So if a song says that the range is from C4 to D5, does that mean it goes from middle C (like one ledger line below the staff in treble clef) to D on the staff, like a bit more than one octave higher? where do the numbers come from/what do they refer to? sorry, I'm not positive if I've even got middle C defined correctly. Yes, you're absolutely correct. C4 = "Middle C", and D5 = the D an octave above middle C. The usage of numbers to indicate octaves is part of Scientific Pitch Notation.
http://en.wikipedia.org/wiki/Scientific_... | 