JP2004297723A - Transducer processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the sound of a component not originally existing in the audible band, from being generated in a transducer processing apparatus. <P>SOLUTION: Into the configuration of a conventional transducer processing apparatus equipped with a modulator 8 for modulation processing based on an audio signal from a signal source, a power amplifier 10 for amplifying the signal from the modulator 8 and a radiator 11 as an electroacoustic transducer for transducing the signal from the power amplifier 10 into a sonic wave; a high-pass filter 9 that includes a cutoff frequency near an upper limit of the audible band and cuts off a signal component in the audible band, is provided on the pre-stage of the power amplifier 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter processing device that prevents generation of unnecessary sound in an audible band when audible sound is radiated directionally.
[0002]
[Prior art]
A conventional converter processing device includes a modulator, a power amplifier, and an electroacoustic converter. In the modulator, a process of multiplying a coefficient (m) by a coefficient unit, a process of adding a DC bias to the processed signal, and a process of processing the same are performed. A square root process of the processed signal and a process of multiplying the processed signal by an ultrasonic carrier signal to perform amplitude modulation are performed.
A signal from the modulator is amplified by a power amplifier, and the amplified electric signal is converted into a sound wave by an electroacoustic converter (for example, see Patent Document 1).
In this case, the output of the modulator is a signal having a spectrum whose band is widened by the square root process and the multiplication process or by signal processing other than these processes (for example, see Non-Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Publication No. 4-58758 (pages 1-3, Fig. 1)
[Non-patent document 1]
IEICE Technical Report, IEICE Technical Report Vol. 102, no. 171, EA2002-30), p. 5-8, "Prototype of envelope modulator for driving parametric speaker using DSP"
[0004]
[Problems to be solved by the invention]
Since the conventional converter processing device is configured as described above, a spectrum having a wide band is generated by the square root process and the multiplication process, or by signal processing other than these processes, and thereby, the spectrum is not originally present in the audible band. There is a problem that component sound is generated.
[0005]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a converter processing device that prevents generation of unnecessary sound in an audible band.
[0006]
[Means for Solving the Problems]
A converter processing device according to the present invention includes a high-pass filter that blocks a signal component in an audible band included in an output of a modulator, provided in a stage preceding a power amplifier.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a converter processing device according to Embodiment 1 of the present invention.
In FIG. 1, an audio signal generated by a modulation signal source 1 is input to a coefficient unit 2, and an output of the coefficient unit 2 is input to an adder 3. A DC source 4 is also connected to the adder 3. The output of the adder 3 is input to a square root converter 5, and the output is input to a multiplier 6. An ultrasonic band oscillator 7 is also connected to the multiplier 6.
The range from the coefficient unit 2 to the ultrasonic band oscillator 7 constitutes the modulator 8.
[0008]
The output of the multiplier 6, that is, the output of the modulator 8 is input to a high-pass filter (hereinafter, referred to as “HPF”) 9. The output of the HPF 9 is input to a power amplifier 10, and the output of the power amplifier 10 is input to an ultrasonic emitter (hereinafter, “radiator”) 11 as an electroacoustic transducer.
[0009]
Next, the operation will be described.
The audio signal S (t) generated by the modulation signal source 1 is input to the modulator 8.
As described above, the modulator 8 includes the coefficient unit 2 to the ultrasonic band oscillator 7, and the specific operation is as follows.
The input audio signal S (t) is multiplied by m by the coefficient unit 2 to obtain a signal of m · S (t). The signal of m · S (t) is added to the DC bias from the DC source 4 in the adder 3 to obtain a signal of 1 + m · S (t).
The signal of 1 + m · S (t) is subjected to square root processing in the square root converter 5.
The multiplier [6] multiplies the signal [1 + m · S (t)] ^1/2 obtained by the above processing by the carrier signal of the ultrasonic wave from the ultrasonic band oscillator 7. By this multiplication processing, amplitude modulation is performed, and a modulated signal is obtained.
[0010]
As described above, the above process of the modulator 8 is a process in which the audio signal S (t) having the modulation factor m is subjected to the square root process and “amplitude modulated”.
Here, the square root converter 5 in the modulator 8 has an effect of reducing the second harmonic distortion of the reproduced sound pressure. However, when the output signal of the square root converter 5 is processed by the multiplier 6, it is shown in FIG. Such a frequency spectrum. FIG. 2 shows a frequency spectrum of a modulated wave when a 1000 Hz sine wave is used as an input signal S (t) (for example, see Non-Patent Document 1).
As can be understood from the figure, a spectrum is generated at intervals of 1000 Hz above and below a carrier signal of about 40 KHz (the signal of the maximum level in the center of the figure), and has a spectrum component that gradually decreases.
[0011]
Although these spectral components are invisible at the level of −60 dB on the vertical axis in FIG. 2, they are theoretically infinite, and there are also components at 30 KHz or less. That is, these components also exist in the audible sound band, and when these components drive the radiator 11 (vibrate the sound generating element), they become audible sounds and are heard as unnecessary sounds.
In such a situation, the spectrum affecting the audible band increases as the carrier frequency decreases and approaches the audible band, or the frequency of the input signal increases, and the spectrum interval increases.
Therefore, it is necessary to cut off spectral components that affect the audible band.
Therefore, the output signal of the modulator 8 is input to the HPF 9. The cutoff frequency of the HPF 9 is set near the upper limit of the audible band, for example, 20 KHz.
[0012]
As shown in FIG. 3A, the transmission characteristic of the HPF 9 has such a characteristic that the frequency is sharply attenuated below the cutoff frequency. Due to this characteristic, in the output signal frequency spectrum of the modulator 8 shown in FIG. 3B, frequency components below the cutoff frequency of the HPF 9 (near the upper limit of the audible band) are cut off, thereby suppressing generation of audible sound. be able to.
Further, it is desirable that the cutoff characteristic of the HPF 9 is set to -12 dB / octave or more.
[0013]
The output of the HPF 9 is amplified by the power amplifier 10 and supplied to the radiator 11, where the radiator 11 emits a sound wave. This sound wave causes nonlinear interaction in the process of being propagated in the air as a finite amplitude sound wave which is a powerful ultrasonic wave, and is self-demodulated into a super-directional sound in an audible band composed of low frequency components, etc. You will be able to hear it.
[0014]
In the above-described HPF 9, the spectrum of the square root process in the modulator 8 has been described, but the present invention is not limited to this. That is, the audible band component generated by processing such as distortion reduction and transmission characteristic improvement other than the square root processing in the transmission (signal processing) system of the modulator 8 is also cut off.
[0015]
As described above, according to the first embodiment, the modulator 8 that performs modulation processing based on the audio signal from the signal source, the power amplifier 10 that amplifies the signal from the modulator 8, A radiator 11 as an electro-acoustic transducer for converting a signal from the ultrasonic wave into a sound wave, and obtaining a audible signal by a parametric action due to the non-linearity of the finite amplitude sound wave of the ultrasonic wave. Since the high-pass filter 9 that blocks the audible band signal component included in the output is provided at the front stage of the power amplifier 10, the bandwidth is widened by the square root process and the multiplication process in the modulator 8, or the signal process other than these processes. Even if a spectrum is generated, generation of unnecessary sound in the audible band can be prevented.
[0016]
The HPF 9 has a cutoff frequency near the upper limit of the audible band, has a cutoff characteristic of -12 dB / octave or higher, and has a steep attenuation characteristic. The effects can be avoided.
[0017]
Embodiment 2 FIG.
FIG. 4 is a block diagram showing a configuration of a converter processing device according to Embodiment 2 of the present invention.
In the first embodiment (FIG. 1), the HPF 9 is shown in a configuration independent of the modulator 8, but this HPF 9 is integrated with the modulator 8 in FIG. 1, and as shown in FIG. The container 12 may be used.
[0018]
As described above, according to the second embodiment, since the high-pass filter 9 is the modulator 12 integrated with the modulator 8 of the first embodiment, the effects of the first embodiment can be obtained. The configuration of the entire converter processing device can be rationalized.
[0019]
【The invention's effect】
As described above, according to the present invention, a high-pass filter that blocks a signal component in an audible band is provided in a stage preceding a power amplifier to constitute a converter processing device. Therefore, a square root process and a multiplication process in a modulator, or these processes are performed. It is possible to prevent generation of unnecessary sound in the audible band even if a spectrum having a wide band is generated by signal processing other than the above.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a converter processing device according to a first embodiment of the present invention.
FIG. 2 is for describing Embodiment 1 of the present invention, and is a diagram illustrating frequency spectrum components when a converter processing device operates.
3A and 3B are frequency characteristic diagrams for explaining the first embodiment of the present invention, wherein FIG. 3A is a transmission characteristic diagram of an HPF 9 and FIG. 3B is a frequency spectrum diagram of an output signal of a modulator 8.
FIG. 4 is a block diagram showing a configuration of a converter processing device according to a second embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1 Modulation signal source, 2 coefficient unit, 3 adder, 4 DC source, 5 square root converter, 6 multiplier, 7 ultrasonic band oscillator, 8, 12 modulator, 9 high-pass filter (HPF), 10 power amplifier, 11 Radiator.

Claims (4)

A modulator that performs modulation processing based on an audio signal from a signal source;
A power amplifier that amplifies a signal from the modulator;
An electroacoustic converter that converts a signal from the power amplifier into a sound wave,
In a converter processing device that obtains an audible signal by a parametric action due to the nonlinearity of a finite amplitude sound wave of an ultrasonic wave,
A converter processing device, wherein a high-pass filter for blocking a signal component in an audible band included in an output of the modulator is provided in a preceding stage of the power amplifier. The converter processing device according to claim 1, wherein the high-pass filter has a cutoff frequency near the upper limit of the audible band, and has a cutoff characteristic of at least -12 dB / octave. The modulator includes a process of multiplying the audio signal from the signal source by m, a process of adding a DC bias to the m-processed signal, a square root process of the added signal, 2. The converter processing apparatus according to claim 1, wherein the multiplication processing is performed with a carrier signal of a sound wave. The converter processing device according to claim 1, wherein the high-pass filter is integrated with the modulator.

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