David Higdon said:
What's a good setting for voice so the controller doesn't sound like a Charlie Brown cartoon?
Peter has answered all questions correctly and in detail, I just thought to add a little bit to the answer on this question.
First, in your FSFDT control panel (part of FSINN), browse to the Vatsim settings and
uncheck the "realistic distortion" option. The voice protocols and codecs used by Vatsim and the pilot clients are bad enough and there's certainly no need to add extra distortion on top of that
Second, regarding the radiocheck: it's always a good practice to request a radiocheck from the controller at the beginning of your session, especially if it's not a busy frequency, the typical response will contain two digits, i.e. "... I read you 5 by 5". These are 2 separate scales ranging from 1 to 5. The first scale evaluates sound clarity, the second one evaluates sound strength. Hence "5 by 5" means "loud and clear". "5 by 4" would mean "not very loud, but clear", "4 by 5" would mean "loud but not very clear", etc etc. Occasionally, when the reception is both loud and clear, to save time, the controller will just answer "readability 5", which implies 5 on both scales.
I've found out that not many pilots are aware of this two-scale subtlety so there you have it