Fiio R7 Manual page 29

Lowpass filter mode
There are three different filters on the R7, you can choose them according to
your listening preferences.
Filters are some effects that come with the original DAC chips, and the
adjustment is subtle for the sound. The following is the hearing description of
some filters, for reference only:
fast roll off: the sound is full and mellow, the vocals are in the behind, rich and
full, with strong reverberation, suitable for pop music;
slow roll off: the sound is clean, the vocals are in the front, clear and original,
suitable for classical music;