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Audjoo Helix

Wave-table-shaping-subtractive-hybrid.

Four oscillators with individual 16 voice "unison" for an amazing 64 oscillators per voice.

Powerful spectral morphing through innovative wave-table-shaping.

A plethora of filters, ranging from standard low pass to per-voice- phaser

Overview

Goals during development:

Audjoo Helix is divided into a few parts, the following chapters will describe them in detail.

Get the sourcecode at http://sourceforge.net/projects/audjoo-helix

Helping Out

As the license states, you are under no pressure whatsoever to "give back" to this project. If you feel like helping me out, I would really appreciate any of the following:

Modulation sources

Envelope Generator (EG) x3

Inspired by SQ80

  • Attack Time
  • Attack Level
  • Decay Time1
  • Decay Level
  • Decay Time2
  • Sustain
  • Release Time1
  • Release Level
  • Release Time 2
  • Attack Time Velocity Sensitivity
  • Decay Time Keyboard Tracking
  • Level Time Velocity Sensitivity

Low Frequency Oscillator (LFO) x3

  • Shape
  • Period
  • Hold
  • Attack
  • Release

Step Sequencer (SE) x2

Period Lag / Low pass filter 16 Steps (range is -1 to 1)

Keyboard input (KBD) x1

The keyboard is a modulation source just like any other. To have a traditionally tuned setup you need to modulate the pitch of the oscillators with the keyboard.

Pitch bend input (?) x1

<to be described>

Modulation Matrix

The philosophy of Audjoo Helix is that most features of the oscillators and filers that can be controlled from somewhere go through the same system. This system is the mod-matrix.

<to be described>

Since even the pitch of the oscillators is controlled through the mod-matrix, it has to be set up properly to get even the simplest patch. (The default patch has a default mod-matrix-setup)

Audio Signal Path (Routing)

Oscillators, Filters and Shapers in Audjoo Helix are all stereo. To understand the signal flow, imagine a waterfall. At certain points in the fall are basketball-hoops that the water flows through. Between these hoops you can aim a garden hose and add water to the stream. In this imaginary world, water represents sound, the hoops represents filters and shapers, and the garden hoses represents oscillators.

Voice (Serial)

-> (F) -> (S) -> (F) -> (S) -> (F) -> (S) -> (Mix)

Voice (Parallel)

-> (F) -> (S)
              -> (F) -> (S) -> (Mix)
-> (F) -> (S)

An oscillator can be inserted at any of the 5 stages (represented by "->") in the signal path.

Oscillators

The most advanced component of Audioo Helix is with no doubt the oscillators. They are band limited and have a lot of features available for modulation.

  • Stage (where in the chain they should be mixed in)
  • Type (Wave, Noise)
  • Form (choose between some ROM-forms and user waveforms)
  • Two sets of a bunch of shaping controls in both time and "voltage"
  • Amplification (M)
  • Pan (M)
  • Harmonics / Band Limit (M)
  • Morph (M) morphs between the two sets of shaping controls
  • Pitch (M)
  • Unstable
  • Start Phase
  • Start Phase Freedom
  • "Super" Count (1-16)
  • "Super" Phase start
  • "Super" Phase Freedom
  • "Super" Width
  • "Super" Spread (M)

To add user waveforms add wave files to the folder "audjoo_helix_cycles", the samples need to meet the following criteria:

  • Mono
  • <= 4096 samples in length
  • 8,16,24,32 bit integer and 32 bit float supported

All samples in the folder will be loaded, so if you put a big number of samples Helix will keep them in memory (to prevent disk-access during performance).

The oscillators creates all harmonics up to 18 kHz (the upper threshold for human hearing), this gives enough brightness.

The oscillators only create the first few hundred harmonics, so when playing low notes you might miss some high frequencies.

Filters

The basic function of a filter is to amplyfy or attenuate frequencies already present in the signal.

The exception is the Ring Modulation and Phase Modulation that adds extra frequencies known as sidebands.

  • Cookbook Low Pass
  • Cookbook Band Pass
  • Cookbook High Pass
  • Cookbook Low Shelf
  • Cookbook High Shelf
  • Cookbook Peaking EQ
  • 4 pole LP (over-sampled nonlinear)
  • Stereo Delay
  • Feedback Stereo Delay
  • Ring Mod (with sine)
  • Phase Mod (with sine)

All have:

  • Center Frequency (M)
  • Resonance
  • Mix
  • Gain

Shapers

A shaper is a stateless transfer function. It adds harmonics related to the frequencies already present in the signal.

A bunch of types

  • Soft
  • Hard
  • HF0
  • HF1
  • HF2 // need to name these...
  • Add-Sine // can create FM like tones
  • Rectify (and DC-block)
  • Bit Cruch
  • Digital Clip

Global Effects

After all voices are mixed to the global bus, global effects are applied.

Ping Pong Stereo Delay

  • Left Delay
  • Right Delay
  • Feedback
  • Level When no Key is Down
  • Level When a Key is Down

Reverb

A pretty simple (for CPU reasons) reverb.