Pre-distortion Adaptive Filter for Ultra Directional Speaker Distortion
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Solution Overview
Problem
Conventional ultra directional speakers suffer from poor sound quality due to distortion caused by isotropic sound transmission and the limitations of parabolic dish designs, as well as the inefficiencies of ultrasonic speaker technologies, which result in limited acoustic output and hardware complexity.
Innovation Solution
The implementation of a pre-distortion adaptive filter and VSB modulation to minimize signal distortion in real-time, combined with the use of a predetermined filter for the ultrasonic converter to generate an inverse filter model, simplifies hardware design and improves sound quality by dynamically modulating the modulation index and compensating for non-linear demodulation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional ultrasonic speaker technology is used to achieve ultra directional sound transmission, then directionality is improved, but sound quality deteriorates due to serious distortion
Solution Approach 1:
The patent applies pre-distortion filtering to the audio signal before modulation, anticipating and compensating for the non-linear distortion that will occur during ultrasonic demodulation. This preliminary correction of the signal waveform ensures that after the non-linear air demodulation process, the reproduced sound maintains high fidelity with minimal distortion, thus improving sound quality while preserving ultra directional transmission.
2Manufacturing precision
If modulation index is decreased to reduce distortion, then sound quality is improved, but acoustic output deteriorates
Solution Approach 1:
The patent dynamically adjusts the modulation index based on the signal characteristics and uses pre-distortion filtering to compensate for distortion. This allows the system to maintain a higher modulation index for better acoustic output while the pre-distortion correction ensures that distortion remains minimal, thus resolving the trade-off between sound quality and acoustic output power.
3Manufacturing precision
If repetitive error compensation method is used to compensate distortion, then sound quality is improved, but device complexity increases
Solution Approach 1:
Instead of using repetitive error compensation that requires complex feedback loops and multiple processing stages, the patent applies a single pre-distortion filter before modulation. This preliminary correction approach achieves distortion compensation in one processing stage, significantly reducing hardware complexity and computational requirements while maintaining high sound quality.
4Manufacturing precision
If SSB modulation is used for distortion compensation, then sound quality is improved, but device complexity increases due to sharp filter requirements
Solution Approach 1:
The patent extracts and compensates for the dominant non-linear distortion components through pre-distortion filtering, rather than attempting to perfectly implement SSB modulation which would require extremely sharp filters. By targeting and correcting the specific distortion mechanisms present in ultrasonic air demodulation, the system achieves high sound quality with practical, realizable filter designs that do not require excessive complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes distortion, reduces hardware complexity, and enhances sound quality by allowing real-time pre-distortion compensation and efficient modulation, effectively addressing the limitations of existing technologies.
Implementation Method 1
an ultrasonic converter for actually generating an ultrasonic wave in the air
Implementation Method 2
an ultrasonic speaker technology using a non-linear interference of an ultrasonic wave with the air in the air
Data Source
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AI summary
The present invention relates to an ultra directional speaker system and a signal processing method thereof. The ultra directional speaker system in accordance with the present invention comprises: a first envelop calculator for calculating an envelop of an audio input signal currently being inputted; a square root operator for calculating a square root of a first envelop signal calculated by the first envelop calculator to generate a square root signal of the first envelop signal; a pre-distortion adaptive filter for applying an adaptive filter coefficient update term according to an adaptive filter coefficient determined in a previous stage to the audio input signal currently being inputted to carry out a distortion compensation and generate a compensated signal; a second envelop calculator for calculating an envelop the compensated signal to generate a second envelop signal; an error calculator for comparing the second envelop signal and the square root of the first envelop signal to generate an error signal; an adaptive filter coefficient updater for calculating the adaptive filter coefficient update term and the adaptive filter coefficient from the error signal; a dynamic VSB modulator for dynamically modulating the compensated signal to an ultrasonic band to generate a modulation signal; an ultrasonic converter model for modeling a inverse filter corresponding to a frequency characteristic of an ultrasonic converter and applying the inverse filter to the modulation signal to generate a filtering signal; an ultrasonic amplifier for amplifying the filtering signal; and the ultrasonic converter for converting the amplified filtering signal to an ultrasonic signal. In accordance with the embodiment of the present invention, the pre-distortion compensation may be applied to the input signal in real time and a signal to be modulated is subjected to a VSB modulation to minimize the distortion according to a level of the signal, and a signal difference compensation according to an envelop detection of a current signal and a signal in previous stage to minimize a hardware and maximize a sound quality improvement.