Human physiology throws up a number of examples where differences are not always consciously realizable.

For example, most of us are unaware of the rate of our heart-beats, except under exceptional circumstances - such as after running for a bus. On the other hand, a trained Yogi is far more aware of minor variations.

I wonder whether listening can affect us sub-consciously. In other words, whether changes take place below our threshold of awareness which can nonetheless influence how we feel about the sound of a system over the longer term.

Just a thought.