That's probably not even close to true. Without wading into the morass of what an "idea" is, a boilerplate employee agreement might list things like:
technical information, methods, processes, formulae, compositions, systems, techniques, inventions, machines, computer programs, research, business information, customer lists, pricing data, sources of supply, financial data, and marketing, production, or merchandising systems or plans
If your employer is working with a concept or idea and can tangibly tie it to anything like these (or any of a similar list of "artifacts") that employees had access to, then it's very dangerous for employees to start their own firms based on those concepts or ideas.
(I have no idea what's going on with Smule/Shred! Shred sounds very credible right now.)
technical information, methods, processes, formulae, compositions, systems, techniques, inventions, machines, computer programs, research, business information, customer lists, pricing data, sources of supply, financial data, and marketing, production, or merchandising systems or plans
If your employer is working with a concept or idea and can tangibly tie it to anything like these (or any of a similar list of "artifacts") that employees had access to, then it's very dangerous for employees to start their own firms based on those concepts or ideas.
(I have no idea what's going on with Smule/Shred! Shred sounds very credible right now.)