Littoral

Three oscillators, one reference pitch · Radish · Vulpus Labs

Littoral is a bank of three oscillators for making drones. All three start from the same reference pitch, but each has a BEAT knob that lets you tune it a precise number of hertz above or below that pitch. Set two voices 0.2 Hz apart and they beat against each other once every five seconds, whatever note they're playing.

The oscillators are based on the kind of circuitry found in large modular synths. Each starts with a sawtooth wave, shapes it into a triangle, then rounds that into a sine. The result isn't quite a pure sine: there's a little of the third and fifth harmonics, a trace of the second, and a tiny tick each time the waveform restarts.

These imperfections are deliberate. When two voices beat against each other, their harmonics beat too, at three and five times the fundamental rate. Each creates its own pattern of movement in a different register. The result is a shifting, interlocking shimmer that you don't get from a bank of perfectly pure sine waves.

The pitch also drifts slowly, like the oscillators in a real cabinet as they warm up and settle. Most of this drift is shared by all three voices, so the overall pitch moves more than the relationships between the voices do.

To get started: connect MIX to your output. All three voices start on sine, at the same pitch. Turn voice 2's BEAT slightly to the right and voice 3's slightly to the left. Listen to the three voices beating against one another. Hover over a BEAT knob to see its exact rate.

The reference

REF sets the pitch that all three voices are tuned from. It covers three octaves below C2 to three octaves above, using 1 V/oct, with C2 at 0 V. The default is C2, or 65.41 Hz.

Hover over REF to see the frequency and nearest note, for example Reference: 65.41 Hz (C2).

V/OCT adds to the reference at one octave per volt. Connect a keyboard or sequencer here to play the whole bank.

Turning REF glides between pitches over a few milliseconds. V/OCT and REF IN respond immediately, so notes land straight away and connected banks follow the same pitch exactly.

REF IN overrides the internal REF setting. Connect another Littoral's REF output here and both banks will share one reference pitch. That's six voices working together; chain three banks for nine. V/OCT still transposes the whole chain.

The voices

The three rows each have the same controls.

OCT moves the voice up or down by whole octaves, up to two octaves in either direction.

COARSE adjusts the pitch further. Its switch selects how the knob works:

• SEMI (middle, the default): moves in equal-tempered semitones, up to an octave in either direction.
• JUST (down): selects just intervals relative to the reference. Each semitone position corresponds to a just interval. Switching from SEMI to JUST moves the voice to the nearest just interval. Above the reference, the intervals are 1/1, 16/15, 9/8, 6/5, 5/4, 4/3, 7/5, 3/2, 8/5, 5/3, 7/4, 15/8 and 2/1. Below the reference, the same intervals are available an octave lower. A just fifth is exactly 3/2, so a 100 Hz reference produces a 150 Hz voice.
• HZ (up): adds or subtracts a fixed frequency, up to 100 Hz either way.

Hover over COARSE to see its current setting, such as Coarse: +7 semitones, Coarse: 3/2 or Coarse: +12.5 Hz.

FINE tunes the voice up or down by up to 50 cents.

BEAT adds a fixed frequency offset after all the other pitch controls. It ranges from -5 Hz to +5 Hz, with very fine adjustment near the centre: a tenth of the knob's travel corresponds to 0.005 Hz.

This is the main tool for setting precise beats. Two voices that differ only in BEAT will beat at exactly the difference between their BEAT settings, regardless of the reference pitch.

Hover over BEAT to see its rate to three decimal places. Click the tooltip and type a frequency to set it exactly.

CV and AMT beneath BEAT let you control the beat rate with a voltage. AMT is off at its centre setting. Turn it to the right to make the voltage increase the beat rate; at full right, each volt adds 1 Hz. A ±5 V signal can therefore sweep across the full range of the knob. Turn AMT left of centre to reverse the effect.

For example, connect a slow Glacial lane to the BEAT CV input to make a voice's beat change gradually over the course of an hour.

The small switch beside AMT sets the input's range:

• x1 (down, the default): 1 Hz per volt at full AMT.
• FM (up): 20 Hz per volt. At full AMT, ±5 V can move the frequency by ±100 Hz. An audio-rate input produces linear frequency modulation, deep enough to hear as FM rather than just a slow shimmer.

At these settings, a low voice can be driven through zero frequency and into reverse, then back again, without stopping or clicking. Hover over the switch to see its range.

WAVE selects the waveform: saw, square, pulse, triangle or sine. The selected waveform is shown around the knob. The default is sine. The triangle includes the small tick from the oscillator core; the sine includes that tick and the extra harmonics introduced by the shaping circuit.

Levels

Each voice has its own VCA, at the right of its row.

LEVEL sets the voice's output level. It starts at 80%.

CV and AMT beside LEVEL let you control the level with a voltage. AMT is off at the centre.

Turning LEVEL or AMT produces a smooth change rather than abrupt steps. The CV input is smoothed just enough to prevent clicks when the voltage jumps, while still responding to fast signals such as tremolo.

The input range is ±5 V. At full-right AMT, +5 V adds the full range of LEVEL's travel and -5 V subtracts it.

For example, set LEVEL to zero, connect a Glacial lane set to POS (0 to +5 V) and turn AMT fully right. The lane will fade the voice from silence to full level.

The level uses a square-law response, which is closer to how we perceive loudness. This makes slow fades more even, rather than leaving most of the change until the end.

OUT is the voice's signal after its VCA. At full LEVEL, its range is ±5 V.

Drift

DRIFT controls how much the pitch wanders over time.

At its default setting, the shared drift moves the pitch by a few cents over several minutes, while each voice has its own additional drift of about a cent. Turn DRIFT fully right to double both effects. Turn it fully left to stop all drift, leaving the voices at exactly the frequencies set by their controls.

Hover over DRIFT to see its setting, for example Drift: 50%.

At 100 Hz, one cent is about 0.06 Hz. Even a few cents of movement can make a 0.2 Hz beat slow down, stop and speed up again during a piece. The drift is slow enough to sound like the music changing, rather than the oscillators wobbling.

WARM simulates the oscillators warming up from cold. A cold bank starts a few cents flat and gradually rises towards its normal pitch over about twenty minutes, with most of the change happening in the first ten. Each voice warms up slightly differently.

The small button triggers the same process manually. The WARM input triggers it whenever its voltage rises above 0 V.

A new Littoral starts cold, as does a bank whenever its patch is loaded.

When REF IN is connected, a bank takes its shared drift from the incoming reference. Chained banks therefore drift together, like oscillators in one cabinet. Its own WARM control still restarts the individual voices' warm-up.

Mains

MAINS adds the effect of electrical supply hum to the voices.

With the switch up at 50 (the default), it adds sidebands 100 Hz above and below each harmonic. Switch down to 60 for sidebands at 120 Hz.

The small knob beside the switch controls their level. At its default centre setting, the sidebands sit 46 dB below each component of the tone. They're faint, but can create their own slow beats near the harmonics of a low drone.

Turn the knob fully left to remove them. Fully right raises them to 34 dB below the tone, making the hum clearly audible.

Hover over the knob to see the level.

Outputs

REF, on the vermilion block, outputs the reference pitch as 1 V/oct, including V/OCT and the shared drift. Connect it to another Littoral's REF IN to chain the banks. A keyboard connected to the first bank's V/OCT will then play all the voices in the chain.

MIX combines the three voices after their VCAs, at one third of each voice's level. If all three are at full level and in phase, the combined output peaks at 5 V.

Jacks

All unpatched inputs read 0 V.

Notes

The voices start at the same pitch. With all BEAT knobs centred, the voices gradually drift apart if DRIFT is at its default setting. Turn DRIFT fully left to keep them locked together.

The sine wave isn't perfectly pure. Its third harmonic is about 35 dB below the fundamental, and its fifth is about 45 dB below. These harmonics are slightly stronger at higher pitches because the shaping circuit is driven harder there. Each voice differs slightly.

TICK controls the small transient that occurs when each oscillator's waveform restarts. It's the small knob beside WARM. At its default centre setting, the tick is faint: about 66 dB below the tone at 50 Hz. Turn it fully left to remove it, or fully right to make it 12 dB louder.

The tick is easiest to hear at low pitches, where each cycle is long enough for it to sound like a faint series of clicks. The ticks of different voices beat against each other too. At a few hundred hertz and above, they tend to disappear into the tone.

Hover over TICK to see its level relative to the default, for example Tick: +6.0 dB.

BEAT and FINE do different things. FINE adjusts pitch in cents, so the frequency difference depends on the note. A 10-cent offset produces a beat of about 0.4 Hz at 65 Hz, but 3 Hz at 520 Hz. BEAT works directly in hertz, so the same setting produces the same beat at any pitch.

Starting points

Slow beating. Connect MIX to your output. Set voice 2's BEAT to +0.1 Hz and voice 3's to -0.15 Hz, leaving REF at its default. The three fundamental frequencies beat against one another at 0.1, 0.15 and 0.25 Hz. The third and fifth harmonics beat three and five times as fast.

A just chord. Set voices 2 and 3 to JUST mode, with COARSE at 3/2 and 7/4 respectively. Move each BEAT a few hundredths of a hertz away from zero. Listen to the seventh's harmonics beating against those of the reference: the patterns move more slowly than you might expect.

Two banks. Connect the first Littoral's REF output to the second's REF IN. You now have six voices sharing one reference and one pattern of shared drift.

A composed beat. Connect a Glacial lane to voice 2's BEAT CV and turn AMT slightly right of centre. Draw a lane that rises slowly over the course of the drum's rotation. The beat speeds up, slows to a stop and reverses as the lane crosses zero.

FM. Leave voice 1 on sine. Set voice 2 an octave lower and select triangle. Connect voice 2's OUT to voice 1's BEAT CV, then switch voice 1's modulation range to FM. Gradually turn voice 1's AMT up from the centre. The sine develops sidebands as the modulation deepens. Take the signal from voice 1's OUT rather than MIX if you want to hear only the modulated voice.

A swell. Set LEVEL to zero on all three voices. Connect three Glacial lanes, each set to POS, to the three LEVEL CV inputs. Turn each AMT fully right and set the lanes to rise and fall at different points in the drum's rotation.