MIDI-THRU

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A MIDI-THRU (output) is an auxiliary output for MIDI signals, mostly found on musical instruments such as synthesizers. It started to be added soon after the introduction of MIDI into the market, in order to improve performance. It is mostly used to 'daisy-chain' MIDI devices, in effect, re-transmitting unchanged MIDI data along to the next MIDI device.

MIDI consists of a ring of cables, with a transceiver between each cable inside each device. The transceivers physically separate the two cables, meaning that signals not intended for that device have to be re-sent onto the output line. This introduces a delay, one that is long enough to become audible on larger MIDI rings.

The MIDI-THRU port avoids this delay by linking the THRU port to the MIDI-IN socket almost directly. The MIDI-OUT port is then used only for signals originating in that device.

Example, device 1 out to device 2 in, device 2 thru to device 3 in, and so on. This will pass the MIDI data generated by device 1 thru device 2 to device 3 and so on. The difference between the out and thru ports is that data coming from the out port has been generated on the device containing the out port. Data that comes out of a device's thru port is an exact duplicate of the data received at the in port. Note that some gear has the ability to merge the data together to one port, but this does require the use of all 5 pins or some tricky rigging on a user's part.