i'm not used to having my DSP or EE expertise questioned like this. i don't even have the problem at the math SE or the physics SE.
This is covered in the Privileges section of the Help Center; it's 2,000 reputation.
Edit questions and answers
Privilege type: Moderation privilege
Awarded at: 2,000 reputation
What is edit questions and answers?
We believe in the power of community editing. That means once you've generated enough reputation, we trust you to edit anything in the system without it going through peer review. Not just your posts—anyone's posts!
Note that anything is not entirely true; you can't edit tag wikis and excerpts unsupervised, you need 20,000 reputation for that.