Sound Synthesis
How the Draw.Audio synthesizer works: waveforms, ADSR envelope, sub oscillator, noise, unison, drift and warmth, plus 6-operator FM and wavetable modes.
- Waveform
- Picks the basic tone: sine, sawtooth, triangle, square, or pulse. Keys 1 to 5 select them in that order. The picker is dimmed in FM and Wavetable mode.
- Note Length
- Sets the length of the notes you draw: 1, 2, 3, 4, 6, or 8 steps. Shift+1 to Shift+8 sets any length from 1 to 8 steps.
- ADSR Envelope
- Shapes the volume of each note over time. It is in the Envelope tab of the Oscillator panel. Attack: fade-in time Decay: time to drop from peak to sustain level Sustain: level held while the note is on Release: fade-out time after the note ends Drag the points on the envelope graph to set each stage, or drag the handles on the attack and release segments to bend their curves. The preset shapes (Pluck, Pad, Organ, Bell, and more) set all four stages and both curves at once.
- Sub Oscillator
- Adds a second, lower tone underneath your main sound. Level: mix amount of the sub Waveform: sine, saw, triangle, or square Octave: -1, -2, or -3 octaves below the main oscillator
- Noise
- Mixes in noise alongside the oscillator. Level: mix amount of noise Type: white (flat), pink (-3dB/oct), brown (-6dB/oct), blue (+3dB/oct)
- Unison
- Stacks detuned copies of the oscillator for a thicker sound. Voices: number of copies, 1 to 8 (1 = off) Detune: pitch spread between copies in cents Spread: pans voices across the stereo field Wave: waveform of the extra voices; Mixed picks a random waveform for each voice on each note Phase Spread: staggers the start phase of the voices for a wider, smoother stack Free Phase: keeps the oscillator phase running between notes, so each attack sounds slightly different
- Drift
- Random, subtle pitch wandering, like analog oscillator instability. Where Pitch LFO gives periodic vibrato, Drift is random and never repeats. Amount: how far the pitch wanders, in cents Rate: how quickly the wandering evolves
- Pulse Width
- Sets the duty cycle of the pulse waveform, from 1% to 50%. At 50% it is a square wave; lower values give a thinner, more nasal tone. The slider appears only when Pulse is selected. Add a Pulse width LFO for classic PWM sounds.
- Warmth
- Subtle harmonic saturation on the raw oscillator, before the filter. Adds gentle analog color without heavy distortion. Amount: how much saturation Color: pre-saturation low-shelf position (0 = classic 400 Hz, − cuts bass, + lifts highs) Bias: asymmetric clipping offset (0 = symmetric, + adds 'tube' character, − inverts)
- Stereo Spread
- Widens the stereo image by adding a shadow copy of each voice, panned opposite to the main one. Width sets how far apart the two copies sit: 0% keeps both at the voice's pan, 100% puts them hard left and right. Detune sets how far the copy is tuned away from the voice, in cents: at 0 the copy is a clean double a few milliseconds behind the voice, higher values beat against it. Detune with Width at 0 gives a thick mono double.
- FM Mode
- Switches the track to a 6-operator FM synth modeled on the DX-7. Turn on FM Mode in the FM tab of the Oscillator panel. FM is not available on drum tracks. Each operator is a sine (or saw, square, half-sine, abs-sine, or noise) oscillator with its own ratio, envelope, level, and pan. Pick one of 32 algorithms to set how the operators connect as carriers and modulators. Amount: overall FM modulation depth Dice: rolls a random FM patch: algorithm, ratios, envelopes, levels, and feedback Algorithm: the current algorithm and its diagram; click Change to pick another MIX: level, pan, and feedback for each operator; S and M solo or mute an operator PITCH: ratio and fine tune for each operator, FIXED to lock an operator to a frequency in Hz, and a patch transpose ENV: a 4-stage rate/level envelope for each operator, plus an optional pitch envelope MOD: key scaling, velocity, rate key scaling, AM sensitivity, and waveform for each operator, plus noise routing LFO: one DX-7-style LFO for vibrato and tremolo, shared by all operators The Presets dropdown has FM patches and 256 classic DX-7 patches. To add your own, click Upload DX-7 bank… in its DX-7 section, or drop a 32-voice .syx file on the list. To rename or remove uploaded banks, see Presets & Drum Kits.
- Wavetable Mode
- Switches the track to a wavetable oscillator: a stack of single-cycle waveforms (frames) you sweep through for a continuously morphing tone. Turn on Wavetable Mode in the Wavetable tab of the Oscillator panel. It is not available on drum tracks. The filter, unison, sub, noise, and effects all still apply. Wavetable: which table to scan. There are 13 built-in tables, such as Analog Morph, Formant Vowel, PPG Digital, and Vocal Choir, plus tables in the WaveEdit and FreeSound groups Position: where in the table you are, from the first frame to the last; sweep it to morph the timbre Morph Envelope: an ADSR that moves Position on its own at each note, with its own amount and attack/release curves Warp: reshapes each frame as it's read (Bend, Asym, Mirror, or Sync); Amount sets how far Dice: picks a random table, position, warp, and morph envelope Position and Warp are also LFO targets, so an LFO can animate the morph.
FM Synthesis Basics
Instead of filtering a single oscillator, FM uses six oscillators ("operators") that modulate each other's frequency. Each operator has its own ratio, envelope, level, waveform, and pan.
- Algorithm
- The algorithm sets which operators modulate which. There are 32 algorithms, the same set as the DX-7. Carriers are the operators you hear; modulators change the tone of the operators they feed. In each diagram, carriers are filled boxes with a line to the output and modulators are outlines. The MIX page marks each operator CAR or mod.
- Ratio
- An operator's pitch relative to the played note. Integer ratios (1, 2, 3…) sound harmonic; fractional ratios sound bell-like or metallic.
- Feedback
- An operator modulating itself. Each algorithm allows feedback on one operator only; on the others the control is dimmed. Small amounts brighten a sound; large amounts get raspy.
- Pan
- Per-operator stereo placement. With multi-carrier algorithms, panning carriers apart widens the sound.
- Operator activity
- During playback, the OP labels on the MIX page pulse to show which operators are sounding.
- Tip
- The fastest way to learn FM is to press the dice button until you find a sound you like, then look at which algorithm it used.