different voltages and "more headroom"
 

Hi, this may be a bit of a dumb question, but I hear about using differing voltages for "more headroom," but I'm not sure what that means practically. Since this is specifically in the context of overdrive/distortion pedals, I'll ask simply---for two identical pedals at the same drive/gain settings, one at 9V and one at 12V or 18V (if this is allowed by the pedal), which pedal has more drive/gain?

Results may vary by pedal, but in my limited experience the lower voltage one will distort more easily and more often, like a lower wattage amp. Like a higher watt amp, the one with more volts will stay somewhat cleaner, and have more dynamics, arguably sounding "bigger."

I'm guessing this is referring to higher voltages meaning the clipping can happen further from the noise floor, meaning less noise at higher gains.

+1

It will be different from one pedal to the next, but generally lower voltage means earlier (more) distortion.