JPH06164390A - Compander - Google Patents

Abstract

PURPOSE:To reduce a capacity of an expansion characteristic table used when a compressed digital signal is expanded. CONSTITUTION:An analog signal is compressed by an analog compression circuit 14 and the compressed signal is converted into a digital signal by an A/D converter 34 and the digital signal is fed to a digital expansion processing circuit 36. The digital expansion processing circuit 36 applies linear interpolation arithmetic operation to the inputted digital signal based on the expansion characteristic stored in an expansion characteristic table 38 to expand the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression / expansion device which, when digitizing an analog signal, compresses the analog signal, digitizes the analog signal and expands the digital signal.

[0002]

2. Description of the Related Art Generally, when an analog signal is digitized, if an inexpensive A / D converter is used, the number of used bits is small and the quantization step is large, or the number of used bits is large and the quantization step is small. Due to the influence of noise, a sufficient S / N ratio cannot be obtained especially when quantizing an analog signal of a small level.

Further, when a distortion device or an overdrive device used as an effect device for converting the tone color of an input musical tone signal is realized by a digital signal in the musical instrument industry, since the musical tone is amplified and distorted, it is originally converted into a musical tone signal. Even if the included noise is small, it is amplified and becomes large,
It became more audible and required further noise reduction in the A / D converter.

In order to solve such a problem, conventionally, A
It has been practiced to reduce the influence of noise by providing a compression circuit before the / D converter and a decompression device having characteristics opposite to that of the compression circuit after that.

An example of such an expanding device is an RO as disclosed in Japanese Patent Application Laid-Open No. 64-13817.
There is a method in which a conversion table is stored in M or the like, a digital signal from an analog-digital converter is input to this ROM as an address signal, and a conversion table value is read from an address of a value corresponding to this digital signal.

[0006]

However, if a conversion table is prepared for all the values of digital signals that can be generated by the A / D converter, the conversion table needs to have a large capacity. Further, in the case where a means for measuring the compression circuit is provided and the conversion table of the decompression device is to be created based on the measurement result, a large amount of measurement data is required, and it takes a long time to create the conversion table. It had drawbacks.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an analog compression means for compressing an analog signal and an output signal of the analog compression means are converted into a digital signal. And A / D conversion means for performing the expansion processing, and digital expansion processing means for expanding the digital signal from the conversion means. The digital expansion processing means is an expansion characteristic storage means for storing expansion characteristics and an interpolation means for performing an interpolation operation on an input digital signal based on the expansion characteristics stored in the expansion characteristic storage means. It has and. Although various kinds of interpolation calculations can be used,
In the present specification, a case will be described in which linear interpolation, which is the simplest in arithmetic processing, is used.

[0008]

According to the present invention, the analog signal compressed by the analog compression means is converted into the digital signal by the A / D conversion means and then supplied to the digital expansion means. The digital signal input to the digital expansion means is expanded with the characteristics stored in the expansion characteristics storage means. The digital expansion means is provided with means for performing an interpolation operation, and when the input digital signal indicates data between the data stored in the expansion characteristic storage means, by performing the interpolation operation, Get the conversion data you need.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, the present invention is applied to a signal processing device for performing tone color conversion processing on a musical tone signal of an electric guitar. As shown in FIG. 1, a pickup 10 for detecting vibration of a string is used. Have The string vibration detected by the pickup 10 is supplied to the analog compression circuit 14 via the changeover switch 12.

The analog compression circuit 14 is shown in FIG.
As shown in the figure, it is composed of an operational amplifier 16, diodes 18, 20 and resistors 22 to 34,
Each of the resistors 22 to 34 has the resistance value shown in FIG. 2, the forward resistance value of the diodes 18 and 20 is rf, the break point voltage of the diodes 18 and 20 is Vf, and the voltage applied to the resistor 22 is + V, the voltage applied to the resistor 28-
V, when the absolute value of the input voltage ei is Vf or less as shown in FIG. 3, the input voltage ei is amplified with a slope -R2 / R1 and when the input voltage ei becomes smaller than -Vf, -R2.
Amplification is performed with a slope K1 as shown in FIG. 3, which is looser than / R1,
When the input voltage ei becomes larger than + Vf, -R2 / R1
Amplification is performed with a slope K2 as shown in FIG. That is, when the absolute value of the input voltage ei (string vibration) becomes larger than Vf, it is compressed and amplified.

The string vibration thus compressed is converted into a digital signal by the A / D converter 34. This digital signal is composed of, for example, 16 bits,
The upper 8 bits represent the integer part, and the lower 8 bits represent the decimal part. This digital signal is supplied to the expansion processing circuit 36.

The decompression processing circuit 36 has a decompression characteristic table 38, and the higher 8 bits of the digital signal are supplied to the table 38 as address signals. At each address, an expansion value expanded according to the reverse characteristic of the analog compression circuit 14 is stored as shown in FIG.

In the digital signal supplied from the A / D converter 34, in addition to the high-order 8 bits supplied to the expansion characteristic table 38 as described above, the low-order 8 bits representing the data obtained in the table 38 are also included. Contains. And
In the present invention, the conversion data corresponding to the value represented by the lower 8 bits is obtained by interpolation.

That is, the value of the upper 8 bits of the digital signal from the A / D converter 34 is the integer value i, and the value of the lower 8 bits is the decimal value 0. Let f be the digital signal i. f can be represented by linear interpolation as shown in FIG. If this is expressed by a linear interpolation calculation formula, it becomes as shown in Formula 1. It should be noted that the data (expansion value) of the table 38 at the addresses indicated by the integer values i and i + 1 is T (i), T
Let (i + 1).

[0015]

## EQU00001 ## T (if) = [T (i + 1) -T (i)] * 0. f + T (i) When this is modified, it is expressed as in Equation 2.

[0016]

## EQU00002 ## T (if) = T (i + 1) * 0. f + T (i) (1-0.f)

Therefore, when the digital signal is input from the A / D converter 34, the expansion processing circuit 36 outputs the upper 8 bits.
The decompressed value is read from the address obtained from the bit and the address that is one greater than this address, and the interpolation operation is performed according to equation 2 using the remaining lower 8 bits,
The calculated value is output as a decompression output value. This decompressed output value is supplied to a digital signal processing circuit (not shown), processed for example in tone color, converted into an analog signal by a D / A converter (not shown), and output. It

The embodiment of the present invention is provided with a function of measuring the characteristic of the compression circuit and setting the expansion characteristic table 38. The operation will be described below. The setting of each expansion value in the expansion characteristic table 38 is performed by the compression characteristic measuring unit 40.
Using. The compression characteristic measuring unit 40 has a D / A converter 42 and a computing unit 44. Before setting each extension value, switch the selector switch 12 to change the D / A
The output voltage from the converter 42 is made ready to be supplied to the compression circuit 14.

In this state, the D / A converter 42 sequentially outputs from the minimum output voltage to the maximum output voltage with an appropriate step size, and this is output via the compression circuit 14 to the A / D converter 3.
4 and digitized the result, for example, as shown in FIG.
The characteristic as shown in (a) is the measured compression characteristic. By the way, the value supplied to the compression circuit 14 is the horizontal axis x, and the value output from the expansion processing circuit 36 after the expansion processing is the vertical axis y.
Then, the input / output characteristics that one would originally want to obtain are shown in the graph of FIG.
The straight line characteristic is as shown by B in (b). Also,
The characteristic indicated by A in the figure represents the above-mentioned measured compression characteristic.

In the above drawings, the method for obtaining the expansion characteristic table is shown. When the value xp is input to the compression circuit 14, the value a is obtained. Therefore, when the value a is input to the expansion processing circuit 36, the table 38 may be created so that the value b is output from the output. Therefore, a table is obtained by making a correspond to the address of the table 38 and repeating the following processes 1 to 3 for each address.

1. A (address) from the measured compression characteristics
The value of xp corresponding to is calculated. 2. The value is substituted for x of the equation y = kx of the straight line B to obtain b (k is a constant). 3. The obtained b is stored in the address a of the table 38. It should be noted that the measured compression characteristic data does not always include data that matches a, and therefore, if there is no matching data, xp may be obtained from the data before and after that data by linear interpolation calculation. The expansion characteristic table is completed by performing the above processing for all the addresses in the table 38. And the completed extension characteristic table is shown in FIG.
It becomes like (c). The expanded value b of the address a is stored.

The value of the expansion characteristic table 38 may be updated at an appropriate time interval when the compression characteristic of the compression circuit 14 may change due to temperature change or the like, or it may be manually operated. May be instructed to update.

The configuration shown in FIG. 1 is a principle one, and is actually configured as shown in FIG. That is, the string vibration detected by the pickup 10 is compressed by the compression circuit 14 via the change-over switch 12, and then the A / D converter 34.
Is converted into a digital signal by the digital signal processor and supplied to a DSP (digital signal processing device) 46. The DSP 46 functions as the expansion processing circuit 36 shown in FIG. 1 in cooperation with the expansion characteristic table 38a. Further, the DSP 46 functions as a digital signal processing circuit, and the processed signal is analogized by the D / A converter 48 and output.

Further, the CPU 50 uses the DSP 46, D / A
It functions as the compression characteristic measuring unit 40 in cooperation with the converter 48.

In the above embodiment, the present invention is applied to the signal processing device for performing the voice processing on the musical tone signal of the electric guitar, but the present invention is not limited to this and can be applied to various cases of digitizing an analog signal. it can. Further, although linear interpolation is used in the above embodiment, other interpolation methods can be used. Further, although the expansion characteristic tables 38 and 38a are configured so that they can be updated, if the characteristics of the compression circuit 14 are stable, there is no need to update them and the expansion characteristic table 3
The ROMs 8 and 38a can also be formed. Further, as the compression circuit 14, various known circuits other than those shown in FIG. 2 can be used.

[0026]

As described above, according to the present invention, since the interpolation is performed when the compressed signal is expanded again, the compression characteristic is measured and the expansion characteristic is created based on the result. In the case of one, since the number of pieces of expansion characteristic data may be small, the labor for creating the expansion characteristic data can be saved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a signal processing device implementing a compression / expansion device according to the present invention.

FIG. 2 is a circuit diagram of an analog compression circuit used in the embodiment.

FIG. 3 is a diagram showing compression characteristics of the analog compression circuit of FIG.

FIG. 4 is a diagram showing extension characteristics stored in an extension characteristic table of the circuit of FIG.

5 is an explanatory diagram of linear interpolation performed in the circuit of FIG.

FIG. 6 is a diagram illustrating a process of storing expansion characteristics in an expansion characteristics table in the circuit of FIG.

FIG. 7 is a block diagram of another embodiment of a signal processing device that implements the compression / expansion device according to the present invention.

[Explanation of symbols]

 14 compression circuit (analog compression means) 34 A / D converter 36 expansion processing circuit (expansion processing means) 38 expansion characteristic table (expansion characteristic storage means)

Claims (2)

[Claims] 1. An analog compression means for compressing an analog signal, an analog / digital conversion means for converting an output signal of the analog compression means into a digital signal, and a digital expansion processing for expanding a digital signal from the conversion means. The digital expansion processing means is based on the expansion characteristic storage means for storing the expansion characteristics and the expansion characteristics stored in the expansion characteristic storage means for the input digital signal. A compression / expansion device, comprising: an interpolation unit that performs interpolation calculation. 2. The compression / expansion device according to claim 1,
The compression / expansion device, wherein the interpolation calculation performed by the interpolation means is linear interpolation.