How did you determine that the effects you perceived were due to the equipment, and not to neural accomodation on your part?
He mentioned 'letting the smoke out'...
burning in... and it doesn't work afterwards.
I thought the phrase was 'letting the magic smoke out'.
To be honest.. I have encountered a few times that when you switch off a DUT, that lets out the magic smoke, quick enough you can repeat that action a few times.
Definitely for me "burn in" helped me have sound for my Onkyo AVR.
reflow did
The problem for such advice is this: if a blind test is taking long enough, the device would have burn in (if indeed there is such thing as burn in and how ever brief it is) and I would have failed the blind test.
I can tell you this. For a day job I design, build and service railway sensor technology (based on fibre optic sensors).
Of course all of these devices (in the thousands) are all thoroughly tested and once every few years have to be inspected (re-measured) to see if all still works perfectly. If burn-in for analog circuits and ADC's existed I am sure I would have found any evidence.
Have been in audio for over 40 years and 30 years in service/repair. Have been tinkering with and measuring headphones for years and years. Also tested prototypes (sometimes 3 of them) and have attempted to 'prove' burn in. This is very difficult to do as one needs to fix the headphone to the test fixture for days and not move it 1mm. Then you have to test immediately, 'burn-in', test again and repeat with time intervals. You also need to make sure the temperature does not change.
I am convinced some of the burn-in comes from temperature differences, time of day when testing and long term 'burn-in' is more likely to come from pads softening up and people getting used to the sound than actual properties of the headphone changing.
Rtings, Tyll and I have done some test and did not find any 'worthwhile' changes that would warrant thinking that the sound 'changed' noticeably.