Unify's built-in MIDI Filter effect does what its name implies: filters incoming MIDI events, in order to:
The Channel and Range section allows you to select only events on a specific MIDI channel, and/or note-events in a specific range. The controls in this section work the same as their counterparts on each MIDI and INST layer in the layer-stack view.
The Modify section contains two more controls which also have direct counterparts on each MIDI and INST layer in the layer-stack view.
There are four options for Sustain Pedal (CC#64) events:
The first two options are self-explanatory, but Emulate and Em + Latch require a bit of explanation.
Emulate mode is useful for plug-ins which either ignore MIDI CC#64 events entirely, or don't handle them properly. (Unfortunately, there are quite a few plug-ins like this, including the BlueARP arpeggiator, and literally hundreds of free VSTi's) In Emulate mode, MIDI note-off events are suppressed while the Sustain pedal is down, and sent all at once when the pedal is released. Hence notes are held (sustained) while the pedal is down, just as you would expect if the downstream plug-in was interpreting CC#64 itself.
Em + Latch (emulate with latch) mode is basically the same as Emulate mode, except that you don't have to hold the sustain pedal down. Instead, you press and release the pedal once to activate sustain (the letters “SUS” will appear in green text next to the menu), and a second time to de-activate it.
The Suppress (filter OUT) section is mainly about removing selected events from the MIDI data stream, but the Multiple Note-On Events checkbox is an exception; it actually inserts events when required.
Most MIDI keyboards will transmit a MIDI note-on event when a key is pressed down, and a corresponding note-off event when the key is released. A few keyboards (in particular Casio's Privia digital pianos) do not send note-off events during legato runs, and this can confuse some software instrument plug-ins (in particular KORG's TRITON).
Checking the Multiple Note-On events box will cause MIDI Filter detect when note-off events are missing, and re-insert them into the output stream (immediately before the next note-on).
When working with multiple instrument layers, you may occasionally want to ensure that only some layers respond to Pitch Bend or Channel Pressure (aka aftertouch events).
To filter out mod-wheel events, see below under CC filtering.
A few MIDI controllers transmit MIDI System Common, System Exclusive (aka SysEx), and Real-Time messages, and there are rare cases of plug-ins which may get confused by these.
An earlier version of MIDI Filter featured a checkbox to filter out Mod Wheel (CC#1) events. This has been expanded to a set of six buttons as follows: