There is no definitive model on human perception of sound. The more recent ones try to develop a mathematical model based on the ears own self-generated harmonics at various SPLs, coupled with the well known phenomenon of masking. A couple of recent models were developed coming at the problem from different directions. I have no idea if they come up with the same result, however, both clearly acknowledge that THD and IMD as monolithic numbers are utterly useless in making predictions about what listeners think of as a more natural sound.Although Riviera and Lamm both use the research about human perception of sound, they do sound quite different to me. I have Riviera APL 01se which I have tried with Lamm M1.2 (owned for a year) and Riviera AFM100se (used for few weeks). In my system Lamm sounded quite forward, midrange based, with a bit of artificial energy. On the other hand Riviera sounds to me very balanced, natural, organic, musical. From what I have heard at shows, I guess closer to Wadax. Riviera and Lamm obviously must have used different research
It is no surprise then to see amps designed with some kind of hearing model (the assumption being each company derived their own model) having significantly higher THD than electronics designed by distortion optimization. If the companies models differ in some significant way, the resulting sound is also likely to be significantly different.
