About Local On and MIDI THRU

Normally, when you play your MIDI keyboard, keys you play produce sound. This is probably what you want when working with the keyboard on its own.

However, when using your keyboard together with a MIDI sequencer, things are different. This article tries to explain the terms "local on", "local off" and "MIDI THRU".

Local On

Normally, when you play a note on your MIDI keyboard, two things happen: the note plays and a message is sent to the MIDI OUT port of the keyboard. In other words, the key message is sent to the sound generator and also to MIDI. From the point of view of the sound generator, the command was generated locally - it came from the keyboard, not from an external source via MIDI.

When you connect a sequencer to your keyboard, the sequencer listens to the notes coming from your keyboard's MIDI port. It is possible that the sequencer may perform some processing on the MIDI messages it receives and then (if the sequencer has MIDI THRU) send the result back to your keyboard. These messages will arrive at the keyboard's MIDI IN port.

Messages received by the keyboard's MIDI IN port are sent to the sound generator to produce sound. If your keyboard has a MIDI THRU port, any message received at MIDI IN is also sent there as well.

So, if the keyboard is functioning in Local On mode, the normal case, it is possible that when you play a note to a sequencer, it actually plays twice: one note from the local keyboard and a second (perhaps identical) note received back from the sequencer via MIDI IN. This "note doubling" is not ideal for several reasons - not least, it sounds a bit strange.

Local Off

The solution, when using a sequencer, is to turn the locally generated notes off. In other words, to break the internal connection between the keyboard and the tone generator. When this is done, notes you play are only sent to the MIDI OUT port, a bit like a controller keyboard.

You should be able to turn Local on and off using the buttons on your keyboard, though the setting is likely to be buried somewhere in the menu system. Alternatively, you can send MIDI messages from the sequencer to turn Local on or off. They are standard messages so most keyboards should understand them.

So, in short, when you start using a sequencer, you should probably send a Local Off message to your keyboard. When you've finished, make sure you turn Local back on again, otherwise your keyboard may be completely silent when you play without the sequencer.


If your MIDI keyboard has three MIDI sockets, it is likely that the third is the MIDI THRU. MIDI THRU simply echoes whatever comes in at MIDI IN. The practical upshot of this is that you can link two or more MIDI devices together, connecting the MIDI THRU of one device to the MIDI IN of the next.

Assume, for example, you have a keyboard, a sequencer and a sound module. However, the sequencer only has one MIDI port. For best results when sequencing, you could make the following MIDI connections: The MIDI OUT from the keyboard goes to the MIDI IN of the sequencer as usual. The MIDI OUT from the sequencer goes to the MIDI IN of the keyboard, again as usual - and remember about Local Off. Finally, connect the MIDI THRU from the keyboard to the MIDI IN of the sound module.

Now, when you play a note on the keyboard, it first goes to the sequencer. When the sequencer has processed it, it is sent back to the keyboard and the keyboard will play the note. The note is simultaneously sent on to the sound module and it will also play the note too.

Again, we have a note doubling situation. However, this time as the notes are sounded by two different instruments, the solution is different too.

In this situation, the best way to have different MIDI instruments handle different parts from your song is to make the instruments respond to different MIDI channels. For example, assume that you want the sound module to play the drums (on channel 10) and the keyboard to play the piano (on channel 1), you would set the keyboard to receive MIDI channel 1 and the module to receive on channel 10.

The details of how to make your MIDI instruments respond to different channels depend on your instrument. Many instruments have a single channel and a multichannel (multitimbral or performance) mode. In the single channel mode, you can set the instrument to respond to a given single MIDI channel. In the multi mode, you may be able to select which channels it will respond to, or it can respond to all sixteen. Details will be in the manual for your MIDI gear.

In order to be able to use both the keyboard and module totally independently and use all sixteen channels of each, you will need two MIDI OUT ports on the sequencer; for example, a MIDI interface with two or more out ports from your computer.

When using MIDI THRU to connect MIDI instruments, you should not connect more than three in a chain. Any more than this and the MIDI data may not transmit correctly.


Return to QWS articles