Audio Distortion Measurement Using Dual-Frequency Phase 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 distortion and frequency modulation, leading to discrepancies in sonic performance and inability to detect Wow and Flutter in non-mechanical systems.
Innovation Solution
A new testing method that measures induced phase and frequency modulation by coupling two or more frequencies to the input of the device under test, allowing for the measurement of phase and frequency modulation effects on the output, including harmonics and intermodulation components, using a modifier circuit to reduce interference and detect these effects with a Wow and Flutter meter or phase detector.
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 is achieved, but phase and frequency modulation distortions remain undetected
Solution Approach 1:
The patent segments the measurement process into distinct components: applying pure sine wave tones at specific frequencies (e.g., 19kHz and 20kHz), measuring the fundamental outputs, and separately measuring intermodulation distortion products (e.g., 38kHz, 40kHz, 16kHz, 22kHz). This segmentation allows independent analysis of different distortion mechanisms that conventional tests conflate together.
Solution Approach 2:
The patent extends measurement into the frequency domain by analyzing intermodulation products at frequencies significantly different from the input tones. By measuring phase and frequency modulation at these higher frequency components (e.g., measuring 16kHz and 22kHz when inputs are 19kHz and 20kHz), the method detects distortion mechanisms invisible to conventional single-frequency or low-frequency tests.
2Productivity
If conventional test methods measure only at nominal bias points, then simple harmonic distortion is obtained, but dynamic phase and frequency variations under different signal conditions are missed
Solution Approach 1:
The patent employs periodic testing by applying continuous sine wave tones and measuring steady-state outputs. The method uses periodic signal application at specific frequencies to induce and measure periodic intermodulation products, enabling systematic exploration of device behavior under different operating conditions through repeated measurements.
Solution Approach 2:
The patent changes testing parameters by using multiple input frequency combinations (e.g., 19kHz+20kHz, different amplitude ratios) and measuring outputs at corresponding intermodulation frequencies. This parameter variation reveals how phase and frequency modulation distortions change with operating conditions, providing dynamic characterization beyond single-point measurements.
3Reliability
If Wow and Flutter meters are designed for mechanical systems only, then mechanical speed stability is measured, but phase and frequency modulation in electronic amplifiers remain undetected
Solution Approach 1:
The patent makes the measurement method universal by demonstrating that the same technique for detecting phase and frequency modulation (originally developed for mechanical Wow and Flutter measurement) can be applied to electronic amplifiers and digital-to-analog converters. The method measures frequency deviation caused by phase modulation in electronic systems using the same fundamental principles as mechanical speed variation measurement.
Solution Approach 2:
The patent replaces mechanical measurement mechanisms with electronic signal processing. Instead of using mechanical tachometers or speed sensors, the method uses electronic frequency counters and phase detectors to measure frequency deviations. This substitution enables the measurement of phase and frequency modulation in purely electronic systems where mechanical measurement methods are inapplicable.
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.