JPH0870225A - Output characteristic setting device and coefficient setting device - Google Patents

Abstract

PURPOSE: To control a dynamic range by setting a mixing output characteristic of plural input signals based on a gain coefficient by a coefficient setting means and a gain coefficient by a coefficient generating means in a way that no overflow nor underflow takes place to a digital arithmetic word tone. CONSTITUTION: At first, a sum output XM is fed to the device, in which an absolute value is detected and subject to envelope detection and an envelope signal Xe is outputted from an envelope detection section 38. A gain calculation section 39 calculates a gain coefficient by a prescribed function arithmetic operation based on the envelope signal Xe . A comparator 41 compares the envelope signal Xe with a reference value Xth . A gain coefficient calculated by the calculation section 39 is fed to a terminal 42a of a switch section 42 and a gain coefficient from a gain generating section 40 is fed to a terminal 42b, and the changeover of the connection terminals 42a, 42b is controlled depending on an output of the comparator 41. An output of the switch section 42 is fed to a multiplier 34 as a gain coefficient (g).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an output characteristic setting device for obtaining a predetermined input / output characteristic by applying coefficient calculation processing to an input digital signal and outputting it, and a coefficient used for the coefficient calculation processing. And a coefficient setting device.

[0002]

2. Description of the Related Art In recent years, many audio devices use recording media in which audio signals are recorded in the form of digital data, and are widely used as, for example, CD players, DAT players, mini disk players and the like. Also, cassette tape players, AM / FM radio tuners, etc.
There is also an audio source that outputs an audio signal as an analog signal, and in many cases there is a composite type audio device in which these are integrated with the device section that serves as the digital source.

Here, various processes relating to the audio signal are collectively performed by digital calculation, so that advantages such as reduction of the number of parts and reduction of the board area are produced as compared with the case where the analog signal processing circuit is constituted. Furthermore, acoustic effects such as reverb and compression, which were difficult with analog signals, can be realized relatively easily with digital signal processing.

For this reason, audio data from a digital source is processed in a digital stage, and particularly in the above-mentioned complex type equipment, an audio signal from an analog source is once digitized to be processed in the same manner as a signal from a digital source. It is considered that the digital signal processing unit is configured to supply the digital signal processing unit.

[0005]

By the way, when the signals from various sources are processed by the digital signal processing section regardless of whether they are digital sources or analog sources, the digital signal processing section particularly performs a predetermined calculation. It is important not to cause overflow or underflow for the word length. That is, it is necessary to execute a process corresponding to the dynamic range control conventionally known in the AGC circuit or the like in the analog signal system.

For example, when it is desired to output the karaoke reproduction voice and the microphone input to the speaker at the same time, the digital signal processing section mixes the two systems of inputs inputted by digital data and outputs them. , It is necessary to prevent the added value from overflowing for mixing. Further, even in the case of the processing of one system of input, it is necessary to prevent the overflow by the limiter processing or the like.
Further, it is also possible to further execute an expanding process or the like.

In any case, in the digital signal processing, it is first necessary to control the output characteristic. For this purpose, as shown in FIG. 12, the gain coefficient g is set in the gain calculating section 50 according to the input value x. , The gain coefficient g of the multiplier 51
By multiplying the input value x with, the output y having a desired output characteristic is obtained.

As a method of obtaining the gain coefficient g according to the input value x, either of the following two methods has been mainly taken. First, a desired gain characteristic is created by a linear function or the like after logarithmic transformation is applied to an input, and the value obtained by inverse logarithmic transformation is used as a gain coefficient. The other is a method in which a memory table in which a desired gain characteristic is uniquely obtained for input information is prepared and the gain coefficient is determined by referring to this.

When the gain coefficient g is obtained by logarithmic conversion, the gain calculator 50 has the configuration shown in FIG.
First, the input x is logarithmically converted by the logarithmic converter 52 to obtain an output x _G. For example, the logarithmic conversion unit 52 calculates the output x _G by the following calculation using the input value x and the constant a _N.

[Equation 2]

The output x _G thus obtained is input to the function operation unit 53, and the function operation unit 53 performs output _{G on the} input x _G by a linear function operation such as the following (Equation 3). To get It should be noted that c and d are constants set to obtain a predetermined characteristic.

(Equation 3)

Further, the output G of the function computing section 43 is supplied to the antilogarithmic transformation section 54. Then, the inverse logarithmic conversion unit 54 uses the input G and the constant b _N to obtain the output g by the following calculation of (Equation 4), for example.

[Equation 4] This output g becomes a gain coefficient, and the multiplier 5 of FIG.
1 is supplied.

However, in such a system, there is a problem that a considerable amount of calculation (calculation step) is required for calculation processing such as logarithmic conversion, function calculation, and inverse logarithmic conversion. Therefore, if this method is adopted, it is against the intended purpose of simplifying the configuration by digital processing.

Further, in the case of the method of providing the memory table, a ROM table, for example, is provided as the gain calculating section 50, but in order to improve the resolution to some extent,
Since it is necessary to secure a considerable storage area as a memory capacity such as a ROM, this also goes against the intended purpose of simplifying the configuration by digital processing. On the contrary, if the memory area is limited to simplify the configuration, the characteristics will be deteriorated.

[0014]

In view of such problems, the present invention provides an output characteristic setting device suitable for dynamic range control by digital processing, and a gain coefficient used for coefficient calculation for performing dynamic range control. It is an object of the present invention to provide a coefficient setting device that can obtain the value by a simple calculation.

To this end, first, as an output characteristic setting device suitable as a mixer having a plurality of inputs, a mixer means, an envelope detection means, a comparison means, a coefficient setting means, a coefficient generating means, a selecting means, and a gain. And a calculation means. The mixer means adds a plurality of input signals and outputs the added signals. The envelope detecting means obtains envelope information about the output of the mixer means. The comparing means compares the output of the envelope detecting means with a predetermined value. The coefficient setting means performs a function operation on the output of the envelope detection means to obtain a gain coefficient. The coefficient generating means generates a fixed gain coefficient.
The selecting means selects and outputs either the gain coefficient by the coefficient setting means or the gain coefficient by the coefficient generating means according to the comparison result of the comparing means. The gain calculating means gives a gain to the output of the mixer means based on the gain coefficient output from the selecting means, and outputs the gain. Configured like this,
The gain coefficient by the coefficient setting means and the gain coefficient by the coefficient generating means are selectively used to set the mixed output characteristics of a plurality of input signals.

Further, an envelope characteristic detecting means, a comparing means, a coefficient setting means, a coefficient generating means, a selecting means, and a gain calculating means are provided as an output characteristic setting device suitable as a limiter. Then, the envelope detecting means obtains envelope information of the input signal. The comparing means compares the output of the envelope detecting means with a predetermined value. The coefficient setting means performs a function operation on the output of the envelope detection means to obtain a gain coefficient. The coefficient generating means generates a fixed gain coefficient. The selecting means selects and outputs either the gain coefficient by the coefficient setting means or the gain coefficient by the coefficient generating means according to the comparison result of the comparing means. The gain calculation means gives a gain to the input signal based on the gain coefficient output from the selection means, and outputs the input signal. With this configuration, the gain coefficient by the coefficient setting means and the gain coefficient by the coefficient generating means are selectively used to set the input / output characteristics of the signal.

Further, as an output characteristic setting device suitable as an expander, an envelope detecting means, first and second comparing means, coefficient setting means, first and second coefficient generating means, and selecting means. And gain calculation means. And
The envelope detecting means obtains envelope information of the input signal. The first comparing means compares the output of the envelope detecting means with a first predetermined value. The second comparing means compares the output of the envelope detecting means with a second predetermined value. Coefficient setting means Coefficient setting means
A function operation is performed on the output of the envelope detecting means to obtain a gain coefficient. The first coefficient generating means generates a first fixed gain coefficient. The second coefficient generating means generates a second fixed gain coefficient. The selecting means selects one of the gain coefficient by the coefficient setting means, the gain coefficient by the first coefficient generating means, and the gain coefficient by the second coefficient generating means according to the comparison result of the first and second comparing means. Output. The gain calculation means gives a gain to the input signal based on the gain coefficient output from the selection means, and outputs the input signal. With this configuration, the input / output characteristic of the signal is set by selectively using the gain coefficient by the coefficient setting means, the gain coefficient by the first coefficient generating means, and the gain coefficient by the second coefficient generating means. To

As the coefficient setting device for calculating the gain coefficient g according to the input signal value x, the gain coefficient g for the input signal is calculated by the following function calculation of (Equation 5).

(Equation 5) However, k _n is a coefficient, j is a value that satisfies (1 / k _max ) ≧ 2 ^j for the maximum value k _max of the coefficient k _n , and C _F is (1 /
2) Fixed value satisfying ≦ │C _F │ <1, n is a fixed value,
M is the operation order, x _F is the input signal value x (1/2)
A value obtained by shifting x to satisfy ≦ x _F <1, and m is a shift amount for setting the input signal value x to x _F.

Further, as a coefficient setting device for performing the calculation of (Equation 5), (1/2) ≤x for the input signal value x.
A first shifter means for obtaining a x _F performs m-bit shift to satisfy _F <1, a register means for holding the coefficient k _n, to perform M following computation for the coefficients k _n and x _F An arithmetic means for performing one or more additions and one or more multiplications, and (m + fixed value) for the output of the arithmetic means
Second shifter means for performing a bit shift and outputting a gain coefficient g is provided.

[0020]

With the output characteristic setting device having the above structure, overflow due to digital signal processing can be eliminated. That is, by performing dynamic range control on the added signals of a plurality of inputs by the gain calculation means, it is possible to provide a mixer in which the output does not overflow. Further, similarly, by performing the dynamic range control on the input by the gain calculating means, it functions as a limiter for a large input level. Further, by controlling variously the coefficient characteristic in the gain calculation means according to the input, it functions as an expander. The gain coefficient supplied to the gain calculation means can be obtained by a simple calculation process by the coefficient setting device, so that the configuration can be simplified.

[0021]

EXAMPLES Examples of the present invention will be described below in the following order. 1. 1. Configuration of essential parts as audio equipment adopting the present invention Digital processing mixer 3. Limiter by digital processing 4. Expander by digital processing 5. Gain coefficient setting device

<1. Configuration of Main Part as Audio Equipment Adopting the Present Invention> FIG. 1 is a block diagram of a main part of an audio equipment equipped with an output characteristic setting device and a coefficient setting device of an embodiment. In this figure, IN _{1 to} IN _n are digital audio signals (DS _{1 to} DS) from various audio signal sources.
_n ) input terminal. The various audio signal sources correspond to a CD player unit, a mini disk player unit, a cassette tape player unit, a radio tuner unit, a microphone input unit, etc., which are integrally provided in the audio device of FIG. Alternatively, the audio signal may be supplied by being connected as an external device.

As these audio signal sources, there are one that can supply an audio signal as digital data and one that can be an analog audio signal source. For example, since the reproduction signal can be output in the form of digital data in the CD player section, the mini disk player section, etc., it is input terminal IN ₁
~ IN _n . Also, an audio signal from an analog audio signal source such as a cassette tape player, a radio tuner, or a microphone input unit is input after the analog audio signal output from the source is converted into a digital data form by an A / D converter. Terminal I
Any of N _{1 to} IN _n will be supplied.

There are various types of digital data transfer methods before and after the input terminals IN _{1 to} IN _n , such as a so-called three-wire transfer method and a digital audio interface transfer method, but any method may be used. In the case of the three-wire transfer method, a signal having a cycle of a sampling frequency f _S called LRCK, a signal having a period of (32 to 64) × f _S called BCK, and actual voice data are transmitted. Will be.

Reference numerals 1 and 2 are selectors, each of which is a digital audio signal (DS) supplied to the input terminals IN _{1 to} IN _{n.
1 to} DS _n ), one of them can be selected and output. The output of the selector 1 is the signal x
₁ is input to the DSP (digital signal processor) 3. The output of the selector 2 is DS as the signal x _2.
Input to P3.

In the case of this embodiment, it is assumed that the DSP 3 is capable of inputting the signals x ₁ and x ₂ in two systems. However, it is possible to input more than two systems by using the function as a mixer by digital processing described later.
This is necessary when the SP3 has, and the DSP3 may have one system input for functions such as a limiter and an expander. Further, in the actual IC as the DSP, the internal processing can be performed for the operations of the selectors 1 and 2, that is, the selectors 1 and 2 and the DSP 3 in the drawing.
Each block can be configured with one chip.

Both or one of the signals x ₁ and x ₂ is supplied to the DSP 3
Predetermined signal processing is performed by and output to the D / A converter 4. The D / A converter 4 converts the output of the DSP 3 into analog. This analog audio signal is supplied to the power amplifier 5, amplified, and output as audio from the speaker 6.

Reference numeral 7 is a controller composed of a microcomputer. The controller 7 controls the switching of the selectors 1 and 2 and controls various processes executed by the DSP 3.

<2. Digital Processing Mixer> For example, in an audio device having such a configuration, D
FIG. 2 shows the configuration when the SP3 functions as a mixer for the signals x ₁ and x ₂ . As the signal processing in the DSP 3, various kinds of processing such as echo, reverb, and equalizing may be executed as so-called sound effect processing. The description of the sound effect of is omitted.

In FIG. 2, reference numerals 31a and 31b are input sections of the DSP 3, and the signals x ₁ and x ₂ of two systems are input as described above. It should be noted that the input of the DSP 3 is two systems for the sake of explanation, and the inputs of three or more systems may be possible.

The plurality of input signals x ₁ ~x _n maximum amplitude value of | x _Mn |, when the attenuation amount for each input signal x ₁ ~x _n and ATT _n, the maximum value taken by the sum of all the inputs,

(Equation 6) Becomes The DSP 3 is required to have the ability to process up to this value without overflowing. For this,
In this embodiment, the mixer shown in FIG. 2 is used as a digital mixer. Hereafter, input two systems (x ₁ , x
₂ ) and proceed with the explanation.

Reference numeral 32a is an attenuator, which can attenuate the signal x ₁ . Reference numeral 32b is an attenuator capable of performing an attenuation process on the signal x ₂ . 33 is an adder, attenuator 32
The outputs of a and 32b are added and output. Addition output is x _M
And Reference numeral 34 denotes a multiplier that multiplies the addition output x _M and the gain coefficient g. The addition output x _M is provided with a gain by the gain coefficient g in the multiplier 34 and is output, and is supplied to the output terminal 36 via the amplification unit 35. To be done. Output y of output terminal 36
Will be supplied to the D / A converter 4 in FIG. 1 after being subjected to acoustic processing such as reverberation or directly.

Here,

(Equation 7) Defined as, the convertible range in the D / A converter 4 |
For x _DAC |

[Equation 8] And for the output y of the DSP3, Y = 20log y
Considering this as (dB), this value of Y must satisfy (Equation 8). However, the addition output x of the adder 33
_M is

[Equation 9] (However, x _M1 is the maximum amplitude value of input x ₁ , x _M2 is the input x
The maximum amplitude value of ₂ is ATT ₁ ≦ 1, ATT ₂ ≦ 1), and even if these are directly used as the output Y, the conversion in the D / A converter 4 cannot be performed correctly.

Therefore, in the present embodiment, the output characteristic that limits the output Y to 0 dB when the added output x _M becomes 0 dB or more is obtained by the arithmetic processing in the multiplier 34, as shown in FIG. 3A. I am trying.

As a structure for this purpose, an absolute value detecting section 37 is first provided, and the addition output x _M is supplied to detect the absolute value. Reference numeral 38 denotes an envelope detection unit, which is supplied with a signal in which the addition output x _M is converted into an absolute value by the absolute value detection unit 37. Then, the envelope detection unit 38 performs envelope detection and outputs the envelope signal x _e .

Reference numeral 39 denotes a gain calculating section, which calculates a gain coefficient by a function calculation described later based on the input envelope signal x _e . Reference numeral 40 denotes a gain generator that generates a fixed gain coefficient. Reference numeral 41 is a comparator, which compares the envelope signal x _e with the reference value x _th . A switch unit 42 supplies the gain coefficient calculated by the gain calculating unit 39 to the terminal 42a and the gain coefficient from the gain generating unit 40 to the terminal 42b. Then, the connection terminal 42
Switching between a and 42b is controlled according to the output of the comparator 41. The output of the switch unit 42 is supplied to the multiplier 34 as the gain coefficient g.

The gain characteristic is obtained for the gain G (where G = 20log g, X _M = 20log x _M ) as shown in FIG. 3B by each of the parts from the envelope detection part 38 to the switch part 42. Thus, the output characteristic of FIG. 3A is realized as the output of the multiplier 34.

The gain calculator 39 calculates the gain coefficient by the calculation of G = -X _e , that is, the gain g is obtained by the functional calculation of g = 1 / x _e . Although this function calculation will be described later, it can be approximated by a polynomial, and the amount of calculation is considerably smaller than that in the conventional method of performing logarithmic conversion and inverse logarithmic conversion. Further, in the gain generator 40, G = 0 as a fixed gain coefficient, that is, g
The gain coefficient of = 1 is output.

Then, the reference value x _th for the comparator 41 becomes a value corresponding to 0 dB, and the comparison result is X _e <0.
In the case of dB, the switch 42 connects the terminal 42b, and in the case of X _e ≧ 0 dB, the switch 42 connects the terminal 42a. That is, as the gain coefficient g supplied to the multiplier 34, when the addition output x _M is 0 dB or less, the gain coefficient g = 1, and when the addition output x _M exceeds 0 dB, the gain calculation unit 39 Addition output x
_The gain coefficient g calculated according to _M is supplied. That is, the gain characteristic shown in FIG.

As a result, the output characteristic shown in FIG. 3A can be obtained. Therefore, in this embodiment, the output characteristic is realized as a mixer which does not generate an overflow. Further, in this case, since the output y is not simply clipped at a certain level or more, the signal waveform is not greatly deformed, which is also preferable in terms of sound quality.

When calculating the gain, the addition output x _M is not directly used, but the envelope signal x _e is calculated by the gain calculating unit 39.
The reason why it is used as an input parameter of is as follows. If the addition output x _M is directly used, when the addition output x _M changes abruptly, the gain coefficient g also changes abruptly. In this case, the sound output from the speaker 6 with respect to the output y is very uncomfortable. To prevent this, the envelope signal x
_e is used, that is, the effect of a sudden level change is canceled.

It should be noted that although the description has been made with respect to a mixer having two input systems, it is of course possible to apply the present invention as a mixer for three or more input systems.

<3. Limiter by Digital Processing> Next, FIG. 4 shows a configuration in the case where the DSP 3 functions as a limiter for an input signal in the audio device as shown in FIG. In FIG. 4, the same functional parts as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 31 is an input terminal, which corresponds to the input terminals 31a and 31b in FIG. However, when it is assumed that one system input is supported and the DSP 3 is compatible with two system inputs as shown in FIG. 1, one attenuator (32a or 32a in FIG. 2 is used.
It can be considered that b) attenuates _one input signal (x ₁ or x ₂ ) to the zero level. Of course, when the DSP 3 has one system input, 31 becomes an input terminal of the DSP 3 itself.

That is, in FIG. 4, the mixer part is removed from the structure of FIG. The input signal x is the multiplier 3
4 is multiplied by the gain coefficient g to be output y from the output terminal 36 via the amplifier 35. Then, in order to obtain the gain coefficient g, the input signal x is input to the absolute value detection unit 3
7. The envelope signal x _e is supplied via the envelope detector 38 and supplied to the gain calculator 39.

Further, the envelope signal x _e is compared with the comparator 41.
And is compared with a reference value x _th . Then, the terminals 42a and 42b of the switch unit 42 are switched according to the comparison result, and the gain coefficient from the gain generation unit 40 or the gain coefficient calculated by the gain calculation unit 39 is supplied to the multiplier 34.

Now, the transfer function from the input x to the output y is 1
When (y = x), the input / output characteristics are as shown in FIG. On the other hand, if it is desired to obtain the input / output characteristic shown in FIG. 5B, the gain coefficient g is obtained as shown in FIG. 5C. Then, in the multiplier 34, the gain coefficient g and the input signal x are multiplied to obtain the input / output characteristic as shown by the broken line in FIG. 5B, and this can be adjusted (gain up) to the level of the solid line.

To obtain the gain characteristic of FIG. 5C,
As in the above embodiment as the mixer, the gain coefficient g uses a fixed value depending on the level of the input signal x (envelope signal x _e ) and a value calculated by a function operation using the envelope signal x _e. The case will be switched. That is, the envelope signal x _e and the reference value x _th
The gain generation unit 40 and the gain calculation unit 39
One is selected.

When a certain set reference value x _th and envelope signal x _e are represented by X _th and X _e in the logarithmic domain (X _e = 20log x _e , X _th = 20log x _th ), X _e ≧
In the case of X _th , the gain g calculated by the gain calculator 39
Are supplied to the multiplier 34. At this time,

[Equation 10] Therefore, the gain coefficient g calculated in this way is used.

If X _e <X _th , the gain generator 4
The gain g calculated at 0 is supplied to the multiplier 34. At this time,

[Equation 11] That is, the fixed gain coefficient of g = 1 output from the gain generator 40 is used. As described above, by supplying the gain g to the multiplier 34, the input / output characteristic as shown in FIG. 5B can be obtained.

The above is an example in which the gain characteristic has a slope of −1 when X _e ≧ X _th . Here, although the gain calculation operation of the gain calculation unit 39 will be described later, since the gain calculation operation is a process of approximating the function f (x _e ) with a polynomial, for example, a gain characteristic as shown in FIG. 6B is obtained. The input / output characteristics shown in FIG. 6A can be realized, and the input / output characteristics can be set flexibly in various ways. In the case of FIG. 6, when X _e ≧ X _th ,

[Equation 12] Further, when X _e <X _th , g = 1 similarly according to the above (Equation 11).

<4. Expander by digital processing>
Next, in the audio device as shown in FIG.
FIG. 7 shows a configuration in which the function as an expander for an input signal. Note that, in FIG. 7, the same functional parts as those in FIGS. 2 and 4 are denoted by the same reference numerals, and the description thereof will be omitted.

The input signal x from the input terminal 31 is supplied to the multiplier 34 to be multiplied by the gain coefficient g, and the amplifying section 35.
The output y is output from the output terminal 36 via. Then, in order to obtain the gain coefficient g, the input signal x is input to the absolute value detection unit 3
7. The envelope signal x _e is supplied via the envelope detector 38 and supplied to the gain calculator 39. Further, the envelope signal x _e is supplied to the comparator 41 and the comparator 44.
The comparator 41 compares the reference value x _th with the envelope signal x _e , and the comparator 44 compares the set minimum value x _min with the envelope signal x _e .

In addition to the gain generating section 40, a gain generating section 43 for generating a fixed gain coefficient is provided.
The gain coefficient g from the gain generating section 43 is supplied to the terminal 42c of the switch section 42, and the gain coefficient g
= 0. Terminals 42a, 42b of the switch unit 42,
The switching of 42c is executed according to each comparison result of the comparators 41 and 44, and the gain coefficient from the gain generating unit 40,
Alternatively, the gain coefficient from the gain generator 43 or the gain coefficient calculated by the gain calculator 39 is selectively applied to the multiplier 34.
Will be supplied to.

With this configuration, for example, the gain characteristic as shown in FIG. 8B can be obtained and the input / output characteristic as shown in FIG. 8A can be realized. In addition, in FIG. 8, X _e = 20 lo
g x _e , X _th = 20 log x _th , X _min = 20 log x _min
Is.

First, when the comparator 41 outputs the result of X _e ≧ X _th , it is the region where it is desired to obtain linear characteristics as input and output, so the switch 42 selects the terminal 42b and the gain generator. The gain coefficient g = 1 from 40 is supplied to the multiplier 34.

When the comparator 44 outputs the result of X _e <X _min , the switch section 42 receives the terminal 42c.
Is selected, and the gain coefficient g = 0 from the gain generator 43.
Are supplied to the multiplier 34. If the operation word length in digital operation processing is 16 bits, underflow occurs if the output Y becomes smaller than -96 dB, but X _e
The region of <X _{min is} a region where the output Y is smaller than -96 dB, and in this case, the gain coefficient g = 0 is forcibly set for the input X to prevent underflow.

Further, from the outputs of the comparators 41 and 44, X _th
When the result of> X _e ≧ X _min is detected, the switch 42 selects the terminal 42 a, and the gain coefficient g calculated by the gain calculator 39 is supplied to the multiplier 34.

In this case, when the straight line of the input / output characteristic in the region of X _th > X _e ≧ X _min is X = Y = X _th and the inclination is m,

[Equation 13] Then, if the functional expression of the gain characteristic for obtaining this input / output characteristic is G = AX + B, then Y = (1
+ A) X + B can be derived.

From (Equation 13), A = m-1, B =
Since it is X _th (1-m), the gain coefficient g can be derived by the following (Equation 14). However, in this (Equation 14), G = 20log g, X = 20log x,
Let X _th (1-m) = 20 log c.

[Equation 14] Therefore, the calculation of the gain coefficient g in this (Equation 14) is performed by the gain calculation unit 39, so that X _th > X _e
The input / output characteristics in the region of ≧ X _min can be set as shown in FIG.

<5. Gain coefficient setting device> An example of executing the processing of the DSP 3 as the mixer, limiter, and expander has been described above. Next, the gain coefficient setting device that functions as the gain calculation unit 39 in these configurations will be described. To do.

Now, in the gain characteristic of FIG. 10, x ≧ x
Consider a gain curve that is a characteristic in the _th region. If C _G is the G axis intercept of the gain curve, the gain curve is

(Equation 15) Becomes

In order to express the expression in the logarithmic domain in the linear domain, G = 20log g, X = 20log x, C _G = 20.
If log c is (Equation 15),

[Equation 16] And therefore,

[Equation 17] Becomes Note that C is

(Equation 18) Is.

Therefore,

[Formula 19] The gain can be obtained by g = C · g ′ by also solving the equation with polynomial approximation.

Since the approximation of (Equation 19) can be similarly approximated, g = (1 / x) will be taken up to explain the polynomial approximation. First, x is defined as follows.

[Equation 20] Then, for g = (1 / x),

[Equation 21] Becomes _{Here, g F = (1 / x} F) and then, also the x _F from general constraint _{approximation, (1/2) ≦ x F <} 1
The condition that occurs occurs.

The approximate polynomial used is -1 <w <1,

[Equation 22] Is. To fit the approximate polynomial, as shown in FIG.

[Equation 23] And

G _F = (1 / x _F ) and g is

[Equation 24] From this, the following (Equation 25) can be derived.

(Equation 25)

The equations (a) to (h) in the equation (25) are derived as follows. Equation (b) ... (a) is truncated to a finite degree and is corrected to a power-law coefficient a _n . (C) Equation ... To improve approximation accuracy, Chebychev (Che
bychev) Polynomialization (d) Equation ... Reducing the order (e) Equation ... Returning to a power-law coefficient of w (f) Equation ... x _F Resolving to a power series (g) Normalize the expression ... K _n 'here, k _n ' = 2 ^j · k _n , and when k _n 'is normalized by 1, | K _n | ≦ 1. j is the maximum value k of the coefficient k _n
The value normalized by _max ,

(Equation 26) Is a value that satisfies. To normalize k _n 'by 1,
j = 5 (2 ⁵ = 32). In this case, for j, 2 ^j ≧ (maximum value of k _n ')> 2 ^j-1 is satisfied, and j
As a condition for calculating = 5, it is assumed that g _F = (1 / x _F ) and the order M = 5. Equation (h) is derived using this j. And from (Equation 25),

[Equation 27] Is obtained.

Here, g = Cg 'and C = 2- ⁿ
・ C _F , (1/2) ≦ | C _F | <1,

[Equation 28] Becomes

That is, the gain coefficient setting device of this embodiment is
By obtaining the gain coefficient g by the operation of (Equation 28), the gain coefficient g according to the input can be obtained by multiplication of the approximate polynomial and the constant, and the logarithmic conversion, the function operation, and the
Compared to performing inverse logarithmic conversion, the amount of processing calculation is greatly reduced, and the simplicity of the algorithm in the DSP is increased. Then, the gain calculation unit 3 mounted on the DSP 3 as the mixer, the limiter, the expander, or the like described above.
9 is also very suitable.

The configuration of the gain coefficient setting device for obtaining the gain coefficient g based on the method of (Equation 28) will be described below with reference to FIG. In (Equation 28), “j”, “n”, “ _CF ” and k
_{The values of n, that} is, “k ₀ ”, “k ₁ ” ... “K _n ”, are fixed at the stage of designing the gain curve. Further, m is a value that changes according to the input x. Further, M is a calculation order.

Therefore, assuming that (j−n) = m _f and K _n = C _F · k _n for the purpose of reducing the number of calculation steps, when the calculation order M = 5, the calculation calculation of the gain coefficient g is as follows. It becomes like (Equation 29).

[Equation 29]

The block for executing the operation of (Equation 29) is as shown in FIG. Reference numeral 11 is an input terminal for the input signal x, 12 is a barrel shifter, and 13 is a temporary register. When the gain coefficient setting device is used as the gain calculating section 39 in FIGS. 2, 4, and 7, the input signal x is the envelope information x _e .

The barrel shifter 12 performs so-called linear-float conversion. By shifting the input x by m bits, when the input signal x is defined as in the above (Equation 20), x _F becomes ( 1/2) ≦ x
_It satisfies the condition of _F <1. And
The shift result x _F is output, and the value of m in the m-bit shift operation is supplied to the temporary register 13 to be stored therein.

14 _{0 to} 14 ₄ are coefficients K _{0 to} K _4, respectively.
Is a register for holding. Further, 15a to 15d are multipliers, and 16a to 16d are adders. The output of each part is as follows.

Output x _{F of} barrel shifter 12 and register 1
The output of the multiplier 15a to the coefficient K ₄ is supplied from 4 ₄ becomes (x _F K _4). Output of multiplier 15a (x _F K ₄ )
A register 14 adder ₃ coefficients from K ₃ is supplied 1
The output of 6a is (K ₃ + x _F K ₄ ).

Output x _{F of} barrel shifter 12 and adder 16
Multiplier 15b to which the output (a) of (a) (K ₃ + x _F K ₄ ) is supplied
Output is (x _F (K ₃ + x _F K ₄ )). Multiplier 1
5b output (x _F (K ₃ + x _F K ₄ )) and register 14
The output of the adder 16b to which the coefficient K ₂ from ₂ is supplied is (K ₂ + x _F (K ₃ + x _F K ₄ )).

Output x _{F of} barrel shifter 12 and adder 16
The output of the multiplier 15c supplied with the output of b (K ₂ + x _F (K ₃ + x _F K ₄ )) is (x _F (K ₂ + x _F (K ₃ + x
_F K ₄ ))). Output of multiplier 15c (x _F (K <sub>2
+ X F (K 3 + x</sub> F K 4))) and the output of the adder 16c to the coefficient K ₁ is supplied from the register 14 ₁ (K ₁ + x
_F (K ₂ + x _F (K ₃ + x _F K ₄ ))).

Output x _{F of} barrel shifter 12 and adder 16
c output (K ₁ + x _F (K ₂ + x _F (K ₃ + x _F K
₄ ))) is supplied to the output of the multiplier 15d as (x _F (K
₁ + x _F (K ₂ + x _F (K ₃ + x _F K ₄ ))).
Then, the output of the multiplier 15d (x _F (K ₁ + x _F (K ₂
+ X _F (K ₃ + x _F K ₄ ))) and the output K _P of the adder 16d supplied with the coefficient K ₀ from the register 14 ₀ are g
_P = (K ₀ + x _F (K ₁ + x _F (K ₂ + x _F (K ₃ + x
_F K ₄ )))).

As can be seen from the above (Equation 29), the gain coefficient g is obtained by multiplying this g _P by 2 ^{m + mf} . Reference numeral 19 is a barrel shifter, and multiplication of g _P and 2 ^{m + mf} is performed by a bit shift operation in this barrel shifter 19.

Here, m _f = (l−n) is set as described above, and the value of this m _f is a fixed value.
It is held at 7. The m held in the temporary register 13 and the m _f held in the register 17 are added in the adder 18 and supplied to the barrel shifter 19 as S (= m + m _f ).

Then, in the barrel shifter 19, the output g _P of the adder 16d is shifted by S bits. That is, the calculation is g = 2 ^{m + mf} · g _P , and the gain coefficient g is obtained at the output terminal 20.

As described above, in this coefficient setting device, the gain coefficient g corresponding to the input x can be obtained with a considerably small amount of calculation and without requiring a ROM table or the like. By using this coefficient setting device as the gain calculation unit 39 in the above-described mixer, limiter, expander, etc., it is possible to greatly reduce the calculation processing load and hardware configuration load in the DSP 3.

This coefficient setting device has a calculation order M = 5.
Needless to say, if the calculation order is changed, the configuration changes accordingly. That is, the register 14 _{0-14 4,} multipliers 15 a to 15 d, the adder 16a
The number of calculation steps in the region of 16d increases or decreases.

As an embodiment of the output characteristic setting device, a mixer, a limiter and an expander are used as specific examples. However, various kinds of gain characteristics can be set to be applied to other signal processing devices. For example, it can be realized as a compressor of an input signal. Further, if the band of the input signal is limited and the signal passed through the compressor is added to the original input signal, it can be realized as a so-called bass boost device. Further, it can be used for a noise gate, that is, the present invention is effective as a device for performing so-called dynamic range control. Then, by adopting the coefficient setting device described above for setting the gain coefficient in them, simplification of the configuration and reduction of the digital processing load can be realized.

[0085]

As described above, in the output characteristic setting device of the present invention, it is possible to perform dynamic range control so as not to cause overflow or underflow with respect to a digital operation tone, and a mixer, limiter, expander, etc. It is suitable to be applied as a device of the above, and by this, the effect of improving the sound quality can be obtained.

Further, the coefficient setting device of the present invention has the effect of significantly reducing the coefficient calculation processing load for dynamic range control and simplifying the hardware configuration, and is very suitable for various audio equipment. It will be

[Brief description of drawings]

FIG. 1 is a block diagram of an audio device to which the present invention has been applied.

FIG. 2 is a block diagram of an embodiment as a mixer of the output characteristic setting device of the present invention.

FIG. 3 is an explanatory diagram of output characteristics and gain characteristics of an embodiment as a mixer.

FIG. 4 is a block diagram of an embodiment as a limiter of the output characteristic setting device of the present invention.

FIG. 5 is an explanatory diagram of output characteristics and gain characteristics of the embodiment as a limiter.

FIG. 6 is an explanatory diagram of another output characteristic and gain characteristic of the embodiment as a limiter.

FIG. 7 is a block diagram of an embodiment as an expander of the output characteristic setting device of the present invention.

FIG. 8 is an explanatory diagram of output characteristics and gain characteristics of the embodiment as an expander.

FIG. 9 is a block diagram of an embodiment of a coefficient setting device of the present invention.

FIG. 10 is an explanatory diagram of a gain characteristic setting operation by the coefficient setting device of the embodiment.

FIG. 11 is an explanatory diagram of an equation used for polynomial approximation by the coefficient setting device of the embodiment.

FIG. 12 is an explanatory diagram of a conventional dynamic range control method.

FIG. 13 is an explanatory diagram of a conventional coefficient setting device.

[Explanation of symbols]

3 DSP 4 A / D converter 11 input terminals 12, 19 barrel shifter 13 temporary registers 14 ₁ to 14 ₄ register 15a~15d multiplier 16a~16d adder 17 registers 18 the adder 20 the output terminal 31, 31a, 31b input terminal 32a , 32b Attenuator 33 Adder 34 Multiplier 35 Amplifying unit 36 Output terminal 37 Absolute value detecting unit 38 Envelope detecting unit 39 Gain calculating unit 40,43 Gain generating unit 41,44 Comparator 42 Switch unit

[Equation 30]

Claims (5)

[Claims] 1. A mixer means for a plurality of input signals, an envelope detecting means for obtaining envelope information about the output of the mixer means, a comparing means for comparing the output of the envelope detecting means with a predetermined value, and A coefficient setting means for performing a function operation on the output of the envelope detecting means to obtain a gain coefficient, a coefficient generating means for generating a fixed gain coefficient, and a coefficient setting means for changing the coefficient setting means according to the comparison result of the comparing means. Selecting means for selecting and outputting any one of the gain coefficient and the gain coefficient by the coefficient generating means; and a gain calculating means for applying a gain to the output of the mixer means based on the gain coefficient output from the selecting means and outputting the gain coefficient. And a mixed output characteristic of a plurality of input signals is set by the gain coefficient by the coefficient setting means and the gain coefficient by the coefficient generating means. Output characteristics setting apparatus characterized. 2. An envelope detecting means for obtaining envelope information of an input signal, a comparing means for comparing the output of the envelope detecting means with a predetermined value, and a function operation for the output of the envelope detecting means. A coefficient setting means for obtaining a gain coefficient, a coefficient generating means for generating a fixed gain coefficient, and a gain coefficient by the coefficient setting means or a gain coefficient by the coefficient generating means according to the comparison result of the comparing means. A selecting means for selecting and outputting; and a gain calculating means for giving a gain to an input signal based on the gain coefficient output from the selecting means and outputting the gain, the gain coefficient by the coefficient setting means and the coefficient generating means The output characteristic setting device is characterized in that the input / output characteristic is set by the gain coefficient by the. 3. An envelope detecting means for obtaining envelope information of an input signal, a first comparing means for comparing an output of the envelope detecting means with a first predetermined value, and an output of the envelope detecting means. Second comparing means for comparing with a second predetermined value; coefficient setting means for performing a function operation on the output of the envelope detecting means to obtain a gain coefficient; and a first fixed gain coefficient generating means. 1 coefficient generating means, a second coefficient generating means for generating a second fixed gain coefficient, and a gain coefficient by the coefficient setting means according to a comparison result of the first and second comparing means. Selecting means for selecting and outputting either the gain coefficient by the first coefficient generating means or the gain coefficient by the second coefficient generating means; and applying a gain to the input signal based on the gain coefficient output from the selecting means. Output gain performance Output characteristics, wherein the input / output characteristics are set by the gain coefficient by the coefficient setting means, the gain coefficient by the first coefficient generating means, and the gain coefficient by the second coefficient generating means. Setting device. 4. A coefficient setting device for calculating a gain coefficient g for an input signal by performing the following function operation of the following (Equation 1) on the input signal value x. [Equation 1] However, k _n ... Coefficient j ... The value C _{F for which} the maximum value k _max of the coefficient k _n and the normalized value S satisfy S ≧ 2 ^j × k _max. ) ││C _F │ <1 fixed value n ・ ・ ・ ・ Fixed value M ・ ・ ・ ・ Calculation order x _F・ ・ ・ ・ for input signal value x satisfies (1/2) ≦ x _F <1 A value obtained by shifting x in order to obtain the input signal value x is x _F. 5. For input signal value x, (1/2) ≦ x _F
<A first shifter means for obtaining a x _F performs m-bit shift to satisfy one, a register means for holding the coefficient k _n, to perform M following computation for the coefficients k _n and x _F 1
Or a plurality of additions and one or a plurality of multiplications; and a second shifter means for performing (m + fixed value) bit shift on the output of the calculation means and outputting a gain coefficient g. The coefficient setting device according to claim 4, wherein the coefficient setting device is configured to have.