From my experience with lots of currently sold IEMs - most of them having elevated upper mids to bring more emotional and engaging sound. Some have more evident effect and some are not. It seems that I am not very sensitive cause I don't want to change anything in the sound of U1. But I would for some other IEMs... I've tried to take a graph but my mic is having more influence than it should - most of the IEMs show the same graph with it. So, I have to think of buying some special microphone with specified FR to subtract it from the IEMs grap.