Rhythmic Sequence

A 16-step acid bassline at 120 BPM: a saw through a resonant lowpass that snaps open on every struck note, with two notes slid into the way a 303 slurs them, warmed with distortion and pushed along by a dotted-eighth echo, over a ticking line of noise hi-hats. It plays itself, and it's built to be tweaked while it runs. Grab the filter's Cutoff and Res knobs and play them like a 303.

Load it: choose 📚 Examples → Rhythmic Sequence in the toolbar and press ▶ Play. It needs no keyboard. The patch file is patches/rhythmic-sequence.json.

Or play it here: press ▶ Play in the corner. The full app is a click away under Open in Soba. Two envelopes from the sequencer's gate: one squelches the filter, one shapes the volume. Along the bottom, the clock plays noise hi-hats.

What it teaches

• Sequencing a bassline. Pitches, rests and an octave jump, all in one 16-step pattern.
• The filter envelope as the instrument. Short decay and high resonance are the sound of acid.
• Slides. Two notes glide in from the note before without striking the envelopes again, so the line slurs like one player's phrase.
• Tempo sync. The delay locks to the Clock's tempo, so its echoes land on the beat.
• Noise as a drum. An envelope into a Noise module's Level turns hiss into a hi-hat, with no VCA needed.

Modules

How it's built

Clock and pattern

[Clock Gate] ──> [Step Sequencer Clock]
[Step Sequencer Pitch] ──> [Oscillator V/Oct]

At 120 BPM with Div at 1/16, the Clock pulses four times a beat, every 125 ms, and each pulse moves the sequencer one step. The sixteen steps make one bar:

A dash is a step with its gate off: a rest. The line sits on the root, C2, and moves through notes of C minor (D# is the minor third) with an octave leap on the downbeat of the second half. The rests do as much as the notes: they're what make it groove rather than drone. The two slides are covered below.

The squelch

[Oscillator Out] ──> [SVF Filter In]
[Step Sequencer Gate] ──> [ADSR (filter) Gate]
[ADSR (filter) Out] ──> [SVF Filter Cutoff]

The filter sits low, at 300 Hz, with Res at 70%. The filter envelope kicks it open on every struck note, then drops it back in 200 ms. That fast sweep of a sharp resonant peak is the acid sound.

The filter's Cutoff input works in octaves, and an envelope peaks at 1.0. The filter's CV Amt sets how many octaves that peak is worth: at 2, each step's envelope throws the cutoff two octaves up, to 1.2 kHz, and lets it fall back to the bass.

Volume, drive and echo

[Step Sequencer Gate] ──> [ADSR (amp) Gate]
[SVF Filter LowPass] ──> [VCA In]
[ADSR (amp) Out] ──> [VCA CV]
[VCA Out] ──> [Distortion In]
[Distortion Out] ──> [Stereo Delay In L]
[Stereo Delay Out L] ──> [Audio Output Left]
[Stereo Delay Out R] ──> [Audio Output Right]

The amp envelope is short and punchy, so each note is a distinct pluck. With Gate at 50%, each of the sequencer's gates lasts 50 ms (Gate of is set to 100 ms, so Gate is a share of a fixed 100 ms), well inside the 125 ms step. The exception is a note that leads into a slide, which holds its gate until the slide begins.

Soft distortion at 30% drive, mixed at 70%, rounds and thickens the bass and makes the resonant peak growl.

The Stereo Delay's Sync is set to 1/8D, a dotted eighth. It takes its tempo from the Clock, so at 120 BPM each echo comes 375 ms after its note: three sixteenths later, falling between the notes and filling the gaps. Its LoCut keeps the echoes out of the bass register, so they don't muddy the line.

Slides

Steps 9 and 16 are slides, each marked on the grid by an orange slur from the step before. When a slide step comes round, two things happen:

• The pitch glides from the note before over the sequencer's Glide time, 70 ms, instead of jumping. C2 rises an octave into C3 on the downbeat of the second half, and at the end of the bar F2 slurs up a step to G2.
• The gate stays high across the join, so neither envelope is struck again. The filter envelope keeps falling through the slid note, and the amp envelope sinks toward its 30% sustain, so the note arrives darker and about 3 dB softer than a struck one.

That contrast is the 303's sound: most notes are plucked, and a few melt into the note before, so the line sounds like one player's phrase. Each slide is a short two-note gesture, and step 1 is always struck, so every bar still starts with a pluck.

Hi-hats

[Clock Gate] ──> [ADSR (hats) Gate]
[ADSR (hats) Out] ──> [Noise Level]
[Noise Pink] ──> [SVF Filter (hats) In]
[Noise Random] ──> [SVF Filter (hats) Cutoff]
[SVF Filter (hats) HighPass] ──> [Audio Output Mono]

The hats take the Clock's pulse directly, so they tick on every sixteenth whether or not the bassline plays. That steady pulse under the rests is what makes the line swing.

The Noise module's Level knob is at 0, so it is silent until the envelope opens it. Each pulse snaps it to full in 1 ms and lets it die away in 45 ms: a short burst of noise, which is all a closed hi-hat is. An envelope into Level does the job of a VCA, and Level follows CV instantly, so the attack stays sharp.

The highpass filter at 4.5 kHz keeps only the sizzle. Pink noise rather than white keeps the hats from getting harsh and sitting on top of the bass. Noise's Random output drifts the filter's cutoff an octave either way, over several seconds, so the hats darken and brighten as if a drummer were working the pedal. The hats go to Mono, past the delay, so they stay dry and tight in the middle.

Variations

Play the filter. While it runs, sweep Cutoff between 150 Hz and 1 kHz and push Res toward 90%. Lengthen the filter envelope's Dec to 400 ms for longer squelches, and turn CV Amt up to 3 or 4 for wider ones.

Change the line. Click a step to toggle its gate. Drag a step up or down to change its note, or right-click it and play a new line on its piano: each key writes a step and moves to the next.

Different tempo. Turn the Clock's BPM. The delay follows, staying on the dotted eighth.

Move the slides. Ctrl + click a step to slide into it, and Ctrl + click again to strike it. Slide into step 8 as well, so D#2 falls to C2 and leaps to C3 in one breath, three notes on a single strike. Or clear both slides to hear how much plainer the line plucks without them. Raise Glide to 200 ms for a lazier, more vocal slur.

Slide everything. Patch the sequencer's Pitch through a Slope on its way to the Oscillator's V/Oct, with Rise and Fall at 60 ms and Shape at 0. Every note now glides into the next: the octave leap to C3 in 60 ms, a fifth in 35 ms, so each glide is over well inside its step and the line still lands on its notes. Unlike a slide step, Slope only moves the pitch, so every note is still struck. Repeated notes don't glide, so the pattern keeps its stabs.

Shorter loop. Set Steps to 12 or 7 for a pattern that cycles against the bar.

Fatter. Swap the SVF for a Ladder Filter and use its LP24 output. Raise its Drive to 3x.

Harder. Set the Distortion's Type to Hard or Fold and raise Drive. Turn Out down to keep the level in check.

Open hats. Raise the hat envelope's Dec to 250 ms, so each hat rings into the next and the line turns to a shimmering wash. Switch the filter to BandPass for a trashier, more metallic hat.

Related

• Clock – tempo and divisions
• Step Sequencer – editing steps
• Noise – the hi-hats' source, and what else it can do
• Generative Ambient – the same clock and sequencer, slowed right down
• Shoreline – noise as surf, and as the chooser of notes