With the advent of the *logue synthesizers (e.g. the Prologue and the Minilogue XD) Korg introduced a phantastic new feature – the possibility to program custom oscillators and effects for the machines. To accomplish that, Korg published the logue-sdk via Github.
The keybeds of the synths do not provide aftertouch. However, since a recent OS update (AFAIR that was Firmware 2.0 as released November 9, 2019), aftertouch received by external keybeds can be used to control a whole bunch of parameters, including the filter’s cutoff frequency.
While I really like those synths, I’m not content yet with the velocity support. Velocity can only control the two most essential parameters, the envelope amounts of the two envelope generators. The first one always controls the amplifier (e.g., velocity controls the volume of the sound). The second one is limited (as it only consists of an attack and decay phase instead of a standard ADSR envelope), but can not only control the filter cutoff, but also two pitch destinations. However, when using the latter two, there’s absolutely no possibility to still control the filter’s cutoff by velocity.
Further, the velocity value also cannot be used as a parameter in custom oscillators. This really is a pity, since velocity is essential e.g. for FM synthesis. I really wonder why so many parameters can be mapped to aftertouch (which the synths cannot produce by themselves), while the much more common and important velocity was omitted. At least for the MInilogue XD one could argue, that the target audience, due to its mini keys, are not performing keyboarders (though the famous Yamaha Reface DX impressivly shows how responsive a mini keybed can be). But the Prologues are designed as performance instruments while suffering from the very same omission.
I really wish it will appear via a future update, but I fear it was left out intentionally and with reason.