Many different "transports" can be used for MIDI messages. The speed of the transport determines how much MIDI data can be carried, and how quickly it will be received.
Each transport has its own performance characteristics which might make some difference in specific applications, but in general the transport is the least important part of MIDI, as long as it allows you to connect all the devices you want use!
5-Pin MIDI DIN
Using a 5-pin "DIN" connector, the MIDI DIN transport was developed back in
1983, so it is slow compared to common high-speed digital transports available
today, like USB, FireWire, and Ethernet. But MIDI-DIN is almost always
still used on most MIDI-equipped devices because it adequately handles
communication speed for one device. Also, if you want to connect one MIDI
device to another (without a computer), MIDI cables are usually
It used to be that connecting a MIDI device to a computer meant
installing a "sound card" or "MIDI interface" in
order to have a MIDI DIN connector on the computer. Because of space
limitations, most such cards did not have actual 5-Pin DIN connectors
on the card, but provided a special cable with 5-Pin DINs (In and Out)
on one end (often connected to the "joystick port"). All
such cards need "driver" software to make the MIDI
connection work, but there are a few standards that companies follow,
including "MPU-401" and "SoundBlaster". Even with
those standards, however, making MIDI work could be a major
task. Over a number of years the components of the typical sound card and
MIDI interface (including the joystick port) became standard on the
motherboard of most PCs, but this did not make configuring them any
Serial, Parallel, and Joystick Ports
Before USB and FireWire, personal computers were all generally equipped with serial, parallel, and (possibly) joystick ports, all of which have been used for connecting MIDI-equipped instruments (through special adapters). Though not always faster than
MIDI-DIN, these connectors were already available on computers and that made them an economical
alternative to add-on cards, with the added benefit that in general
they already worked and did not need special configuration.
The High Speed Serial Ports such as the "mini-DIN" ports available on early Macintosh
computers support communication speeds roughly 20 times faster than MIDI-DIN, making it
also possible for companies to develop and market "multiport" MIDI interfaces that
allowed connecting multiple MIDI-DINs to one computer. In this manner it
became possible to have the computer address many different MIDI-equipped devices at the same time.
Recent multi-port MIDI interfaces use even faster USB or FireWire
ports to connect to the computer.
USB and FireWire
All recent computers are equipped with USB and possibly FireWire connectors, and these are now
the most common means of connecting MIDI devices to computers (using
appropriate adapters). Adapters can be as simple as a short
cable with USB on one end and MIDI DIN on the other, or as complex as
a 19 inch rack mountable CPU with dozens of MIDI and Audio In and Out
ports. The best part is that USB and FireWire are
"plug-and-play" interfaces which means they generally
configure themselves. In most cases, all you need to do is plug in
your USB or FireWire MIDI interface and boot up some MIDI software and
off you go.
Current USB technology generally only supports communication between a
host (PC) and a device, so it is not possible to connect two USB
devices to each other as it is with two MIDI DIN devices. (This may
change sometime in the future with new versions of USB).
Since USB MIDI devices only communicate through the PC, two devices can use
different schemes for packing up MIDI messages and sending them over
USB, and each device's driver on the host will know how to unpack
those message and convert them back to MIDI messages. That way all USB MIDI devices can talk to each other (through
the host) even if they do not all use the same translation format.
However, most devices actually follow the format specification for
MIDI that was defined by the USB-IF; Windows and Mac PCs already come
with "class compliant" drivers for devices that follow the
USB-IF MIDI specification.
Most FireWire MIDI devices also connect directly to a PC with
a host device driver and so can talk to other FireWire MIDI devices
even if they use different methods for formatting their MIDI data.
But FireWire itself also supports "peer-to-peer"
connections, so MMA (with the 1394TA) produced a specification for
transport of MIDI over IEEE-1394 (FireWire), which is available for download on this
site (and incorporated in IEC-61883).
If you are connecting a number of MIDI instruments to one or more
computers, using Ethernet seems like a great solution. In the MIDI industry there is not yet agreement on the market
desire for MIDI over Ethernet, nor on the net value of the benefits vs. challenges of
using Ethernet, and so MMA has not yet adopted a standard for MIDI over
However, other Standard Setting Organizations
have specifications for MIDI Over Ethernet, and we think it appropriate that people know about
those solutions. There are also proprietary solutions for MIDI Over Ethernet, but because they are not
open standards they are not appropriate for discussion by MMA.
The IETF RTP Payload Format for MIDI
was developed with significant input from MMA, and is the foundation of Apple's
"Network MIDI" implementation of MIDI over Ethernet. Though
not officially adopted or endorsed by MMA, the RTP-MIDI approach is
acceptable to MMA members and is already being used in hardware and/or software products. More information about
RTP-MIDI can be found at www.rtp-midi.org.
For the past several years, the IEEE has been developing a suite
of protocols for low-latency audio and video transport over Ethernet
with high quality of service, collectively known as
Audio/Video Bridging, or AVB. The effort is part of the larger IEEE 802.1
Working Group, which develops networking standards that enable
interoperability of such ubiquitous devices as Ethernet switches.
The AVB protocols provide precision time synchronization and stream
bandwidth reservation at the network level. (However, the AVB protocols do not provide a standard means for
interoperable communication of content such as a live video stream.)
The IEEE-1722 AVB Transport
Protocol (AVBTP) standard uses the AVB protocols and provides content
encapsulation in an evolutionary manner by adopting the existing
IEEE 1394 (Firewire) audio and video streaming mechanisms already in
use by millions of A/V devices. However, the AVBTP specification
also supports other media formats (Payload Types), so the MMA has collaborated with IEEE to
define a separate Payload Type identifier for MIDI (and possibly future content formats defined by the MMA).
The P1722 standard references an MMA specification that is not yet
published, but will be completed in the near future.