[Gordonjcp]

Exactly, and if you synthesize a signal in discrete time you must take care to bandlimit it by calculating what it would be if you'd already brickwall filtered it.

You can't create a naive sawtooth (for example) and *then* filter it because the damage has already been done. That being said, the "supersaw" oscillator in the Roland JP8000 generated a bunch of naive saws and *highpass* filtered them just below their fundamental to remove the gurgly "beat note" from aliased partials.