Sorry, but you're incorrect.
This depends entirely on the state and country that you live in, and it will always be best to consult a lawyer who is familiar with your localities laws and your situation in specific.
Some states are known as "single-party consent" states where only one of the participants in the conversation has to know that a recording is taking place.
Other states are what are known as "all-party consent" states, where everyone taking place in the conversation must consent to being recorded, otherwise the recording is illegal.
Both of these normally only apply for conversations that would have an expectation of privacy. (Phone calls, conversations in private spaces, etc.) Conversations which occur in public are subjected to more scrutiny, but still may fall under the wiretap/interception of communication laws of various states. For instance, it's often not allowed for surveillance cameras to record audio, because no parties in the conversation are aware that they're being recorded. Auditoriums frequently have "Audio recording in progress" signs placed in obvious locations when a performer may be recording.
