MIDI is an acronym for Musical Instrument Digital Interface; it is a set of instructions describing musical elements (technically it is a software protocol). It is not the music itself. Many musicians get confused about the difference between MIDI and digital audio; while the end results of either can be sounds we hear, they are fundamentally different animals.
Digital audio is a digitized version of actual sound. That is, the sound is recorded and the sound wave is turned into a set of numbers by subdividing it into individual events called samples (CD audio is 44.1K, or 44,100 samples per second). Each sample is stored as a number (through an “analog-to-digital converter”) and later changed back into sound (through a “digital-to-analog converter”).
MIDI contains information about music: what note to play, when to start playing it, how loud to play it, and so forth. A synthesizer is required to turn MIDI into actual sounds. But MIDI contains plenty of information to generate good notation. Below (ex. 1, 2, 3) are three different ways of looking at MIDI information, taken from the Emagic‘s sequencer, Logic.
In the first example, the MIDI information is displayed in standard notation.
The second example displays the same information as an “event list.” In it, the first three columns show the location of the event (Measure 9, beat 1, tick 1–each quarter note can be subdivided into 480 ticks, or “parts-per-quarter note”). Column five tells the type of MIDI event (a “note” event). Column six tells which MIDI channel the information is being sent on. The next column shows the actual pitch, followed by the MIDI velocity (which determines the volume), and finally the duration of the event (note that the notation view rounds out the actual length of the notes).
The third example shows the same data in “piano-roll” view. With this view it is easy to see exact durations of all notes and many types of edits can be done quickly in this view.
MIDI can also include information such as (these are just a sample):
- “play this pitch” [MIDI note number]
- “start playing it now” [start]
- “stop playing it now” [stop]
- “play it this loud” [MIDI velocity]
- “get louder as you hold the note out” [MIDI volume]
- “add modulation” (such as vibrato or pitch bend).
While the notation programs will usually only display music in standard notation, one must always remember that the actual MIDI information may be more precise than notation can display. And both Finale and Sibelius can include additional embedded MIDI data for more accurate playback.