Review: Sequential Prophet X

Get inside Dave Smith's newest hardware, the sample-powered Prophet X

Combining algorithmic oscillators with sample playback, the Prophet X is only the second new synthesizer since 1987 to bear the Sequential moniker. It contains a 256GB solid-state drive (SSD) with 150GB of 16-bit, 48 kHz factory samples onboard, but it is neither a sampler nor a traditional ROMpler.

The Prophet X combines lots
 of multisampled content,
 DSP-generated waveforms,
 and an analog low-pass filter
 with a slick user interface

The Prophet X combines lots  of multisampled content,  DSP-generated waveforms,  and an analog low-pass filter  with a slick user interface

Soundware developer 8DIO supplied all the sampled content, which runs the gamut from acoustic and electronic instruments to unique sound effects and atmospheres. Everything else about the Prophet X makes it a subtractive synthesizer, from the analog-style waveforms generated by its digital signal processors to its true analog low-pass filter designed by E-mu founder Dave Rossum of Rossum Electro-Music.

The Prophet X is bi-timbral, allowing you to play two sounds simultaneously, either stacking them or splitting the keyboard to play the A and B layers independently. Maximum polyphony is 16 voices, but when you’re playing stereo samples, polyphony is limited to eight voices.


The all-black Prophet X takes its design cues from previous keyboards from Dave Smith Instruments — Sequential’s name from 2002 until recently — with simple lines, lots of knobs, buttons that illuminate orange-red when engaged, and three bright white-on-black OLED displays. The 61-note keyboard responds to velocity and channel aftertouch, and a pair of latching touch sliders accompanies the pitch and modulation wheels for real-time expressivity.

On the back panel are two unbalanced 1/4-inch main outputs that double as outputs for the A layer, as well as separate outputs for the B layer. Alongside a USB connector and MIDI In, Out, and Thru on DIN jacks are 1/4-inch jacks for a sustain footswitch, a volume pedal, an assignable expression pedal, and a pedal to start and stop the sequencer or arpeggiator. You can also route an audio signal to the sequencer jack to control tempo. A type-A USB connector lets you connect a flash drive for importing samples.

The Prophet X is ready to play about 25 seconds after you switch on the power. Functions you’ll use most often are all on the front panel, and you access deeper functions in the main display. Turning any knob or pressing any button changes what appears in the display, which is flanked by four soft knobs and four soft buttons that control the parameters and values displayed.

Select presets by scrolling though banks and programs with their respective knobs. Internal locations provide 12 banks, each containing 128 programs. Four banks are user programs, four are factory programs, and four are reserved for future, third-party content. As shipped, rewritable user banks duplicate the factory banks, giving you a total of 512 factory programs. Factory banks can’t be rewritten, and you can’t currently save to thirdparty banks.

The Prophet X has four sound sources, a single low-pass filter, four envelope generators, and four LFOs. Two of the sources play stereo samples, and the two others generate basic synthesizer waveforms — sine, sawtooth, pulse, and supersaw. Unlike on most DSI synths, oscillator waveforms are not continuously variable, which means you can’t transition smoothly from one to the next. However, you can modulate them using the Shape knob, which itself can be modulated. You control each source's level in the 4-input Mixer section.

The Prophet X’s fat low-pass filter has a fixed 24dB-per-octave slope and overdrive. It operates in stereo when the synth is in 8-voice mode, and Stereo Split lets you raise the cutoff in one channel while lowering it in the other. Samples can bypass the filter entirely, if desired. You’ll also find a resonant digital high-pass filter in the Effects section.

The front panel provides knobs to control ADSR parameters, with additional envelope parameters in the main display menus. These include an initial delay and repeat, making the envelopes more versatile than they appear.

The Effects section’s 1.25-inch-square OLED displays parameters for two simultaneous stereo effects processors. Types include delays, distortion, modulation effects (chorus, flanger, etc.), and a nice assortment of reverbs. Knobs control the effects type, wet/dry mix, and three pre-assigned parameters for each effect.



The internal SSD gives the Prophet X much more capacity than any hardware synth or sampler I know, enabling it to compete head-to-head with computer-based sample players. Although Sequential promises it will import user samples after an update in December, for now, it imports only samples from libraries you purchase, including specially formatted 8DIO libraries. The SSD reserves 50GB for importing samples.

In the front panel’s Sample Playback section, the Type knob selects the instrument family (Strings, Ethnic, or Perc Tonal, for example), and the Instrument knob scrolls through multisamples within the selected type, whose names are shown in the section’s dedicated OLED.

With so much disk space, the Prophet X delivers a huge selection of pristine sampled content. You get basses, brass, choir, drums, guitars, pianos, strings, winds, and so on, as well as Ambience and Cinematic types that assign a different texture to each note. Another instrument type, Effects, assigns mostly orchestral effects or unusual phrases played on one or more acoustic instruments to each note.

You can play samples backward, move their start and end points, or enable a sustain loop and then change the loop’s size and center point, which you waveforms are not shown in the main display, your edits appear in a simplified graphical form. Samples have only one loop, and you can adjust the crossfade time. You can also keep loops in tune with samples or in sync with global tempo by changing the loop mode. When you make an edit and then change instruments, the synth retains those edits from one instrument to the next.

Many traditional instruments have samples so long that they decay naturally, often negating the need for sustain loops, resulting in particularly detailed and realistic pianos and guitars, for example. Other standout types include Choir and Solo Vox, many furnishing vocalized words or phrases you can selectively truncate using the sample Start and End knobs.

The Sample Stretch feature is especially useful with Ambience, Cinematic, and Effects types, because it allows you to select a single sample from a multisample and then map it across the entire keyboard. You’ll also need Sample Stretch to take advantage of the 97 single-cycle VS waves, which were inherited from the Prophet VS (introduced in 1986) and mapped to 97 different notes. Sample Stretch opens up a fascinating world of almost limitless creative possibilities.

Additional features include the sequencer and arpeggiator — with functionality borrowed from other recent synths designed by Dave Smith and company — and Play List, which lets you arrange as many as 160 programs into sets for quick recall. Two other features I’m more than happy to see are support for alternate turnings and the ability to adjust glide independently for the two DSP-generated oscillators.


The modulation matrix is as logical and straightforward as any I’ve seen. The Modulation section displays 16 routing assignments, where you can easily select and change sources, destinations, and positive or negative modulation depth, making it simple to assign and reassign modulators and instantly view their status. Velocity, the mod wheel, and other real-time controllers give you an additional 11 fixed routings. Selecting any LFO displays all its relevant parameters, including an LFO Destination tab to view and change one of its modulation targets.

One extraordinary modulation capability is that sampled instrument to modulate an oscillator’s frequency or shape, for example, lets you achieve sounds impossible to produce any other way, because the oscillator responds to the sample’s frequency and contour. You can even modulate one sampled instrument with another. I found this especially worthwhile when using percussion samples as sources.

The Prophet X’s limited polyphony makes it easy to run out of voices in stereo. When playing stereo samples on a split keyboard, each half of the split has only four voices. If one layer is a piano, for example, voice-stealing could quickly become an issue. I wish you could specify how many voices are assigned to each layer, meaning you could play a monophonic bass part with your left hand and have enough voices left for a 7-voice melodic part.

Because the audio output has such a strong signal, the acceptable range of loudness the Volume knob affords with headphones is much too narrow. Near the bottom of the knob’s travel, the level quickly goes from too soft to too loud when you barely turn it. When I turned Volume up to normal levels for the main output, I had to disconnect the headphones to keep them from blasting.


The Prophet X doesn’t deliver groundbreaking new synthesis techniques, just a tried-and-true combination of digital sampling and subtractive synthesis. Fortunately, the content and the electronics are superb. Almost without exception, the factory programs are lovely, unique, evocative, and/or versatile. With such outstanding sound design, plenty of memory, and so many carefully crafted, full-fidelity samples with room for more — unprecedented in a hardware instrument — variety and audio quality make this synth suitable for almost any application.

Although the Prophet X is undoubtedly an object of desire, its high price puts it out of reach for most musicians. Nonetheless, that price is justified by its remarkable capabilities. If your primary keyboard is a ROMpler (whose sound sources are samples stored in ROM), don’t expect the Prophet X to completely replace it, because you may need more polyphony, and factory presets aren’t organized like they are in ROMplers. For sound designers, serious synthesists, and working keyboardists looking for something different, though, the Prophet X is one you shouldn’t ignore.


Excellent sound. Ample storage. Tremendous timbral versatility. Intuitive user interface. Expressive performance features.


Maximum eight stereo voices. Unbalanced outputs. Headphone issues. Only one filter slope. Costly technology.