The aliasing phenomenon consists in the aparition of phantom frequencies non-harmonicaly related (“alias”), when audio is digitized at low sample rates. Also called downsampling or redux, the lower the sample rate, or the higher the frequencies present in the signal, the more dramatic the effect results.
The sample rate can be modified in two ways: using the low frequency numerical oscillator, which generates arpeggios based on alias tones; and by the trigger, which generates an alias change every time a new note is detected. Both modes can be set at random, which introduces a random factor into the modulation. The low bit resolution of the audio adds to the characteristic sound of this pedal. To achieve a sound that is also musical and intelligible, the ALU9 adds back a proportion of dry audio, carefully filtered to enhance the depth of the effect.
Given the nature of the effect, the ALU9 responds better to simple signals with few prominent frequencies, so avoid applying it to complete or distorted chords, although it can be used satisfactorily on all types of instruments. Also, using distortion after the ALU9 can mask part of the effect.