Right now, there’s no way to use the spectrum pane while designing an instrument within a single window – the scopes/spectrum pane buttons disappear when you switch over to an instrument editor tab.
I propose keeping those buttons visible. If space concerns are the reason that the scopes/spectrum pane is disabled whilst on an instrument editor tab, then you could reduce the minimum scope/spectrum pane size AND/OR convert the instrument editor accordion into a set of tabs.
I see there could be a design issue here – the ‘pop out’ button replaces the scopes/spectrum pane buttons whilst on an instrument editor tab. I propose moving ‘pop out’ to over near the tabs themselves.
I’ve seen this feature request pop up in a few threads, one of which asked what the use case was. The use case which is immediately obvious to me is checking the spectrum as I’m building an instrument e.g. during Sample FX chain editing. It’s a very useful learning tool, helping users discover phenomena such as aliasing artefacts, additional harmonics created by distortion etc…