The « denoiser » is an effect that helps detect, to then remove, background parasite noises.
Denoisers require a very high processing power so to pull the parasite noise out of the clean signal. This is why live denoisers are pretty rare. Most of the time, they are used in post-production to clean up the records.
Unfortunately, even if it corresponds to a disturbance, deleting part of the signal is rarely imperceptible for the remaining signal. Therefore, it is necessary to be quite careful and patient with the use of denoisers, in order to make the best of it.
When performing with your electric violin, other effects can be used to reduce, or remove parasite noises, such as the gate.
References: Denoiser from Sourceforge – audio-maniac.com, Techivation