Blind tests demonstrate that differences may be too subtle to notice easily. They don't prove there are no differences but they do show that the differences are very subtle and at a level where it may not matter to some listeners. That serves a purpose. It also shows who is a better critical listener. Just like wine tasting. Some are a lot better than others. I can guess a French red wine region from blind tasting. I am hopeless with white wine. I guess my interest is red wine so that is hardly surprising.
I agree that more than 30 secs may be necessary as I believe that a variety of tracks may actually be needed to eventually highlight a difference between components. It takes time to home in on a difference but once you find it and know what to listen for then you can find it.
To the contrary, sighted tests run the risk of being influenced by expectations. Sighted tests are of limited value when performance is very close as it is hard to remove the bias about the equipment. The old adage "looks can be deceiving" applies.
I agree that more than 30 secs may be necessary as I believe that a variety of tracks may actually be needed to eventually highlight a difference between components. It takes time to home in on a difference but once you find it and know what to listen for then you can find it.
To the contrary, sighted tests run the risk of being influenced by expectations. Sighted tests are of limited value when performance is very close as it is hard to remove the bias about the equipment. The old adage "looks can be deceiving" applies.