Parametric Array Audio Modulation With Delayed Envelope Alignment
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Solution Overview
Problem
Existing parametric arrays face challenges in faithfully reproducing audio signals due to nonlinear response of transmission media and non-flat frequency responses of ultrasound transducers, leading to distortion and bandwidth issues during ultrasonic sound beaming.
Innovation Solution
The solution involves using an envelope detector to provide an adjusting offset to the audio signal, ensuring it remains entirely positive, allowing for nonlinear preprocessing methods like square rooting, and anticipating peak values by delaying the signal to minimize residual noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional modulation with separate carrier and envelope signals is used, then audio signals can be transmitted through ultrasonic beams, but distortion occurs due to non-flat frequency response and nonlinear characteristics of transducers and transmission medium
Solution Approach 1:
The patent combines the carrier signal and envelope signal into a single modulated ultrasonic signal where the envelope is summed with the audio signal to create a unified waveform. This merging allows the nonlinear preprocessing to act on the combined signal, ensuring that the envelope of the audio signal when added to the audio signal is entirely positive, thereby eliminating distortion caused by separate signal processing paths with different response characteristics
Solution Approach 2:
The patent applies nonlinear preprocessing functions (such as square root or other nonlinear functions) to the modulated signal to compensate for the non-flat frequency response and nonlinear characteristics of the transducers and transmission medium. By transforming the signal parameters through these nonlinear functions, the system achieves faithful reproduction of the original audio signal despite the nonlinear environment
2Manufacturing precision
If nonlinear preprocessing functions are applied to the modulated signal, then distortion is reduced, but the envelope signal must be carefully controlled to remain entirely positive
Solution Approach 1:
The patent performs preliminary action by summing the envelope with the audio signal before applying the nonlinear preprocessing function. This ensures that the argument to the nonlinear function is entirely positive, allowing accurate application of the nonlinear transformation. The envelope detector supplies an adjusting offset to the source audio signal in advance, preventing negative values that would cause distortion in the nonlinear processing stage
3Measurement precision
If the envelope signal changes rapidly to follow audio peaks, then signal fidelity improves, but high-frequency residue noise is generated
Solution Approach 1:
The patent employs dynamic control of the envelope signal by using an envelope detector that supplies an adjusting offset to the source audio signal. The envelope follows the peak levels of the audio signal but changes only gradually, ensuring that the signal remains faithful to the original audio while limiting the rate of change to prevent generation of high-frequency residue noise during demodulation
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 effectively reduces distortion and maintains low-frequency residue, ensuring accurate reproduction of audio signals with improved signal alignment and reduced bandwidth requirements.
Implementation Method 1
The parametric array uses the nonlinear response of a transmission medium such as air or water to convert or demodulate ultrasonic frequency waves into audio frequency waves
Data Source
AI summary
A system using the nonlinearity of a propagation medium to demodulate an ultrasonic wave having audio modulated onto the ultrasonic frequency, audio signal processing circuitry providing a delayed audio signal and an envelope signal which is a function of peaks of the audio signal over a predetermined interval. The delayed audio signal and the envelope signals are combined with the delay in the audio allowing the envelope signal to accurately be aligned with the audio signal in the combination.