The MIDI Merge 4, merges the data from up to four separate MIDI sources like master keyboards or controllers, into a single MIDI data stream which appears at both of the MIDI out sockets. Merges all MIDI data including MIDI Clock, MIDI time code and SysEx.
I'm using this to merge 3 controllers to a multi-voice synth. Inputs: The master sends the clock, the second device is a keyboard and the 3rd device is drum pads. There is room for 1 more input. Outputs: Synth and to my PC midi interface. It was a bit expensive for something I imagine is quite simple, but it was not more expensive than alternatives. But, now I have it and it worked exactly as I need it to with no fuss I am very happy with it.
The build quality of this product leaves a little to be desired, especially at this price, but it does what it says it does and is very easy to use. My only complaint is that it came with a 2 pin European plug! WHY? I live in the UK and have had to use an adaptor.