Most MIDI setups will have multiple synths or synth modules that all need to be played from a single MIDI source, such as a computer or workstation or even a more complex setup with multiple keyboards and controllers.

Kenton MIDI THRU boxes take a single MIDI source, for instance the output of the computer, and produce identical copies of that MIDI signal which appear at the THRU outputs.

For example you might have five synth modules – each set to a different MIDI channel. Using a THRU-5, these modules will all receive all of the MIDI information from the MIDI source, but will only respond to MIDI messages on the MIDI channel they are set to “listen” on. They will ignore anything on another MIDI channel.