Littoral

Three oscillators on one reference pitch · Radish · Vulpus Labs

Littoral is a bank of three oscillators for drones. All three are tuned from one reference pitch, and each can be set a precise number of hertz away from it with its BEAT knob. Two voices set 0.2 Hz apart beat once every five seconds, at any pitch, every time.

The oscillators are made the way the studio oscillators of the large modular systems were: a sawtooth core, folded into a triangle, and the triangle rounded into a sine. That sine is not quite pure. It carries a little of the third and fifth harmonics, a trace of the second, and a tiny tick once a cycle where the core resets. When two such sines beat, the fundamental beats at the rate you set, the third harmonic three times as fast and the fifth five times as fast, each in its own register. That interlocking shimmer is what a drone made of pure sines lacks.

The pitch also drifts, slowly, as a cabinet of oscillators does as it warms up and settles. The drift shared by all three voices is larger than the drift between them, so the beats wander less than the pitch does.

To begin: patch MIX to your output. All three voices load on sine, at the same pitch. Turn voice 2's BEAT a little to the right and voice 3's a little to the left, and listen to the three beat against each other. Hover over a BEAT knob to read its rate.

The reference

REF sets the pitch all three voices are tuned from: from three octaves below C2 to three above, as 1 V/oct, where C2 is 0 V. It loads at C2, 65.41 Hz. Hover over it for the frequency and the nearest note, as Reference: 65.41 Hz (C2).

V/OCT adds to REF, a volt an octave, so the whole bank can follow a keyboard or a sequencer. Turning REF glides over a few milliseconds; V/OCT and REF IN do not, so notes land at once and a chained bank follows the first exactly.

REF IN replaces REF. Patch another Littoral's REF output into it and the two banks share one reference: six voices, all beating against the same pitch. A chain of three gives nine. V/OCT still adds to it.

Each voice

The three voices are the three rows. Each has the same controls.

OCT moves the voice by whole octaves, from two down to two up.

COARSE moves it further, in whatever its switch says:

• SEMI, the middle, where it loads: equal-tempered semitones, up to an octave either way.
• JUST, down: just intervals over the reference, one for each semitone, so switching from SEMI to JUST moves a voice to the nearest just interval. Up from the reference they 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; left of centre the same an octave lower. A just fifth, 3/2, is exact: a voice on it over a reference of 100 Hz runs at 150 Hz.
• HZ, up: a frequency added to the voice, up to 100 Hz either way.

Hover over COARSE for its setting: Coarse: +7 semitones, Coarse: 3/2, Coarse: +12.5 Hz.

FINE tunes the voice up to 50 cents either way.

BEAT sets the voice a number of hertz away from where the controls above put it: up to 5 Hz either way, and very finely near the centre, where a tenth of the way round is five thousandths of a hertz. It is added after everything else, so two voices that differ only in BEAT beat at exactly the difference of their BEATs, whatever the reference. Hover over it for the rate, to a thousandth of a hertz; click the tooltip and type a rate in hertz to set it exactly.

CV and AMT under BEAT: a CV on the beat, through its amount. AMT loads at its centre, where the CV does nothing. At full right each volt adds a hertz, so ±5 V moves the beat as far as the knob does; left of centre inverts it. A slow Glacial lane into it composes a voice's beat over an hour.

The small switch beside AMT sets the CV's range. Down, at x1, where it loads, it is the hertz a volt above. Up, at FM, it is twenty: ±5 V at full AMT moves the voice ±100 Hz, and an audio-rate CV is linear FM, deep enough to be heard as FM rather than a shimmer. A low voice driven that far goes through zero and runs backwards, and comes back the same way, without a stall or a click. Hover over the switch for its range.

WAVE chooses what the voice puts out, drawn round the knob: saw, square, pulse, triangle and sine. It loads on sine. The triangle carries the core's tick; the sine carries the tick and the shaper's residue.

Levels

Each voice's output passes through its own VCA, on the right of its row.

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

CV and AMT beside it: a CV on the level, through its amount, off at the centre. LEVEL and AMT glide when they are turned, so they do not zipper; the CV is smoothed only a little, enough that a sudden step on the cable does not click, so a fast CV such as a tremolo still comes through. The CV is ±5 V: at full right, +5 V adds LEVEL's whole travel and -5 V takes it away. With LEVEL at zero, a Glacial lane set to POS (0 to +5 V) fades the voice from silence to full. The level follows a square law, close to how loudness is heard, so a slow fade moves evenly rather than rushing at the end.

OUT is the voice, after its VCA: ±5 V at full level.

Drift

DRIFT sets how far the pitch wanders. Where it loads, the shared drift wanders a few cents over several minutes and each voice's own drift about a cent. Fully right doubles both; fully left holds every voice still, and the beats are exactly what the BEAT knobs say. Hover over it for the setting, as Drift: 50%.

At 100 Hz a cent is about 0.06 Hz, so a few cents is enough to make a beat of 0.2 Hz slow, stall and speed up again over the course of a piece. The drift is slow enough that you hear it as the piece changing, not as the oscillators wobbling.

WARM starts the warm-up from cold. A cold bank starts a few cents flat and rises towards pitch over the next twenty minutes or so, most of it in the first ten, each voice a little differently. The small button does the same by hand, and the WARM jack does it on each rise above 0 V. A Littoral is cold when it is first made and whenever the patch loads.

A bank whose REF IN is patched takes its shared drift from the cable, so the whole chain drifts together, as one cabinet. Its own WARM then restarts only its voices' own warm-ups.

Mains

MAINS puts the hum of the supply on the voices: sidebands 100 Hz either side of each harmonic with the switch up at 50, where it loads, and 120 Hz with it down at 60. The small knob beside the switch, under the same label, sets how much. At its centre, where it loads, the sidebands are 46 dB under each component of the tone: faint, but near the harmonics of a low drone they make slow beats of their own. Fully left there is none; fully right they are 34 dB down, and the hum is plain. Hover over it for the level.

Outputs

REF, on the vermilion block: the reference, as 1 V/oct, with V/OCT and the shared drift on it. Patch it into another Littoral's REF IN to chain the two; a keyboard into the first bank's V/OCT then plays the whole chain.

MIX: the three voices, after their VCAs, each at a third, so three voices in phase at full level peak at 5 V.

Jacks

Every input reads 0 V when nothing is patched.

Notes

The voices load at the same pitch. With every BEAT at the centre and DRIFT where it loads, the three drift apart slowly by themselves. With DRIFT fully left they stay locked together.

The sine is not pure, on purpose. Its third harmonic is about 35 dB down, its fifth about 45 dB, and a little louder at the top of the range than the bottom, as the shaper was driven a little harder there. Each voice's are slightly different.

The tick is set by TICK, the small knob beside WARM: at its centre, where it loads, the tick is faint, about 66 dB under the tone at 50 Hz; fully left it is gone; fully right it is 12 dB louder. It is loudest relative to the tone at low pitches, where a cycle is long enough to hear it as a faint click train. It beats against the other voices' ticks. Above a few hundred hertz it disappears into the tone. Hover over TICK for its level against where it loads, as Tick: +6.0 dB.

BEAT and FINE are different tools. FINE is in cents, so the beat it makes changes with pitch: 10 cents is 0.4 Hz at 65 Hz and 3 Hz at 520 Hz. BEAT is in hertz, so a beat set at one pitch is the same beat at any other.

Starting points

Slow beating. MIX out. Voice 2's BEAT at +0.1 Hz, voice 3's at -0.15 Hz. REF where it loads. The fundamental beats at 0.1, 0.15 and 0.25 Hz; the third and fifth harmonics, three and five times as fast.

A just chord. Voices 2 and 3 on JUST, COARSE at 3/2 and 7/4. Each BEAT a few hundredths of a hertz off. The seventh's beats against the reference's harmonics are slower than you expect.

Two banks. The first Littoral's REF out into the second's REF IN. Six voices, one reference, one drift.

A composed beat. A Glacial lane into voice 2's BEAT CV, AMT a little right of centre. Draw the lane rising slowly over the turn: the beat speeds up, stalls and reverses as the lane crosses zero.

FM. Voice 1 on sine as it loads; voice 2 an octave down, on triangle, its OUT into voice 1's BEAT CV, voice 1's switch on FM. Bring voice 1's AMT up from the centre: the sine grows sidebands as it goes. Take voice 1's OUT rather than MIX if only the FM is wanted.

A swell. LEVEL at zero on all three voices. Three Glacial lanes on POS into the three LEVEL CVs, AMT full right, each lane rising and falling at a different place on the drum.