JPH0537371A - D/a converter - Google Patents

Abstract

PURPOSE:To obtain a D/A converter with a low distortion ratio in which the influence of a zero-cross distortion is reduced, and an S/N is audibly satisfactory by adding the digital periodic signal of a low frequency out of an audio frequency band to an input digital signal. CONSTITUTION:Performance information is inputted from a keyboard device 3 to a waveform generator 4, and a digital music waveform according to the performance information is generated. A low frequency digital sine wave is generated by a sine wave generator 5, added to the output of the device 4, and the signal is inputted to a D/A converter 6. This signal is converted into an analog sound signal by the converter 6, and inputted through a high-pass filter 7 to an acoustic device 8 so that the acoustic device 8 can be operated. The output of the device 5 is controlled by the amplitude of the digital music waveform so that the output of the device 5 can be reduce when the output of the device 4 is large, and that the output of the device 5 can be increased when the output of the device 4 is small. Thus, the saturation of the circuit can be prevented, and the ratio of the zero-cross distortion amounts to the size of the music can be held to be almost constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter for converting a two-polarity digital signal into an analog signal, and more particularly to a D / A converter for audibly reducing the influence of zero cross distortion generated at a zero cross point. .

[0002]

2. Description of the Related Art Conventionally, a musical tone is stored as a digital signal, or a digital signal representing the musical tone is generated, and this digital signal is digital-analog converted (hereinafter referred to as D / A conversion) to be an analog signal. There is known an electronic musical instrument that generates a sound and produces a musical sound from a speaker or the like based on the analog signal. Such an electronic musical instrument requires a D / A converter that converts a bipolar digital signal into an analog signal. This D / A converter is used when converting a bipolar digital signal into an analog signal. There is a property of generating zero-cross distortion when the signal crosses zero, which deteriorates the S / N ratio and the distortion rate of the analog signal. Therefore, techniques have been developed to reduce the zero-cross distortion, for example,
Japanese Unexamined Patent Publication No. 60-83423 and Japanese Unexamined Patent Publication No. 2-3124.
The technique is disclosed in Japanese Patent Publication No. 09.

The system disclosed in Japanese Patent Laid-Open No. 60-83423 is a digital adder circuit at the input part of the D / A converter and an analog subtraction circuit for subtracting the analog amount corresponding to the digital amount added at the output part. Is provided to digitally add a constant offset and then D / A-converts, and subtracts an analog amount corresponding to the added offset value after conversion.

Further, in the method disclosed in Japanese Patent Laid-Open No. 2-312409, switching waveforms of analog data and bias data after D / A conversion are performed by adding / subtracting predetermined high frequency bias data to / from input digital data. An analog output corresponding to the input digital data is obtained from the combined wave of and through a low-pass filter. Further, a technique of providing a low pass filter after the output of the D / A converter is passed through a cancel circuit for canceling the switching waveform of the bias data is also introduced.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The conventional examples disclosed in Japanese Patent No. 83423 and Japanese Patent Laid-Open No. 2-312409 have the following problems. That is, since the analog amount corresponding to the value of the data added before D / A conversion is subtracted, there is a drawback that the analog circuit section becomes complicated. Further, if the data to be added before D / A conversion is set to a constant value (DC offset), the analog circuit section can be configured relatively easily as compared with the case where a high frequency bias is applied, but it is good when the input signal is at a low level. When the value exceeds a certain level, the zero cross distortion suddenly increases, which is unnatural in terms of hearing.

The present invention solves these problems and provides a D / A conversion device in which the influence of zero-cross distortion is reduced regardless of the input level and the analog circuit is extremely simple compared to the prior art. Is an issue.

[0007]

The present invention solves the above-mentioned problems and adopts the following technical means. That is, (1) an adder for adding a digital periodic signal having a low frequency outside the audible frequency band or a frequency lower than the lowest frequency carried by the digital signal to the digital signal to generate a digital addition signal; A D / A converter comprising a D / A converter for converting a digital addition signal into an analog signal.

[0008]

According to the present invention, the low-frequency digital periodic signal added before the conversion is a low-frequency signal which is not reproduced by the converted analog circuit for audio or a low-frequency signal lower than the audible frequency. It is characterized by.
Although FIG. 1 shows an example in which a sine wave signal is used as the periodic signal, when a digital signal 2 of the audible frequency band and a digital sine wave signal 1 of a lower frequency are added to generate a digital addition signal, this digital addition signal The signal reduces the number of times it crosses zero, thus reducing the amount of zero-cross distortion per unit time. Note that FIG. 1 is shown in an analog manner for easy understanding.

That is, since the opportunity of the digital addition signal crossing zero is limited to the vicinity of the zero-cross point 1a of the digital sine wave signal 1, the time per unit time is compared when the low frequency digital sine wave signal 1 is not added. The amount of zero cross distortion will be greatly reduced. The filter required for the analog circuit on the output side of the D / A converter may be, for example, a simple high-pass filter such as a capacitor, or an analog audio circuit such as an amplifier itself outputs a low frequency signal such that the digital sine wave signal is carried. If the circuit configuration is such that it does not transmit, or if the frequency of the digital sine wave 1 applied before conversion is lower than the audible frequency, it is not necessary to provide a high-pass filter in particular, and therefore the circuit configuration is simple and It is possible to configure a D / A converter having a low distortion ratio that has a good S / N ratio in hearing.

Further, unlike the conventional example, the number of times the digital input signal crosses zero suddenly does not increase at a certain sound volume level, so that an unnatural hearing feeling is not given. Further, by reducing the amplitude of the digital low frequency sine wave signal to be added as the average amplitude of the digital signal in the audible frequency band input to the D / A converter increases, the saturation of the circuit is prevented and the musical tone is generated. The S / N ratio can be flattened regardless of the size.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electronic musical instrument will be described with reference to the drawings. FIG. 2 shows an example of a digital tone generating device in an electronic musical instrument. Tap the key of the keyboard device 3,
The performance information is input to the waveform generator 4, and the waveform generator 4 generates a digital tone waveform corresponding to the performance information. A low-frequency digital sine wave is generated by the sine wave generator 5, the output of the waveform generator 4 is added to each other, and the sum is input to the D / A converter 6. After being converted into an analog audio signal by the D / A converter 6, the audio device 8 such as an amplifier and a speaker is operated via a high pass filter 7.

The high-pass filter 7 can be omitted when the frequency of the digital sine wave signal added before conversion is lower than the audible frequency or lower than the pass frequency band of the acoustic device 8. Further, when the amplitude of the digital tone waveform generated by the waveform generator 4 is large, the amplitude of the output waveform of the sine wave generator 5 is small, and conversely when the amplitude of the digital tone waveform is small, the output waveform of the sine wave generator 5 is small. If the amplitude of the output waveform of the sine wave generator 5 is controlled by the amplitude of the digital tone waveform so that the amplitude of the tone waveform is increased, circuit saturation when the amplitude of the tone waveform is large is prevented and the amplitude of the tone varies. Therefore, the ratio of the amount of zero-cross distortion to the volume of the musical sound can be kept substantially constant.

That is, when the amplitude of the digital tone waveform is small, the amplitude of the output waveform of the sine wave generator 5 is increased, and the crossing angle of the sine wave with the horizontal axis at the zero cross point is increased, so that the tone waveform of the digital tone waveform is increased. The number of zero crossings per unit time is reduced to improve the S / N ratio, and the amplitude of the digital tone waveform is large (S is large).
At this time, the amplitude of the output waveform of the sine wave generator 5 can be reduced to prevent linear distortion and saturation of the analog circuit. In this case, since S is large even if the amplitude of the sine wave is reduced, there is no problem of a decrease in S / N ratio.

In this embodiment, the frequency of the sine wave of the sine wave generator 5 is preferably around 10 Hz. Further, the sine wave generator 5 does not have to be provided separately from the waveform generator 4, and an empty channel of the waveform generator 4 can be used and a low frequency sine wave can be stored therein.

In this embodiment, the digital sine wave signal is used as the digital periodic signal, but the sine wave generator 5 is used.
Can also use a waveform including a harmonic wave that is unnoticeable to the sense of hearing, such as a triangular wave or a composite wave of a plurality of sine waves.

[0016]

The present invention has the following excellent effects. (1) It is possible to reduce the influence of zero-cross distortion at any input level, and to configure a low distortion D / A converter having a good audible S / N ratio. (2) The filter on the output side of the D / A converter is simple,
Alternatively, this filter can be omitted, thus simplifying the circuit configuration.

[Brief description of drawings]

FIG. 1 is an explanatory view of the operation of the present invention.

FIG. 2 is an explanatory diagram of a configuration of an embodiment in which the present invention is applied to an electronic musical instrument.

[Explanation of symbols]

 1 sine wave 1a zero-cross point of sine wave 2 input signal 3 keyboard device 4 waveform generator 5 sine wave generator 6 D / A converter 7 high-pass filter 8 acoustic device

Claims (1)

Claim: What is claimed is: 1. An adder for adding a digital period signal having a low frequency outside the audible frequency band or a frequency lower than the lowest frequency carried by the digital signal to the digital signal to generate a digital addition signal. And a D / A converter for converting the digital addition signal into an analog signal.