yeah, sorry the terminology can be a bit tricky, as there are multiple regions of memory on the axoloti board.
SRAM, SRAM2, CCMSRAM - are all onboard and are pretty limited in size.
without going into to too many (boring) complications, these are used by things like the firmware local variables, static variables (by default)
SDRAM - is an 'extra' (yes unrelated to SDCard) , and we have a 'fair amount' of, in comparison to the onboard, hence why we recommend using it.
most of this only matters for things like tables, and delay lines which can get quite large,
so the general advice is to use SDRAM for these, and thus keep the onboard memory available for stack variables/firmware etc.
(of course if you allocate lots of large tables/delay lines as reverbs could, then you will run into a wall at some point!)
I think we should really probably move things like delay lines in the factory objects to SDRAM.
the reason this hasn't been done was to maintain compatibility with the discovery boards,
I don't think really this is a good reason now...
@johannes what do you think, change things like stomp/reverb to use sdram?