The GRAIN CONTROLS of Portal are where most of the sound processing happens. Incoming audio is sampled into an audio buffer and is then sliced into tiny pieces called grains. Grains can be stretched, overlapped, delayed, panned, smoothed, and reversed using STRETCH, SPEED, REVERSE, PITCH, PAN, OFFSET, SHAPE, DENSITY, GRAIN SIZE, TIME, and FEEDBACK controls.
DENSITY - How often in time grains are sampled from the audio buffer.
DENSITY DIAMOND - Add random modulation to DENSITY on a per grain basis.
OFFSET - Offset the start point of concurrent grains when more than 1 grain is generated.
OFFSET RATIO LOCK - Lock OFFSET to a ratio of DENSITY. For example, if DENSITY is set to 1/8 note and OFFSET is ratio locked at 1:2, then OFFSET will equal 1/16 note.
GRAIN SIZE - Length in time of grains being sampled from the audio buffer.
GRAIN SIZE DIAMOND - Adds random modulation to GRAIN SIZE on a per grain basis.
GRAIN SIZE RATIO LOCK - Lock GRAIN SIZE to a ratio of DENSITY. For example, if DENSITY is set to 1/4 note and GRAIN SIZE is ratio locked at 2:1, then GRAIN SIZE will equal 1/2 note.
COUNT - Number of grains being generated at one time.
PITCH - Shift pitch on a per grain basis.
SCALE - Quantize PITCH to a set scale, interval, or chord so that only tones within the selected SCALE will be played.
***Note: When set to chromatic, step readouts equal semitones. When set to any scale other than chromatic, step readouts equal scale step. For Example: If SCALE is set to Major Chord, then 1 step is equal to a Major 3rd, 2 steps are equal to a Perfect 5th, and 3 steps is equal Octave.
PITCH DIAMOND - Adds random modulation to PITCH following the set SCALE. As the knob is increased, more randomness is introduced.
PAN - Pan the granulated signal left or right.
PAN DIAMOND - Add random panning on a per grain basis.
DRY / WET - Control PRE FX DRY / WET amount of the granulator.
STRETCH - Power button for SPEED / RETRIGGER controls.
SPEED - Control playback speed of the audio buffer. Speed can only be slowed down, it cannot be sped up because that would require looking into the future, which isn’t possible… yet.
SPEED SYNC - Snap SPEED to exact time divisions.
RETRIGGER - Snap the playhead at a synced rate to the current position in the audio buffer while being slowed down by STRETCH.
TIME - Add delay to the audio buffer which is then fed back into the input of the granulator.
TIME SYNC - Snap delay TIME to exact musical values.
FEEDBACK - Control the amount of signal sent back into the granulator.
***Note*** BE CAREFUL!!! If DENSITY is small, and GRAIN SIZE is large, volume spikes in the signal can cause the feedback to get very loud.
HP - Apply the high-pass filter to the feedback signal.
LP - Apply the low-pass filter to the feedback signal.
***Note*** To hear the delay effect, GRANULATOR DRY / WET must be below 100%. Otherwise, only the delayed signal is audible.