There are formats/protocols (eg. Scala, Midi Tuning Standard…) used for import by many synths (eg. Sequential, Hydrasynth…) but personally, I find that a huge hassle, and much prefer to tune on the instrument directly (I’m basically with Richard D. James on this: “Scala is only good for non-intuitive tuning creation, purely mathematical. I love this approach, but really prefer making tunings intuitively, note-by-note.“). It’s possible to implement both import[/export] and on-device creation together though, as Korg did on the ‘logues, and Novation on the Summit/Peak, both under the consultation of Richard D. James. Those have the best, most complete implementation of user scales/tuning that I’m aware of on hardware synths (actually DX7ii is pretty good for my purposes too, but only has two user tuning slots internally, which isn’t as many as I’d like).
A simpler implementation, which is still a huge help, is found on the Dirtywave M8 (with 16 user scale slots I believe). This is only for up-to-12-note, octave-repeating scales. A lot of synths, like some Rolands and older Korgs (see microtonal-synthesis.com for a list that goes up to the early 2000s I think) have something similar (with only a single user slot), but usually are limited to only adjusting fine tuning of each of the “normal” 12 pitch classes, within a narrow range (usually 50-63 cents) which is a quite annoying limitation, since it prevents more unequal tunings (for example, if one wanted to have a few “enharmonic” versions of the “same” note, very close together). The M8 fortunately has both a coarse tuning (adjust by semitones, from -24 to +24) and fine tuning (adjust by cents, allowing 100 gradations between each semitone) parameter for each scale degree, which is sort of like the Korg and Novation implementations, although, again, the M8 is limited to 12-note octave-repeating sets, whereas the Korg and Novation give this freedom across the entire MIDI note range (and very importantly, the coarse retuning is not even confined to any range like the M8’s +/-24; each MIDI note number can be individually assigned to any pitch across the synth’s entire range.)
The M8-style implementation (12notes) goes a long way toward including most non-Western traditions like Maqam (as far as I know. I seem to recall Khyam Allami making this point somewhere, maybe in a Clubhouse discussion although I don’t recall for sure; of course, there are aspects of say, Raga, that really aren’t accounted for at all in the Western concept of scale–that is, the nature of the movement between steps and microtonal embellishments of a “single” scale degree–still, let’s take this one step at a time.), although the full-128 note retuning is generally necessary for more intensely experimental or densely harmonic approaches à la Harry Partch, Ben Johnston string quartets, Sevish, Wendy Carlos’ Beauty in the Beast, La Monte Young drone structures (to be fair, LMY’s style also requires much more fine tuning precision than 1-cent, so for instance, the Dream House sound environment uses a custom synthesizer and/or software), etc.
Also, besides setting up the scale itself, it’s nice to have both a coarse and fine tuning adjustment for the root/key as an independent parameter (so the whole scale can be transposed freely. Note that the vast majority of scales/tunings that have ever been used, even in the West, do not have equal step sizes like 12ed2 chromatic, so you cannot simply use the same set of pitches for an isomorphic scale in different key). M8 has only coarse (semitone) adjustment of this (although you can use a sequencer workaround for fine adjustment I believe), and I believe the Korg and Novation implementations have both coarse and fine root/key adjustment, although I haven’t looked at those for a while. I don’t need this feature often myself, but it’s quite essential for completeness’ sake.
Whew. I hope this is fairly comprehensible. These are audible truths to me; not so fun to write about as to hear.
