They are smooth
This is my subjective opinion, I dislike smooth signatures.
My objective opinion is that many will love LCD-4 and it sounds really good, has a fast signature, great details, textures and transients. Tone is natural and it is one of the best headphones made.
Please understand that my subjective impression cannot be changed regardless of how good it is, I need bright sound.
My listening levels begin from "I can't hear you, Grandma" to "Stop that plane, it is killing me ears!"
Anything from normal to un human loud.
LCD4, while really good, lacked some treble spark that I desperately need. This is why I won ie800 and why I like HD800S. Kinda my type of signature.
Tested LCD4 from everything starting at ifi iDSD and ending at Wa22. A lot of in between.