How Do You Measure Audio When Clocks Differ?
And How is “Open-Loop” Testing Done with APx?
These questions, and more, will be answered via Audio Precision papers, presentations and demos during the AES international convention in New York, October 17 – 20 at the Jacob Javits Center.
Paper: Measuring Audio When Clocks Differ
Authored by a trio of AP engineers, this paper examines what happens when a digital audio signal is measured with respect to a digital reference signal based on a different clock. The resultant change in frequency and time depends on the degree of mismatch between clocks and may introduce a significant amount of distortion into the measurements. But the distortion is different from, and may obscure, the types normally considered important in audio systems. Since a difference in clocking essentially creates a difference in sample rates, sample rate conversion methods can be used to mitigate the discrepancy.
While effective, this approach can be computationally intensive, and it cannot be used when the sample rate difference is too small, nor can it entirely eliminate the effects of a clocking difference. The AP paper describes a much simpler and more effective technique that requires minimal computation. The paper is part of the Signal Processing (Part 2) session, P05, and the track is scheduled to run 2:30 p.m. – 5:30 p.m. on Wednesday, October 17.
In addition, AP will also conduct live presentations and demonstrations in Demo Suite #1E01, with an emphasis on capabilities added in APx500 software release version 4.6. Open-loop measurements using log-swept sine (i.e., exponentially-swept sine, chirp or continuous sweep) should be of particular interest to AES attendees, especially those involved in the design, manufacture and evaluation of smart devices.
The 145th International AES Convention runs October 17-20 in New York, New York. http://www.aes.org/events/145/