I wouldn't myself use 'fréquence', since we are in fact talking about another characteristic of the sound, i.e. its amplitude or level, rather than its frequency; that would rather tend to suggest that the radio link was making people's voices all squeaky!

However, the EN expression is technically inaccurate: although the level can be high, it cannot be distorted; it would have been more accurate to say "if your voice is received at a particularly high level or is distorted"

I'd be inclined to get away altogether from 'level', but you'll need to find a way to work in the 'voice' if you want to use something along the lines of my suggestion. Or you could just say 'if your voice is received too loud or distorted'

Note that the kind of distortion they're talking about here is that due to overload (overmodulation of the radio TX level) — the audible effect of this will be saturation (in both EN and FR); this can be a desirable effect for rock musicians, but would be unwelcome in a communications context!