KR-20260062901-A - Ultra Directional Speaker System And Signal Processing Method thereof

Abstract

The present invention comprises: a first envelope calculation unit for calculating the envelope of a currently input audio input signal; a square root calculation unit for generating a square root signal of the first envelope signal by calculating the square root of the first envelope signal calculated by the first envelope calculation unit; a pre-distortion adaptive filter unit for generating a compensation signal by performing distortion compensation by applying an adaptive filter coefficient update term according to the adaptive filter coefficients determined in the previous stage to the currently input audio input signal; a second envelope calculation unit for generating a second envelope signal by calculating the envelope of the compensation signal; an error calculation unit for generating an error signal by comparing the second envelope signal with the square root signal of the first envelope signal; an adaptive filter coefficient update unit for calculating an adaptive filter coefficient update term and adaptive filter coefficients from the error signal; a dynamic signal modulation unit for generating a modulated signal by dynamically modulating the compensation signal into an ultrasonic band; and an ultrasonic transducer model for modeling an inverse filter corresponding to the frequency characteristics of the ultrasonic transducer and applying it to the modulated signal to generate a filtered signal. The present invention provides a super-directional speaker system comprising: an ultrasonic amplifier for amplifying the filtering signal; and an ultrasonic transducer for converting the amplified signal into an ultrasonic signal, wherein the dynamic signal modulation unit comprises: an AM signal modulation unit for generating an AM modulation signal of transmission data; a first sideband signal modulation unit for receiving the AM modulation signal and performing a Hilbert operation to obtain a first sideband modulation signal with the carrier removed; and a second sideband signal modulation unit for receiving the first sideband modulation signal and adding the carrier to obtain a second sideband modulation signal.

Inventors

• 제영호
• 이 신 렬
• 박찬휘
• 박찬일

Assignees

• 주식회사 제이디솔루션

Dates

Publication Date

20260507

Application Date

20260128

Claims (1)

1. An adaptive filter calculation unit that calculates current adaptive filter coefficients by comparing the envelope of the current audio input signal with the envelope to which adaptive filter coefficients obtained from the previous audio input signal have been applied; A dynamic signal modulation unit that dynamically modulates an audio input signal to which the above adaptive filter coefficient values are applied; It is equipped with an ultrasonic transducer that converts a modulated signal into ultrasound, and The above dynamic signal modulation unit comprises: an AM signal modulation unit that generates an AM modulation signal of transmission data as in Equation (1) below; a first sideband signal modulation unit that receives the AM modulation signal and performs a Hilbert operation for signal modulation as in Equation (2) below to obtain a first sideband modulation signal with the carrier removed; and a second sideband signal modulation unit that receives the first sideband modulation signal and adds the carrier as in Equation (3) below to obtain a second sideband modulation signal, wherein The first sideband signal modulation unit performs a sideband signal generation operation to obtain only the upper sideband signal with the carrier removed, and A super-directional speaker system characterized in that the AM modulated signal modulated in the first sideband signal modulation unit is generated as a signal in which the carrier wave is removed and the envelope is destroyed. (1) At this time, is a sound wave signal, and m is the modulation degree of AM modulation. (2) In the above equation (2), is a Hilbert transformed sound wave signal, , It is displayed as, is a carrier wave. silver With the Hilbert transformed sound wave signal, When am. (3)

Description

Ultra Directional Speaker System and Signal Processing Method thereof The present invention relates to an ultrasonic speaker that reproduces ultra-directional audio, and more particularly to an ultra-directional speaker system and a signal processing method to which a new signal processing method capable of improving the sound quality of the ultrasonic speaker system is applied. Generally, speakers generate sound by converting electrical signals into vibrations and transmitting them through the air. These speakers transmit vibrations in an isotropic manner. Consequently, listeners can hear the sound emanating from the speaker from all directions relative to it. However, this isotropy of speakers can sometimes cause unnecessary problems. For instance, when an installation such as an art gallery or museum houses various artworks or exhibits and is designed to provide explanations via speakers, interference occurs between the sounds generated by the speakers due to the confined space of the venue. Furthermore, if a large number of people simultaneously listen to explanations for different artworks and exhibits, the volume of audio guidance interferes with and is distorted, turning into significant noise. To address these issues, super-directional speakers have emerged, capable of reproducing sound so that it can be heard only from a specific direction. One of the conventional super-directional speaker methods is the use of a parabolic dish. A parabolic super-directional speaker is designed so that a standard speaker is installed at the focal point of a parabolic dish, causing the speaker's acoustic output to reflect off the dish and travel in a straight line. Because this type of speaker is frequently used in places like museums, it is also widely known as a museum speaker. However, this conventional super-directional speaker method using a parabolic dish has several drawbacks: the diameter of the dish is considerably large, the distance over which sound is transmitted with directionality is short (less than 10m), and the sound quality is significantly poor, making it very difficult to achieve satisfactory characteristics. Accordingly, ultrasonic speaker technology utilizing the nonlinear interference phenomenon that ultrasound causes with air is being widely applied in the implementation of super-directional speakers. Although ultrasonic speaker technology has been under development since the 1960s, commercialization was delayed due to the sluggish development of various peripheral devices and issues regarding industrial profitability, but it is now being developed in earnest. A supercardioid speaker system consists of a signal processing unit for obtaining appropriate sound quality, a modulation unit for efficiently modulating the processed signal into the ultrasonic band, an ultrasonic amplifier for driving the ultrasonic transducer, and an ultrasonic transducer that actually generates ultrasound in the air. Theoretically, the audible signal p(t) demodulated in air is proportional to the second-time derivative of the square of the envelope E(t) of the amplitude-modulated signal, as shown in Equation 1. In Equation 1, the second-time derivative can be solved using an equalizer of 12 dB/octave, and the resulting envelope E(t) can be expressed as shown in Equation 2. where m is the modulation index and x(t) is the original audible audio signal. In the above mathematical formula, if the audible signal p(t) heard through the ultrasonic speaker is proportional to the original audible audio signal x(t), it is possible to reproduce audible sound without distortion. However, in reality, as shown in Equation 1, severe distortion corresponding to the square of the original signal x(t) occurs. As a method to reduce this distortion, conventional ultrasonic speakers can reduce distortion by decreasing the modulation index m, but this lowers the reproduction efficiency, making it difficult to obtain high acoustic output. A distortion compensation method to compensate for other distortions is to modulate the square root of the original signal, as shown in Fig. 1. Theoretically, according to this method, the original signal can be faithfully reproduced, but due to the non-linear operation of the square root, the spectrum of the original signal x(t), whose bandwidth is limited, appears on a bandwidth of almost infinite. Therefore, without an ultrasonic transducer that reproduces an infinite bandwidth, the ultrasonic speaker of the method shown in Fig. 1 is bound to have an absolute limit in reducing distortion. To solve the problem illustrated in Fig. 1, ATC of the United States presented an iterative error compensation method without increasing bandwidth in its patent application titled "Modulator Processing for a Parametric Speaker System (US 6,584,205)" illustrated in Fig. 2. Briefly, the patent invented by ATC of the United States is a method that compensates for sound quality distortion by calculating an ideal modulatio