Paul Seydor of The Absolute Sound interviews John Siau, VP and chief designer at Benchmark Media Systems. The interview accompanies Paul's review of the LA4 in the December, 2020 issue of TAS.
"John Siau, Director of Engineering and chief designer at Benchmark Media, knew from an early age that he wanted to design electronic equipment. He enrolled at Syracuse University in 1976 and graduated four years later with a bachelor’s degree in Computer Engineering. Along the way he’d cobbled together an audio system and worked as the sound engineer and mixer for a local band. The fifteen years following his graduation include long stints at CBS and General Electric, plus independent consulting, through all of which he acquired extensive experience in HDTV (receiving two patents for video-image stabilization systems) and developed high expertise with high-speed A/D and D/A converters, ultra-low-jitter phase-locked loops, high-speed digital logic, digital filters and FPGA cores. In 1995 Benchmark hired him to design its first digital product, the AD2004, a 20-bit A/D converter that set new standards for low distortion and won some awards. Soon afterward he joined the company full time, eventually becoming part owner. Away from Benchmark, his musical training includes trumpet and tuba; he is an avid skier; and he and his wife have a large family who on vacations enjoy exploring remote trails and locations. They own a farm, which they lease, though they do enjoy working it from time to time."
"Siau’s many white papers and other pieces about audio are well worth investigating on the Benchmark website."
"His essay “Rules of Thumb for Music and Audio,” which combines useful information, solid practical advice, and wise counsel, will enlighten both tyros and seasoned audiophiles and reviewers."
[Paul Seydor] "Benchmark publishes by far the most exhaustive technical information about its products yet listening also plays an important part in your product design and development."
[John Siau] "At Benchmark listening is the final exam that determines if a design passes from engineering to production. But since listening tests are never perfect, it’s essential we develop measurements for each artifact we identify in a listening test. An APx555 test set has far more resolution than human hearing, but it has no intelligence. We have to tell it exactly what to measure and how to measure it. When we hear something we cannot measure, we are not doing the right measurements. If we just listen, redesign, then repeat, we may arrive at a solution that just masks the artifact with another less-objectionable artifact. But if we focus on eliminating every artifact that we can measure, we can quickly converge on a solution that approaches sonic transparency. If we can measure an artifact, we don't try to determine if it’s low enough to be inaudible, we simply try to eliminate it."
[Paul Seydor] "Can you provide an example from your own work as to how listening revealed something the tests did not and how you went about discovering (with tests) what it was and how you fixed it?"
[John Siau] "One of the most elusive artifacts is caused by inter-sample peaks that exceed 0dBFS. These peaks ..."
Read the entire interview at The Absolute Sound.
At Benchmark, listening is the final exam that determines if a design passes from engineering to production. When all of the measurements show that a product is working flawlessly, we spend time listening for issues that may not have shown up on the test station. If we hear something, we go back and figure out how to measure what we heard. We then add this test to our arsenal of measurements.
Benchmark's listening room is equipped with a variety of signal sources, amplifiers and loudspeakers, including the selection of nearfield monitors shown in the photo. It is also equipped with ABX switch boxes that can be used to switch sources while the music is playing.
Benchmark's lab is equipped with Audio Precision test stations that include the top-of-the-line APx555 and the older AP2722 and AP2522. We don't just use these test stations for R&D - every product must pass a full set of tests on one of our Audio Precision test stations before it ships from our factory in Syracuse, NY.
Myth - "Damping Factor Isn't Much of a Factor"
Myth - "A Damping Factor of 10 is High Enough"
Myth - "All Amplifiers Have a High-Enough Damping Factor"
These myths seem to trace back to a well-know paper written by Dick Pierce. His analysis shows that a damping factor of 10 is virtually indistinguishable from a damping factor of 10,000 when it comes to damping the motion of a loudspeaker cone. This analysis has been examined and repeated in many more recent articles, such as a well-written post on Audiofrog.com by Andy Wehmeyer. Articles such as these are often cited as evidence that amplifier damping factor doesn't matter. The mathematical analyses are correct, but the conclusions are incomplete and misleading!