Audio Distortion Testing with Modulated Signals and Filter Banks
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Solution Overview
Problem
Conventional methods for testing audio equipment, such as analog to digital converters and amplifiers, fail to accurately measure time-varying harmonic and intermodulation distortion, particularly in non-mechanical systems, as they rely on fixed bias points and single-tone tests, which do not account for dynamic changes in frequency or phase response.
Innovation Solution
The use of filter banks and arbitrary low-frequency signals with multiple tones to measure dynamic harmonic and intermodulation distortion, allowing for the detection of phase and frequency modulation effects across different bias points, enabling a more comprehensive evaluation of audio equipment performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional harmonic and intermodulation distortion tests are used with fixed bias points, then the testing method is simple and equipment requirements are basic, but the measurement precision is insufficient for time-varying distortion in electronic systems
Solution Approach 1:
The patent applies dynamics by transitioning from fixed bias point measurements to time-varying measurements. The test system dynamically adjusts the bias point of the device under test over time, allowing measurement of distortion characteristics across different operating conditions. This enables detection of time-varying harmonic and intermodulation distortion that would be missed by static measurements, directly improving measurement precision for electronic systems while accepting increased system complexity.
Solution Approach 2:
The patent implements parameter changes by varying the bias point parameter over time during measurement. Instead of measuring distortion at a single fixed bias point, the system continuously or periodically changes the bias point parameter, enabling measurement of how distortion characteristics evolve with changing operating conditions. This parameter variation approach allows detection of dynamic distortion behavior in electronic systems that remains invisible to conventional fixed-point testing.
2Measurement precision
If single-tone tests are used for measuring distortion, then the test setup is simple, but the ability to detect frequency and phase modulation effects is insufficient
Solution Approach 1:
The patent applies merging by combining multiple test tones into a composite test signal. Instead of using a single test tone, the system superimposes multiple tones with different frequencies and amplitudes, creating a rich test signal that simultaneously excites various operating points of the device under test. This combined signal approach enables detection of frequency and phase modulation effects that single-tone tests cannot reveal, while the complexity is managed through systematic signal generation and analysis methods.
3Reliability
If conventional distortion measurement methods are applied to non-mechanical electronic systems, then the testing approach is familiar and straightforward, but false negatives occur because electronic systems exhibit dynamic behavior not captured by static tests
Solution Approach 1:
The patent implements periodic action by applying time-varying bias signals to the device under test. The bias point is modulated periodically or continuously over time, causing the device to operate through different regions of its transfer characteristic. This periodic variation in operating conditions enables detection of dynamic distortion effects in electronic systems that would remain undetected by static measurements, significantly improving testing reliability while establishing a structured periodic measurement methodology.
Data Source
AI summary
A system is provided to analyze distortion in an electronic or electromechanical device, which may include testing with one or more modulated signals and/or with one or more demodulators. In one embodiment a change in pitch (or frequency) is measured at an output of the device. One or more signals from a demodulator output may be measured for an amplitude, noise, phase, aliasing, spurious signal, and/or frequency modulation effect. In another embodiment a musical signal may be used as a test signal. Providing additional test signals to the device can induce a cross-modulation distortion signal (or time varying cross-modulation distortion signal) from an output of the device. Also utilizing at least one additional filter, filter bank, demodulator and or frequency converter and or frequency multiplier provides extra examination of distortion. Also frequency and/or phase response can be measured with the presence of a de-sensing signal and or another signal that induce near slew rate limiting or near overload condition of the device under test. Another system is provided to analyze modulation index differences between input and output signals for a test signal including modulation. Another system includes providing a nested or layered modulated signal and/or a nested or layered demodulation apparatus or method.