Home Recording Basics: MIDI Ports - dummies

By Jeff Strong

MIDI is a protocol that musical instruments use to communicate with one another. They do this through a cabled connection and a language that allows each one to understand the other, regardless of the manufacturer or instrument. All that’s required is an instrument equipped with MIDI ports (jacks). Three types of MIDI ports exist:

  • The out port sends messages.

  • The in port receives incoming messages.

  • You use the thru port when you create a daisy chain to connect more than two devices. The thru port sends the messages that one device receives directly to the in port of another instrument. The following illustrates a daisy chain setup.


MIDI signals travel in only one direction. Data flows from the out port of a device to an in port of another device, but not the other way around. Likewise, data going through the thru port originates from the first device in the chain and not the device whose thru port is being used.

The way that data flows allows a lot of flexibility in how you can connect different devices. Here are some examples:

  • Example 1: The illustration above shows, three synthesizers are connected in a daisy-chain lineup. A cable connects Device A’s out port to Device B’s in port. Another cable connects Device B’s thru port to Device C’s in port. In this scenario, Device A controls Devices B and C. Devices B and C can’t control any other device, because neither Device B nor Device C has a connection from its out port.

  • Example 2: Suppose you connect Device B to Device C by using Device B’s out port instead of its thru port. In this case, Device A sends messages to Device B but not to Device C. Device B controls Device C. Device C has no control over either A or B because neither one is connected to Device C’s out port.

  • Example 3: Now take a look at the following illustration. In this example, two devices (a synthesizer and a computer sequencer) have MIDI cables running from the out port of each to the in port of the other. (The MIDI interface in this illustration is necessary to make MIDI connections in a computer.) This allows the communication to go both ways.

    For example, a master synthesizer and a computer sequencer are frequently connected this way so that you can send performance information from the synthesizer to the sequencer when you’re recording your part and from the sequencer back to the synthesizer when you want to play the part back.


A connection to a MIDI device’s in port or through a device’s thru port doesn’t allow the device to control another device. A MIDI device can control another device only if the cable is connected from its out port to the other device’s in port.