Estension of the first post about validity of measurements

To expand on my previous post, I want to address the absolute elephant in the room when it comes to audio measurements: Total Harmonic Distortion (THD). It is the very first number everyone looks at in product catalogues and user manuals, yet it is arguably the biggest marketing trap in the entire industry. [1]

Psychoacoustic science has proven time and again that the human ear cannot detect THD below a threshold of 0.05% to 0.1% when listening to actual music. Pushing distortion lower than 0.05% offers absolutely zero audible benefit to the listener. It is completely invisible to our ears. Yet, we see these modern "bench gurus" losing their minds over amplifiers that boast absurdly low distortion figures like 0.0001% THD, using those numbers to judge high-end sound quality. [1, 2]

How do manufacturers achieve these textbook-perfect catalogue numbers? They do it by cranking up Negative Feedback (NFB) to massive, aggressive levels. And here lies the bitter irony of modern audio engineering: to eliminate a microscopic harmonic distortion that is already completely inaudible to human ears, they introduce a massive micro-delay in the circuit loop.

The moment you play real, chaotic music instead of a static 1 kHz laboratory tone, this loop delay triggers Transient Intermodulation Distortion (TIM). So, in the desperate pursuit of a meaningless number on a graph to make newbies drool, they create a devastating form of intermodulation distortion that is highly audible. The result? The amplifier's excessive negative feedback chokes the circuit. The dynamic range is drastically flattened, and the music sounds compressed, sterile, and stripped of life. [1, 2]

Legendary high-end brands are perfectly content with an "honest" THD of 0.05% or 0.08% because they let the circuit breathe with minimal feedback. On an oscilloscope, a cheap mass-market chip amp might look "cleaner" in a manual, but inside a real car cabin, the low-feedback audiophile amplifier will completely crush it in dynamics, speed, and raw musical emotion. Stop buying audio gear with your eyes.