We can certainly compare the input to the output and measure the differences, and from those differences make objective comparisons.
Many people actually prefer an amp that adds certain distortions to the output. Some don’t. Subjective preferences don’t have to, and often fail to, align with the actual objective performance.
@kuribo But you can’t tell how an amp really sounds just by looking at measurements either. You can have two amps that measure similarly but sound completely different. Why? Because we don’t have near enough the measurements that can measure everything that has an impact on sound. Case in point, you can buy an amp and upgrade capacitors, resistors, etc. and the measurements won’t show any difference but the sound can change significantly. Measurements are useful as a piece of assessing performance but are FAR from being able to sufficiently describe the complete sound of a component.
What are objective measurements missing, other than subjectivity?
Wait…ASR is calling — they need you back there ASAP! Go!!!