True SPL Limiter With Anti-Startle Control for Fast-Rise Audio
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Solution Overview
Problem
Existing audio devices, such as headsets and loudspeakers, often produce sound pressure levels that can cause discomfort and acoustic startle due to sudden increases in sound, even if they comply with legal limits, as current methods for limiting sound pressure levels can result in lower overall levels than necessary and may not effectively address fast-rise time signals.
Innovation Solution
The implementation of a sound pressure level limiter with an anti-startle feature that detects fast-rise time signals and slows their rise using a delta incident detector and delta limiter, applying an anti-startle gain to prevent acoustic startle, while also employing a true SPL processor to estimate sound pressure levels accurately and adjust gain accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional audio limiting devices clip or compress the electrical signal to limit maximum sound level, then the maximum sound pressure level is reduced, but the overall sound levels become lower than necessary and desirable
Solution Approach 1:
The patent changes the parameter being limited from electrical signal voltage to actual sound pressure level. The true SPL processor converts the electrical signal to an estimate of the sound pressure level at the listener's ear, then the limiter acts on this SPL parameter rather than the electrical signal, allowing accurate limiting at the correct sound pressure level while maintaining proper overall levels.
Solution Approach 2:
The patent introduces a true SPL processor as an intermediary between the electrical signal and the limiter. This processor converts the electrical signal into an estimate of the actual sound pressure level, serving as a mediator that allows the limiter to control the actual acoustic output rather than just the electrical input, resolving the discrepancy between electrical signal levels and acoustic output levels.
2Object-affected harmful factors
If the sound pressure level is limited to comply with legal limits, then acoustic safety is improved, but user comfort deteriorates due to loud sound levels and acoustic startle
Solution Approach 1:
The patent limits the sound pressure level parameter directly rather than the electrical signal amplitude. By measuring and limiting the actual SPL at the listener's ear, the system can enforce safety limits while maintaining comfortable overall levels, because the limiting is applied based on the actual acoustic output rather than a fixed electrical signal level.
Solution Approach 2:
The patent implements a feedback mechanism where the true SPL processor continuously monitors the estimated sound pressure level and feeds this information back to the limiter. The limiter then adjusts the electrical signal in real-time based on the actual SPL measurements, creating a closed-loop control system that maintains both safety and comfort.
3Ease of operation
If the rise time of fast-rise time signals is slowed to prevent acoustic startle, then user comfort is improved, but the transient response time increases
Solution Approach 1:
The patent applies dynamic control to the signal processing, where the limiter's response characteristics change based on the detected signal conditions. The system dynamically adjusts the limiting action based on the estimated SPL and its rate of change, allowing fast response when needed while providing smoother transitions that prevent startle when appropriate.
Solution Approach 2:
The patent prepares for potential acoustic startle by continuously monitoring the SPL and its rate of change. When a rapid increase is detected, the system applies limiting action in advance to cushion the transition, slowing the rise time before the full increase occurs, thereby preventing startle while minimizing the impact on transient response.
Data Source
AI summary
Sound pressure level limiter with anti-startle feature for audio systems are disclosed. The anti-startle feature may be implemented with a delta incident detector for detecting delta acoustic incidents that exceed a predetermined acoustic startle boundary, a delta limiter for determining an anti-startle gain, and an amplifier to apply the anti-startle gain to the input signal. The delta incident detector may detect delta incidents based on an estimated true SPL delivered by a transducer to a predetermined datum point. The estimated true SPL may be determined by based on a measured receiving frequency response of the transducer. An SPL limiter may also determine an SPL gain in response to detecting an SPL acoustic incident that exceeds a predetermined SPL threshold, and an amplifier may apply the SPL gain to the input signal to reduce it below the threshold.