From the poster:

In this work, we propose a light-weight (~20M param.) causal voice conversion solution that can run in real-time with low latency on a commercially available mobile device. The key design elements are: (1) using a causal encoder to learn soft speech units; (2) injecting whitened f0 to improve pitch stability without leaking source speaker info.

In our later V2 version, we found that f0 rescaling followed by a NSF-style harmonic-plus-noise conditioning (as is done in RVC) results in better quality.