On Distortion Measurement
Extremely low level distortion measurement. In the past, IC designer developed opamps and related parts that had such low distortion that it couldn't be measured even with state of the art equipment. Engineers had to invent new ways to characterize these parts. Michael Steffes has been involved in such adventures and has written it all up in 2019 for AudioXpress. His January 2020 column has a reference to work done by his collegue Xavier Ramus. That referenced article gives a very good insight into the challenges and solutions of very low distortion measurements. The original has been lost but Michael has resurrected it, and it can be downloaded here.