Audio Distortion Testing for Differential Phase and FM Effects
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Solution Overview
Problem
Conventional methods for testing audio equipment, such as harmonic and intermodulation distortion tests, fail to accurately measure the performance of non-mechanical systems like amplifiers and processors, as they do not account for frequency and phase variations that can lead to sonic distortions.
Innovation Solution
A new testing method that measures induced phase and frequency modulation by applying multiple frequencies to the input of the device under test, allowing for the measurement of phase and frequency variations at the output, which can reveal Wow and Flutter effects even in non-mechanical systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional harmonic and intermodulation distortion tests are used, then basic equipment performance can be evaluated, but frequency stability and phase modulation effects remain undetected
Solution Approach 1:
The patent introduces an intermediary measurement approach by using phase modulation detection as a mediator to reveal frequency stability issues. Instead of directly measuring frequency variations, the system modulates a test signal with the audio signal and detects phase changes in the modulated carrier, thereby indirectly measuring frequency stability and Wow/Flutter effects that conventional distortion tests miss.
2Reliability
If single tone testing is used for Wow and Flutter measurement, then mechanical speed stability can be assessed, but electronic amplifier frequency modulation effects cannot be detected
Solution Approach 1:
The patent creates a universal testing method that works for both mechanical and electronic equipment. By using phase modulation detection of a carrier signal, the system can measure frequency stability in mechanical systems (Wow and Flutter) and electronic systems (amplifier-induced frequency modulation) with the same apparatus, making the test versatile across different equipment types.
Solution Approach 2:
The patent replaces mechanical testing methods with an electronic substitution approach. Instead of using mechanical turntables or tape decks to generate test signals, the system uses electronic signal generators and phase modulators to create and detect frequency variations, thereby substituting mechanical systems with electronic equivalents that can test both mechanical and electronic equipment.
3Measurement precision
If conventional distortion testing is used, then harmonic distortion can be measured, but induced phase and frequency modulation effects remain undetected
Solution Approach 1:
The patent adds another dimension to distortion measurement by moving from amplitude-only detection to phase-sensitive detection. Conventional distortion tests measure only amplitude variations of harmonic and intermodulation products, while this patent introduces phase measurement as an additional dimension, enabling detection of phase modulation and frequency stability effects that exist in the quadrature component of the signal.
Data Source
AI summary
A testing method or apparatus utilizes multiple frequencies applied to a device under test for measuring newly discovered frequency modulation effects. An embodiment may include a lower frequency signal with a smaller amplitude higher frequency signal to test a dynamic change in frequency response, gain, and or phase. This dynamic test can reveal frequency modulation effects. Another embodiment may include the use of a multiple frequency signal to dynamically induce a time varying phase or frequency distortion for the device that has differential phase distortion. The device's output is then measured with an FM detector to measure a shift in one of the frequencies used in the test signal or to measure frequency modulation effects of any signals, including distortion products, from the device. Yet another embodiment of the invention may include biasing a device with a voltage to span the output voltage range of the device while measuring harmonic or intermodulation distortion or phase or frequency response at the various operating points.