Audio Distortion Measurement Using Multi-Frequency Phase Detection

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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 multiple frequencies to the input of the device under test, using a modifier circuit to isolate and remove lower frequency signals, allowing for the measurement of phase and frequency variations at the output, which is not possible with standard Wow and Flutter tests.

Engineering Contradictions & Design Principles

VSEngineering 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 discrepancies in sonic signature evaluation occur and phase/frequency modulation effects remain undetected

Engineering Contradiction:

Improvedistortion measurement accuracyVSAvoidphase and frequency modulation information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The measurement process is segmented into distinct functional blocks: signal generator, device under test, bandpass filter, and phase/frequency detector. This segmentation allows each component to perform its specific function optimally, enabling the detection of phase and frequency modulation effects that were previously undetected by conventional distortion measurement methods.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A bandpass filter is introduced as an intermediary component between the device under test and the phase/frequency detector. This intermediary isolates the specific frequency components of interest, removing lower frequency signals and intermodulation products that would otherwise interfere with the measurement of phase and frequency modulation effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If standard Wow and Flutter tests are applied to non-mechanical audio systems, then the test procedure is simplified, but the tests fail to detect frequency modulation effects in amplifiers and processors

Engineering Contradiction:

Improvetesting procedure simplicityVSAvoidfrequency modulation detection capability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The testing method transitions from static single-frequency measurement to dynamic multi-frequency analysis. By applying multiple frequencies simultaneously and detecting the resulting phase and frequency modulations, the method dynamically captures the behavior of non-mechanical systems under realistic operating conditions, thereby reliably detecting Wow and Flutter effects that static tests miss.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The measurement approach changes the detection parameters from amplitude-only measurement to phase and frequency measurement. By using phase detectors and frequency discriminators instead of conventional amplitude meters, the system becomes sensitive to frequency modulation effects, enabling reliable detection of Wow and Flutter in non-mechanical audio equipment.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If single frequency testing is used for harmonic distortion measurement, then the test setup is simplified, but phase and frequency modulation effects caused by multiple frequency interactions cannot be measured

Engineering Contradiction:

Improvetest setup complexityVSAvoidphase and frequency modulation measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The measurement system is designed with multi-functionality to handle both conventional distortion measurement and phase/frequency modulation detection. The phase detector and frequency discriminator can operate on various frequency components simultaneously, making the system universal for detecting multiple types of distortions including intermodulation products and phase modulation effects that single-frequency tests cannot detect.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8624602B2Method and apparatus to measure differential phase and frequency modulation distortions for audio equipment

Publication Date: 2014.01.07 QUAN RONALD

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 or a modulated signal such as an amplitude modulated to dynamically induce a time varying phase or frequency distortion for the device that has differential phase distortion. In another embodiment, the device's output is then measured with an FM detector, Wow and/or Flutter meter, phase detector, and or spectrum analysis system to measure a shift in one of the frequencies used in the test signal or to measure phase and or frequency modulation effects of any signals such as a distortion product, a carrier signal, and or a distortion product of the carrier signal from the device.