Prophet X Review

What follows is my original review after my first few weeks with the instrument. It has been edited for typos and to reflect DSI's rebranding as Sequential, but otherwise is remains unchanged as a snapshot of my early thoughts. It doesn't reflect some of the major additions with v2 of the firmware (32-voice mode, new modulation destinations, stereo preservation of samples that bypass the filters in 16-voice mode, new looping modes, etc.)

It also doesn't reflect the current state of user sampling which led to the VCO Pack on this site. The official tools are still in beta and have significant restrictions but it's a start, and more is expected to come.

Overview: It’s About Time

I’m an unabashed fan of digital synthesis. Of course that doesn’t stop me from appreciating classic subtractive analog synthesis, and in particular I adore what a well-designed filter can do for a sound. Still, I’ve been biding my time patiently for the last few decades, waiting for the purist fixation with the analog revival to move on to the stage where we see what modern digital and analog can do together.

Evidently the time is now.

It’s great to see instruments like the Korg Prologue, Waldorf Quantum, and Sequential’s Prophet X taking a shot at creating a modern classic. I had spent quite a bit of time researching the first two, but when Sequential made their announcement I placed a pre-order within hours. Roughly six weeks later, serial number 40 arrived, and I’ve been enjoying exploring it ever since.

There’s no denying that it’s an expensive piece of kit, but the exquisite construction and feature set match the price. The highlights are clear enough:

  • Voices consist of two DSP-sourced oscillators paired with two sampled “instruments.”
  • 150GB of factory samples from 8Dio installed on the internal SSD, with room for another 50GB of third-party or (eventually) user-provided samples.
  • Sixteen 24dB/octave analog low pass filters.
  • Five-octave Fatar keybed with channel aftertouch.
  • Modulation includes 4 LFOs, 4 envelopes, 28 sources in total routable to 88 destinations through 11 dedicated and 16 fully assignable slots.
  • True stereo voicing by default, producing eight voices sourced from stereo samples and oscillators individually placed in the stereo image.
  • Selectable 16-voice mode which reduces oscillators and samples to mono whether or not they’re routed through the filter. Each resulting voice can still be panned freely.

The true stereo signal path from beginning to end is a revelation. There’s so much subtle stereo imaging in many of the samples that they bring a lot of life individually. Still, the eight stereo voice limit can feel limiting, especially when stacking two layers or splitting the keyboard where each layer is reduced to 4-voice polyphony. The 16-voice mode is therefore a nice option to have a dedicated button for, lit when active. Better yet, the current state is saved when storing a preset.

Above All: Usability

One of the primary reasons I was looking for a new instrument was immediacy of interface. Having a dedicated array of controls and little or no menu diving was a huge draw, and the Prophet X does not disappoint in this regard.

The interface will be largely familiar to anyone who has used a Sequential keyboard recently. Fifty six knobs and fifty buttons (many of which light to indicate status) provide direct access to a wide range of parameters. It’s quick and easy to make changes, and while doing so one of the three OLED screen reflects what’s going on immediately.

Effects and sample selection have their own dedicated screens next to the relevant controls, but everything else uses the larger central display. When a change is made (or a parameter is shown by holding or pressing the show button before touching a control) the display will show the affected parameter and additional related values that can be further manipulated with four soft knobs and four soft buttons. This is a great way to get to extra depth without menu diving: envelope looping or delay stages, configuring oscillators to run freely or reset on keypress, sample rate decimation and bit crushing are all available in this manner.

It’s a joy to use, well thought out from start to finish, but it isn’t as deep or as flexible as a classic workstation. More on that later.

8Dio Samples

Part of the early buzz regarding the Prophet X is attached to the origin of the factory samples. These are culled from 8Dio’s extensive collection and cover a lot of sonic territory. They’re arranged in seventeen categories, each offering multiple keymaps: 12 in Ambiance, 52 in Bass, 95 in Brass, 94 in Choir, 56 in Cinematic, 14 in Drums, 18 in Effects, 34 in Ethnic, 41 in Guitar, 66 in Keyboard, 33 in Percussion, another 74 specifically for Tonal Percussion, 39 in Piano, 97 in Strings, 37 in Synth, 35 in Solo Vox, and 61 in Winds. Whew. 841 keymaps in total with each mapping multiple samples across the keyboard, frequently with multiple samples per key selected by velocity range or rotated through in round-robin fashion on subsequent triggering to provide some natural variety. More than 200,000 individual samples at 48kHz, largely in stereo.

There is a staggering array of sound available as a result, but also a lot of overlap. 8Dio is known for their “deep sampling” approach and it’s on display here. Many takes were recorded from multiple microphone positions and so there are frequently two or more keymaps of the same sound taken from near and far microphones and, in the case of the piano, also from the player’s position. There are also multiple playing styles represented including short notes on many instruments and ensemble swells of orchestral staples. So there’s good variety but perhaps not as much as you might think at first. The far samples tend to have a lot of ambiance baked in, and I would have traded all of them for something else entirely.

Some of the keymaps offer an array of different textures on different keys. For example, one has a Prophet VS waveform per key. Several others have an array of ambient textures. Still more have special effects or acoustic instrument miscellany like a trumpet fall or flute trill. These maps aren’t generally intended to be used as-is but in conjunction with Sample Stretch. Just hold down the key that triggers a sample you like, press the Sample Stretch button, and it’s now pitched across the entire keyboard.

Most of the samples are stellar with some disappointing exceptions. The pianos in particular were not to my taste. They tend toward dark, moody, muted recordings, especially at lower velocities. While they’re not going to cut through a mix they do blend in well with other sounds and honestly, that’s really the whole point. All the sample material serves well when you combine it with synthetic sounds and apply modulation subtly or aggressively. Samples make fascinating sources for amplitude or frequency modulation of oscillators - and vice versa.

Sample looping can also be modulated, but while I’ve heard some presets that do this to good effect I haven’t had much success. There are clever looping modes that ensure pitched samples stay in tune, or to take rhythmic content and set the loop length based on MIDI clock tempo. These work great, with adjustable cross fading at the loop point doing its job. Where things get unacceptably click-y is when I’ve tried to modulate a short loop to create something akin to wavetable movement or granular synthesis. Perhaps there are other tricks to learn, or maybe I just need to feed it sample material intended specially for the purpose. Right now, though, all I’ve got to work with are factory samples.

That’s because user sample support is due to arrive in December 2018. Sequential has stated that the Prophet X firmware can already load new samples, but that it will take time to finish the Mac and PC software used to prepare keymaps from collections of raw samples. In the meantime, 8Dio is in the unique position of being able to offer aftermarket samples. They had originally announced plans to do so at launch but have pushed the two announced packs back to August. One nice touch is that in addition to four banks of factory presets (512 in total), and an equivalent number of user slots, there are another four add-on banks reserved for programs that showcase newly added sample content.

One incredibly pleasant surprise is just how fast everything loads. Each keymap can have a maximum of 1.5GB of associated samples, so a program with two layers can require as much as 6GB to be loaded into RAM from the internal SSD. In practice they load quickly enough that I’ve never felt like I was waiting. Likewise, switching among keymaps while editing a program feels essentially instantaneous. Impressive, though I’m sure in part it’s due to the fact that most keymaps are actually much smaller than the maximum size.


The are two DSP derived oscillators per voice, and they’re doubtless a derivative of past Sequential synthesizers that forgo analog oscillators like the Pro 2 and Prophet 12. They’re limited to square, saw, sine, and supersaw shapes. Reviewing their output in an oscilloscope reveals a subtle second harmonic that doubtless counters what might otherwise be an aggressively digital sound. This additional harmonic on the sine and saw can be emphasized with a shaping parameter that can be modulated in real time. With the supersaw the second harmonic starts out prominent and the shaping appears to adjust how detuned it is. On the square wave the shaping parameter adjusts pulse width, and can erase the pulse completely at extremes.

There’s a selectable amount of slop as a dedicated control to allow the tuning of the oscillators to drift, along with a hard sync button. Additional parameters without dedicated controls switch between free-running and resetting when a voice is triggered, along with a selectable phase when oscillators are reset.

No white noise or sub-oscillators are present, but the sampled instruments are more than capable of filling this gap with a wide range of noise types, waves from the classic Prophet VS, even sampled ensembles of analog synthesizers playing conventional oscillator shapes.

Those Sweet Filters

The filters bring a wonderfully smooth, warm character to the Prophet X sound that is a clear defining characteristic. The lack of a 12dB/octave option is offset by the care that has been lavished on this single slope design. Resonance can be used to restore a little edge and can be driven to self-oscillation. There’s also a selectable (and modulatable) drive parameter that can add some overdrive grit. I found something to like about every aspect of the filter.

These are modern recreations of the classic SSM2044 immortalized in synthesizers ranging from the PPG Wave 2.3 to the Korg Monopoly, Polysix and Trident. The new SSI2144 has lower noise and other key improvement while retaining the sonic character of the original, in part because Dave Rossum is back to improve on his original design.

There’s a dedicated filter envelope and many more modulation options are available. The cutoff of the left and right channels can be modulated independently, for example, and applying modulation to drive or resonance opens up a lot of possibilities. Audio rate filter modulation leads to some extreme options I’ve only begun to explore.

On a per-instrument basis sample keymaps can also bypass the filter entirely if desired.


The effects section is fairly basic, but perfectly capable of adding either character or ambiance. Each layer has two effects in series, selectable from a list that includes delays (BBD and clean stereo), Leslie simulation, reverbs (spring, room, hall, and “super plate”), chorus / phaser / flanger, as well as distortion and a high pass filter. Wet/dry mix and three other parameters are immediately available from the front panel and can be modulated.

The super plate reverb is an impressive standout, capable of long smooth tails, continuously adjustable dark or bright character. Paired with a percussive sound it’s easy to get lost here – but it’s also something you’re likely to turn off for recording. Defeating the effects is trivial, with two dedicated buttons that illuminate to show when each effect is active.

Not a Workstation

Yes, samples are a significant part of the instrument but no, this isn’t your next workstation. For starters, it’s only bi-timbral. Each preset consists of two independent layers that can be played one at a time, split at a selectable key, or layered. When split or layered, half the instrument’s polyphony is allocated to a layer. That means a monophonic bass in a split configuration still limits the right hand part to four notes.

There is a global setting to enable Multi Mode where two layers are fully addressable on two distinct MIDI channels. This even allows program changes to load unrelated A and B layers rather than the usual pairing, but it’s a far cry from a sixteen channel multitimbral setup with dynamic voice allocation you’d find in a classic workstation.

Sequential’s dedication to making an easy to approach instrument also limits the depth of editing available. Keymaps are pre-baked arrangements with key assignment and velocity mapping baked in. There’s no provision for reassigning samples to different keys, which would be handy for drums kits, nor can you mix-and-match samples from different keymaps to create velocity switching from a smooth bass to slapping techniques. Either it’s designed in, or it isn’t.

The same kind of simplicity applies to all of the synthesis options at your disposal. Want to subtly reinforce your bass drum with a sine wave oscillator? Great! Hope you like it on your cymbals, too, because it applies to the entire layer. Likewise for filtering, which would have been wonderful to tweak per-drum. You can adjust keytracking, but that’s the extent of your control.

So no, it’s not a workstation. It’s a wonderfully immediate performance synthesizer, and if you approach it on those terms it isn’t likely to disappoint.

Strengths and Weaknesses

I’ve been pleasantly surprised by the array of fresh-feeling modern sounds packed into the Prophet X. It’s easy to get around, seems to strike a healthy middle ground between purely experimental and usable when it comes to presets, and there’s a lot of promise in expanded potential as new sound banks and user samples make their appearance. In short, it’s the blend of classic subtractive and sample-based synthesis I’ve been waiting for.

Polyphony and programming depth can feel like constraints easily enough, but they can also be helpful by focusing on creative use of the tools that are present. The 512 factory presets explore a lot of territory without getting redundant. They also lean toward exuberant sonic territory with lots of modulation options. There are a few bread and butter sounds, but they’re in the distinct minority, overshadowed by showier fare.

If you have a chance to try the instrument out or purchase one, don’t forget that every preset comes with a pre-programmed sequence using Sequential’s basic step sequencer. These can be a good way to hear what the sound designer had in mind. Presets that don’t come up in stacked or split mode also have a “layer B” that’s worth trying out. Most of them are interesting variations on the base sound.

Shout-Out re: Responsive Support

I had concerns initially about quirks with one of the display showing visual corruption, and also the response of rotary encoders used as soft knobs above the central display which would frequently skip values.

Both were addressed with software updates in just a few days after I reported them to Sequential support. I am beyond impressed and satisfied that I’ll be treated equally well should any other problems arise with my purchase.