Let me add some answers to the original question now:
1. The important thing about training is to start from bottom up. That means whatever distortion you are seeking, you need to hear it in excess and with absolute clarity. Do not start to learn compression artifacts by encoding into AAC at 320 Kbps. Even I can fail such tests. Instead encode something into MP3 at 64 kbps. Do a bunch of comparisons with the original to make sure you can identify what is different.
If you want to hear difference in speaker cable, get a 100 foot spool of cheap speaker cable and test that against your short better one. If that is not enough go to 500 or even 1000 foot. Until you have achieved this step, you cannot proceed to other ones.
In formal listening tests this is called a "control" by the way.
2. After #1, go up one step at a time and see if you can continue to hear the artifacts. If you cannot and the artifacts are reliably there (e.g. in lossy compression) then go back to the beginning again. Cycle back and forth until you can climb the ladder reliably.
3. As I explained to Greg, you must guarantee that the only thing you are using to evaluate these impairments by ear and ear alone. You cannot allow any other senses to intervene or you are fooling yourself to put it bluntly. If you don't believe in this then don't bother going this path.
4. When you go through #1 try a lot of different stimulus (i.e. music). Some are more revealing than others. For speaker and room for example, research shows that content that is full spectrum brings lower threshold of detection. Reason is simple: if there is a frequency response anomaly -- which there always is in this situation -- the content needs to "hit it" or you won't hear the impairment. See this article I wrote for a deeper dive on perceptual aspects of hearing small differences:
http://www.audiosciencereview.com/forum/index.php?threads/audibility-of-small-distortions.67/
And for selection of tracks that are more revealing based on research see this thread:
http://www.audiosciencereview.com/f...sic-tracks-for-speaker-and-room-eq-testing.6/. If you are looking for music that "moves you," you are in the wrong thread. Again, that is not the task at hand. The task at hand is to hone your hearing. You want to enjoy your music, leave this thread and go do that.
5. Knowledge of the domain can be super useful. It will let you triangulate what you are hearing versus what is supposed to be happening. I think it was Rob who said DIY speaker building helped him hearing artifacts there. As with blind testing, if you are against engineering and science of audio, please don't bother going down this path. The foundation of training listeners is based on what we want to test for. If you don't believe in that, then the value is very limited here. In the Ethan ADC/DAC loop I used this knowledge to zoom into critical segments that were revealing.
6. Domain specific training gets rid of a lot of homework here. Seek those out. They don't always exist and many are proprietary but some are not. For compression artifacts for example search for "MPEG codec killers."
I think that is it for now.
I will probably write a longer article on this one day.