In digital audio recording, a sequencer is a program in a computer or stand-alone keyboard unit that puts together a sound sequence from a series (or sequence) of Musical Instrument Digital Interface ( MIDI ) events (operations). The MIDI sequencer allows the user to record and edit a musical performance without using an audio-based input source. The performance is recorded as a series of events that would ordinarily be played in from a keyboard instrument. The MIDI sequencer does not record the actual audio, but rather the events related to the performance - what note was played at what time, how hard the key was pressed, when did the sustain pedal get depressed, and so forth. This data is then played back into a MIDI instrument or sound module. Using this method, the performer can select a piano sound for a musical passage and later decide that the passage would work better as an organ sound. The editor can simply change the sound program on the MIDI keyboard to alter the sound without needing to rerecord the entire performance.
Using sound modules and keyboards that can respond on different MIDI channels, the player can layer the sounds of different instruments to create the illusion of an entire band or orchestra. There is sequencing software available in a range from that which would suit a beginner all the way to the most advanced film composer.