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Audio Midi

October 17th, 2009 Leave a comment Go to comments

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Audio Midi

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 side of MIDI, including MIDI ports that are available, MIDI channels and how to use them, and the General MIDI Standard that allows a MIDI file to be read consistently over a variety of MIDI-capable instruments (hardware and software).

MIDI Ports

As in every other audio or music related technology, MIDI has an IN and OUT port. To explain the use of these two ports, lets use the example of a MIDI keyboard and a computer (in this case a MIDI to USB converter is necessary for the computer). The MIDI OUT port on the keyboard is connected to the MIDI IN port on the computer. This means that the keyboard sends MIDI data to be played back or recorded inside the computer. Vice versa, the MIDI IN port on the keyboard can be connected to the MIDI OUT port of the computer allowing the recorded MIDI data inside the computer to be sent back to the keyboard in order for the keyboard to play back the MIDI data (this means you can record yourself playing, edit the MIDI data in a music software, and then play it back on the keyboard and record the audio coming out the keyboard for a better edited performance).

Besides MIDI IN and OUT, there is a MIDI THRU port that is sometimes available on a MIDI instrument. MIDI THRU functions to pass on the MIDI data received at the MIDI IN port to another MIDI instrument or device. Take for example the keyboard receives MIDI data from the computer in it's MIDI IN port. If the keyboard has a MIDI THRU port, it can continue the data it receives from the computer to another MIDI instrument's MIDI IN port. This is useful to chain several MIDI instruments receiving data from a single MIDI OUT port from the computer (for example, to play multiple string parts using different string sounds on different keyboards).

In more recent technology, keyboards can be connected to computers via straight USB connection without needing 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 every 1 MIDI Port. That means any one MIDI Port can send and receive 16 channels of MIDI data. Each MIDI channel contains all the MIDI information regarding a particular track. For example, if Track 1 is Acoustic Piano, then MIDI Channel 1 will contain the note pitch, note length, sustain, and other performance data to be played back by a sound source. The sounds played back are determined by the Bank and Patch number inside the MIDI Channel. For example, using the General MIDI Standard, Acoustic Piano is always Patch #1 and Acoustic Guitar (Nylon) is always #25. There are 128 Patches overall.

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 comp 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 reserved especially to play percussion sounds regardless of the patch number you program in). If you need more channels, then you need more MIDI ports!

General MIDI (or GM) Standard

The GM Standard is the standard used in order to be able to play back MIDI files consistently between different MIDI devices. I mentioned above about Patch numbers and MIDI Channels. These Patch numbers contain the type of sound to be played back (#1 for Acoustic Piano). In order for another device to understand that MIDI Channel 1 is MIDI data for a piano sound, it applies the GM Standard and confirms that Patch #1 is a piano sound (it will then call up it's own version of the piano sound, sometimes this can be better sounding or it can be simpler sounding depending on the internal sound synthesizer that is used to play back the MIDI data). Most keyboards and software when saving MIDI data saves it under the GM Standard. I hope this article can be of use for you to further your understanding of modern digital music technology. To your music success.

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