Chapter 3 · The Hardware 51 MIDI Jacks MIDI is distributed from device to device using three types of MIDI jacks: MIDI In, MIDI Out, and MIDI Thru (Figure 3.5). These three connectors use 5-pin DIN jacks as a way to connect MIDI Instruments, devices, and computers into a music or production network system. As a side note, it's nice to know that these ports[NCS1] (as strictly defined by the MIDI 1.0 spec.) are opti- cally isolated to eliminate possible ground loops that might occur when connecting numerous devices together. MIDI In Jack The MIDI In jack receives messages from an external source and communicates this performance, control, and timing data to the device's internal microprocessor, allowing an instrument to be played or a device to be controlled. More than one MIDI In jack can be designed into a system to provide for MIDI merging functions or for devices that can support more than 16 channels (such as a MIDI interface). Other devices (such as a controller) might not have a MIDI In jack at all. MIDI Out Jack The MIDI Out jack is used to transmit MIDI performance and control messages, or SysEx from