These videos were taken with an oscilloscope, real time and have not been manipulated. You can extract your own conclusions.
We used to test an Neutral X-DREi PRO switching between BYPASS and DREI ON
Modulation & Overdrive
You can see the square waves are modified without affecting the sine.
Triangle & Square waves
You can watch as triangular and square waves are rounded to be more like sine waves and avoid problems with sound reproduction.
All videos together.
Bigger definition of lines,