From the Nura app homepage you can swap between “Neutral” and “Personalized” while listening to music:
Personalized: Your Nuraphone's frequency response is adjusted to the way you hear.
Neutral: The natural frequency response of your Nuraphone's drivers without any adjustments.
Neutral is not intentionally designed to sound worse than personalized mode.
Most headphones tune the frequency of their drivers to achieve their desired sound signature, whereas your Nuraphone requires a particular frequency response to allow us to tune to how you hear. We call this ‘Neutral’ mode, and what you hear is the natural frequency response of the drivers. The natural frequency response of the drivers is not designed to be used as a "Flat" EQ.
To experience the full effect of personalized sound, we recommend listening to other user’s unique hearing profiles.