Could you elaborate a bit about your "flat sound wave" comment?
Normal sound waves aren't always curved. There are many, many basic forms of a sound wave. Sine (what you probably know as curvy), Sawtooth, Square, and triangle. Mixing these basic waves together creates the complex wave that normally makes up any given sound. That's basically how synthesizers make sound (in a very basic manner of speaking).
Now, to say that the wave is FLAT... you're either saying it's a square wave (which would be an inaccurate description), or.... silence.
Please elaborate.