MIDI stands for Musical Instrument Digital Interface, and it is a standard way for computers, keyboards, drum pads, and synthesizers to communicate. It matters because it lets one device control another without sending actual recorded sound. A laptop can tell a keyboard which note to play, how hard it was pressed, and when to stop.
This makes MIDI a powerful tool for composing, performing, and controlling music technology.
Understanding Music & Sound: What Is MIDI
A MIDI performance is built from small events placed on a timeline. Each event has a time, a type, and values that describe what happened. Music software records these events into a track, often shown as a piano roll.
Each horizontal block represents one note. Its left edge shows when it begins, its length shows how long it lasts, and its vertical position shows pitch.
Students can move, lengthen, shorten, copy, or delete these blocks without rerecording a performance. This is why MIDI is useful when a player makes a small timing mistake or chooses the wrong note.
Timing needs careful attention. A song has a tempo, measured in beats per minute, and a grid divides each beat into smaller parts. Quantizing moves recorded notes closer to that grid.
It can make a drum pattern sound steady, but too much quantizing can remove the small timing differences that make a human performance feel natural. A good workflow is to listen before correcting everything. Some music needs strict timing, such as electronic dance beats.
Other music benefits from notes that arrive slightly early or late. MIDI files can store tempo changes, so a piece can gradually speed up or slow down during playback.
Pitch in MIDI follows a numbered system. Moving up one note number usually moves up one semitone, the smallest step on a piano keyboard. Twelve semitones make an octave, so doubling a sound frequency raises it by one octave.
In the common equal tempered tuning system, the note numbered 69 has a frequency of 440 hertz. To find another note frequency, start with 440, multiply by two raised to the power of the note number minus 69, then divide that result by 12. Students do not need to calculate this for everyday composing, but it explains why the gaps between piano keys sound evenly spaced while their frequencies are not evenly spaced.
MIDI can carry much more expression than note timing and pitch. Controllers send changing values while music plays. A modulation wheel can add vibrato.
A foot pedal can hold notes after keys are released. A pitch bend wheel can smoothly raise or lower a note between keyboard keys. Knobs on a controller can be assigned to filter cutoff, volume, reverb amount, or many other sound settings.
These controls make a programmed part feel less mechanical. Standard MIDI has limited detail in some values, since many controls use steps from zero through 127. Fast or subtle movements may therefore sound slightly stepped.
Different instruments can interpret the same control differently, so it is important to test a project on the sound source that will actually be used. When a MIDI part sounds wrong, check the selected instrument, channel assignment, octave setting, tempo, and controller data before assuming the notes themselves are incorrect.
Key Facts
- MIDI sends performance instructions, not audio waveforms.
- A Note On message tells an instrument to start a note, and a Note Off message tells it to stop.
- Middle C is usually MIDI note number 60.
- Velocity usually ranges from 0 to 127 and often controls loudness or intensity.
- One MIDI channel can carry messages for one instrument part, and standard MIDI has 16 channels.
- Frequency for equal-tempered notes can be calculated with f = 440 × 2^((n - 69)/12), where n is the MIDI note number.
Vocabulary
- MIDI
- MIDI is a digital communication standard that sends musical instructions between electronic instruments, computers, and controllers.
- Note On
- A Note On message tells a MIDI device to begin playing a specific note with a specific velocity.
- Velocity
- Velocity is a MIDI value, usually from 0 to 127, that represents how strongly a note was played.
- Synthesizer
- A synthesizer is an electronic instrument that creates sound, often in response to MIDI messages.
- MIDI Channel
- A MIDI channel is a numbered pathway that helps separate messages for different instruments or parts.
Common Mistakes to Avoid
- Thinking MIDI is sound, but MIDI contains instructions such as note number, timing, and velocity rather than an audio waveform.
- Confusing velocity with speed, but MIDI velocity usually describes how hard a key was struck, not how fast the note travels.
- Forgetting Note Off messages, which is wrong because a synthesizer may keep sounding a note until it receives an instruction to stop.
- Assuming every MIDI device sounds the same, but the final sound depends on the instrument, synthesizer patch, or software receiving the MIDI data.
Practice Questions
- 1 A MIDI melody uses notes 60, 62, 64, 65, and 67. If note 60 is middle C, identify the solfege or scale-degree pattern in a C major scale.
- 2 A keyboard sends a Note On message for note 69 with velocity 100. Using f = 440 × 2^((n - 69)/12), what frequency should a synthesizer play for note 69?
- 3 A laptop plays a MIDI file through two different synthesizer sounds, one piano and one trumpet. Explain why the notes and rhythm can stay the same while the sound quality changes.