We know that all MIDI Interfaces are not created equally. Most common interfaces will have a MIDI IN and a MIDI OUT port. If all you will ever use is one MIDI instrument, then that will probably work quite nicely for you. But, if you are a gadget freak like me, then you will wind up owning several MIDI devices and will want to hook them all together and have an all night recording session. If you want to control more than one instrument using a single device (like a sequencer or master keyboard controller), then you will need a way to pass outgoing information to every MIDI device in your setup. This is where the MIDI THRU port comes in.

The MIDI THRU port takes all information that comes into the MIDI Interface by way of the MIDI IN port and passes it on to the next device. In essence, it makes a copy and anything that comes in and sends it back out. For example: let’s say that you are using a PC-based MIDI sequencing program and that you have two external MIDI devices, a keyboard and a drum machine. If all you do is hook up the keyboard using the MIDI IN/OUT scenario, then you will not be able to pass information to the drum machine when you are recording or playing back your sequence. Most decent external MIDI devices will have a MIDI THRU port. If you take a MIDI cable and plug it into the keyboard’s MIDI THRU port and take the other end and plug it into the drum machine’s MIDI IN port, then all of the MIDI data that the keyboard receives will be duplicated and passed along to the drum machine. Cool, huh? Not only that, if your MIDI sequencer has MIDI THRU option, you will be able to triggers sound that are on the drum machine from your keyboard as long as you have the PC’s MIDI Sequencer up and running. If your MIDI sequencer does not have a THRU function – get rid of it… it sucks. If your drum machine has a MIDI THRU port as well, you can hook another MIDI instrument into your chain by “daisy-chaining” it off of the drum machine. Using the daisy-chain method, you can attach a total of sixteen external MIDI devices to your PC!

Why sixteen? Sixteen is a crucial number in the MIDI specification. Your sequencer has to know which instrument a MIDI data stream is intended for. If there was no way to give your external devices a way to ignore multiple MIDI streams, then each instrument would try to play all the MIDI data that it receives whether it was intended for that device or not.


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