Splitter duplicates MIDI information from 1 up to 4 channels. Each “voice” is transposable and can be set to span an arbitrary range of notes on the keyboard.

Splitter can be used alone, to drive virtual instruments live, or together with a DAW where its output channels can be recorded on separate tracks.


Splitter is built both as native “Apple silicon” and Intel code. Requires MacOS 10.12 or higher.

Splitter app

IAC Driver

Inter-Application Communication Driver allows MIDI applications to communicate through MacOS. It is not enabled by default. Before using the application, make sure that the IAC Driver is active on your Mac. Open Audio MIDI Setup (in the /Applications/Utilities/ folder), display the MIDI studio window and double-click the IAC Driver icon. Enable it by checking the “Device is online” box.


The following drawing should clarify the workflow:


Notes entry

Splitter accepts notes from all MIDI inputs, on the selected channel.


Most MIDI messages are forwarded through Splitter:

Other messages (Fx) are ignored.

The notes are filtered by taking into account the Splitter settings. If an incoming note is not within the range defined for a voice, it will not be forwarded to the voice's output channel. This allows you to define zones on the keyboard driving different instruments, or on the contrary, with overlapping zones, create layered instruments. You can also send the same channel several times with different transpositions.

Only notes are affected by this filtering. Other MIDI messages are transmitted as soon as a voice is active, on its selected output channel.

MIDI output, recording

In the DAW, create an instrument track (or MIDI track). Use IAC Driver for its MIDI input, selecting the same channel as in Splitter for the desired voice's output.

A typical use of Splitter: create several instances of a virtual instrument with distinct ranges on the keyboard, for example to play basses, cellos, violas and violins distributed on the keyboard with appropriate split points. Each instance will be played and recorded to its own track, but via Splitter it becomes possible to record them all at once in the most natural way.


Using IAC inevitably introduces some latency. Fortunately it is easy to compensate:

Glenn's Corner

This octave selection for middle-C has no effect on the MIDI actions. It merely changes the octave displayed in the buttons, not the actual MIDI note.

See this web page for more info: liveabout.com/illustrated-guide-to-middle-c


1.1: better handling of MIDI input buffer.