How Do You Measure Audio When Clocks Differ?

And How is “Open-Loop” Testing Done with APx?

These questions, and more, to be answered via Audio Precision papers, presentations and demos during AES New York

BEAVERTON, OREGON, September 10, 2018: Audio Precision previewed today its planned contributions to the 145th International AES Convention happening next month in New York. AP’s participation in this key industry event includes both the technical program and the exhibition. In the latter case, attendees can check out the latest in audio test or discuss their specific application with the AP team in Demo Suite #1E01.

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. This 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.

Example of APx Open Loop Chirp MethodologyOpen-Loop Testing
In addition to the paper above, 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. Visit for details.

About Audio Precision
Audio Precision (AP) is a recognized world leader in electronic audio and electro-acoustic test instrumentation. Since 1984, AP’s analyzers have helped engineers to design and manufacture innovative solutions ranging from semiconductor devices to consumer, automotive, and professional audio products. For more information, visit