midi 101

Musical Instrument Digital Interface (midi) was developed in the late 70's as way for various devices (instruments, etc.) to communicate with one another. In the mid-80's, manufacturers adopted midi as a standard communication protocol providing compatibility between brands. Today, nearly every electronic keyboard (and myriad other instruments) is implemented with midi.

How it Works

Midi works by dividing all of the necessary information to play notes into individual commands called messages. Additionally, this information can be arranged along a timeline. Think about what happens when you play a note on a keyboard. Pressing a key tells your keyboard's internal electronic wizardry to play a note and also how loud to play it. There are three messages involved up to this point; note on tells the brains to play a note, note number describes which note to play, and velocity provides information about volume. At this point you could bend the pitch wheel or mod wheel. These messages are transmitted as pitch and mod. Finally, releasing the key sends a note off message indicating that the note should not continue to play. The combination of these messages required to create one note constitutes one event. Since, the internal "brain" of the keyboard only recognizes this information as data, it really doesn't care where this data comes from. This is where the possibilities begin to emerge.

Connecting Instruments

Midi allows you to play the sounds from one keyboard using the keys from another. This is useful for layering sounds; piano and strings, for example. Since its not necessary (or convenient) to have two sets of keys to layer sounds, many synthesizers are available as sound modules. A sound module contains all of the sounds and controls of a normal synthesizer less the keyboard. To access these sounds, midi is used to tell the sound module what to do.

Recording (Sequencing)

As stated earlier, midi data can be arranged along a timeline. The timeline is called a midi clock. Many midi events can be arranged simultaneously along the midi clock's timeline to be played back in sequence. Recording midi data in this manner is called sequencing. Sequencing differs from traditional recording in that no actual sound is recorded; only the data required to play back notes. By starting the sequence, the sequencing device plays the keyboards and modules rather than the player. The key benefits to this type of recording is that sequenced data can be easily edited and allows all midi enabled devices to be recorded to the master in the first generation (more later).

Technically, sequencers are not recorders in the traditional sense. They are great for remembering and moving around events for playback, but have no capability for actually recording sounds. Midi cannot record your voice or guitar. It's only function is to work with midi data (which can be incredibly powerful).