Transfer Function Measurement Using a Virtual Reference Signal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing systems for measuring the transfer function of devices with inaccessible input signals, such as proprietary or encrypted inputs, face challenges in obtaining live copies of input signals, leading to inconveniences and inaccurate measurements, particularly in smart speakers.
Innovation Solution
A method and system using a transfer function analyzer with a first channel for a test signal and a second channel for the device output, employing a virtual reference test signal stored separately, which is played into the analyzer after aligning its playback speed with the device's output, compensating for any differences in playback speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-channel analyzer receives live copies of both input and output signals, then measurement accuracy is improved, but it becomes impossible to measure devices with proprietary, encrypted, or wireless input protocols
Solution Approach 1:
The patent creates a virtual reference signal that is a copy of the original input signal stored in the playback device. This virtual copy is then fed to the first channel of the transfer function analyzer, eliminating the need to physically access the device's input connector. The virtual reference signal allows the system to measure transfer functions of devices with proprietary, encrypted, or wireless inputs by using a separate stored copy of the input signal.
Solution Approach 2:
The patent introduces a virtual reference module as an intermediary that bridges the gap between the playback device and the transfer function analyzer. This module captures the input signal from the playback device's output, stores it as a virtual reference, and provides it to the analyzer's first channel. The intermediary allows measurement without direct access to the device under test's input interface.
2Measurement precision
If the virtual reference test signal playback speed is adjusted to match the DUT test signal playback speed, then measurement accuracy is improved, but additional complexity is introduced in speed synchronization
Solution Approach 1:
The patent implements a feedback mechanism where the transfer function analyzer continuously monitors the coherence between the virtual reference signal and the device under test output. When coherence falls below a threshold indicating speed mismatch, the system adjusts the playback speed of the virtual reference signal to restore coherence. This closed-loop feedback ensures accurate synchronization without requiring complex pre-calibration.
Solution Approach 2:
The patent makes the virtual reference signal playback system dynamic by allowing real-time adjustment of playback speed. Rather than using a fixed playback rate, the system can dynamically change the playback speed of the virtual reference signal to match variations in the device under test's playback speed, ensuring continuous measurement accuracy despite speed variations.
Data Source
AI summary
A method for performing transfer function measurements on a device such as a loudspeaker (referred to as a device under test or DUT) using a two-channel transfer function analyzer without a live copy of the DUT test signal. A virtual reference test signal, which is a copy of the DUT test signal, begins playing into a channel of the transfer function analyzer at the estimated start time and estimated play-back speed of the DUT test signal. The known play-back speed of the virtual reference test signal is compared to the estimated play-back speed of the DUT test signal and any detected differences between these two signals compensated for by either adjusting the play-back speed of the virtual reference test signal or the play-back speed of the DUT output, or both. A system for performing this method includes a virtual reference module having a detection part and adjustment part.