Certain parameters for the DSP ( Digital Signal Processing ) effects ( see Settings > Playback > DSP Effect )
are stored in so-called "profiles", see Settings > Profile
and can by activated, duplicated and edited there.
The two profiles shown above are the ones initially provided. The "Default" profile is activated per default. Changes to the DSP effects are automatically persisted in the profile currently active.
As to "Bit-perfect": that's a marketing buzzword and means an audio processing that doesn't change the signal between decoding and DAC, so this profile just switches all DSP effects off. Of course the bit-perfect-profile is only ever suitable for bit-perfect-processing as long as you don't change it . And bit-perfect-processing requires not only no DSP, but also no resampling, so just in case that you're aspiring to process your music bit-perfect make sure the sampling rate is supported. And using bluetooth of course isn't bit-perfect at all. Btw all this only ever makes sense if you can afford sound transducers that don't require DSP, which normally isn't the case. So best just forget about it .