What does harsh or uncomfortable treble mean or sound like?
For me personally, it can range from needing a break from listening to giving me a headache. Commonly, people will use terms such as too forward or bright.
Ever hear a cymbal clash near your ears and that extremely loud hissing sound just rubs your ears the wrong way? That sound yeah lol. In the case of a sharp treble anytime you hear the SSS sound it will be very sharp sibilant and can be uncomfortable and painful to the hearing though not everyone finds it uncomfortable. However, I tend to prefer a sharp treble for vocals especially female vocals due to just how good it makes them sound. Bright headphones are not technically for everyone but are still a good addition, though not all bright headphones are sibilant