Digital Sound & Music: Concepts, Applications, & Science, Chapter 6, last updated 6/25/2013
Figure 6.7 Note On message with data bytes
Let’s say that the key is pressed and a second later it is released. Thus, the playing of a
note for one second requires six bytes. (We can set aside the issue of how the time between the
notes is stored symbolically, since it’s handled at a lower level of abstraction.) How does this
compare to the number of bytes required for digital audio? One second of 16-bit mono audio at a
sampling rate of 44,100 Hz requires 44,100 samples/s * 2 bytes/sample = 88,200 bytes/s.
Clearly, MIDI can provide a more concise encoding of sound than digital audio.
MIDI differs from digital audio in other significant ways as well. A digital audio
recording of sound tries to capture the sound exactly as it occurs by sampling the sound pressure
amplitude over time. A MIDI file, on the other hand, records only symbolic messages. These
messages make no sound unless they are interpreted to do so by a synthesizer. When we speak
of a MIDI “recording,” we mean it only in the sense that MIDI data has been captured and stored
– not in the sense that sound has actually been recorded. While MIDI messages are most
frequently interpreted and synthesized into musical sounds, they can be interpreted in other ways
(as we’ll illustrate in Section 188.8.131.52.3). The messages mean only what the receiver interprets
them to mean.
With this caveat in mind, we’ll continue from here under the assumption that you’re
using MIDI primarily for music production since this is MIDI’s most common application.
When you “record” MIDI music via a keyboard controller, you’re saving information about what
notes to play, how hard or fast to play them, how to modulate them with pitch bend or with a
sustain pedal, and what instrument the notes should sound like upon playback. If you already
know how to read music and play the piano, you can enjoy the direct relationship between your
input device – which is essentially a piano keyboard – and the way it saves your performance –
the notes, the timing, even the way you strike the keys if you have a velocity-sensitive controller.
Many MIDI sequencers have multiple ways of viewing your file, including a track view, a piano
roll view, an event list view, and even a staff view – which shows the notes that you played in
standard music notation. These are shown in Figure 6.8 through Figure 6.11.