects the level of the output signal of the attenuator 83 (specifically, the peak level is detected).

Here, FIG. 1 shows an example in which an AGC according to the characteristics of a total of three input audio signals, for example, a line input and two first and second microphone inputs can be realized.

Therefore, the feedback unit 70 of the present embodiment includes, for example, a record, FM broadcast, TV.
AGC that can maintain the level stability and force corresponding to the line input, which is often a signal (processed signal) compressed so as to have a narrow dynamic range such as broadcasting
The control value calculation unit 85 for line which calculates the above control value with the characteristics of the above, and the microphone input (the two microphones of the first and the second) which are often supplied with various signals having a wide dynamic range such as external sound. The first control value is calculated according to the characteristics of the AGC which has a high volume compression and a high trackability corresponding to the input
A microphone control value calculation unit 88 and a second microphone control value calculation unit 89 are provided. Further, in the feedback unit 70, changeover switches 84 and 86 which are changed over according to a changeover control signal from the microphone input terminal 82, and a microphone characteristic changeover switch which is changed over according to the first and second microphone inputs. A selector switch 8 which is switched according to a switching control signal from 71.
7, 90 are also provided.

The output from the level detecting circuit 5 is supplied to the changeover switch 84 of the feedback unit 70. The changeover switch 84 selects the switched terminal b when the switching control signal from the microphone input terminal 82 indicates the microphone input, and selects the switched terminal a when the switching control signal indicates the line input. .. here,
When the line input switched terminal a is selected by the changeover switch 84, the output of the level detection circuit 5 is sent to the line control value calculation unit 85. The control value from the line control value calculation unit 85 is the same as that of the changeover switch 84.
It is sent to the attenuator 83 via 6. When the changeover switch 84 selects the microphone-switched terminal b, the output of the level detection circuit 5 is sent to the changeover switch 87.

The changeover switch 87 selects either one of the terminals to be changed over c or d according to a changeover control signal indicating either one of the two microphone inputs from the microphone characteristic changeover switch 71. For example, when the switched terminal c of the changeover switch 87 is selected, the level detection circuit 5 described above is selected.
Is sent to the first microphone control value calculation unit 88, and the control value formed by the first microphone control value calculation unit 88 is switched to the switched terminal c like the changeover switch 87. It is sent to the attenuator 83 through the changeover switch 90 and further through the changeover switch 86 which is changed over to the terminal b to be changed over. Further, for example, when the switched terminal d of the changeover switch 87 is selected, the output of the level detection circuit 5 is sent to the second microphone control value calculation unit 89, and this second microphone control is performed. The control value formed by the value calculation unit 89 is transmitted through the changeover switch 90 which is changed over to the changeover terminal d, similarly to the changeover switch 87, and through the changeover switch 86 which is changed over to the changeover terminal b. Sent to.

As described above, in the level control circuit of this embodiment, the AGC characteristics (parameters) in the feedback unit 70 are, for example, two for microphone and one for line (in the example of FIG. Since there are three, there are a total of three), and these are switched in accordance with, for example, a switching control signal of the microphone input and the line input (switching control signal from the microphone input terminal 82).

Therefore, in the circuit of this embodiment, in the case of a microphone input in which a wide dynamic range and a variety of signals such as external sounds are often supplied, the AGC of the above-described AGC which realizes volume compression and tracking performance is realized. It becomes possible to form a control value with the characteristics and send it to the attenuator 83, and a signal (processed signal) compressed so that the dynamic range of a record, FM broadcast, TV broadcast, etc. is narrowed is supplied. In the case of line input, which is often the case, it becomes possible to form a control value with the characteristics of the AGC capable of stabilizing the level and maintaining the force, and send the control value to the attenuator 83.

That is, according to the level control circuit of the present embodiment, the characteristic of the AGC is switched by utilizing the difference in the characteristics of the input audio signals, so that the sound is distorted at the time of later recording in the tape recorder, It enables high-quality recording without becoming smaller.

The configuration of the present embodiment shown in FIG. 1 will be concretely described below with reference to FIG. 2 which is applied to a level control circuit used in, for example, a digital tape recorder.
In FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals. In addition, the configuration of FIG.
Not only GC but also manual gain control is possible, and this manual gain control and AGC can be switched.

In FIG. 2, the manual gain control mode and the AGC mode are switched between the switched terminals of the switches 41 and 42 which are switched according to the manual / AGC mode by the switched terminal side of the AGC mode side or the manual side. It is realized by switching to the selected terminal side of the gain control mode side. First, A
The configuration of the GC mode will be described.

In FIG. 2, for example, an analog audio signal of a microphone input or a line input is supplied to the input terminal 91 and sent to the analog attenuator 1. In FIG. 2, the line input terminal 80,
Illustration of the microphone input terminal 82 and the changeover switch 81 is omitted. The analog attenuator 1 has the terminal 91
The analog audio signal from the device is arbitrarily attenuated (macro gain control), and the A / D converter 2 in the next stage is
Send to. The analog attenuator 1 is designed to set the attenuation value in steps of 2 dB. In addition to its original purpose, this attenuator also aims to widen the input operation range.

The A / D converter 2 converts the analog audio signal pre-attenuated by the analog attenuator 1 into a digital signal. The digital signal is sent to the next digital multiplier 3.

The digital multiplier 3 adjusts a fine gain that cannot be adjusted by the analog attenuator 1. That is, the digital multiplier 3 is
The audio signal digitally converted by the converter 2 is multiplied by a coefficient of 1 or less to reduce the value (attenuation), and 2 dB of the analog attenuator 1 is used.
It is used to interpolate between steps to perform fine level adjustment. The digital multiplier 3 is set to a resolution of about 0.25 dB step. Further, for example, in the manual gain control mode to be described later, in the case of a large attenuation such as a fade-out, the digital multiplier 3 can also be attenuated to attenuate the noise including the A / D converter 2. .. In FIG. 2, the analog attenuator 1 and the digital multiplier 3 (A /
The D converter 2 is included) corresponds to the attenuator 83 in FIG.

DSP of the next stage of the digital multiplier 3
The (digital signal processor) 4 further processes the digital signal converted in the preceding configuration to form a signal to be recorded on a recording medium such as a magnetic tape. The output of the DSP 4 is output from the output terminal 92 and recorded on a magnetic tape or the like by the configuration of a recording system in the latter stage (not shown).

The audio signal passes only from the attenuator to the DSP 4 path. The other constituent elements in FIG. 2 are all configured to form the control value of the attenuator (other than the input side of the peak detection circuit 5 described later), and the other constituent elements perform processing once in 1/50 seconds, for example. I do. Further, in the present embodiment, the audio signal system is composed of hardware and the rest is composed of software, but each part can be composed of either software or hardware.

Here, in order to perform AGC, the audio signal whose gain has been adjusted by the attenuator is passed through the peak detection circuit 5, the logarithmic compression circuit 6 and the monaural conversion circuit 7 and used as the measurement level. That is, first, the output of the digital multiplier 3 is sent to the peak detection circuit 5. In addition,
In FIG. 2, the peak detection circuit 5 corresponds to the level detection circuit 5 of FIG.

The peak detection circuit 5 converts the digital data converted in the preceding stage into a fixed time (for example, 20 ms).
ec), the maximum volume of the section is detected, and this is used as a representative of the current digital audio level for performing AGC. The output of the peak detection circuit 5 is sent to the logarithmic compression circuit 6.

The logarithmic compression circuit 6 performs logarithmic conversion of the value (peak value) detected by the peak detection circuit 5 in accordance with human auditory characteristics. In this embodiment,
Floating format of so-called broken line approximation (Since the exponent part is logarithmic, the mantissa part is connected to this, MSB
Is non-transmission). Here, in the logarithmic compression circuit 6, the floating format for the polygonal line approximation is used as it is. Therefore, when the exponent part becomes zero, the bits below it are linear, which makes a big difference from the actual logarithm. Therefore, when the exponent part is zero, the exponent part is compressed in the negative direction like a broken line approximation so that the error does not become abnormally large.
In addition, in the polygonal line approximation, the part corresponding to the exponent part does not have a negative value, but the true exponential expression has a negative value.
The output of the logarithmic compression circuit 6 is sent to the monaural circuit 7. The output of the logarithmic compression circuit 6 is also used for the level meter.

The monaural circuit 7 outputs the larger value of the stereo L channel and R channel values supplied from the logarithmic compression circuit 6. That is,
In AGC, if the gains of the left and right channels of L and R are controlled separately, the localization is disrupted. Therefore, this processing is performed so that both measurement and control are common to the left and right. Therefore, the measured value is monaural (the one with a larger volume on the left and right because the emphasis is on the loud volume). The output of the monaural conversion circuit 7 is sent to the reverse backlash circuit 8.

The inverse backlash circuit 8 is provided with a backlash element (backlash circuit 14) inserted in a feedback loop system described later for the AGC.
Backlash is corrected to make the system look like it is linear so that the system does not make unnecessary vibrations. That is, when the attenuator was set last time (or in some cases, the previous previous time), the difference is set by the backlash in the backlash circuit 14 described later. Therefore, since the peak level measured correspondingly has a large or small value, the above-mentioned backlash amount is added to calculate the peak level when the backlash process is not performed. This makes it appear that there is no dead zone element in the feedback loop, and can suppress unnecessary vibration going back and forth between the dead zones.
The output of the reverse backlash circuit 8 is sent to the limiter unit 11, the normal unit 12, and the basic unit 13 of the feedback unit (corresponding to the feedback unit 70 in FIG. 1) of the feedback loop system.

The limiter unit 11 is a feedback unit which responds to a sudden large input with the fastest reaction (for example, 0.1 seconds or less).

The normal unit 12 responds to a normal change in the volume of music or the like at a medium speed (for example, 1 to
It is a feedback unit that reacts in about 10 seconds. Further, the characteristics are switched between line input and microphone input. Here, the characteristics that are switched depending on the line input and the microphone input are, as described later, an upper and lower operation level, an upper and lower feedback loop gain, an attack time constant, a recovery time constant, and the like.

The basic unit 13 corresponds to the difference in sound volume due to the difference in sound source, etc., and has the lowest speed (for example, 10 to 1).
It is a feedback unit that responds in about 00 seconds. Also in this unit, the characteristics are switched between line input and microphone input.

In FIG. 2, the block corresponding to the line input is indicated by L in the figure, and the block corresponding to the microphone input is indicated by M in the figure.

Calculation is performed in each feedback unit of the limiter unit 11, the normal unit 12, and the basic unit 13, and the sum of the outputs of the limiter unit, the normal unit, and the basic unit is output as the control value of the attenuator in the AGC. .. The details of this feedback unit will be described later.

The output of the monaural circuit 7 is also sent to the silence detecting circuit 10. The silence detection circuit 10
Is a circuit for detecting whether or not the input is silent, and changes the silent flag when the silent is detected. The silence flag corresponds to each of the feedback units 11,
Used in 12,13. For example, the absolute level of the currently input signal is calculated from the current value of the attenuator and the value of the peak detection circuit 5 {absolute level = peak level (logarithm) + attenuation (logarithm)}, and this is, for example, below a certain value. Then each feedback unit 1
The inputs of LPFs, which will be described later, inside 1, 12, 13 are set to zero. This prevents the volume of the AGC from being unnecessarily raised between music pieces, for example. That is, the feedback unit receives a silence flag (silence detection signal) from the silence detection circuit 10 and slows or stops (holds) the signal level adjustment speed of the attenuator.

More specifically, in the level control circuit of this embodiment, the silence detecting circuit 10 has a signal level of an input audio signal and a predetermined silence detecting level (eg, -40 dB) as shown in A of FIG. 3, for example. ), And if the comparison detects that the input audio signal level becomes equal to or lower than the silence detection level (or becomes lower than the silence detection level), for example, between music songs, From the silence detection circuit 10 to B in FIG.
The silence flag (silence detection flag) as shown in FIG. The silence detection circuit 10 outputs the silence flag only when the input audio signal level is below a certain reference level (for example, 0 dB) and below the silence detection level in order to accurately detect the silence. It is also possible to

The silence flag from the silence detecting circuit 10 is sent to the feedback unit. In the feedback unit, when the silence flag is received, even if the signal level of the input audio signal is very low such as during the music piece, the loop gain of the AGC is not rapidly increased. As shown in FIG. 3C, the AGC operation is delayed or held to prevent a rapid level increase in the attenuator.

Further, in this embodiment, when the feedback unit receives the silence flag from the silence detecting circuit 10, it controls the attenuator in the same manner as when the reference level is input from the attenuator. It is also possible to do so. In this case, the level control circuit according to the present embodiment adjusts the level with the original time constant (that is, the time constant that is not shortened by the loop gain). There is nothing to lose.

In FIG. 3D, for comparison, the abrupt level by the variable gain means in the case of the conventional example in which the operation of the AGC is not delayed or held in response to the detection of silence as in the present embodiment. It shows how it is rising.

The above feedback units 11, 1
The outputs of 2 and 13 are added by the adder 44 and then sent to the backlash circuit 14. The backlash circuit 14 attaches a dead band to the output calculated by each feedback unit 11, 12, and 13 so that the attenuator in the subsequent stage does not operate to produce an unnatural sound with respect to a fine fluctuation of the input. Is. The details of the operation of the backlash circuit 14 will be described later.

The delay unit 15 provided between the backlash circuit 14 and the reverse backlash circuit 8 is set to 1 at the time when the peak is detected when the audio signal level falls.
Since a sample time delay occurs, this is for delaying one sample time only when the level falls. That is, the peak level detected by the peak detection circuit 5 is the value at the attenuator value one time before when the audio signal is increasing and the value at the attenuator value twice before the audio signal is decreasing. Therefore, the backlash value corrected by the inverse backlash circuit 8 must be the backlash value one time before when the audio signal increases and the backlash value two times before when the audio signal decreases. This processing is realized by way of the delay device 15. The details of the backlash delay by the delay device 15 will be described later.

The level rise / fall determination circuit 9 detects the level fall. The level rise / fall determination circuit 9 measures the audio signal level in order to switch the delay in the delay device 15 and sets a flag according to the rise / fall for the next reverse backlash.

The output of the backlash circuit 14 is sent to the offset addition circuit 16 via the switch 41 whose AGC-side switched terminal is selected. The offset addition circuit 16 arbitrarily determines the amount of attenuation in advance for the case where the calculated value of the feedback unit becomes zero with respect to a certain reference input, and the feedback unit via the backlash circuit 14 This predetermined addition amount is added to the calculated value of. In other words, the offset addition is an attenuator value (control value) when the reference input value is input, is a value determined at the time of design, and is a gain that can be increased from the reference. In the present embodiment, the gain increased by the offset addition is set to 10 dB, for example. The output of the offset addition circuit 16 is sent to the attenuator operation range limiting circuit 17.

The attenuator operating range limiting circuit 17
Limits the control value within the operating range of the attenuator volume. That is, the attenuator operation range limiting circuit 17 limits the control value that exceeds the operation range of the attenuator because it is calculated depending on the setting of the loop gain or the like.

The rounding circuit 18 in the subsequent stage of the attenuator operation limiting circuit 17 performs rounding to cut off the non-matching part when the number of digits of the value calculated by each feedback unit does not match the resolution of the attenuator. Is. Specifically, in the rounding circuit 18, the error due to the quantization of the control value of the attenuator in the subsequent stage is halved. In addition, this value is the silence detection circuit 10 described above.
It is also used for silence detection. The output of the rounding circuit 18 is the digital / analog distribution circuit 1
Sent to 9.

The digital / analog distribution circuit 19
Is for distributing the amount of attenuation for linking the analog attenuator 1 and the digital multiplier (digital attenuator) 3. That is, in the digital / analog distribution 19, the output of the rounding circuit 18 is rounded down with analog resolution to be the control value of the analog attenuator 1, and the control value less than that is the control value to the digital multiplier (digital attenuator) 3. Distribute as. Specifically, in the present embodiment, the resolution of the analog attenuator 1 is 2 dB and the resolution of the digital multiplier 3 is 0.25 dB. Therefore, for the analog attenuator 1, a control value that is a 2 dB step is 2 dB for the digital multiplier 3
The control value is distributed so that the step is filled with 0.25 dB steps. Although not shown in the figure on the digital side, since there is a time delay due to the A / D converter 2, an appropriate delay is inserted so that the change time matches the analog attenuator 1.

An inverse logarithmic conversion circuit 20 is inserted and connected between the digital / analog distribution circuit 19 and the digital multiplier 3. The inverse logarithmic conversion circuit 20 is a converter for converting the logarithmically compressed control value into a linear numerical value so that the digital multiplier 3 operates as an attenuator. That is, the inverse logarithmic conversion circuit 20
Is a logarithmic expression of the control value of the digital attenuator (digital multiplier 3) output from the digital / analog distribution circuit 19, the linear ratio of the linear attenuator is used for the digital attenuator to perform the attenuation. It has been converted into quantity.

Further, in this embodiment, the control value from the feedback unit is the backup RAM 24.
It is designed to be retained at all times. The backup RAM 24 is a memory for holding a value as an initial value for the next AGC operation even after the power is turned off. That is, for example, when the power of the set is turned on, the data is transferred from the backup RAM 24 to the manual adjustment register 22. The backup RAM 24 has its storage location switched between line input and microphone input (blocks L and M in FIG. 2).

Further, the output of the limiter unit 11 is added to the control value stored in the backup RAM 24. That is, since the limiter unit 11 corresponds to a large instantaneous input and does not represent an average level, the control value from the limiter unit 11 is subtracted from the current control amount as the initial value of the next AGC. Use the specified value. Specifically, in the backup RAM 24, a value obtained by subtracting the control value of the limiter unit 11 from the original value of the control value of the attenuator by the subtractor 45 is further rounded off by the rounding circuit 21 to the bit width of the memory of the backup RAM 24. The data rounded down to (for example, 8 bits in the embodiment) is stored. Considering that the limiter unit 11 is not operating normally, it is more current that the current control value is a value with backlash (output of the backlash circuit 14).

The output of the backup RAM 24 is sent to the backup limiting circuit 23.
The backup limiting circuit 23 limits the range transferred to the manual adjustment register 22 in the subsequent stage from the backup RAM 24 only once when the power is turned on. Further, the limit value in the backup limit circuit 23 can be set to different values for the line and the microphone (blocks L and M in FIG. 2). Therefore, the backup limiting circuit 23 limits the range separately for the microphone input and the line input. Furthermore, regardless of the current microphone / line input mode, both microphone input and line input are transferred simultaneously.

Here, the configuration of this embodiment is also capable of manual gain control. That is, in the case of this manual gain control, the analog attenuator 1 is based on the manual control value output from the manual adjustment register 22 according to the operation amount from the recording volume (not shown) supplied via the terminal 43. , Attenuate the analog audio signal, for example.

That is, the operation amount from the recording volume is, for example, the rotation angle data of the dial or the operation data output from the volume increase / decrease button of the remote controller, and this operation data is sent to the manual adjustment register 22. The manual adjustment register 22 holds a control value for adjusting the level by the attenuator in advance, and the control value is increased / decreased from the held control value according to the operation amount of the recording volume. The value is to be retrieved. Further, in the present embodiment, as described above, the attenuator is configured by combining the analog attenuator 1 and the digital multiplier 3, and therefore these attenuators are manually adjusted in accordance with the operation amount of the recording volume. Manual gain control is realized by being controlled by the manual control value from the register 22. In addition to the original purpose, the attenuator also aims to widen the input operation range.

Further, the manual control value output from the manual adjustment register 22 changes the level of the sound adjusted by the attenuator when it is supplied to the attenuator in, for example, 2 dB steps (that is, it changes in a stepwise manner). It is such a value. The manual control value from the manual adjustment register 22 is sent to the low pass filter 26.

Here, the low-pass filter 26 has a time constant of, for example, about 1 second, and converts the manual control value from the manual adjustment register 22 which changes intermittently into a smooth motion. For example, the manual adjustment register 2
When the level adjustment by the attenuator is performed in the 2 dB step, for example, based on the manual control value from 2, the output of the low-pass filter 26 is shown in association with the change in the volume level. As indicated by A, it changes smoothly.

The output of the low pass filter 26 is distributed by the digital / analog distribution circuit 19. When the control value of, for example, 10 bits is supplied from the manual adjustment register 22, the digital / analog distribution circuit 19 distributes, for example, the upper 3 bits to the analog attenuator 1 side and, for example, the lower 7 bits. It distributes to the digital multiplier 3. This allows
The analog attenuator 1 roughly adjusts the signal at eight levels, and the digital multiplier 3 finely adjusts the output level data of the A / D converter 2 with a level difference of 1/2 ⁷ , for example.

Table 1 shows the control values distributed by the digital / analog distribution circuit 19 in association with the change in the volume level adjusted by the attenuator.

[0059]

[Table 1]

According to Table 1, the volume level adjusted by the analog attenuator 1 is 2 dB step, and the volume level adjusted by the digital multiplier 3 is 0.25 dB step. That is, the control value sent from the digital / analog distribution circuit 19 to the analog attenuator 1 is a value for changing the volume level in 2 dB steps as shown in B of FIG. , Digital /
The control value sent from the analog distribution circuit 19 to the digital multiplier 3 is a value for changing the volume level in 0.25 dB steps as shown in C of FIG. 4 when associated with the change of the volume level.

As a result, in the present embodiment, when manual level control is performed, level control in which the level does not change rapidly or the level does not change discontinuously can be realized.

In the circuit of this embodiment, the A / D ratio is adjusted by matching the control value output from the manual adjustment register 22 with the resolution of the analog attenuator 1.
The dynamic range of the converter 3 is not impaired. That is, by limiting the control value held in the manual adjustment register 22 to a value at which only the analog attenuator 1 operates as described above,
The dynamic range of the D converter 2 is not impaired.

As described above, according to this embodiment, when performing a manual operation, the variable value noise is removed by smoothing the control value from the manual adjustment register 22 by the low pass filter 26. You can
Further, in this embodiment, since the control amount of the manual adjustment register 22 according to the operation amount of the recording volume is matched with the dynamic range of the A / D converter 2, there is no loss in the dynamic range.

Furthermore, the manual adjustment register 2 of the present embodiment.
As described above, 2 outputs a manual control value according to the volume value (manipulation amount of the recording volume) when manually adjusting the recording level, and, for example, when switching between the AGC and manual gain control modes. In order to prevent gain discontinuity, the current adjustment amount (volume value) calculated by the rounding 21 is always input through the switch 42 during the AGC operation. The manual adjustment register 22 of this embodiment holds independent manual control values corresponding to the line input and the microphone input.

By the way, in the configuration capable of switching the manual mode and the AGC mode as in the configuration of FIG. 2, for example, when the AGC is switched to the manual operation or vice versa. , The output of the feedback unit (total of outputs of limiter, normal and basic units) is used as it is as a manual initial value, or the manual control value is directly used as an initial value of the basic unit 13 when shifting to AGC. Can be considered. In this case, the AGC
In the configuration for performing the above, the above-mentioned backlash element is put in the loop in order to prevent the gain from being moved unnecessarily, but as described above, the output of the feedback unit (limiter, normal, output of each basic unit is If the total) is set as the manual initial value, the backlash error may result in a gain jump. Also,
If the limiter unit shifts from AGC to manual during operation, the instantaneous value may be sampled, and the gain may be far from the true value. Furthermore,
For example, immediately after fading out by manual operation, A
If the operation shifts to the GC operation, the initial gain of the AGC becomes zero, and it may take a long time to reach the proper range. In addition, only the limiter unit may be operated in order to cope with a sudden large input even in the manual operation, but at this time, a backlash may cause a gain jump.

From the above, in the configuration of FIG. 2 of the present embodiment, for example, in the case of changing from AGC to manual, the limiter unit 11 is subtracted from the value subjected to the backlash process during the AGC operation by the subtractor 45. The output value of is subtracted, and this is put in the manual adjustment register 22.
Specifically, in the present embodiment, when the recording is started from the manual and the gain control mode is changed from AGC to manual, the value of the manual adjustment register 22 is loaded into the register of the low pass filter 26. Since the manual adjustment register 22 is 1 byte in this embodiment, it is loaded into the same unit of the register of the low pass filter 26 and the other bytes are cleared. As a result, the low-pass filter 26
Has already converged, the gain is not changed by the low-pass filter 26 in the initial stage of the manual. After that, the operation of the manual gain control described above can be executed.

Here, the value after backlash processing is used because this is the current attenuator value.
This is because there is no change even when shifting to the manual. In addition, the subtractor 45 subtracts the output of the limiter unit 11 as described above, and when the limiter unit 11 responds to a sudden large input, sampling this represents an average control value. This is because the sum of outputs from the normal and basic units 12 and 13 represents a long-term average value. Further, since the manual adjustment register 22 generally has only the resolution of the adjustment step unit, the error due to the quantization can be halved by rounding off the control value with a digit of the resolution. Considering this, the rounding circuit 21 is inserted.

Further, in the case of changing from manual to AGC, for example, when an uncommon value such as a fade-out due to a manual operation amount is included in the manual adjustment register 22, the range limiting circuit 25 limits the range. Is added to initialize the basic unit 13 of the AGC feedback unit (zero is cleared for the limiter and the normal) so that insane settings at the initial stage of the AGC can be avoided. That is, the range limiting circuit 25, for example, when the REC is started or when the gain control mode is changed from manual to AGC operation, the initial value of AGC operation is set as a backup value or a manual setting value (both are set in the manual adjustment register 22). However, in the present embodiment, for example, when the manual control value is an insane value (for example, when the previous fade-out ended).
In addition, by limiting this, the problem of AGC error at the beginning of recording is alleviated. In this case, backlash is zero. Specifically, when the gain control mode is changed from manual to AGC mode, the value of the manual adjustment register 22 is set to the range limiting circuit 2.
The range is limited by 5 and is initially set in the LPF register (register 114 of the low-pass filter in FIG. 5) of the basic unit 13 of the feedback loop system. The range limitation in the range limiting circuit 25 determines how much range influences the initial value of the previous AGC depending on the nature of the sound source. Also in this case, the manual adjustment register 22 is
Since it is 1 byte, it loads to the same unit of LPF and clears the other bytes.

Further, in the specific configuration of this embodiment shown in FIG. 2, the limiter, normal, and basic feedback units 11, 12, and 13 are installed in the manual AG.
Along with the transition to C, for example when REC starts (REC
(Including PAUSE and REC PLAY PAUSE)
It is also initialized when the operation mode is switched. In this case, the limiter unit 11 and the normal unit 12 are initialized to zero, and the basic unit 13
Is initialized by limiting the range of the value of the manual adjustment register 22.

That is, the configuration of FIG.
When REC starts (eg RECPAUSE, REC
PLAY PAUSE, etc.) and a mode setting switch 32 for performing various operations, and a controller 31 as a mode recognition means for recognizing an operation mode corresponding to various operations on the mode setting switch 32. Corresponding to the recognition of the operation mode, the backup RAM 24 stores the control value set by the feedback unit immediately before the operation mode is switched.
When the operation mode is switched, the control value stored in the backup RAM 24 is supplied to the feedback unit as an initial value and the control value supplied to the control value calculation unit 71 as the initial value. It is used as a control value for adjusting the signal level in the attenuator 83.

Next, the specific structure of the feedback loop unit will be described with reference to FIG. The limiter, normal, and basic units 11, 12, 13
Is actually composed of one configuration, and executes five operations by changing internal parameters for each unit and for each microphone / line input mode. 5, a block indicated by L in the figure is a block holding a parameter corresponding to a line input, and a block indicated by M in the figure is a block holding a parameter corresponding to a microphone input. Medium M and L are blocks that hold the same parameters for microphone and line inputs. These parameter holding blocks are provided according to the operation of each of the basic, normal, and limiter units (only the limiter has the same parameters for the microphone and the line input).
Note that, substantially, the blocks M and L in the drawing of FIG. 5 are portions that hold each parameter (characteristic) of each control value calculation unit of FIG.

That is, in FIG. 5, the terminal 121
Is supplied with the output of the reverse backlash circuit 8.
The input signal is supplied to the subtractors 116 and 120.
The subtracter 116 is supplied with each parameter from the holding unit 115 that holds each parameter of the upper operating point (upper operating level), and the subtracter 120 is supplied with the lower operating point (lower operating level). Each parameter is supplied from the holding unit 122 that holds each parameter of (1).

The output of the subtractor 116 is sent to the comparator 117, and the output of the subtractor 120 is sent to the comparator 123. When the supplied signal (difference) is negative (that is, the terminal 121
When the input signal supplied to is smaller than the above lower operating point)
When the switched terminal b to which the output of the subtractor 120 of the switch 119 is supplied is selected, the signal (difference) supplied in the opposite is positive (that is, the input signal supplied to the terminal 121 is the lower operating point). In the above case), a switching control signal for selecting the switched terminal a (zero input) of the switch 119 is output.
The comparator 117 is supplied with the output of the subtractor 116 of the switch 118 when the supplied signal (difference) is positive (that is, when the input signal supplied to the terminal 121 is larger than the upper operating point). When the switching terminal a is selected and the supplied signal (difference) is negative (that is, when the input signal supplied to the terminal 121 is below the upper operating point), the output of the switch 119 of the switch 118 is supplied. A switching control signal for selecting the switched terminal b to be output is output.

In other words, the output from the switch 118 is divided into the case where the input from the terminal 121 is larger than the upper operating point, the case where the input is smaller than the lower operating point, and the intermediate case. If it is larger than the upper operating point, the difference with the upper operating point is sent to the next stage configuration if it is smaller than the lower operating point. That is, with these configurations, the feedback is not performed at the intermediate level, and the dead zone is in which the AGC does not operate. Also, by setting the lower operating point to the minimum value, it is possible to make a unit that responds only to a large input like a limiter. Further, by making the upper operating point and the lower operating point the same, it is possible to eliminate the dead zone and create the characteristics of the basic unit.

The output terminal of the switch 118 is connected to the switched terminal b of the switch 105. The switched terminal a of the switch 105 has zero input. The switch 105 is switched according to the silence flag supplied from the silence detection circuit 10 via the terminal 101, and when the silence flag is supplied (when silence is detected), the switched terminal a side. When the zero input is output and there is no silence flag, the terminal is switched to the switched terminal b side.

The output of the switch 105 is the multiplier 106.
Sent to. The parameters from the parameter holding units 102 and 103 for the upper gain and the lower gain are supplied to the multiplier 106 via the switch 104 that is switched according to the switching control signal of the comparator 117. .. The switch 104 is connected to the switched terminal a when the switching control signal from the comparator 117 is positive.
Is selected, and conversely, when it is negative, the switched terminal b is selected.

That is, in the multiplier 106, the process of multiplying the upper gain when the input of the terminal 121 is higher than the upper operating point and the lower gain when the input of the terminal 121 is lower than the lower operating point is executed. Done. The upper and lower gains are feedback loop gains.
When the gain is increased, the level is compressed and becomes close to the reference level. Further, when the gain is lowered, the compressive force is weakened, and the force for approaching the reference level is also weakened.

The output of the multiplier 106 is sent to the multiplier 112 via the subtractor 111 and the comparator 1
It is also sent to 07. The comparator 107 outputs a switching control signal for selecting the switched terminal a side of the switch 110 when the output of the multiplier 106 is zero or more, and the switch 110 when the output of the multiplier 106 is less than zero.
A switching control signal for selecting the terminal b to be switched of is output. The parameter holding unit 10 holding each parameter of the attack time constant at the switched terminal a of the switch 110.
8 is supplied, and the switched terminal b is supplied with each parameter from the parameter holding unit 109 that holds each parameter of the recovery time constant. The output of the switch 110 is sent to the multiplier 112.

The multiplier 112 and the subtractor 111 together with the adder 113 and the register 114 in the subsequent stage constitute an IIR type low pass filter. That is, the output of the multiplier 112 is sent to the register 11 via the adder 113.
4 and the output of the register 114 is fed back to the adder 113 and the subtractor 111, and the multiplier 112 receives the parameter (multiplication coefficient) from the parameter holding units 108 and 109. By being supplied, the IIR low-pass filter is configured. Specifically, by passing through the low-pass filter, the oscillation of the system is prevented and the movement of the AGC is delayed to form the characteristics of each feedback unit.
Since the time constant of this low-pass filter can be set separately for attack and recovery, the integration characteristic can also be adjusted.

The output of the register 114 of the IIR low-pass filter is taken out from the terminal 124 as the output of the feedback loop unit. The register 114 is loaded with the initial value supplied through the terminal 125.

FIG. 6 shows a flowchart of the backlash in the backlash circuit 14.

Here, when the control value to the analog attenuator 1 and the value logarithmically compressed by the logarithmic compression circuit 6 have different units, the backlash amount output from the backlash circuit 14 is compared with the output value. Multiply the coefficient by
I have to correct it. In the present embodiment, the attenuator side is in 2 dB units and the peak detection side is in 6 dB units, so the backlash amount is divided by 3 for correction.

That is, in FIG. 6, the value input to the backlash circuit 14 is subtracted from the previous output value in step S1. Then, in step S2, it is checked whether or not the difference in step S1 exceeds the width of the backlash (the upper and lower sides of the backlash width are checked).

If it is determined in step S2 that the backlash width is not exceeded, the process proceeds to step S8. In step S8, one third of the difference is output to the backlash output (the difference at this time is the backlash amount, and the backlash output is used as the reverse backlash value). Thereafter, in step S9, the output of the backlash process remains unchanged (dead zone), and the backlash process ends.

If it is determined in step S2 that the backlash width is exceeded, step S3
Proceed to. In step S3, it is determined whether the difference is positive. When it is determined to be positive in step S3, the process proceeds to step S5, and in step S5, one-third of the minus backlash width is output as the backlash output. Next, in step S7, the output of the backlash process is set to a value obtained by subtracting the backlash width from the current input value (that is, a value smaller by the backlash width is output). Then, the backlash process is completed.

If it is determined to be negative in step S3, the process proceeds to step S4. In step S4, a third of the backlash width is output to the backlash output. Next, in step S6, the output of the backlash process is set to a value obtained by adding the backlash width to the current input width (that is, a value larger by the backlash width is output). Then, the backlash process is completed.

The backlash width in the above flow chart is a value on one side and is 0.75 in the embodiment.
It is set to dB. Further, the backlash output is input to the inverse backlash circuit 8 through the delay device 15, so it is divided by 3 in advance to match the unit.

The backlash delay by the delay device 15 will be described with reference to FIGS. 7 and 8. FIG. 7A shows an example in which the audio signal is increasing, and FIG.
In A of FIG. 4, an example in the case where the audio signal is decreasing is shown. B of FIG. 7 and B of FIG. 8 show the execution period of AGC, C of FIG. 7 and C of FIG. 8 show the data of the backlash amount one time before, and D of FIG. 7 and D of FIG. The data of the backlash amount two times before is shown. Further, T _C in FIGS. 7 and 8 indicates the timing of the changing point of the attenuator, and T _P in the drawings indicates an example of the peak detection point.

That is, for example, as shown in FIG. 7A, while the audio signal is increasing, when the control value of the attenuator is changed, the level in the latter half of the peak detection section is affected by the new control value. And since the signal is increasing, the maximum value of the section is in the latter half. Therefore, for the next peak detection, the peak level reflecting the new control value is detected. Therefore, when the backlash correction is performed in the case where the audio signal is increasing as shown in FIG. 8, for example, as shown by an arrow R ₆ in the figure, the error amount of the new control value is indicated by C in FIG. Use the backlash amount data from the previous time.

Further, for example, as shown in FIG. 8A, while the audio signal is decreasing, when the control value of the attenuator is changed, the new control value is affected in the latter half of the peak detection section. Since the maximum value of the section is decreasing, it is in the first half, and the peak value before the new control value will be the peak value in the next peak detection. Therefore, the peak detection value reflected by the new control value becomes the next (D in FIG. 8). Therefore, when the audio signal decreases as shown in FIG.
When the backlash correction is performed, for example, as shown by an arrow R ₇ in the figure, data of the backlash amount two times before D in FIG. 8 is used.

FIG. 9 shows a specific structure of another embodiment of the present invention. In the configuration of FIG. 2 described above, the feedback loop system is turned off in the manual gain control mode. However, in FIG. 9, the feedback loop limiter unit 11 also operates in the manual gain control mode. The limiter operation is the same as that described above. In FIG. 9, the same components as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 9, an adder 51 is provided in place of the switch 41 of FIG.
A switch 52 which is turned on in the manual gain control mode between 1 and the low pass filter 26.
And a subtracter 53 that subtracts the value of the backlash width from the output of the low-pass filter 26.
In addition, the rounding circuit 21 and the backup RAM 24
Between the normal unit 12 and the adder 44, and between the basic unit 13 and the adder 44, switches 56, 54 and 55 that are turned on in the AGC mode are provided.

That is, when a limiter is attached to the manual operation, the backlash output for AGC (output of the limiter unit 11 via the adder 44) and the manual operation output (output of the low pass filter 26) of FIG. Addition is performed (however, the backlash width is subtracted from the output of the low-pass filter 26), and this is input to the offset addition circuit 16.

Here, the subtraction of the backlash width from the output of the low-pass filter 26 by the subtractor 53 is as follows.
For the following reasons. For example, after the limiter unit 11 operates for a moment and returns, the backlash always has a backlash width in the positive direction (a large input for which the limiter operates for a moment is sufficiently larger than the backlash width). After the limiter operates even once, this state becomes a steady value. Therefore, if the backlash width is subtracted, a correct manual control value that is not affected by the limiter operation is output to the attenuator.

In addition, before the limiter operates, there is an error by the subtracted amount in that case. Therefore, when the mode is changed to the manual mode, the backlash is initialized so that the backlash has the backlash width in the positive direction. To do. That is, the backlash output value is + backlash width, and the backlash output is + backlash width / 3.

As described above, according to the configuration of this embodiment,
Even with AGC with backlash, manual and AG
It is possible to avoid a problem such as a gain jump when switching between C operations.

[0097]

As described above, in the level control circuit of the present invention, the level adjustment by the variable gain means is
Since it is performed based on the control value corresponding to the signal switched by the switching means supplied from the control value setting means, for example, a plurality of audio signals having different characteristics such as a microphone input and a line input are generated. Even if it is supplied, the level can be controlled without the sound being distorted or reduced.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a basic configuration of a level control circuit according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a specific configuration of a level control circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between silence detection and level adjustment according to the present embodiment.

FIG. 4 is a diagram showing a volume change corresponding to a manual control value of a specific configuration of the present embodiment.

FIG. 5 is a block circuit diagram showing a specific configuration of a feedback unit.

FIG. 6 is a flowchart of backlash processing.

FIG. 7 is a diagram for explaining a backlash delay when an audio signal is increasing.

FIG. 8 is a diagram for explaining delay of backlash when the audio signal is decreasing.

FIG. 9 is a block circuit diagram showing another specific configuration of the present embodiment.

[Explanation of symbols]

 1 ... ・ ・ ・ Attenuator 2 ・ ・ ・ ・ ・ ・ A / D converter 3 ・ ・ ・ ・ ・ ・ Digital multiplier 4 ・ ・ ・ ・ ・ ・ DSP 5 ・ ・ ・・ ・ ・ ・ ・ Peak detection circuit 6 ・ ・ ・ ・ ・ ・ Logarithmic compression circuit 7 ・ ・ ・ ・ ・ ・ Monaural circuit 8 ・ ・ ・ ・ ・ ・ Inverse backlash circuit 9 ・ ・ ・・ ・ ・ ・ Level up / down judgment circuit 10 ・ ・ ・ ・ ・ ・ Silence detection circuit 11 ・ ・ ・ ・ Limiter unit 12 ・ ・ ・ ・ Normal unit 13 ・ ・ ・ ・ Basic Unit 14 ... Backlash circuit 15 ... Delay device 16 ... Offset addition circuit 17 ... Attenuator operating range limiting circuit 18, 21 ...・ ・ ・ Rounding circuit 19 ・ ・ ・ Digital / analog distribution circuit 20 ........ Inverse logarithmic conversion circuit 22 ..... Manual adjustment register 23 ..... Backup limit circuit 24 ..... Backup RAM 25 ........ .Range limiting circuit 26 ........ Low pass filter

Claims (1)

[Claims] 1. A switching means for switching a plurality of input signals, a variable gain means for adjusting the signal level of the input signal, and a signal level adjustment in the variable gain means based on the output level of the variable gain means. And a control value setting means for calculating a control value for calculating the control value, the control value setting means calculating a control value corresponding to the signal switched by the switching means.