Step Sequencer: A Simple Drum Machine

We now take the four drum voices we built — kick, snare, closed hat and open hat — and add a simple timing system that decides when each voice is triggered.

Core idea: the drum synth makes the sounds; the sequencer decides when those sounds happen.

1. A simple drum-machine architecture

Clock / Tempo
how fast?

→

Step Counter
which step?

→

Trigger Grid → Drum Voices → Mix

This is deliberately simplified — much like a basic Max/MSP metro → counter → select → trigger system.

Real drum machines and DAWs commonly add velocity, accents, swing, probability, automation, pattern chaining, microtiming and song arrangement. Here we expose the underlying mechanism first.

2. Interactive drum machine

Master Volume

Tempo

Loop length

Resolution

1/16 notes

4/4 time

Timing

Manual trigger pads

These fire the same drum voices immediately. The sequencer simply triggers them automatically at selected steps.

Pattern presets

Clickable step grid

Click any cell on or off — including while the loop is running. The highlighted column is the current sequencer step.

BAR 1

BAR 2

Current step

—

BPM

120

Step duration

125 ms

Loop duration

2.00 s

3. What is the sequencer actually doing?

step 1 → check four rows → trigger active cells → step 2 → check four rows → … → loop

If the playhead reaches an active snare cell, the sequencer sends a trigger to the snare voice. The snare synthesizer then generates the sound using the tone/noise/filter/envelope patch from the previous lesson.

Sound generation

Kick / Snare / Hats
Oscillators, noise, filters and envelopes create the audio.

Sequencing

Clock / steps / pattern
The timing system determines when each sound is triggered.

4. One bar vs two bars

At 1/16-note resolution in 4/4:

1 bar = 16 steps 2 bars = 32 steps

A two-bar loop simply gives the pattern more time before returning to step 1. The underlying clock and trigger mechanism are unchanged.

5. Musical time ↔ real time

quarter-note duration = 60 / BPM

At 120 BPM, one quarter note lasts 500 ms. A sixteenth note is one quarter of that duration, so each sequencer step lasts 125 ms.

The timing readout above updates as you change BPM.

6. Drum machine fundamentals complete

synthesised drum voices + clock + trigger pattern = simple drum machine

More sophisticated systems extend the same idea with velocity, accents, swing, probability, automation, longer patterns and arrangements — but the fundamental mechanism remains recognisable.