Step sequencers

The sequencer in where pitch comes from stored only a pitch for each step, and the oscillator sounded continuously from one step to the next. A full step sequencer stores a gate for each step as well, so that it sets when each note starts and stops as well as its pitch. The clock sets the rate, and each pulse moves the sequencer on by one step, usually a sixteenth note. Hardware step sequencers lay the steps out as a row of knobs or buttons. Sequencers in software and in grooveboxes usually show them as a grid.

The tool below is an eight-step sequencer driving a small synthesiser voice. Click the upper grid to set each step's pitch. The three rows underneath set whether each step has a gate, how many times it repeats within the step, and whether it slides into its pitch from the step before.

Pitch and gate

Each step sends two signals. The pitch sets the note, and the gate sets when it starts and how long it lasts. Because the two are separate, a step can be a rest: with its gate off, the step still lasts as long as the others, and its pitch has no audible effect because no gate starts an envelope. Gate length sets how much of each step the gate is high for, as described in gates and triggers. Many sequencers can also tie a step to the next, holding the gate high across both so the note is not restarted.

Length and direction

The length setting sets how many steps the pattern uses before it starts again. A pattern whose length does not divide evenly into the bar, such as five or seven steps against four beats, starts again at a different point in the bar each time round, so the melody shifts against the drums until the two line up again. Direction sets the order the steps are read in. Backward reverses the pattern, pendulum plays it forward and then backward without repeating the end steps, and random chooses any step on each pulse, so the pattern's notes play in an order that changes each time round.

Ratchets and slides

A ratchet divides a step into several equal gates, so a single step is heard as a quick repeated note. It is common on drum sequencers for rolls and on melodic sequencers for a burst of rhythm within an otherwise even line. A slide makes a step glide into its pitch from the previous note. The previous gate is held high into the sliding step, so the envelopes do not restart and the two notes join. The Roland TB-303 bass synthesiser, released in 1981, combined slides with accents in its built-in sequencer, and that combination is still often called a 303 line. The next chapter looks at sequencers that store only gates, one row per sound, which is how drum patterns are usually programmed.