QuadEG

The Quad Envelope 60B represents another milestone in the world of modular synthesis, bringing together traditional modular UI with the extended feature set of an imbedded microcontroller based design.
The easy availability of high clock rate uCs has allowed us to design an envelope that is both snappy and more versatile than any standard hardware envelope generator currently available.
The use of 12bit DACs provide super smooth output with no audible stepping.

This design uses a "paging" interface with four individual contour generators programmed by a common set of 7 panel
control knobs and 3 switches. A panel with 28 knobs would be required to access all the stages if done the traditional way. The EDIT SEL momentary switch selects one of four channels to edit indicated by the panel LEDs. The knobs become "live" for that channel with the final edit settings stored to non-volatile internal EEprom memory. All settings are automatically restored on power up.

Each channel has three modes of operation: Envelope, Gated Loop
Envelope and LFO mode. Modes can be selected on any of the four channels independently of the other. The possibilities for inter module patching using a combination of these modes makes this module extremely flexible. It would require three or more modules to match the functions of just one channel. Some functions would be difficult to replicate with any number of modules.

Mode description :
Six stage Envelope mode:
This mode functions as an envelope generator with a standard +5V gate firing the envelope.The stages include DELAY, ATTACK, HOLD, DECAY, SUSTAIN and RELEASE. The HOLD stage is a new feature unique in a modular Envelope. HOLD adds a variable width delay stage that holds the envelope at full amplitude between the attack and decay stages
see fig.1

The HOLD stage adds "punch" to the attack portion of the envelope, simulating the effect that compression has on peak transients. This is the purported "Holy Grail" for getting that Moog envelope shape.
HOLD coupled with the sub-millisecond attacks, gives the envelope
more impact than a standard ADSR can produce.

Programmable CV AMT control for each channel sets the depth of modulation effect on the envelope stage timing using a 0 to +5V
range. The greater the voltage input the shorter the envelope.

Three curve shapes are available for all modes
Linear, Log and Reverse Log or Exponential. Each envelope curve response is programmable and saved with the mode and knob settings to memory.

Gated Envelope Loop mode
This is a unique modulation source with a wide range of applications.
The Envelope Loop mode uses the Delay, Attack, Hold, Decay and Release stages. The attack, hold and decay stages determine the wave shape and frequency. The DELAY stage can be used to delay the on-set of the loop and the release stage is activated when the gate voltage drops to zero. The loop is active while the gate input is high.
Some example uses: generate trills on a single note in a sequence or as a key activated LFO among others.
The shape selector also effects the shape of the resulting waveforms.

LFO mode
In this mode the channel functions as a 4 stage LFO using
the Delay, Attack, Hold and Decay stages. This provides a huge
variety of wave shapes from pulse/square to triangle, saw and everything in between all with continuously variable spacing and duration right up into low audio range. Great for sweeping filters, as a voltage controlled clock source or as an audio rate modulation source for VCO FM.

Firmware design by Tom Wiltshire .

Features:

4 channels with 3 function modes on each
6 stage envelope with HOLD control
2 Envelope Loop modes or LFOs both free running and gated
All settings stored to internal EEprom memory
Global CV Control of envelope and LFO stages per channel.
Gate inputs are "Normalised" together for single input gating of all channels. Patching to the individual Gates "un-normals" them
3 curve shapes for envelopes and LFOs
12 bit resolution with filtering for step free output
Low current draw @100mA

Specs:

Envelope stage duration:
Delay = 0 to 10seconds
Attack = 0.5mS to 51seconds
Hold= 250uS to 1.5 seconds
Decay = 0.5mS to 51seconds
Sustain 0-5V
Release = 0.5mS to 51seconds

Output sample rate: 25kHz@12bit
Output: 0 - 5V @1Kohms
Input CV: 0 - 5V @100Kohms
Gate Inputs: +4V @100Kohms
Power: +15V @100mA, -15V @0mA

Demo MP3s

Snappy.mp3
Demo was done using the gated Envelope loop mode.
The width of the gate into the channel determines the number
of repeats per step. The output was then used to trigger an envelope
on a neighboring channel for more control over shape.

Bassorama.mp3
Demo showing the thunderous presence of the sound when using
the hold stage to simulate compression.

Envelope & LFO.mp3
Two envelopes where used for filter cutoff and VCA.
A third channel did LFO duty on the filter sweep.

Bass Sequence.mp3
Another example of the punch available for bass sounds

More to come