There have been a few attempts at finding new measurements that better reflect what people hear. For example "transient intermodulation distortion" (TIM) or "slew-induced distortion" (SID) have been put out there to measure distortion caused by an amplifier's inability to respond quickly enough to abrupt changes in the signal level. This is a particularly interesting measurement because, in an attempt to reduce more conventional measurements of distortion, such as harmonic distortion, amp manufacturers may employ a lot of feed back. Feedback adversely affects TIM/SID measurement. I tend to not like amps that employ a lot of feedback so, perhaps, this less common measurement might have some meaning.