A synth interface, on the surface, is just more knobs. So we look to creator Stephan Schmitt to find out what makes his synth invention tick – and his thoughts on synth-building philosophy. Click for larger version of the UI, which you can access to create your own sounds if you have a copy of Reaktor.

If you think there aren’t still exciting things happening in synthesizer design in the age of software, you haven’t met people like Stephan Schmitt. Schmitt, founder of Native Instruments and the “mastermind” of Reaktor, could be seen as a mad sonic scientist behind NI. When I met him for dinner in Berlin in October, he had brought along a stack of signal flow diagrams and Reaktor screen grabs in plastic sheet protectors. I knew something brilliant was coming.

Native Instruments calls Schmitt’s latest creation “Spark,” but I like to think of it as the Schmitt Box – like a mysterious, powerful invention from a designer who loves to experiment. Stephan has been evolving the instrument in Reaktor through some 160 iterations. He uses foot pedals to modulate the sound live, and rails against the evils of dull, repeating LFOs. Spark ships as a Kore soundpack, so for US$59 you can fire it up right away and start playing, even without knowing how it works. Even better, though, is if you have a copy of Reaktor 5, because you can use the full-blown UI seen here to design your own sounds or even dig into the plumbing of the patch beneath. (It’s still worth looking at the Kore sound presets, because they’re consistent with Stephan’s approach of designing the sound for live performance.)

Reaktor Spark [info, download]

I think it’s telling that, while Stephan’s emphasis is on playability, he brought those signal diagrams. It’s tough sometimes to put the nuances of synths into words. NI’s own description, that Spark “combines powerful subtractive synthesis with a sophisticated array of internal feedback loops and various other special sound shaping features” doesn’t quite cover it.

So, I instead asked if we could use Stephan’s own words to describe the new instrument. The following is an excerpt from the guide he wrote for sound designers working on presets for Spark. (Scroll to the end for full diagrams of the signal routing inside, fellow geeks!)

If you’re new to this stuff, this will give you some insight into why Spark sounds the way it does. And if you’re a synth designer yourself, I think you’ll really appreciate Stephan’s personality and approach. And it encourages me that, even with a lot of repetition of basic elements (subtractive synthesis, a feedback loop), there are still many possibilities for personal, idiosyncratic instruments to explore.

Here are Stephan’s thoughts:

In the beginning, the design was inspired by "Weedwacker", a Reaktor instrument created in
the year 2000 by Siegmar Kreie. The main concept behind the Weedwacker was the feedback
of the filtered signal to the pulse-width modulation input of a pulse oscillator. The result was a
surprisingly-complex behavior of the simple one-oscillator/one-filter structure. The rich and
organic sound was appreciated by many users. Another influence was the Evolver from Dave
Smith, a hybrid concept with some interesting feedback paths.

The structure of Spark reflects my personal preferences in regards of synthesizers. Instead of creating a full-blown mega/multi-purpose synth, I try to keep it as small as possible and with a
special character.

A main goal is to allow dramatic real-time influence on the sound source. The synth itself offers
only a few simple automatic movements (2 envelopes and 1 monophonic LFO). Like a natural
instrument, it needs to be played expressively and therefore stays a challenge for the player
and the sequencer programmer.


I deliberately do not make use of the following techniques:

  • samples
  • complex waveforms or wave-tables
  • complex shaping curves
  • noise or random (except a randomization for pitch at note-on)
  • multiple and extensively routable LFOs (the LFO is intended to replace human control or an automation curve)
  • multi-breakpoint envelopes or step-sequencers
  • multi-oscillator structures (like an FM matrix or additive osc bank)
  • pitch envelopes

The idea behind this is that the signals are generated and modified by a small number of very basic mathematical functions. Applied in a certain structure, they can create complex signals that might have their very own nature, behavior, and sound character. That is what fascinates me in synthesizers.

The two oscillators deliver two very basic waveforms which are contrasting and complementary: Pulse and Sine. The Pulse has a bright sound and a wide spectrum of overtones which can be filtered. The Sine has a very soft sound and a narrow spectrum that can be widened up by FM, amplitude modulation or wave-shaping. By using feedback loops which contain linear filters and non-linear functions, complex and quasi-chaotic waveforms become possible. This is why the sound spectrum includes more organic and aggressive timbres than a classical analogue synth.

In some settings, the structure behaves similar to a physical modeling synth. The Oscillator section becomes the exciter, while the feedback loop around the filter, shaper, and delay behaves like a resonator.

My favorite range of sounds is percussive – similar to pianos, mallets and plucked string instruments. Since I was always fascinated by electric guitars, you can get a lot of distorted and feedback sounds out of it.

By its sound and playability Spark might be suitable for:

  • Rock and Blues
  • Jazz, World Music
  • Noise, Free, Experimental
  • Industrial, Dark Wave, Gothic, Psychedelic
  • IDM, Elektro and EBM
  • Sound Tracks
  • Sound-Design (where the output is sampled)

In my music projects, the instrument has replaced the DX7-II (+ external Effects). Spark gives me similar aggressive, non-harmonic spectra, the fast percussive response, and the very wide dynamic and spectral range controlled by velocity. But it also delivers dramatic and fat filter sounds that are hard to get from the old FM synths (not to mention the crazy feedback stuff).

The pedals allow much deeper sound modulation and the effect chain adds a lot of processing. Spark’s character is not always impressive, fat, brilliant and shiny. It can often sound cheap, ugly, and mean. I made no big efforts to minimize aliasing or to optimize the filter behaving in order to achieve the typically-favored analog "sound quality".

Sometimes the behavior is unpredictable and hard to tame. The feedback structure can cause surprising self oscillations and levels, where the limiter has to jump in. But that’s part of the
concept. It can feel a bit like beast in a cage…

How to play it

The velocity sensitivity of the two envelopes plays a great role in the real-time variation of the
sound. It can be used to create a very wide dynamic range of loudness and timbre.

The full expression potential becomes available by moving the three Macro Controllers. The set
of controls is designed to be a great environment for improvising musicians.

The Macro Controllers would be typically assigned to a Volume pedal, an Expression pedal and
the Mod Wheel. But they can also be easily controlled by sequencer automation curves.
Spark needs to be played in an expressive way. In the sequencer environment it takes the role
of the wave generator, that needs intense work with the "movements".

Recently I have added an LFO as an internal source of periodic movements. It can replace
automation or pedal movements (maybe only temporarily) and helps you to get the hands-free
for sound modifications.

Full Block Diagram

(click through for larger version)

Feedback Diagram

(click through for larger version)