JP4522121B2 - Superdirective speaker modulator - Google Patents

Description

  The present invention relates to a modulator for a super-directional speaker that radiates audible sound in a directional manner.

A conventional superdirective speaker modulator multiplies an audio signal of a modulation signal by a multiplier, adds a DC bias to the signal, performs square root conversion, and then outputs an output carrier signal of an ultrasonic band oscillator and a multiplier. Multiplication is performed to obtain a modulated signal. This modulated signal is amplified by a power amplifier and supplied to an ultrasonic transducer array to be emitted as a sound wave.
That is, the processing from the coefficient unit to the multiplier is a process in which an audio signal having a modulation degree m is subjected to square root processing and amplitude-modulated (see, for example, Patent Document 1).

Japanese Examined Patent Publication No. 4-58758 (pages 2 to 3 and FIG. 1)

The conventional superdirective speaker modulator has a problem that the carrier wave signal is output from the radiator as it is when there is no sound source signal. Further, since amplitude modulation is adopted as the modulation method, the modulation rate is lowered when a low level audio signal is input. For this reason, there is a problem that the demodulated sound that is radiated into the air from the ultrasonic vibration element and is self-generated cannot obtain a desired sound pressure level.
In addition, in order to obtain a desired sound pressure level with respect to various types of audio signals, there has been a problem that the gain must be increased in the subsequent amplification device.

The present invention has been made to solve the above-described problems, and enables optimum modulation output by controlling the carrier signal level in accordance with the input audio signal level.
Furthermore, when the audio signal is at a low level, the sound pressure level is increased by increasing the modulation signal gain. Furthermore, the audio signal can be easily heard by changing the modulation signal gain according to the input audio signal. It is possible.

  The superdirective speaker modulator according to the present invention includes an A / D converter that converts an audio signal from an analog signal to a digital signal, and an envelope that obtains an envelope level from an output signal of the A / D converter. A multiplier that multiplies the output of the A / D converter by a coefficient, an adder that adds the outputs of the envelope and the coefficient multiplier, a square root converter that performs a square root process on the output of the adder, and the A / D A signal level control unit that generates period information and level information based on an output signal of the D converter, an ultrasonic band oscillator controlled by an output signal of the signal level control unit, the square root converter, and the ultrasonic band A multiplier for multiplying the output signal of the oscillator, a D / A converter for converting the output signal of the multiplier from a digital signal to an analog signal, and an output signal of the signal level control unit; A gain variable unit for generating a gain value based on the value set in mind, those comprising a multiplier for multiplying an output of said variable gain across the output of the D / A converter.

  According to the present invention, since it is possible to adjust the carrier signal level in accordance with the input audio signal level, it is possible to achieve optimum modulation output and obtain a desired sound pressure level.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a superdirective speaker modulator according to Embodiment 1 for carrying out the present invention. This will be described with reference to FIG. The superdirective speaker modulator includes a modulation signal source 1 that outputs an audio signal, an A / D converter 2 that converts the audio signal from an analog signal to a digital signal, and an output of the A / D converter 2 that is a signal. While being supplied to the level control part 3, it is supplied to the envelope device 4 and the coefficient device 5 which are arranged in parallel. The outputs of the envelope 4 and the coefficient unit 5 are input to the adder 6. The added output is input to the square root converter 7. The output of the square root converter 7 is multiplied by the output of the ultrasonic band oscillator 8 that outputs a carrier wave having a constant frequency higher than that of the audio signal controlled by the output signal of the signal level control unit 3 and then the D / A conversion. Is input to the container 10. The output of the D / A converter 10 is multiplied by a signal generated by the gain variable unit 11 based on the output signal of the signal level control unit 3 by a multiplier 12 to obtain an output signal.

The super-directional speaker is provided with a radiator (not shown) that is a radiation part of a highly directional speaker that transmits an ultrasonic wave to obtain an audible signal by a parametric action.
Parametric speakers, which are superdirective speakers, use ultrasonic waves that cannot be heard by humans, and distortion components are generated in the process of strong ultrasonic waves propagating through the air. The principle of obtaining (non-linearity) is adopted. Although the conversion efficiency for obtaining an audible sound is low, it can exhibit “superdirectivity” in which sound is concentrated in a beam shape in an area where the sound radiation direction is narrow. Conventional low directivity speakers, like the light of a bare bulb, form a sound field in a wide area including the back, so the area could not be controlled, but the speakers used with parametric speakers are It is possible to limit the area that sounds like a spotlight, making it a highly directional speaker.

Next, the operation will be described with reference to FIG. The audio signal output from the modulation signal source 1 is converted by the A / D converter 2 from an analog signal to a digital signal having a quantized data value. The sampling frequency of the A / D converter 2 can be sampled at a frequency sufficiently higher than the audio signal output from the modulation signal source 1, and the sampling frequency that is sampling can be adjusted in accordance with the input audio signal. To do. The quantized data value is input to the signal level control unit 3 and also input to the envelope 4 and the coefficient unit 5 provided in parallel.
First, the quantized data values input to the envelope 4 and the coefficient unit 5 are obtained as envelope levels by the envelope 4, and are multiplied by m by the coefficient 5 and output. The outputs of the envelope 4 and the coefficient unit 5 are added by an adder 6 and then input to a square root converter 7. The square root converter 7 performs parallel root processing on the added signal and outputs it.
On the other hand, the signal level control unit 3 generates period information and level information from the quantized data value. FIG. 2 is a block diagram showing details of the signal level control unit. The operation of the signal level control unit 3 will be described with reference to FIG. The input quantized data value is input and stored in the memory 13 and output to the differentiator 14. The memory 13 is assumed to incorporate a program for managing accumulated data. Difference processing is performed by the difference unit 14, and the result is output to the increase / decrease detector 15. The increase / decrease detector 15 determines each boundary value of the increasing / decreasing tendency from the difference result data. For example, a level is calculated from two decrease boundary values based on a period (time), two decrease boundary values, and a maximum value therebetween, and the period information and level information are output to the pulse generator 16 via the memory 13. . A pulse is generated based on the period information and level information sent to the pulse generator 16 and output to the ultrasonic band oscillator 8. Ultrasonic band oscillator 8, based on the pulse information sent to output a carrier wave is an ultrasonic according to the level of the pulse to the multiplier 9, is amplitude modulated by the input audio signal. The amplitude-modulated signal is converted into an original analog signal by the D / A converter 10. After the conversion, the multiplier 12 multiplies it with the output of the gain variable device 11 to vary the gain of the modulation signal, and it becomes the modulation signal output. When the gain variable unit 11 is smaller than an arbitrary reference, the gain variable unit 11 outputs a numerical value to be increased to increase the modulation signal gain.

  For example, the level A output from the signal level control unit 3 is set to 0 <A ≦ 1. The gain variable device 11 varies the modulation signal gain according to the equation 1 / (X + A). X in this equation can be set to an arbitrary value based on the audio signal output from the modulation signal source 1. By substituting the level output from the signal level control unit 3 into the 1 / (X + A) equation of the gain variable unit 11, the modulation gain can be increased when the audio signal level is small. For example, when the value of X is 0.3, the output value of the gain variable unit 11 is 1 time when the level output from the signal level control unit 3 is 0.7 for a large audio signal. On the other hand, when the level output from the signal level control unit 3 of the small audio signal is 0.1, the output value of the gain variable unit 11 is 2.5 times, and the modulation signal gain is increased when the audio signal is small. It becomes possible.

Further, according to the level output from the signal level control unit 3, the gain variable unit 11 uses a as a constant and an exponential function such as a ^{(1 / X + A)} , and a monotonically increasing function such as a logarithmic function such as log ^X. You may behave.

It is a block diagram of the modulator for superdirective speakers showing Embodiment 1 of the present invention. It is a block diagram which shows the structure of the signal level control part of this invention.

Explanation of symbols

  1 Modulation signal source, 2 A / D converter, 3 signal level control unit, 4 envelope, 5 coefficient unit, 6 adder, 7 square root converter, 8 ultrasonic band oscillator, 9 multiplier, 10 D / A Converter, 11 Gain variable, 12 Multiplier, 13 Memory, 14 Differentiator, 15 Increase / decrease detector, 16 Pulse generator.

Claims (4)

  An A / D converter that converts an audio signal from an analog signal to a digital signal, an envelope that obtains an envelope level from the output signal of the A / D converter, and the output of the A / D converter is multiplied by a coefficient. A coefficient unit, an adder that adds the envelope and the output of the coefficient unit, a square root converter that performs a square root process on the output of the adder, and period information and level based on the output signal of the A / D converter A signal level control unit for generating information, an ultrasonic band oscillator controlled by an output signal of the signal level control unit, a multiplier for multiplying the square root converter and an output signal of the ultrasonic band oscillator, and the multiplication A D / A converter that converts the output signal of the converter from a digital signal to an analog signal, and a gain value is generated based on the output signal of the signal level control unit and an arbitrarily set value. A gain variable unit for ultra directional speaker for modulator comprising a multiplier for multiplying an output of said variable gain across the output of the D / A converter.   2. The modulator for superdirective speakers according to claim 1, wherein the signal level control unit controls the signal level based on a difference value between data obtained by sampling and quantizing the audio signal. The signal level control unit detects the maximum value of the audio signal based on the boundary value between the increase and decrease of the difference value of the sampled and quantized data of the audio signal, and the signal level based on the period and the maximum value. The superdirective speaker modulator according to claim 1, wherein the modulator is controlled.   2. The modulator for a superdirective speaker according to claim 1, wherein the gain variable unit varies a modulation gain based on an output of the signal level control unit and an arbitrarily set value.

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