JPH06332456A - Distortion adding device - Google Patents

Abstract

PURPOSE:To provide a non-linear converter into which aliasing noise is not mixed so much, in a distortion adder of digital processing type. CONSTITUTION:In a digital processing type distortion adder in which a digital signal converted by A/D converter is inputted to a non-linear converter 4 through a digital filter, nonlinear distortion is given by the non-linear converter 4, desired frequency component is taken out by a filter of a digital filter group from a digital signal to which this nonlinear distortion is given and outputted, this device has such a structure that an up-sampler 8 is arranged at a prestage side of the non-linear converter, a down-sampler 9 is arranged on a poststage side of the non-linear converter 4, while Ny-quist frequency in the non-linear converter is increased by increasing sampling frequency by N times in the up-sampler 8, and a level so aliasing noise at Nyquist frequency is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distortion adding device used for giving a sound to an electronic musical instrument and obtaining various kinds of acoustic effects.

[0002]

2. Description of the Related Art In the field of electronic musical instruments, a technique is used in which a musical tone signal is distorted to obtain various acoustic effects. As a method of giving distortion, there are a method using an analog circuit and a method using a digital circuit. According to the method of giving distortion by an analog circuit, it is possible to obtain a distortion-added sound with good sound quality even if a large amount of distortion is given. However, since analog circuits are difficult to be integrated into ICs, there is a recent tendency to add distortion by digital circuits for reasons such as large size and high cost.

FIG. 3 shows a conventional distortion adding device by a digital system. An analog tone signal A _IN is given to the input terminal 1. The analog tone signal A _IN is converted into a digital signal by the AD converter 2. The digital signal AD-converted by the AD converter 2 removes an ultra-low frequency component generated at the time of DA conversion in the digital low-cut filter 3 and is given to the nonlinear converter 4.

The non-linear converter 4 is constituted by a cascade connection of a multiplier 4A and a saturation characteristic shaper 4B. Multiplier 4A
Is provided with a gain control signal C, and the gain G of the multiplier 4A is changed to control the added amount of distortion. The saturation characteristic shaper 4B has an amplitude limiting characteristic,
In other words, it has a clipper characteristic, saturates a portion with a predetermined amplitude or more, and adds nonlinear distortion.

The digital signal to which the nonlinear distortion is given by the non-linear converter 4 is given to the digital filter group 5. The digital filter group 5 is provided with a low-pass filter, a high-pass filter, a peaking equalizer having a peak at a specific frequency, etc., and any one or a plurality of them are selected to extract a necessary frequency component to obtain a desired frequency. The digital signal having the component is given to the DA converter 6.
The DA converter 6 DA-converts the digital signal, and the output terminal 7 is distorted to produce a timbre-converted analog signal A.
Output _OUT .

[0006]

When a structure that gives distortion by a digital circuit is adopted, aliasing occurs in the digital signal. This aliasing noise has the drawback of significantly degrading the sound quality. In particular, when the amount of distortion is increased, the amount of aliasing noise generated tends to increase, and the amount of distortion applied is limited.

Here, how the folding noise occurs will be briefly described. When there is an input of the single-frequency sine wave A _IN (FIG. 4A) as an analog tone signal A _IN, its frequency spectrum as shown in Figure 4B, the analog tone signal A _IN
Exists only at the frequency f ₀ . If the AD converter 2 performs sampling at the sampling frequency f _s , performs AD conversion, and adds nonlinear distortion in the digital signal system by the non-linear converter 4 as shown in FIG. 4C, the frequency spectrum of the digital signal is As shown in FIG. 4D, a harmonic component F _H having a fundamental wave of f ₀ is generated. If this harmonic component F _H exists up to a frequency range higher than half the sampling frequency f _s (hereinafter, this frequency (1/2) f _s is referred to as the Nyquist frequency), the Nyquist frequency (1/2 ) It is folded back at f _s , and folding noise SN ₁ is generated.

A filter group 5 is provided after the non-linear converter 4, and even if the filter group 5 removes harmonic components in the frequency region above the Nyquist frequency (1/2) f _s (FIG. 4E). Since the aliasing noise SN ₁ exists in the frequency region lower than the Nyquist frequency (1/2) f _s , the aliasing noise cannot be removed by the filter group 5.

From the above description, the higher the frequency f ₀ of the analog tone signal A _IN (the Nyquist frequency (1/2) f _s
It can be understood that the amount of generation of the folding noise SN ₁ tends to increase as the amount of distortion increases (the amount of generated harmonics increases). An object of the present invention is to provide a digital distortion adding device capable of reducing the amount of aliasing noise generated.

[0010]

According to the present invention, an AD converter for AD converting an analog tone signal at a sampling frequency f _s , and sampling of a digital signal AD-converted by the AD converter at a period 1 / f _s. Frequency is N
and upsampler increasing the f _s, and a non-linear converter distorting the digital signal sampling frequency is increased, a down sampler for lowering the sampling frequency of the signal output from the nonlinear converter 1 / N,
The distortion adding device is configured by a DA converter that DA converts the digital signal returned to the original frequency f _s by the down sampler.

According to the configuration of the present invention, the sampling frequency of the digital signal passing through the non-linear converter which gives distortion is increased to N times that at the time of DA conversion. Nyquist frequency that this result aliasing noise is generated based on the Nyquist frequency (1/2) N times the frequency N · (1/2) of f _s
Present in · f _s, this results, occurrence of aliasing noise is suppressed.

[0012]

FIG. 1 shows an embodiment of the present invention. Paired with Figure 3
Corresponding parts are designated by the same reference numerals. In this invention
An upsampler 8 is provided in front of the linear converter 4,
Upsampler 8 Sump in DA converter 2
Ring frequency f_sN times higher sampling frequency
Let Along with this, the down-sampling is performed after the nonlinear converter 4.
A down-sampler 9 is used for sampling
Original frequency f _sCharacterized by a structure that reverts to
It

The up-sampler 8 and the down-sampler 9 can use well-known sampling rate increasing devices and sampling rate decreasing devices. Assuming that the sampling rate f _s is increased by N = 4 times in the upsampler 8, the Nyquist frequency is 4 × (1 /
2) f _s . As the Nyquist frequency is increased to four times, the aliasing noise NS ₂ is increased as shown in FIG.
Is folded at 4 times the Nyquist frequency of 4 × (1/2) f _s , and is 12d in this example in comparison with the conventional folding noise NS _{1 in} the frequency range below the audible frequency range (1/2) f _s.
It could be made smaller than B.

[0014]

As described above, according to the present invention, the sampling frequency in the portion of the non-linear converter 4 is increased to N times the sampling frequency f _s at the time of AD conversion.
The Nyquist frequency is 4 × (1/2) f _{s, where} N = 4
Becomes Thus a possible rate of harmonics nonlinear distortion occurs given reaches the Nyquist frequency N × (1/2) f _s is reduced, if harmonics Nyquist frequency N × (1
Even if it reaches / 2) f _s , its level E ₂ is sufficiently lower than the level E _{1 at} the frequency of the conventional Nyquist frequency (1/2) f _s , as shown in FIG. Therefore, the level of the aliasing noise that folds back at the Nyquist frequency and enters the frequency region (audible frequency region) below the conventional Nyquist frequency (1/2) f _s is sufficiently low. Therefore, the mixing ratio of aliasing noise can be reduced. Further, since the mixing ratio of the aliasing noise can be reduced, it is possible to obtain an advantage that a tone signal with good sound quality equivalent to that of the tone signal generated by the analog circuit can be generated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a graph illustrating the effects of the present invention.

FIG. 3 is a block diagram for explaining a conventional technique.

FIG. 4 is a waveform diagram for explaining the operation of the conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Input terminal 2 AD converter 3 Digital low-cut filter 4 Non-linear converter 5 Digital filter group 6 DA converter 7 Output terminal 8 Upsampler 9 Downsampler NS ₁ Folding noise according to conventional technology NS ₂ Folding noise according to this invention

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03H 17/02 P 7037-5J 21/00 7037-5J

Claims (1)

[Claims] 1. A. An AD converter for AD converting an analog tone signal at a sampling frequency f _s ; The sampling frequency of the digital signal generated with the period 1 / f _s that is AD-converted by this AD converter is N · f _s
Up sampler to raise to C. A non-linear converter that distorts a digital signal with an increased sampling frequency; D. A downsampler for reducing the sampling frequency of the signal output from the non-linear converter to 1 / N; A distortion adding device comprising: a DA converter that DA-converts the digital signal returned to the original frequency f _s by the down sampler.