PNW Section May 2018 meeting featured Bob Smith on DAC measurements.
The May 2018 PNW Section meeting featured Bob Smith of Soundsmith Labs and AES PNW Section Technical Contributor, presenting a tutorial of some pitfalls of audio measurements on D to A converters. The meeting was held at Shoreline Community College, Shoreline WA, and was attended by 16 AES members and 14 non.
In this tutorial, Bob Smith illuminated the world of DAC measurements, demonstrating how reviewers can mislead or worse over the choices they make and the ways they use and misuse measurement techniques. He also described ways that choices about the drivers used within the Microsoft Windows environment and the paths that the audio can take (from application, through driver and USB transport to hardware output) can introduce distortions leading reviewers and users astray.
Bob created two hypothetical reviews of some DACs, each purporting different results and seeming to "prove" the point. Close examination and "comparing apples to apples" proved only that each "review" failed miserably in such areas as using the same software driver, reference levels, and even FFT settings, giving different results.
Further problems were discussed by the nature of the Windows audio architecture. It was shown that different audio software drivers (i.e. ASIO or WDM) can do different things to the audio going through.
As we are reminded through the years, you can prove anything with data. It's up to the user to realize that audio measurements can be very complex. Bob's final reminders:
• Windows driver paths matter.
• Levels are important when using non-ASIO paths.
• Measurements should have a statement of test conditions so others may repeat and verify.
• Look at any measurement graph with a critical eye and skepticism.
• Ask yourself if there may be any biasing motivator by the publisher of the data.
-Don't assume.-
