Recently, I got a Clip Zip and have rockboxed it with the latest official release, and am facing an issue with my Etymotic HF3s.
With all sound settings turned off, including replaygain, EQ and crossfeed:
There is a distinctly audible treble roll-off with the Etymotics on the Zip when compared to my laptop's and my phone's audio output -this applies to all music, white and pink noise.
However, the same effect is not observed with my KSC75, Sony MH1C, Shure SE215 and Ultimate Ears 200 - when compared across my audio sources.
This never happened with my older and now dead Clip+. What do you think is going on here ?