I know you gonna laugh at me but the thing is that months ago when I started learning C♭B, previous REAPER trial period, I actually managed to have 2 tracks, and their own freq. spectrums, analyzed in real time in a single Span window. Span was running in a exclusive BUS, just beside the MASTER BUS... I'm not gonna rely on my memory but that was sort of a SEND and/or PLUGIN PROPERTY setting, can't recall, anyway... Tomorrow is my day off and I gonna try to accomplish it again.