Microphone Processor

To stabilize the voice of the speaker on a constant level, a Microphone Processor is necessary.

This is an audio compressor than can decrease the volume of the voice when it is too loud, or amplify it when it is too low.
Doing so produces a sound that captures all the details of the voice but levels out volume changes.
Too high a volume level could distort the signal; or, if too low, it could make speech incomprehensible.

DBX 286s
Microphone Pre-Amp Processor DBX Harman

A microphone processor helps smooth the audio, minimizes background noise and cleans the signal.
It helps with the mixer control, since it is not necessary to continuously adjust the level of the microphone.
It also helps to get "Radio Sound", so that it always sounds at the right level and the speaker can concentrate on performance – rather than worry about being too close or too far from the microphone, or even speaking in too loud or too soft a voice.

Moreover, it gives more presence to the voice and allows to set it at higher level – because you are sure it will contain the peaks. Adding to it, it removes hissing noises such as those produced with words that contain an "s".

DBX 286 Microphone Preamp or Behringer Ultragain Pro MIC2200 are some of the most popular ones.