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LFO

A staple in synthesis, the Low Frequency Oscillator (lfo) is a sprite which re-invigorates the player's imagination with new energy. It is both a collaborator waiting in the wings to dutifully carry out a repetitive task and an impish source of instability & uncertainty.

speed

The classic control of any lfo! speed affects the frequency of oscillation from around 10 seconds (0.1Hz) at its minimum, up to low audio rate at its highest intensity (around 100Hz). Grabbing hold of speed as you play a patch will bring pure, simple joy!

If you're unfamiliar with modular synths, the concept of audio rate modulation might be a new addition to your toolkit. Essentially, if our lfo is running fast enough to be heard (the range of human hearing starts at approximately 20Hz), then it can introduce tonal & timbral textures to the modulated parameter that are imperceptible at slower rates / lower frequencies.

This is the point where rhythm becomes pitch!

Example:

  • Start with a sine: wave mode, mid-energy, zero timbre
  • Set the lfo's speed to its minimum and set its shape to triangle (the third in the sequence)
  • Map the lfo to increase energy
  • Start increasing speed
  • As speed approaches 2:00, you'll hear the changes start to distort into a new waveshape and a new, lower tone is introduced
  • Different (en)harmonicities await beyond!

shape

At first-touch, Atrium presents four basic shapes, cycled through by its shape key:

1) Ramp: rises smoothly, before sharply resetting to zero.
2) Sine: a smooth up-and-down path with a natural feel.
3) Triangle: a rigid up-and-down motion.
4) Square: alternates between the high and low state.

These shapes each animate the window at the centre of the phase circle, illustrating the progression of the modulator. You'll also see the light nearest the shape key pulsing in time with the modulation.

Each shape presents a different character and will be useful for many different things. An in-house favourite is using ramp to articulate energy, acting out a dramatic plucking of harmonics.

Beyond these first four shapes, Atrium includes 7 more default shapes:

Learn how to access these in the sequences section.

5) Stepped Random: jumps to a new random value every cycle.
6) Smooth Random: slides to a new random value over the course of each cycle.
7) Crease: similar to Ramp, but resets half-way through the cycle and moves with bipolar motion.
8) Sinc: A trigonometric function that smoothly rises once to full level, then a second time to a lower level.
9) Pulse: Similar to Square, but is "high" for only 1/5th of the cycle.
A) Scanner: Similar to Triangle, but compresses the motion to 2/5ths of the cycle.
B) Bubbles: A jagged series of five rising ramps, each reaching higher than the last.

Many of these, and especially shapes 8 through B, will become very useful when exploring phase below.

phase touchplate

Atrium's psychotopography borrows from many somatic experiences, both within music-making and beyond. The lfo's circular phase touchplate evokes memories of the "scroll wheel" navigator from early-aughts digital devices. Run a finger along it in a clockwise circular motion to separate the cyclical modulators for each voice.

phase pushes out four voices, while it's centre channel remains static. This phasing moves from a gentle sequential strumming, to equidistant five-note arpeggios, and far beyond. As you continue to scroll the voices will overlap and pass through one another. All kinds of irregular rhythms, as well as interference cancellations will occur along the way. At the maximum the voices will realign, but with the voice order reversed.

  • Scroll phase to its minimum (counter clockwise) to unify modulation across all voices.
  • Increase phase clockwise to offset the modulation among the voices.
  • Hold clear and tap phase to set to halfway, creating two distinct groups: voices 1/3/5 and voices 2/4.

When lfo is mapped to a monophonic destination, only the centre channel is used. This is the static voice that remains unaffected by phase, furthering the idea that phase is our interface into polyphony for the lfo.