Rob Papen Blue II software synth reviewed

June 13, 2014


I’m in danger of losing my credibility as a grouch. Too many of the soft synths I’m reviewing these days are just fantastic! Case in point: Blue II, from Rob Papen. Blue II is not perfect, but even so, I couldn’t find much to gripe about. The original version, released in 2005, was already a powerhouse. The upgrade to Blue II (which we’ll just call Blue in this review) adds massive new capabilities: double the number of filter modes, double the number of effect types (and four effects modules rather than two), new oscillator controls, a new X/Y modulation source, and more.


Blue’s sound engine serves up six oscillators and two filters. The oscillators can be routed into an FM matrix for old-school DX7-style synthesis, or through the filters for analog-style subtractive synthesis—or you can use both synthesis types in a single patch. For each oscillator, you can choose from a menu containing well over 100 waveforms, including lots of percussion samples. The one thing you can’t do is load your own samples.

The interface is clean and easy to navigate. In the main editing page, the oscillator and filter knobs and menus are in the upper part of the panel, while the lower panel (the blue one) has pages for envelopes, LFOs, modulation routings, and so on. All of the knobs and sliders reset to default values when you double-click, and an Easy page gives you quick access to global settings for things like LFO speed and FM amount. The PDF manual is launched directly from a Help button on Blue’s panel, a small but welcome feature.

The patch browser has been redesigned along the lines of Papen’s Predator synth, with 128 patches per bank instead of the 32 per bank in Blue I. There are way too many great patches in the factory set even to begin to describe them. The bank names include both digital and analog basses, pads, arpeggiator sounds, tempo-based (though non-arpeggiated) sounds, chord clusters, leads, percussion, hip-hop/R&B, and a number of more creative banks from individual sound designers.

The global controls include a one-finger chord mode with a Learn command, detuned layering of up to six voices per key, and the ability to load alternate tuning files in the Scala TUN format.


Blue’s legacy as a six-operator FM synth can be seen in the fact that in addition to the semitone and fine-tuning knobs, it has a tuning ratio menu for each oscillator. This is less useful than it might be, as the ratios given are not related to the fundamental as simple whole-number harmonic fractions such as 1.75. The settings between 1.00 and 2.00, for example, are 1.41, 1.57, and 1.73.

Also part of the FM legacy: Each oscillator has its own ADSR amplitude envelope, a feedback knob so it can modulate itself, and an on/off tracking switch. Using a fixed pitch for an oscillator and setting it to a very low frequency is a standard FM programming technique, but in Blue it doesn’t quite work, as the lowest frequency you can set an oscillator to is about 6Hz.

Each oscillator has a sub-octave amount knob, which can produce either a sine or a square wave. A spread knob produces two detuned signals. A drift knob introduces slow, barely detectable pitch changes, which can be very useful not only for emulating vintage analog gear but for adding a little life to FM patches. Pulse width modulation (from a dedicated LFO) can be applied not just to the square wave but also to any wave. With samples, the results are generally weird and not useful, but maybe “weird and not useful” is what you’re looking for. A Symmetry knob “tilts” the waveform, for example, turning a triangle wave gradually into a sawtooth.

When you twiddle the Shape knob on a default patch, it seems at first not to do anything. To get waveshaping, you need to drop down to the lower panel and do a bit of graphic editing to the shaper curve. Oscillators can be hard-synced to Oscillator A for the classic analog sync sound, but for some reason sync is disabled when you choose the more flexible Matrix option for the six-oscillator algorithm configuration.

Speaking of algorithms, in the “Alg” page in the lower panel you can choose either one of the 32 classic DX7 algorithms (by clicking the Alg button within the Alg page) or a more flexible Matrix routing, in which any oscillator can modulate any other in any amount. The oscillators’ output volume knobs and individual envelopes interact in a straightforward way with the amounts in the Matrix. In addition, you can choose either PM (phase modulation) or FM. The two are similar, but different for technical reasons. When you choose FM, the oscillator output has to be cranked much higher before you’ll hear any change in the timbre.


Blue’s two filters can operate in either series or parallel routing mode, and the two filters are identical. The output of each oscillator in Blue can be routed to filter A, filter B, both filters, or to any of the effects (bypassing the filters). The filters’ outputs can be routed to any of the four effects individually, to effects A and B, to effects C and D, or to all effects in parallel.

The filters have 28 modes, starting with the expected lowpass, bandpass, and highpass choices, with various cutoff slopes. Comb filtering, formant filtering, and ring modulation are also in the menu. Curiously, there are eight filter modes (the ones whose names end with “2”—for instance, 12 LP2) that aren’t explained in the manual. They sound different; that’s all the information I got from the manufacturer.

The controls include frequency and Q (resonance) knobs, plus dedicated knobs for envelope amount, velocity sensing, key tracking, mod-wheel-to-frequency, panning, and output volume. There’s also a distortion knob, but in spite of the marketing terminology in the manual (“analogue modeled filters”), the distortion sounds very digital. Even with maximum Q and distortion settings, these filters don’t bark or squawk the way the filters on my analog modular synth do.


Blue has a generous 14 LFOs, with the usual basic wave shapes (including random sample-and-hold). Waveform symmetry, ramp up and down times, frequency humanize, frequency key tracking, output smoothing, start phase, and other parameters are provided. Ten of the LFOs have “hardwired” outputs for vibrato, tremolo, filter modulation, and so forth, but all of them can be used for other purposes if desired.

Four looping multi-segment envelopes are included in Blue. Each can have up to 16 segments, with individual control of the curvature of each segment. The overall speed of these envelopes can be both edited and modulated, making it easy to use them as complex LFOs. The graphic editing is not perfect. First, there’s no way to drag a given envelope point left or right and drag all of the later points (those to the right of it) along for the ride—a fairly standard editing feature with multi-segment envelopes. Second, while the envelopes can nominally be synced to the host transport clock, all the sync button really does is introduce a graphic grid to the editing window—and the envelope points don’t snap to the grid. Nor are the rhythmic values of the grid labeled. In sum, the multi-segment envelopes are certainly useful, but they could be improved.

The X/Y modulation source, on the other hand, is stellar. The two-dimensional envelope has up to 128 points. As Figure 1 shows at left, you can choose a preset shape such as a diagonal or spiral. Instead, you can record your mouse moves in real time to create a custom shape. The points can then be dragged around or snapped to a graphic grid. Playback location can be looped and quantized to the host tempo. The 16 output routings (eight each for the X and Y directions) are independent of the main modulation routing matrix.

Velocity and keyboard tracking curves are on tap. One important difference between Blue and old-school FM synthesis is that Blue has only one global key tracking curve, not one per oscillator.

The modulation routing matrix itself is simple and easy to use. There are 20 routing slots. For each, you choose a source, an amount, and a destination. A handy mute button is also provided for each routing. Modulation slot amounts are available as destinations, as are all of the amounts in the FM matrix. Numerous MIDI sources are provided, including release velocity and poly aftertouch.

Sequencer and Arpeggiator

The sequencer and arpeggiator are mutually exclusive; you can’t run both at once. Each has 32 steps (twice the length of the same modules in Blue I). In addition, there are three modulation-only sequencers, which will run in conjunction with the arpeggiator or step sequencer. More or less in conjunction, that is—due to a bug, the mod sequencers gradually drift out of sync with the sequencer and arpeggiator. (I’ve reported this bug. Hopefully it will be fixed in the next update.) 

The step sequencer has a few neat tricks up its sleeve. Each step can be assigned a different waveform for each oscillator, for some massively funky percussion rhythms. It has to be said, though, that the editing of waveforms per step is clunky: If you want a waveform that’s well down in the menu, you have to click on a tiny “+” sign dozens or hundreds of times to get to it.

Each step has four modulation outputs: velocity, a “free” value that can be used in the mod routing matrix, and two outputs hard-wired to filter A and B cutoff. A pitch slide can be applied to any step. Individual steps can be “tied” to a previous step, but the tie applies only to retriggering of envelopes: Other settings of the tied step, such as pitch and waveform, are still used. If you want the two or more steps to be truly a single longer note, just program them with the same values and then tie them.

The arpeggiator is also well designed. Each of the 32 steps can have its own on/off toggle, transposition, velocity, note length, and “free” modulation output amount, as well as a pitch slide and envelope tie. The swing slider makes every other note longer or shorter — and because you can also choose the basic rhythm value, switching from eighth-note swing to sixteenth-note swing is a no-brainer. A gate length slider, if active, overrides the individual note lengths of the steps. I was hoping this slider could be assigned as a destination in the modulation matrix, but it can’t be. Also, the arpeggiator’s direction menu has a bug: The up and down choices actually choose the played order (forward or backward) options, and vice-versa. According to the manufacturer, this is a design flaw of long standing, and for compatibility reasons it won’t be changed. 


Blue serves up a mouth-watering set of 35 effect algorithms, including both the standard items (chorus, stereo delay, and so on) and a few that are less common but always nice to see (comb filter, gator, bass boost, lo-fi, auto-wah, amp simulator, and so on). The high-quality (HQ) reverb uses a bit more DSP than the standard reverb, but it sounds great. There’s no fully parametric EQ, but you can choose a five-band graphic or low/high shelving.

Four effects are on tap at once (see Figure 2 at left), and you can choose one of eight different signal paths, not just series and parallel but things like “(A + B) > C > D,” which means A and B are parallel and their output then feeds C and D in series. When you factor in the ability to route the output of any oscillator or filter to any effect, this setup gives you an enormous range of sound design possibilities.

Each effect module has two modulation inputs. Controlling a comb filter’s frequencies from two slow LFOs sounds wonderful.


It’s clear that Blue II is going to become one of my favorite software instruments. It has a powerful and versatile sound, as the hundreds of top-quality factory presets prove, and the features for massaging the presets are both deep and easy to use. It would be nice to see a couple of refinements in the mod sequencer and multi-segment envelopes, but there’s plenty here right now to keep any computer-savvy musician in a state of bliss.

PROS: Great presets. Two filters. Lots of waveforms, signal routing options, and modulation routings. Plenty of filter modes and effect types. Recordable X/Y modulation. Step sequencer and arpeggiator.

CONS: No user sample loading. Only one key-scaling curve. Modulation sequencers don’t sync properly.

Bottom Line: A serious soft synth, whether you’re seeking virtual analog fatness or FM sparkle.

$179 street | $49 upgrade


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