OP-Xa V · Armon.ai

How it works

It is a polyphonic subtractive synthesizer: each voice is a small complete synth with two oscillators, noise, a low-pass filter and an amplifier.

The signal path

Oscillators: two VCOs per voice generate rich waves (sawtooth, square/pulse; in the Arturia version also triangle and saw+square). With sync, oscillator 2 restarts at every cycle of oscillator 1, producing new harmonics; with cross-mod, oscillator 2 frequency-modulates oscillator 1, creating metallic timbres.
Mixer: balances Osc 1, Osc 2 and noise into the filter.
Filter: resonant low-pass switchable between 2 poles (-12 dB/octave, more harmonics, open sound) and 4 poles (-24 dB/octave, darker and more sculpted).
Envelopes: one for the filter and one for the volume (Loudness): they define attack, decay, sustain and release.
Modulation: one LFO hard-wired to pitch, PWM, filter and volume, plus a dedicated vibrato section.

The "fat" character comes from summing analog voices that differ slightly from one another and from the individual panning of the voices in the stereo field.

Character and tone

Timbre

The "Oberheim sound": wide, roaring, with full mids and a Curtis filter that is open and juicy at 2 poles and darker and more compact at 4 poles. The oscillators have a slight instability that thickens every chord.

Where it sits in the spectrum

Very dense between 200 Hz and 2.5 kHz: it is an instrument that "fills the room." Stabs tend to occupy the same zone as distorted guitars and male vocals.

Strengths

Brass and stabs with an impact that is hard to replicate (the Jump riff).
Switchable 12/24 dB filter: the 2-pole setting is the key to the open, "nasal" sound typical of Oberheim.
Stereo Spread and per-voice pan: huge, moving pads.
Arturia brings over the OB-X cross-modulation and adds triangle and saw+square.

Limitations

The original's modulation is basic (one hard-wired LFO, two ADSRs); for complex routing you need the Advanced panel.
The sound is so dense that it often needs thinning out in the mix.

Comparisons

vs Jupiter-8: the OB-Xa is rawer and wider, the Jupiter glossier and more precise.
vs Prophet-5: the Oberheim has more "swollen" mids and a more open 2-pole; the Prophet is more compact and more aggressive at high resonance.
vs SEM: same brand, but the SEM has a 12 dB multimode filter and a lighter character; the OB-Xa uses 12/24 dB Curtis low-pass filters.

Architecture

Original (Oberheim OB-Xa, 1980–1983)

4, 6 or 8 voices with Curtis integrated circuits (CEM3340 VCO), 2 VCOs per voice (sawtooth, square/pulse), sync.
Resonant Curtis low-pass filter switchable between 2 poles/4 poles; mixer with noise.
2 ADSRs (filter, loudness); LFO with hard-wired destinations; the filter envelope can modulate Osc 2 PW / Osc 2 pitch (F-Env switch).
Split and Double modes (two programs on each half of the keyboard or layered), programmable Chord, portamento, memory expandable to 120 programs, per-voice pan via trimpots.

Signal path (per voice)

Osc 1 + Osc 2 + Noise → Mix → LP 12/24 dB filter (Filter Env, LFO, Track) → VCA (Loudness Env, LFO) → per-voice pan → stereo output → effects.

What Arturia adds (OP-Xa V, V Collection 9)

4 waveforms per oscillator (saw, triangle, square, saw+square as on the OB-8) and continuous X-Mod (cross-mod from the OB-X).
Up to 16 voices, Unison up to 8 voices; Stereo Spread (doubles oscillators and filters for the left/right channels with LFO Stereo, Osc Stereo, Filter Stereo, Movement Amt/Rate) or per-voice Pan with 8 trimpots.
Voice Dispersion (Factory/Aged/Out of Calibration/Custom).
Dedicated Vibrato section, Portamento with Quantize (glissando), Arpeggiator (6 patterns, up to 6 octaves), Chord with 11 presets.
Advanced – Modulation: 4 multi-segment envelopes (up to 16 points, loop, poly, sync, presets) assignable to almost any parameter; Input Modulation Matrix (Velocity, Key, Aftertouch, Mod Wheel, Filter Env to free destinations).
Effects: 3 slots, serial/parallel, with 9 effects (Reverb, Delay, Chorus, Flanger, Phaser, Overdrive, Compressor, BitCrusher, Multimode Filter).
Env Reset ("early OB-Xa" behavior), selectable Sync Routing.
Note: in V Collection 9 the instrument also appears as "OB-Xa V," its historical name before the change to OP-Xa V.

The controls, one by one

Master Section

Volume: Output volume.
Hold: Sustains notes indefinitely (not saved in the preset).
Chord: Turns on chord mode: one key plays several notes.
Sel: Programs the chord over two octaves (the lowest note is the key pressed) or chooses among 11 preset chords.
Master Tune: Global tuning from -12 to +12 semitones.

Voices Section

Unison Detune: Detuning between the voices in Unison: low = thickness, high = dissonance/swarm.
Unison: Turns unison on; the number of voices per note is set in the side panel.
Stereo Spread / Pan (switch): Spread: oscillators and filters duplicated for left and right with dynamic variations. Pan: each new note goes to the position of its voice's trimpot.
Spread (knob): Amount of stereo width (at zero the sound is mono); the result depends on the mode chosen.

Stereo Spread Advanced Controls (door above the wheels)

LFO Stereo: Phase offset between the left and right LFO from -180° to +180° (an active LFO destination is required).
Osc Stereo: Relative detuning between the left and right copies of the oscillators.
Filter Stereo: Difference in filter cutoff between the two channels.
Movement Amt: Amount of automatic panning of the two copies.
Movement Rate: Speed of the automatic panning from 0 to 3 Hz.

Voices Pan and Voice Dispersion (doors above the keyboard)

Pan trimpot 1–8: Fixed stereo position of each voice (with 16 voices, trimpot 1 applies to voices 1 and 9, and so on); distance from center set by the Spread knob.
Dispersion 1 / 2 / 3 / Custom: Factory, Aged, Out of Calibration or custom.
Pitch: Detuning between voices (outside unison).
PW: Pulse width variation between voices.
Cutoff: Filter cutoff variation between voices.
Reso: Resonance variation between voices.
Env: Differences in envelope times.
Mod: Differences in modulation depths.

Modulation Section (LFO)

Rate: LFO speed.
Sync: Locks the Rate to tempo subdivisions.
Waveform: Sine, Triangle, Saw, Ramp, Square, Sample & Hold, Smoothed Sample & Hold.
Key Retrig: Restarts the cycle on every note; when off, the LFO free-runs.
Mod Depth 1: Depth of the first modulation path, toward the destinations switched on below.
Osc 1 Freq / Osc 2 Freq / Filter Freq: Destination switches for path 1: vibrato on one or both oscillators, wah on the filter. The LFO is bipolar around the current value.
Mod Depth 2: Depth of the second path.
Osc 1 PWM / Osc 2 PWM / Volume: Destinations of path 2: PWM (requires the square wave) and tremolo.

Oscillator Section

Osc 1 Frequency: Pitch of Osc 1 in octaves.
Osc 2 Frequency: Pitch of Osc 2 in semitones (intervals, power chords, sync).
Osc 1 / Osc 2 Waveform (switch): Switch combinations for Saw, Triangle, Square, Saw+Square.
Sync: Hard sync: the slave oscillator restarts at every cycle of the dominant one (chosen in Sync Routing: 1 or 2). Sweeping the slave's frequency gives the classic sync sweep.
Osc 2 Detune: Fine tuning of Osc 2: a few cents for the Oberheim thickness.
X-Mod: Continuous cross-modulation from Osc 2 to Osc 1: ring-modulator-style timbres, metallic sounds, bells, growls.
Pulse Width: Pulse width (at maximum it is a square wave; reducing it makes it nasal). Affects the square wave of both oscillators.

Filter Section

Frequency: Cutoff of the Curtis low-pass.
Resonance: Emphasis at the cutoff. At 2 poles it adds a peak; at 4 poles it emphasizes the cutoff and attenuates the rest (thinner, more focused sound).
Mod: Amount by which the Filter Envelope opens the filter.
4 Pole: Off = 2 poles -12 dB/octave (open, 'Oberheim'); on = 4 poles -24 dB/octave (darker and more incisive).
Track: Filter keyboard tracking: higher notes are brighter.
Mix: Osc1 / Osc2 / Noise: Input levels to the filter for the two oscillators and the noise.

Envelopes Section

Filter Envelope: Attack / Decay / Sustain / Release: Cutoff envelope (added to the Frequency value, amount set with Mod).
Loudness Envelope: Attack / Decay / Sustain / Release: Volume envelope.
Env Reset (side panel): On: each envelope restarts from zero; Off: early OB-Xa behavior, the voice restarts from the level it is at (smooth, useful with long releases).

Vibrato Section

Osc1 Vibrato / Osc2 Vibrato: Turns on vibrato on each oscillator (vibrato on Osc 2 only creates a 'chorus' between the two).
Vibrato Rate: Vibrato speed.
Vibrato Depth: Depth up to 3 semitones (assignable to aftertouch in the Advanced panel).
Vibrato Shape: Three buttons for the modulation waveform.

Portamento Section

Time: Glide time from 0 s/octave and up.
Quantize: Glide in semitones (glissando) instead of continuous.

Arpeggiator Section

On: Turns on the arpeggiator (also works together with Chord).
Rate: Speed: free 0.1–50 Hz, synced from 1 to 1/64.
Sync: Free or tempo-synced.
Pattern: As Played, Up, Down, Up-down 1 (end notes repeated), Up-down 2 (end notes once), Random.
Octave: From 1 to 6 octaves.

Mod Wheel and Pitch-Bend (wheels)

Bend Amount: Pitch-bend range: 1 or 2 semitones, minor/major third, fourth, fifth, seventh, 1 or 2 octaves.
Osc2 Only: The bend affects only Osc 2: with sync or X-Mod it changes the timbre.
Mod Wheel: Modulation wheel assignable in the Input Modulation Matrix.

Side panel (Settings) and bottom bar

Poly: Maximum voices 1–16.
Unison: Voices per note in Unison; Poly = Unison gives legato mono-unison, Poly as a multiple of Unison gives polyphonic unison.
Env Reset: See the Envelopes section.
Sync Routing: Which oscillator is dominant in the sync (1 or 2).
Macro (4): Four assignable macros.

Advanced: Modulation (4 envelopes)

Envelope 1–4 selection + On/Off: Four multi-segment sources; right-click the frame to copy them.
Destination + Modulation Amount: Almost any destination and a bipolar amount from -100% to +100%.
Breakpoints (up to 16), Point / Level / Time, curves: Drawing the shape; time in ms between points.
Key Trig: Restarts the envelope on every note; when off, it free-runs.
Loop: Repeats continuously (like an LFO or a step sequencer).
Poly: One envelope per voice instead of a common one.
Total Length + Sync: Total duration from 5 ms to 20 s, or in bars/subdivisions.
Presets: Ready-made shapes to use or modify.

Advanced: Input Modulation Matrix

Rows Vel / Key / AT / MW / FEnv: Velocity, Keyboard tracking, Aftertouch, Mod Wheel, Filter Envelope (replaces the original's F-Env switch).
Destination columns: Click the title to choose the parameter (e.g. Filter Freq, Osc2 Pitch, Vibrato Depth).
Cells: Amount -1.000/+1.000 (drag; right-click for precision; double-click to clear).

Advanced: Effects

Serial / Parallel: Effects in series or in parallel.
Slot 1–3: Power, effect menu, Wet/Dry: Reverb, Delay, Chorus, Flanger, Phaser, Overdrive, Compressor, BitCrusher, Multimode Filter.

Sound design tips

Filter

2 poles vs 4 poles: the 2-pole is the secret of Oberheim brass and strings: it lets more harmonics through and sounds "open" even with a low Frequency. The 4-pole is for basses and dark pads. If a brass sounds "closed," first try switching off 4 Pole instead of opening the cutoff.
Mod vs Frequency: for the "Jump" stab, Frequency stays medium-low (30–40%) and Mod medium (40–50%) with a short filter decay: the attack rings out and then settles.
Resonance in 4-pole mode: reduces perceived volume and low end; compensate with volume, not with more resonance.
Track: turn it on for leads and stabs that span several octaves, otherwise the high notes become dull.

Envelopes

Attack vs decay: for percussive stabs, Loudness A 0–5 ms and Filter D 150–300 ms with filter Sustain at 30–50%; for "breathy" brass, Filter A 50–120 ms.
Release and tempo: Oberheim chords with a release over 600 ms at fast tempos (>120 BPM) get muddy; use Env Reset Off only if you want soft legato.

Stereo and width

High Spread + unison + chorus = wall of sound, but with a risk of phase problems in mono: always check mono compatibility, especially for stabs that need to stay centered.
For pads, use Spread mode with Osc Stereo at minimum and slow Movement (0.1–0.3 Hz): the sound moves without seeming out of tune.

Frequencies

The OP-Xa takes up a lot of 250–800 Hz: with guitars and vocals, cut 2–4 dB around 300–500 Hz instead of turning the volume down, and use a high-pass at 100–150 Hz on pads.
The brass "roar" is between 1 and 2.5 kHz: that is where presence is won or lost.

Modulation and performance

Use the Vibrato section instead of the LFO for vibrato: that leaves the LFO free for PWM or filter.
Aftertouch → Vibrato Depth (0.3–0.5) and Velocity → Filter Freq (0.2–0.4) make the instrument expressive.
X-Mod: small amounts add musical grit, large amounts make it inharmonic; lower Osc2 in the mixer to hear only the effect on Osc 1.

Common mistakes

Unison with Poly set too low: the notes steal from each other.
Pulse Width at minimum: the pulse is so narrow that the sound disappears.
Hold not saved: presets always start with Hold off.

Presets to recreate

Jump — brass stab

Brass / Stab · Van Halen — Jump (1983)

The bright, short chord of the Jump riff. On the original recording the keyboard part is played on an Oberheim OB-Xa; here it is recreated with the OP-Xa V, its direct emulation. The 2-pole filter gives the open, slightly nasal sound typical of Oberheim.

Oscillators: Osc 1 Saw, Frequency 0 (8'); Osc 2 Saw, Frequency 0, Osc 2 Detune +6 cents; Sync OFF, X-Mod 0.
Mixer: Mix Osc1 100%, Osc2 100%, Noise 0.
Filter: 4 Pole OFF (2 poles, -12 dB/oct), Frequency 35%, Resonance 10%, Mod 45%, Track ON.
Filter envelope: Attack 5 ms, Decay 350 ms, Sustain 45%, Release 250 ms.
Amplitude envelope (Loudness): Attack 0 ms, Decay 400 ms, Sustain 80%, Release 250 ms.
LFO and modulation: LFO Sine 5 Hz with Mod Depth 1 at 0 (vibrato from the mod wheel only); Input Matrix Vel → Filter Freq +30%.
Voice and glide: Poly 8, Unison OFF, Portamento Time 0; Spread 40%, Dispersion 2.
Effects: light Chorus (Wet 20%) → short hall Reverb (1.5 s, Wet 20%).

Stereo Oberheim Pad

Pad · Synthwave, '80s pop

Wide, warm pad that moves across the stereo field thanks to Spread and slow PWM.

Oscillators: Osc 1 Saw+Square, Frequency 0, Pulse Width 70%; Osc 2 Saw, Frequency 0, Osc 2 Detune -7 cents.
Mixer: Osc1 90%, Osc2 90%, Noise 0.
Filter: 4 Pole ON (-24 dB/oct), Frequency 45%, Resonance 15%, Mod 20%, Track ON.
Filter envelope: Attack 800 ms, Decay 1.5 s, Sustain 70%, Release 2 s.
Amplitude envelope: Attack 500 ms, Decay 1 s, Sustain 90%, Release 2.2 s.
LFO and modulation: LFO Triangle 0.4 Hz, Mod Depth 2 at 30% with Osc 1 PWM ON; Stereo Spread Advanced: slight Osc Stereo, Movement Amt 30%, Movement Rate 0.2 Hz.
Voice and glide: Poly 8, Unison OFF, Portamento 0; Spread mode at 70%.
Effects: Chorus (Wet 30%) → long Reverb (4 s, Wet 35%).

Oberheim Unison Lead

Lead · '80s rock and AOR

Big, singing monophonic lead with four stacked voices.

Oscillators: Osc 1 Saw, Frequency 0; Osc 2 Square, Frequency +12, Pulse Width 70%, Osc 2 Detune +4 cents.
Mixer: Osc1 100%, Osc2 70%, Noise 0.
Filter: 4 Pole ON, Frequency 55%, Resonance 20%, Mod 25%, Track ON.
Filter envelope: Attack 10 ms, Decay 600 ms, Sustain 60%, Release 300 ms.
Amplitude envelope: Attack 5 ms, Decay 300 ms, Sustain 95%, Release 250 ms.
LFO and modulation: Vibrato Section Osc1+Osc2 ON, Vibrato Rate 5.5 Hz, Depth assigned to Aftertouch in the Input Matrix.
Voice and glide: side panel Unison 4; Unison ON, Unison Detune 15%; Portamento Time 60 ms.
Effects: dotted eighth-note Delay (Wet 20%) → plate Reverb (1.8 s, Wet 20%).

Biting Sync Bass

Bass · '80s funk and synthpop

Bass with the bite of sync on the attack, for funk and synthpop.

Oscillators: Osc 1 Saw, Frequency -1 octave (16'); Osc 2 Saw, Frequency +7, Sync ON (Sync Routing: Osc 1 dominant).
Mixer: Osc1 70%, Osc2 90%, Noise 0.
Filter: 4 Pole ON, Frequency 25%, Resonance 25%, Mod 40%, Track 50%.
Filter envelope: Attack 0 ms, Decay 250 ms, Sustain 20%, Release 100 ms; Advanced Envelope 1 (Key Trig ON, 200 ms decay) → Osc 2 Frequency +40%.
Amplitude envelope: Attack 0 ms, Decay 500 ms, Sustain 75%, Release 80 ms.
LFO and modulation: none (Mod Depth 1 and 2 at zero).
Voice and glide: Unison 2 voices, Unison Detune 5%; Portamento 0; Spread 0 to keep the bass centered.
Effects: light Overdrive (Wet 100%, drive 15%) → Compressor 3:1.

X-Mod Bell

Keys / FX · Soundtracks, synthwave

Metallic timbre made with cross-modulation from Osc 2 to Osc 1, which Arturia carries over from the OB-X.

Oscillators: Osc 1 Triangle, Frequency 0; Osc 2 Triangle, Frequency +17 semitones, Osc 2 Detune +10 cents; X-Mod 40%.
Mixer: Osc1 100%, Osc2 0 (modulator only), Noise 0.
Filter: 4 Pole OFF, Frequency 70%, Resonance 0%, Mod 15%, Track ON.
Filter envelope: Attack 0 ms, Decay 1.5 s, Sustain 0%, Release 1.5 s.
Amplitude envelope: Attack 0 ms, Decay 2.5 s, Sustain 0%, Release 2 s.
LFO and modulation: Input Matrix Vel → X-Mod +20% for harder bells when playing loud.
Voice and glide: Poly 8, Portamento 0.
Effects: quarter-note ping-pong Delay (Wet 20%) → Reverb (4 s, Wet 35%).

1999 — Oberheim Stab

Brass · Minneapolis sound, '80s funk-pop

The sixteenth-note synth stab that opens Prince's 1999. On the original recording the instrument is an Oberheim polyphonic, reported as an OB-X or Four Voice; here it is recreated with the OP-Xa V, an emulation of the OB-Xa, the direct successor to the OB-X. The drums on the track are a Linn LM-1.

Oscillators: Osc 1 Square, Frequency 0, Pulse Width 40%; Osc 2 Square, Frequency 0, Osc 2 Detune +8 cents.
Mixer: Osc1 100%, Osc2 90%, Noise 0.
Filter: 4 Pole OFF (2 poles), Frequency 50%, Resonance 15%, Mod 40%, Track ON.
Filter envelope: Attack 3 ms, Decay 350 ms, Sustain 50%, Release 200 ms.
Amplitude envelope: Attack 0 ms, Decay 500 ms, Sustain 80%, Release 200 ms.
LFO and modulation: LFO Triangle 0.8 Hz, Mod Depth 2 at 35% with Osc 1 PWM and Osc 2 PWM ON: this is the chorus-like movement typical of Oberheim.
Voice and glide: Poly 8, Unison OFF, Portamento 0; syncopated sixteenth-note chords with velocity accents; octave-up doubling with filter Frequency at 35%.
Effects: Chorus (Wet 15%) → plate Reverb (1.2 s, Wet 15%).

In genres and records

'80s rock and AOR: the keyboard part of Van Halen's Jump is played on an OB-Xa; documented users include Rush, Queen, The Police, Simple Minds, Jethro Tull, Bon Jovi, Rod Stewart and Cliff Richard. Huge brass and stabs over the guitars.
New wave, synthpop, post-punk: New Order, Depeche Mode, Gary Numan, The Stranglers, Thompson Twins. Chords, pads and basses.
Funk, R&B and Minneapolis sound: Prince and the duo Jimmy Jam and Terry Lewis; synth brass in place of real horns.
Electric jazz: Miles Davis in the '80s.
Soundtracks: Brad Fiedel among the users; epic brass and wide stereo pads.
Electronic: Jean-Michel Jarre and Mike Oldfield.
Modern pop with an '80s aesthetic: Calvin Harris among recent users; wide stabs, stereo pads.
Synthwave and retrowave: Oberheim brass and pads are a cornerstone of the genre.
House, nu-disco, French touch: filtered chords and stabs.