How to add growl/scream effect in Audacity

[Trebor]

… want to make some of the higher vocals sound like scream …

Like microphone overload distortion when you scream into it ?.

How to make your voice like this? (Presumably helmet-radio)

Yes, different hiss & crackle in each channel would be ideal: then it could be used to emulate lo-fi stereo speakers, (e.g. boombox). Helmet Radio 1-5.NY (2.15 KB)