Instruo athru User manual

athrú
Wavefolder
User Manual

2
Contents
3
Description / Features
4
Installation / Specifications
5
Overview
6
Wavefolding
9
Patch Examples
- West Coast Synth Voice
- West Coast Bongo
- Summed Wavefolder
- Burst Generator

3
Description
The Instruō athrú is a full featured analogue wavefolder that creates
incredibly complex timbres from very basic waveforms using an
interesting form of distortion.
Unlike traditional distortion effects where signal amplitudes passing a
threshold are ‘clipped’, wavefolding inverts signal amplitude when it
passes an amplitude threshold. This folding can occur multiple times,
resulting in dynamic control over rich harmonic spectra.
In subtractive synthesis, partials are attenuated from harmonically dense
waveforms. athrú, on the other hand, utilizes additive synthesis by
generating partials from harmonically simple waveforms.
Starting out as a derivative of the West Coast timbre circuit, the
wavefolders in the Instruō system have been tweaked and adapted
with each incarnation. athrú is the latest incarnation in a stand alone
package.
Depth control via an exponential VCA, summing with a scalable
symmetry bias offers everything from subtle boosts in harmonics to full
on spectral devastation.
Features
• Wavefolding
• Symmetry bias with summing capabilities.
• Strike input with definable decay
• Analog drive

4
Installation
1. Confirm that the Eurorack synthesizer system is powered off.
2. Locate 4 HP of space in your Eurorack synthesizer case.
3. Connect the 10 pin side of the IDC power cable to the 2x5 pin
header on the back of the module, confirming that the red stripe on
the power cable is connected to -12V.
4. Connect the 16 pin side of the IDC power cable to the 2x8 pin
header on your Eurorack power supply, confirming that the red
stripe on the power cable is connected to -12V.
5. Mount the Instruō athrú in your Eurorack synthesizer case.
6. Power your Eurorack synthesizer system on.
Note:
This module has reverse polarity protection.
Inverted installation of the power cable will not damage the module.
Specifications
• Width: 4 HP
• Depth: 39mm
• +12V: 30mA
• -12V: 30mA

5
athrú
IO
BIAS
DRIVE
athrú |'ɑ:ɾ·u: | verb (mathematics) an act or process through which
something becomes different; to change, transform, alteration, variation
and mutation
Key
1. Input
2. Output
3. Wavefold
4. Wavefold CV Input
5. Wavefold Attenuverter
6. Symmetry Bias Input
7. Symmetry Bias Switch
8. Symmetry Bias Attenuverter
9. Drive Toggle
10. Strike Input
11 . Strike Decay
5
1
4 6
78
9
10 11
2
3
Front Back

6
Wavefolding
Input: DC coupled signal input.
Output: DC coupled signal output.
Wavefold: The Wavefold fader controls the amount of wavefolding
applied to the signal present at the Input. The folded signal is present at
the Output.
• Moving the fader fully downwards will reduce the Input signal’s
amplitude, resulting in near-silence.
• Moving the fader fully upwards results in a rich, harmonic timbre
(If the Symmetry Bias Switch is in the up position, adjusting the
Symmetry Bias Attenuverter will further affect the
harmonic spectrum).
Wavefold CV Input: The Wavefold CV Input is a bipolar control
voltage input for the Wavefold parameter that utilises an exponential
VCA.
• Control voltage is summed with the fader position following its
inbuilt attenuverter.
Wavefold Attenuverter: The Wavefold Attenuverter will scale and
invert the control voltage signals present at the Wavefold CV Input.
Symmetry Bias Input: A signal present at the Symmetry Bias Input will
replace the normalled reference DC voltage. The external signal can be
scaled and inverted via the Symmetry Bias Attenuverter. The incoming
signal sums with the Input signal before reaching the wavefolding stage.
• External signals can be processed via the Symmetry Bias Input.
The Symmetry Bias Attenuverter controls the external signal’s
amplitude. Decreasing the amount of wavefolding via the Wavefold
fader will isolate only the secondary external signal at the Output.

7
Symmetry Bias Switch: The Symmetry Bias Switch changes the behavior
of the Symmetry Bias Attenuverter.
Symmetry Bias Attenuverter: The Symmetry Bias Attenuverter can
function in two ways depending on the position of the
Symmetry Bias Switch.
When the switch is in the down position, the Symmetry Bias
Attenuverter functions as an attenuverter for incoming control
voltage or audio signals. This means that control voltage can be
applied to the parameter or two audio signals can be summed
together before reaching the wavefolding stage. Turning the
knob anticlockwise will scale and invert the incoming control
voltage or audio signal. Turning the knob clockwise will scale
the incoming control voltage or audio signal.
When the switch is in the up position, the Symmetry Bias
Attenuverter controls the DC offset amount applied to the signal
present at the Input. The amount of DC offset is applied before
the wavefolding stage. Turning the knob anticlockwise applies
a negative bias to the Input signal. Turning the knob clockwise
applies a positive bias to the Input signal. Applied DC bias will
affect the harmonic overtones of the waveform.
• The center position of this knob is calibrated to 0V.
Drive Toggle: Analog overdrive can be applied to the signal present at
the Input, resulting in soft harmonic distortion.
• If the toggle is in the up position, overdrive is enabled. If the toggle is
in the down position, overdrive is disabled.
BIAS
BIAS

8
Strike Input: A gate or trigger signal present at the Strike Input will
momentarily activate the wavefolder.
Strike Decay: The decay of the Strike Input can be adjusted via the
Strike Decay knob located on the back of the module.
Turning the knob anticlockwise will decrease the decay time. Turning the
knob clockwise will increase the decay time. The default position is 50%.
Decay
Envelope
‘Strike Decay’ Sets decay time of the envelope

9
Patch Examples
West Coast Synth Voice:
Summary: The random voltage generator sends voltages to the
oscillator while simultaneously triggering the envelope generator.
The CV output of the envelope generator opens athrú, allowing the
oscillator signal to pass through.
Audio Path:
• Connect the desired waveform of an oscillator to the Input of athrú.
• Monitor the output of the athrú.
• Set the fundamental frequency of the oscillator to a desired position.
• Set the Wavefold fader to its minimum setting.
Control Path:
• Connect the stepped random output of a random voltage generator
to the 1V/Oct input of the oscillator.
White Noise
Output

10
• Connect the gate output of the random voltage generator to the
trigger input of an envelope generator.
• Connect the CV output of the envelope generator to the Wavefold
CV Input of athrú and set the Wavefold Attenuverter to a desired
positive position.
• Set the envelope stages to desired positions.

11
West Coast Bongo:
Summary: The random voltage generator sends voltages to the
oscillator while simultaneously striking athrú, allowing the oscillator
signal to pass through.
Audio Path:
• Connect the desired waveform of an oscillator to the Input of athrú.
• Monitor the output of the athrú.
• Set the fundamental frequency of the oscillator to a desired position.
• Set the Wavefold fader to its minimum setting.
Control Path:
• Connect the stepped random output of a random voltage generator
to the 1V/Oct input of the oscillator.
• Connect the gate output of the random voltage generator to the
Strike Input of athrú.
White Noise
Output

12
Summed Wavefolder:
Summary: Two waveforms are summed via the Input and Symmetry
Bias Input and then sent through the wavefolder.
Audio Path:
• Create a West Coast Synth Voice audio path.
• Connect a desired waveform from a secondary oscillator to the
Symmetry Bias Input.
• Set the Symmetry Bias Switch to the down position and set the
Symmetry Bias Attenuverter fully clockwise.
• Set the Drive toggle to the up position for added distortion.
White Noise
Output
Sine Wave
Oscillator

13
Burst Generator:
Summary: Everytime cèis is triggered, a burst of trigger signals will
stike athrú allowing the oscillator signal to pass through. For added
modulation, multiply the combined trigger output signal and connect it
to both the Strike Input of athrú and the clock input of a random voltage
generator and connect the CV output of the random voltage generator
to the 1V/Oct input of the oscillator.
Audio Path:
• Create the West Coast Synth Voice audio path.
Control Path:
• Connect the combined trigger output of cèis to the strike input
of athrú.
• Set the separate envelope stages at different positions to create the
desired trigger burst.
• Trigger cèis via the Gate/Trig Input or the Gate/Trig Button.
White Noise
Output

14
This device meets the requirements of the following standards: EN55032,
EN55103-2, EN61000-3-2, EN61000-3-3, EN62311.
Manual Author: Collin Russell
Manual Design: Dominic D’Sylva