Audio Distortion Testing Using Differential Phase and FM Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for testing audio equipment, such as analog to digital converters and amplifiers, fail to accurately measure distortion and frequency stability, particularly in non-mechanical systems, leading to discrepancies in sonic performance and inability to detect frequency variations that cause 'sour' tones in sustained notes.
Innovation Solution
A new testing method that measures induced phase and frequency modulation by coupling two or more frequencies into the equipment, using a modifier circuit to isolate and remove lower frequency signals, allowing a Wow and Flutter meter or phase detector to measure frequency variations and phase shifts, thereby assessing frequency modulation effects in electronic amplifiers and processors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional harmonic and intermodulation distortion tests are used to measure audio equipment performance, then basic distortion evaluation can be performed, but the tests fail to accurately detect phase and frequency modulation distortions and Wow and Flutter effects
Solution Approach 1:
The patent changes the measurement parameters from conventional amplitude-based distortion measurements to phase and frequency modulation measurements. By measuring the phase modulation induced by low-frequency signals on high-frequency signals, the method detects distortion components that conventional tests miss, thereby improving measurement precision while maintaining broad applicability to audio equipment
Solution Approach 2:
The patent introduces a new measurement dimension by measuring phase and frequency modulation effects rather than relying solely on amplitude-based distortion measurements. This dimensional shift allows detection of distortion in the phase-frequency domain, revealing Wow and Flutter effects and differential phase distortions that are invisible to conventional testing methods
2Reliability
If single-tone tests are used for mechanical speed stability measurement, then Wow and Flutter can be assessed in mechanical systems, but the method cannot detect frequency variations in non-mechanical electronic amplifiers
Solution Approach 1:
The patent creates a universal testing method that works for both mechanical and non-mechanical systems. By measuring phase and frequency modulation caused by low-frequency signals on high-frequency signals, the method can detect Wow and Flutter effects in mechanical recorders as well as frequency stability issues in electronic amplifiers and digital processors, achieving broad adaptability while maintaining measurement reliability
3Loss of information
If conventional distortion tests measure only amplitude variations, then harmonic and intermodulation distortion can be evaluated, but phase and frequency modulation distortions remain undetected
Solution Approach 1:
The patent uses an intermediary approach by introducing a low-frequency signal that modulates the phase and frequency of a high-frequency signal. The measurement system detects the phase modulation induced by this intermediary low-frequency signal, thereby recovering distortion information that would otherwise be lost in conventional amplitude-only measurements without requiring overly complex apparatus
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.