Metal Detector Audio Rendering for Audible Weak Signals
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Solution Overview
Problem
Current metal detectors face challenges in rendering audio signals effectively, as the dynamic range of metal target detection signals exceeds human hearing capabilities, leading to potential hearing damage from loud signals and missed detections due to quiet signals being inaudible.
Innovation Solution
A method is introduced to modify the dynamic range of the electromagnetic target detection signal by clipping, applying dynamic range compression, and segmenting the signal into portions with local modification rates, allowing for a more complex overall modification that generates an audio signal compatible with human hearing, while maintaining the dynamic variation of the detection signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dynamic range of metal target detection signals is maintained as is, then the full range of signal amplitudes is preserved, but loud signals cause potential hearing damage and quiet signals become inaudible
Solution Approach 1:
The patent applies dynamic range compression by transforming the amplitude parameter of the audio signal. A compression function maps the wide dynamic range of detection signals (spanning several orders of magnitude) to a narrower range suitable for human hearing (typically 20-100 dB), preventing both hearing damage from loud signals and loss of quiet signals through nonlinear amplitude transformation
Solution Approach 2:
The patent implements thresholding and lower-bound clipping before audio output to prevent excessively loud signals from causing hearing damage. By setting a maximum amplitude threshold and clipping signals exceeding this threshold, the system provides beforehand protection against harmful loud sounds while preserving the detectability of quieter signals through the compression function
2Loss of information
If the dynamic range of metal target detection signals is maintained as is, then all signal variations are preserved, but quiet signals become inaudible due to limited human hearing range
Solution Approach 1:
The patent uses a compression function that nonlinearly transforms the amplitude parameter to expand the perceived dynamic range. By applying a function such as f(A) = A^γ where γ < 1, quiet signals are amplified relative to loud signals, making them audible while maintaining the relative dynamic variations that carry detection information
Solution Approach 2:
The patent sets a lower amplitude threshold and applies clipping or boosting to signals below this threshold. This beforehand processing ensures that even very weak detection signals are raised to an audible level, preventing information loss from inaudible quiet signals while maintaining the overall signal structure
3Ease of operation
If dynamic range compression is applied to compress the signal, then loud and quiet signals become audible, but the original dynamic variation of the detection signal is altered
Solution Approach 1:
The patent carefully selects compression parameters (compression ratio, threshold levels, knee points) to achieve audibility while minimizing distortion of the original signal characteristics. By using gentle compression with high thresholds and appropriate knee settings, the system maintains the relative dynamic variations that convey target information while expanding the overall audible range
Solution Approach 2:
The patent applies compression selectively rather than uniformly across all signal amplitudes. By using threshold-based compression that only activates when signals exceed certain levels, and by applying different compression ratios to different amplitude ranges, the system achieves audibility improvement without excessively altering the natural dynamic variation of the detection signals
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 ensures that quiet signals are audible, loud signals do not cause hearing damage, and intermediate-level signals are perceived gradually, improving user experience by compressing the dynamic range of the audio signal to match human hearing capabilities.
Implementation Method 1
an alternating magnetic field is emitted continuously and the detection is based on variations in amplitude and in phase between the frequency components of the emitted signal and those of the received signal
Implementation Method 2
The received electromagnetic signal has an amplitude that varies when the detection head moves above the target, proportionally to the magnetic fields produced by the flow of eddy currents generated in the target
Implementation Method 3
the components of the electromagnetic signal received by one or more receiver coils arranged close to the emitter coil
Data Source
AI summary
A method includes compressing the dynamic range of the target detection signal so as to correspond to the desired dynamic range (60) of the audio signal (81) that is generated in order to acoustically render this detection signal to the user, so that the quietest signals are audible, the loudest signals do not cause hearing damage for the user, and that the sound volume is able to be perceived gradually for the intermediate-level signals. This avoids losing variations in the detection signal that are below the audibility threshold (63) and clipping them above a maximum hearing comfort threshold (64) in the corresponding audio signal (71) that would be generated according to the prior art.