Handbook for Sound Engineers

1112 Chapter 29

• MIDI In—The MIDI In jack receives messages from
  an external source and communicates this perfor-
  mance, control, and/or timing data to the device’s
  internal microprocessor, allowing an instrument to be
  played and/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—The MIDI Out jack is used to transmit
  MIDI performance, control messages or SysEx from
  one device to another MIDI instrument or device.
  More than one MIDI Out jack can be designed into a
  system, giving it the advantage of controlling and
  distributing data over multiple MIDI paths using
  more than just 16 channels (i.e., 16 channels × N
  MIDI port paths).


• MIDI Thru—The MIDI Thru jack retransmits an
  exact copy of the data that’s being received at the
  MIDI In jack. This process is important, because it
  allows data to pass directly through an instrument or
  device to the next device in the MIDI chain. Keep in
  mind that this jack is used to relay an exact copy of
  the MIDI In data stream and isn’t merged with data
  being transmitted from the MIDI Out jack.


• MIDI Echo—Certain MIDI devices may not include
  a MIDI Thru jack, at all. Certain of these devices,
  however, may give the option of switching the MIDI
  Out between being an actual MIDI Out jack and a
  MIDI Echo jack, Fig. 29-15. As with the MIDI Thru
  jack, a MIDI echo option can be used to retransmit an
  exact copy of any information that’s received at the
  MIDI In port and route this data to the MIDI
  Out/Echo jack. Unlike a dedicated MIDI Out jack,
  the MIDI Echo function can often be selected to
  merge incoming data with performance data that’s
  being generated by the device itself. In this way, more
  than one controller can be placed in a MIDI system at
  one time. It should be noted that although perfor-
  mance and timing data can be echoed to a MIDI
  Out/Echo jack, not all devices can echo SysEx data.

Typical Configurations. Although electronic studio
production equipment and setups are rarely alike (or
even similar), there are a number of general rules that
make it easy for MIDI devices to be connected into a
functional network. These common configurations
allow MIDI data to be distributed in the most efficient
and understandable manner possible.

As a primary rule, there are only two valid ways to

connect one MIDI device to another within a MIDI

chain, Fig. 29-16:

1. Connecting the MIDI Out jack of a source device
   (controller or sequencer/computer) to the MIDI In
   of a second device in the chain.


2. Connecting the MIDI Thru jack of the second device
   to the MIDI In jack of the third device in the chain
   and following this same Thru-to-In convention until
   the end of the chain is reached.

The Daisy Chain. One of the simplest and most

common ways to distribute data throughout a MIDI

system is the daisy chain. This method relays MIDI data

from a source device (controller or sequencer/computer)

to the MIDI In jack of the next device in the chain

(which receives and acts upon this data). In turn, this

device relays an exact copy of this incoming data out to

its MIDI Thru jack, which is then relayed to the next

device in the chain. This device can then relay an exact

copy of this incoming data out to its MIDI Thru jack,

which is then relayed to the next device in the chain...

etc. In this way, up to 16 channels of MIDI data can be

chained from one device to the next within a connected

data network—and it’s precisely this concept of trans-

mitting multiple channels through a single MIDI line

Figure 29-15. MIDI echo configuration.

Figure 29-16. The two valid means of connecting one MIDI

device to another.

Microprocessor

Device #1 Device #2 Device #3

MIDI out to MIDI in MIDI thru to MIDI in