Single-Sideband Audio Clipping to Reduce Ultrasonic Distortion
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Solution Overview
Problem
Ultrasonic audio systems suffer from distortion caused by clipping, which results in unwanted harmonics and coloration of the audio signal due to the limitations of the amplifier capacity, leading to a degraded audio experience.
Innovation Solution
The implementation of single-sideband modulation before clipping, followed by filtering to remove distortion components outside the frequency range of the modulated signal, effectively mitigates clipping distortion by spreading it into a broader frequency range where a significant portion can be filtered out, resulting in a signal with fewer distortion products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clipping is applied to the audio signal to limit amplifier output, then amplifier capacity is protected, but distortion products and unwanted harmonics are generated
Solution Approach 1:
The patent applies single-sideband modulation to shift the audio signal from baseband to a higher frequency range before clipping. This frequency translation moves the signal and its distortion products into a different dimensional space (frequency domain), where the distortion products can be selectively filtered. The modulated signal is then clipped, and a bandpass filter removes distortion components outside the single-sideband frequency range, resolving the contradiction between protecting amplifier capacity and minimizing distortion.
2Object-generated harmful factors
If single-sideband modulation is applied before clipping, then distortion products are spread into broader frequency range for filtering, but system complexity increases
Solution Approach 1:
The patent changes the frequency parameter of the audio signal through single-sideband modulation, translating it to a higher frequency range. This parameter change enables the subsequent clipping operation to spread distortion products across a broader frequency spectrum, where they can be effectively separated from the desired signal using bandpass filtering. The modulation alters the signal's frequency characteristics, creating a parameter space where distortion mitigation becomes feasible.
3Power
If clipping is performed on baseband audio signal, then signal level is limited, but distortion products fall within audible frequency range
Solution Approach 1:
The patent performs single-sideband modulation on the audio signal before applying clipping. This preliminary action shifts the signal to a higher frequency range, so that when clipping occurs, the resulting distortion products are also shifted to frequencies outside the audible range or can be filtered out by a bandpass filter. The preliminary modulation prepares the signal in such a way that subsequent clipping does not produce harmful audible distortion.
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 significantly reduces distortion products, preserving the original audio quality by separating the signal and distortion in frequency, allowing for effective filtering and minimizing harmonic distortion, as demonstrated in the example where total harmonic distortion is reduced from 36% to 1.5%.
Implementation Method 1
Electrostatic emitters are generally capacitive devices consisting of two conductive faces with an air gap
Implementation Method 2
The non-linearity of the medium results in acoustic signals produced by the medium that are the sum and difference of the acoustic signals. Thus, two ultrasound signals that are separated in frequency can result in a difference tone that is within the 60 Hz to 20,000 Hz range of human hearing.
Data Source
AI summary
An audio system includes a processor including an input configured to: receive a baseband audio signal and modulate the baseband audio signal to create a modulated audio signal comprising audio signal frequency components in a first frequency range; clip the modulated audio signal to create a clipped, modulated audio signal the clipped modulated audio signal comprising the audio signal frequency components in the first range and further comprising distortion frequency components outside the first frequency range. The system can further be configured to filter the clipped, modulated audio signal to remove frequency components outside the first frequency to remove distortion components outside that frequency range.