The Synthesis Engine

The C15 is a polyphonic instrument based on digital sound synthesis. The purpose of the audio engine is not to model analog machines of the past or to play back samples or complex waveforms. Instead, we have chosen a puristic approach.

Based on elementary mathematic algorithms, the signals are generated, modulated, shaped, and filtered in realtime. Therefore the sound can be dramatically influenced by the dynamic playing of a musician.

The signal processing structure is the result of years of evolution and has been condensed down to an essential, yet powerful arrangement of carefully chosen components. The only signal sources are two sine wave oscillators. They are connected to each other and to a feedback bus for phase modulation and their signals are processed by two wave-shapers, a comb filter, a multi-mode filter, and a chain of five stereo effects.

Quick Links
Block Diagram
Diagram

Block diagram of the synthesis engine. Click to enlarge.

Diagram Diagram

Two mixers combine the signals from different points in the structure and forward their sum to the effects section and to the feedback bus. The sonic results of the feedback can become very complex and organic. With the Comb Filter running as a tuned resonator, the sound approaches that of acoustic instruments.

Our goal was not to create a universal sound engine or the most realistic imitation of existing instruments. Instead, we set out to create a sound source with a unique character, which at the same time offers endless variation and produces surprising results even after long periods of intensive exploration.

All possible sounds are reached without switching between different waveforms, filter types, effects, or signal path configurations. Everything can be continuously modulated, crossfaded, or morphed.

Control

As a pure player instrument, the C15 is built for human control. You will not find modulation sources that create rhythmic patterns. We leave this to the musician. Instead, the C15 offers a large range of sensitivity thanks to the dynamics of the keys and extensive mapping possibilities for the signals coming from the physical (human) control elements, such as ribbons and pedals. LFO-type of control signals can be easily produced by the specially designed pitchbend lever.

The physical controls are routed to the Macro Controls, which are the main elements for influencing the sound of a preset. Each of them is freely assignable to up to 86 target parameters. The Macro Controls are the sources for an intuitive modulation system, where the effect of a modulation is directly shown as a movement of the target parameter. After assigning a Macro Control and adjusting its effect the sound designer also can give it a label that helps to understand its function.

The Preset System

Besides performance, the second important interaction with the C15 is sound design. The creations are stored by an advanced preset system which makes it easy to find and compare presets, to modify them, and to store new versions. They can be organized in a set of user-defined banks by intuitive copy, move and sort functions. The number of banks and presets per bank is not limited.

To help the user to find the right sounds, the preset system will include a database for sound categories and additional information that can be used for searching.

The C15 will also offer morphing as a powerful method to vary the sound. A morph transition can be executed between the parameter settings of two presets, or a sequence of presets, or between the current state and a preset.

Undo

The C15 provides virtually unlimited tree-based undo/redo functionality for all user interactions including parameter editing. This means you can always return to a sound that you had created some minutes ago. You can also jump between different branches of the undo tree which are automatically created when you undo and edit again.

Technologies
computersys

The C15 is powered by three processors, each of them specialized for its tasks, connected by an advanced bus system.
Read more about the technologies.

Two-Part Construction

The housing of the C15 synthesizer consists of two detachable parts: the base unit and the panel unit. The compact base unit contains all of the instrument's processor and audio components; it can be used without the panel unit in "play only" situations. The panel unit is an haptic user interface, mainly for sound design, but it can also be useful for controlling presets and morphing for a complex performance.

Play Interface

For the 61-note keyboard we have chosen the best semi-weighted model from the quality manufacturer Fatar. Experienced musicians will appreciate the long key arms for their improved play feeling.

Unlike with MIDI, the (on and off) velocities of the keys and the values of the physical control elements are precisely resolved into thousands of steps, and there is no loss of precision on the way to the sound engine.

The musician can make use of up to 8 physical controls: aftertouch, a pitchbend lever, two ribbons and up to four pedals. A coefficient matrix gives full flexibility for their mapping to the Macro Controls.

The pitchbend lever is a special design using magnetic forces for fast and natural horizontal movements from a center position.

The most prominent control elements of the C15 are the two long ribbons. Each of them includes an indicator bar of 33 LEDs showing the control position. The ribbons can be used for performance as well as for parameter editing. You can choose if they work in relative or absolute mode, with an optional return-to-center behavior.

A small control panel with an OLED display (128 x 32 dots) provides control over the ribbon functions and is also used for note and octave shift. If the panel unit is not mounted, this panel together with the ribbons will give access to preset selection and morphing, parameter editing and global settings like tune or velocity curves.

Pedals are the best way to control sound parameters while playing with both hands. Therefore the C15 allows up to 4 pedals to be connected. Footswitches are also supported, but for expressive playing we recommend continous damper/sustain pedals instead of switches - for this purpose we are also developing special pedal units.

Open for new sound engines and user interfaces

The C15 's sound engine is based on software running on an embedded computer. This means that the C15 can evolve without falling into obsolescence. Improved and new sound engines will be available in future. This also explains why we have chosen a generic parameter selection interface that can be re-defined by magnetic overlays.

The modular design of the control panels is also open for different hardware components, e.g. user interfaces with displays, knobs, sliders, or XY controls.

Sound Editing Panels

The idea behind the panel unit is to provide a large area with many haptical controls, so that the functionality can be learned by the motoric memory, like the playing of a keyboard.

Four of the five panels are equipped with 24 high-quality buttons and corresponding state-indicating LEDs. Their main purpose is the selection of parameters. The labeling and grouping of the buttons is realized by exchangable magnetic overlays. This makes the user interface flexible. When fast switching between sounds becomes crucial the selection panels can be re-defined as direct access to presets. Future development will also bring new synth engines to which the user interface can be adapted.

The central panel - with a crisp OLED display (256 x 64 dots), an incremental encoder, and 18 buttons with dedicated functions - is the place where parameter values are displayed and edited, preset banks can be browsed and new presets can be stored. Many other functions are accessible here.

The Graphical User Interface

In addition to its hardware user interface, the C15 provides a visual access to its parameters and presets on computer screens and mobile devices. This unique approach is described here.

C15 Photos
C15 Top
C15 Front
C15 Back
C15 Side
Base Unit
Edit Panel
Central Control Area
Pitchbend and Ribbons
Headphones Connector
C15 Top C15 Top

C15 - Top View

C15 Front C15 Front

C15 - Front View

C15 Back C15 Back

C15 - Back View

C15 Side C15 Side

C15 - Side View

Play Interface Play Interface

Base Unit (without the optional Edit Panel)

Edit Interface Edit Interface

Edit Panel

Center Panel Center Panel

Central Control Area

Pitchbend and Ribbons Pitchbend and Ribbons

Pitchbend and Ribbons

Headphones Connector Headphones Connector

Headphones Connector and Pot (updated)

Technical Data
Phase 22 Synthesis Engine
  • 2 Oscillators (sine wave, phase modulation, frequency randomization)
  • 2 Shapers (sine curve, adjustable foldback and asymmetry)
  • Ring Modulator
  • Comb Filter (tunable, with allpass and lowpass)
  • State Variable Filter (multi-mode, 2-4 poles, FM)
  • Feedback Mixer (4 input signals, shaper for the sum)
  • Feedback bus with 4 destinations
  • Output Mixer (stereo, 4 input signals, shaper for the sum)
  • 5 Stereo Effects: Cabinet (amp simulation), 8-pole Gap/Band Filter, Flanger/Chorus, Echo, Reverb
  • 3 ADBDSR Envelopes, adjustable attack curve
  • Velocity sensitivities for envelope levels, attack times, and release times
  • 4 Macro Controls, assignable to up to 86 target parameters
  • 8 Hardware Sources, mappable to the 4 Macro Controls
  • Number of parameters: 305
  • Resolution of the parameters: typically 1000 steps (250 ... 15000 steps)
  • Resolution of key velocity, ribbons, lever, aftertouch, pedals: 4000 steps
  • 12-voice polyphony, variable Unison settings
Play Interface
  • 61-key (5 octave) Fatar keybed with semi-weighted long-arm keys
  • Note-on and note-off velocity sensitivity
  • Monophonic aftertouch
  • Two 800 mm touch strips (ribbons), each with 33 LED dots
  • Ribbon modes: absolute, relative, combinable with return-to-center
  • Lever (magnetic force loaded) for pitchbending and similar applications
  • Control panel with an OLED display (128 x 32 dots) and four buttons
  • Output volume potentiometer (at the front)
  • Headphone level potentiometer (at the front)
Parameter Editing
  • 4 Selection panels, each with 24 buttons and LEDs
  • Labeling by exchangeable magnetic overlays
  • Edit panel with an OLED display (256 x 64 dots), an incremental encoder, and 18 buttons
  • The ribbons are also assignable for editing of parameters.
  • Graphical user interface on any WiFi-enabled device running a browser, unique zoom-and-pan navigation, enabled for touch
Preset System
  • User-definable banks
  • Unlimited number of presets per bank
  • Infos and tags per preset
  • Morphing between the edit buffer and a preset, between 2 presets, or a series of presets
Undo System
  • Unlimited undo for all user interactions, including sound editing steps
  • Undo list with support for different editing branches (tree view)
Connectors
  • Main audio outputs (L, R) (TRS, balanced by transformers)
  • Headphone output at the front (TRS)
  • 4 inputs for analog controls, such as pedals (TRS, flexible pin-assignment)
  • USB host connector for data exchange and software updates
Dimensions
  • Base unit only: 900 x 290 x 100 mm (width x depth x height)
  • Including panel unit: 900 x 410 x 160 mm (width x depth x height)