Digital Calibration Generator for Audio Test Systems
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Solution Overview
Problem
Standard sound cards in computerized test systems for digital audio devices lack precise control over frequency responses, leading to inaccurate measurements of electro-acoustic characteristics due to variations in analog input and output buffers, aliasing filters, A/D and D/A converters, and unknown signal gain or loss in data communication interfaces.
Innovation Solution
A computerized test system with a digital calibration generator that generates a digital calibration signal of predetermined level and spectral content, using a data communication interface to transmit and receive signals, and a switching arrangement to route the signal through a cascaded encoder and decoder for frequency response determination, ensuring accurate characterization of sound card circuits and data communication interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard sound card is used in a computerized test system, then the cost of hardware components remains moderate and the system is easy to operate, but the frequency response accuracy and measurement precision deteriorate due to lack of tight control in test signal generating and response signal receipt channels
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual testing to characterize the frequency responses of the sound card's A/D and D/A converters. The calibration program measures the actual frequency responses and stores calibration data that is used to compensate for inaccuracies during subsequent measurements, thereby improving measurement precision without changing the hardware
Solution Approach 2:
The patent changes parameters by measuring frequency responses at multiple discrete frequencies across the audio spectrum and using these measurements to create a calibrated model of the sound card's behavior. The calibration process varies signal levels and frequencies to characterize the system's response, enabling accurate compensation for non-ideal frequency responses during testing
2Device complexity
If frequency response variations in analog buffers, amplifiers, and converters are not compensated, then the system structure remains simple, but the absolute level accuracy and electro-acoustic characteristic determination deteriorate
Solution Approach 1:
The patent implements feedback by using the measured frequency response characteristics to compensate for inaccuracies in subsequent measurements. The calibration program measures the actual frequency responses and uses this information to correct for variations in analog buffers, amplifiers, and converters during electro-acoustic testing, thereby improving absolute level accuracy without significantly increasing system complexity
Solution Approach 2:
The patent introduces an intermediary calibration layer between the sound card and the measurement process. The calibration program acts as an intermediary that characterizes the sound card's frequency responses and provides correction factors, mediating between the imperfect hardware and the requirement for accurate measurements
3Measurement precision
If a calibration mode is added to the test system, then the frequency response determination capability is improved, but the device complexity and calibration process time increase
Solution Approach 1:
The patent applies universality by designing the calibration program to perform multiple functions: it measures frequency responses, characterizes the sound card's behavior at different signal levels, and provides compensation for various types of inaccuracies. This multi-functional approach consolidates calibration capabilities into a single software tool, minimizing the increase in device complexity while maximizing measurement precision
Data Source
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AI summary
The present invention relates to calibration of a computerized test system (20) for testing digital audio devices (30) through a data communication interface. The computerized test system comprises a sound card and a digital calibration generator (31) for calibrating at least a signal receipt channel (25) of the computerized test system (20).