Audio Distortion Testing for Dynamic Phase and Cross-Modulation
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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 biasing and phase modulation effects.
Innovation Solution
The use of filter banks and arbitrary low-frequency signals to measure Nth order harmonic and intermodulation distortion, combined with multiple tones and a stairstep signal, allows for dynamic distortion analysis and phase modulation detection, enabling the measurement of frequency and phase modulation effects across varying bias points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional harmonic and intermodulation distortion tests are used with zero offset signal, then basic distortion performance can be measured, but time-varying and dynamic distortion effects cannot be detected
Solution Approach 1:
The patent applies dynamics by transitioning from static zero-offset signal testing to dynamic bias-point testing. The test signal is modulated to vary the bias point of the amplifier during measurement, enabling detection of time-varying distortion characteristics that occur in real operating conditions. This resolves the contradiction by making the measurement system adaptive to dynamic distortion effects while maintaining measurement precision through controlled modulation.
Solution Approach 2:
The patent changes the bias point parameter dynamically during measurement by modulating the test signal. This allows the measurement to capture distortion characteristics across different operating points, thereby detecting intermodulation and harmonic distortion effects that vary with bias conditions. The parameter change enables versatile detection of dynamic distortions while preserving measurement accuracy through systematic variation.
2Device complexity
If single-tone tests are used, then simple harmonic distortion can be measured, but intermodulation distortion and phase modulation effects cannot be evaluated
Solution Approach 1:
The patent segments the test signal into multiple frequency components (dual-tone or multi-tone) while maintaining a structured approach to measurement. By using multiple tones with specific frequency relationships, the test can separately identify and measure different types of distortion (harmonic, intermodulation, phase modulation) that would be indistinguishable in a single-tone test. This segmentation enables comprehensive evaluation without excessive complexity through systematic signal design.
3Ease of operation
If fixed bias point testing is used, then measurement setup is simple, but time-varying distortion characteristics are missed
Solution Approach 1:
The patent employs periodic modulation of the test signal to vary the bias point in a controlled, repeating pattern. This periodic action allows the measurement system to sweep through different bias points systematically, capturing time-varying distortion characteristics while maintaining a simple and repeatable test procedure. The periodic nature ensures that dynamic distortion information is captured without complicating the overall measurement setup.
Data Source
AI summary
A system is provided to analyze cross-modulation distortion in audio devices, which may include testing with audio frequencies. One or more distortion signals from the audio device may be measured for an amplitude, phase, and or frequency modulation effect. In another embodiment a musical signal may be used as a test signal. Providing additional test signals to the audio device can induce a time varying cross-modulation distortion signal from an output of the audio 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.