A music sequencer (or audio sequencer or simply sequencer) is a device or application software that can record, edit, or play back music, by handling note and performance information in several forms, typically CV/Gate, MIDI, or Open Sound Control (OSC), and possibly audio and automation data for DAWs and plug-ins.

Modern sequencers

The advent of Musical Instrument Digital Interface (MIDI) and the Atari ST home computer in the 1980s gave programmers the opportunity to design software that could more easily record and play back sequences of notes played or programmed by a musician. This software also improved on the quality of the earlier sequencers which tended to be mechanical sounding and were only able to play back notes of exactly equal duration. Software-based sequencers allowed musicians to program performances that were more expressive and more human. These new sequencers could also be used to control external synthesizers, especially rackmounted sound modules, and it was no longer necessary for each synthesizer to have its own devoted keyboard.

As the technology matured, sequencers gained more features, such as the ability to record multitrack audio. Sequencers used for audio recording are called digital audio workstations (or DAWs).

Many modern sequencers can be used to control virtual instruments implemented as software plug-ins. This allows musicians to replace expensive and cumbersome standalone synthesizers with their software equivalents.

Today the term "sequencer" is often used to describe software. However, hardware sequencers still exist. Workstation keyboards have their own proprietary built-in MIDI sequencers. Drum machines and some older synthesizers have their own step sequencer built in. There are still also standalone hardware MIDI sequencers, although the market demand for those has diminished greatly due to the greater feature set of their software counterparts.

Types of music sequencer

Music sequencers can be categorized by handling data types, such as:

  • MIDI data on the MIDI sequencers (implemented as hardware or software)
  • CV/Gate data on the analog sequencers and possibly others (via CV/Gate interfaces)
  • Automation data for mixing-automation on the DAWs, and the software effect / instrument plug-ins on the DAWs with sequencing features
  • Audio data on the audio sequencers including DAW, loop-based music software, etc.; or, the phrase samplers including Groove machines, etc.

Alternative subsets of audio sequencers include:

  • Digital audio workstation (DAW), Hard disk recorder — a class of audio software or dedicated system primarily designed to record, edit, and play back digital audio, first appeared in the late 1970s and emerging since the 1990s. After the 1990s–2000s, several DAWs for music production were integrated with music sequencer.
  • In today, "DAW integrated with MIDI sequencer" is often simply abbreviated as "DAW", or sometimes referred as "Audio and MIDI sequencer", etc. On the later usage, the term "audio sequencer" is just a synonym for the "DAW".
  • Loop-based music software — a class of music software for Loop-based music compositions and remix, emerging since late 1990s. Typical software included ACID Pro (1998), Ableton Live (2001), GarageBand (2004), etc. And now, several of them are referred as DAW, resulting of the expansions and/or integrations.
  • Its core feature, pitch/time manipulation allows user to handle audio samples (loops) with the analogy of MIDI data, in several aspects; user can designate Pitches and Durations independently on short music samples, as on MIDI notes, to remix a song.
  • This type of software really controls sequences of audio samples; thus, possibly, we can call it an "audio sequencer".
  • Tracker (music software) — a class of software music sequencer with embedded sample players, developed since the 1980s. Although it provides earlier "sequence of sampling sound" similar to grooveboxes and later loop-based music software, its design is slightly dated, and rarely referred as "audio sequencer".
  • Phrase sampler (or phrase sampling) — similar to above, musicians or remixers sometimes remixed or composed songs by sampling relatively long phrases or part of songs, and then rearranging these on grooveboxes or a combination of sampler (musical instrument) and sequencer.
  • This technique is possibly referred as "audio sequencing".
  • Beat slicing — before the DAW became popular, several musicians sometimes derived various beats from limited drum sample Loop by slicing beats and rearranging them on samplers. This technique was popularized with the introduction of "beat slicer" tool, especially the "ReCycle" released in 1992.

Analog sequencers

During the 1940s–1960s, Raymond Scott, an American composer of electronic music, invented various kind of music sequencers for his electric compositions. The "Wall of Sound", once covered on the wall of his studio in New York during the 1940s–1950s, was an electro-mechanical sequencer to produce rhythmic patterns, consisting of stepping relays (used on dial pulse telephone exchange), solenoids, control switches, and tone circuits with 16 individual oscillators. Later, Robert Moog would explain it in such terms as "the whole room would go 'clack - clack - clack', and the sounds would come out all over the place". The Circle Machine, developed in 1959, had dimmer bulbs arranged in a ring, and a rotating arm with photocell scanning over the ring, to generate an arbitrary waveform. Also, the rotating speed of the arm was controlled via the brightness of lights, and as a result, arbitrary rhythms were generated.

Clavivox, developed since 1952, was a kind of keyboard synthesizer with sequencer. On its prototype, a theremin manufactured by young Robert Moog was utilized to enable portamento over 3-octave range, and on later version, it was replaced by a pair of photographic film and photocell for controlling the pitch by voltage.

In 1968 Ralph Lundsten and Leo Nilsson had a polyphonic synthesizer with sequencer called Andromatic built for them by Erkki Kurenniemi.

Digital sequencers

In 1971, Electronic Music Studios (EMS) released one of the first digital sequencer products as a module of Synthi 100, and its derivation, Synthi Sequencer series. After then, Oberheim released the DS-2 Digital Sequencer in 1974, and Sequential Circuits released Model 800 in 1977 

Step sequencers

The step sequencers played rigid patterns of notes using a grid of (usually) 16 buttons, or steps, each step being 1/16 of a measure. These patterns of notes were then chained together to form longer compositions. Sequencers of this kind are still in use, mostly built into drum machines and grooveboxes. They are monophonic by nature, although some are multi-timbral, meaning that they can control several different sounds but only play one note on each of those sounds.

MIDI sequencers

In June 1981, Roland Corporation founder Ikutaro Kakehashi proposed the concept of standardization between different manufacturers' instruments as well as computers, to Oberheim Electronics founder Tom Oberheim and Sequential Circuits president Dave Smith. In October 1981, Kakehashi, Oberheim and Smith discussed the concept with representatives from Yamaha, Korg and Kawai. In 1983, the MIDI standard was unveiled by Kakehashi and Smith. The first MIDI sequencer was the Roland MSQ-700, released in 1983.

It was not until the advent of MIDI that general-purpose computers started to play a role as sequencers. Following the widespread adoption of MIDI, computer-based MIDI sequencers were developed. MIDI-to-CV/Gate converters were then used to enable analogue synthesizers to be controlled by a MIDI sequencer. Since its introduction, MIDI has remained the musical instrument industry standard interface through to the present day.