Understanding MIDI: ports, channels, and the general MIDI standard

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In a previous article I wrote the basic definition about MIDI (Musical Instrument Digital Interface) and how modern musicians can use it in their independent productions. This time I will write about the technical aspect of MIDI, including the MIDI ports that are available, the MIDI channels and how to use them, and the General MIDI Standard which allows a MIDI file to be read consistently on a variety of MIDI-capable instruments (hardware and software).

MIDI ports

Like any other technology related to audio or music, MIDI has an IN and OUT port. To explain the use of these two ports, let’s use the example of a MIDI keyboard and a computer (in this case a MIDI to USB converter is needed for the computer). The MIDI OUT port of the keyboard is connected to the MIDI IN port of the computer. This means that the keyboard sends MIDI data for playback or recording within the computer. Vice versa, the keyboard’s MIDI IN port can be connected to the computer’s MIDI OUT port, allowing MIDI data recorded within the computer to be sent to the keyboard for the keyboard to play back MIDI data (this means it can record itself yourself by playing, editing the MIDI data in music software and then playing it back on the keyboard and recording the audio coming out of the keyboard for a better edited performance).

In addition to MIDI IN and OUT, there is a MIDI THRU port that is sometimes available on a MIDI instrument. MIDI THRU works to pass MIDI data received at the MIDI IN port to another MIDI instrument or device. Take, for example, that the keyboard receives MIDI data from the computer at its MIDI IN port. If your keyboard has a MIDI THRU port, you can continue the data it receives from the computer to the MIDI IN port of another MIDI instrument. This is useful for chaining together multiple MIDI instruments that receive data from a single computer MIDI OUT port (for example, for playing multiple string parts using different string sounds on different keyboards).

In the latest technology, keyboards can be connected to computers via a direct USB connection without the need for a USB-to-MIDI converter. The downside is that it limits your ability to chain multiple MIDI instruments together.

MIDI channels

There are 16 MIDI channels for each MIDI port. That means any MIDI port can send and receive 16 channels of MIDI data. Each MIDI channel contains all the MIDI information about a particular track. For example, if track 1 is an acoustic piano, MIDI channel 1 will contain the note pitch, note length, sustain, and other performance data that will be played by a sound source. The sounds played are determined by the bank and patch number within the MIDI channel. For example, if the General MIDI standard is used, the acoustic piano is always patch n. 1 and acoustic guitar (nylon) is always No. 25. There are 128 patches in total.

Having 16 MIDI channels per port allows you to compose a song using 16 different parts. For example, you can use Channel 1 for the Melody Part using a saxophone sound (Patch # 65 Soprano Sax), create the composition part using a piano (Patch # 5 Electric Piano 1), and compose the rhythm part using bass. (Patch # 34 Electric Bass Finger) and drums (using MIDI channel 10, a channel that is specially reserved for playing percussion sounds regardless of the patch number you program). If you need more channels, then you need more MIDI ports!

General MIDI Standard (or GM)

The GM standard is the standard used to be able to play MIDI files consistently between different MIDI devices. I mentioned earlier about Patch numbers and MIDI Channels. These Patch numbers contain the type of sound that will be played (# 1 for acoustic piano). In order for another device to understand that MIDI channel 1 is MIDI data for a piano sound, apply the GM standard and confirm that patch n. 1 is a piano sound (you will call up your own version of the piano sound later, sometimes this may sound better or it may sound simpler depending on the internal sound synthesizer that is used to play the MIDI data). Most keyboards and software save MIDI data under the GM standard. I hope this article can help you improve your understanding of modern digital music technology. For your musical success.

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