Thank you magiblot and StainlessS
@StainlessS... yes, it's Histogram(mode="StereoOverlay"). The idea is to pick both Left and Right channel when stereo and pick just Front Left and Front Right when is Dolby.
It might not be as complex and detailed as the official waveform provided by Tektronix, but it kinda reminds its layout and it uses the internal filters already available in Avisynth, so I thought it was kinda cool to have a similar layout. ^_^
Thank you both, once again, this is exactly what I wanted. ^_^