I've read how the effects are technically different (i.e., in terms of how they are produced) but I don't have enough experience to identify which is which when I hear them. Can anyone tell which effect is being used on the Queen song Drowse. Whatever it is, the effect itself is quite obvious right from the beginning and used to great effect (no pun intended) in contributing to the subject matter and emotional atmosphere of the song. Lyrics such as "waves of alternatives wash at my sleepiness" could almost be a description of the effect itself.

Thanks