Vult Freak User manual

For the Freak firmware version 3.1.
Introduction
The Freak Manifold Filter is the result of my
obsession with analog filters.
When I started with the idea of building my own
synthesizer, the part that I found the most intriguing
was the Voltage Controlled Filter. Filters for music
synthesis are different from the filters that I learned
during my Electrical Engineering studies. Filters for
synthesis are required to change their parameters
on the fly, while all the theoretical filters I studied
were fixed.
In order to create filters that change, it is
necessary to change the values of some of it’s
components (like resistors or capacitors), which in
principle is not an easy task. To achieve that, the
great designers like Moog and Steiner used the
characteristics of semiconductors, like transistors
or diodes, to emulate variable resistors. In other
designs, like Buchla’s, light-dependent resistors
were used to achieve the trick.
Those methods of changing the parameters of
the filters, combined with the nonlinearities of
other stages of the circuit that use semiconductors,
result in an “imperfect”, “distorted”, “nonlinear” filter
behavior. These imperfections are what give the
personality to every filter design. Non linear filters
sound rich and warm compared to the plain and
cold linear digital filters.
Over the last years I have been obsessively
modeling these filters. Thanks to the knowledge
that I have acquired in my real job, which involves
making mathematical models and simulators, I
believe I have managed to capture the soul of
these analog filters and convert them into efficient
digital models capable or running in a small
microcontroller used as Core of the Freak filter.
These models are not perfect emulations; I have
had to made some compromises to achieve good
performance. However, these models are very
good simulations. The Vult filters have attracted
the attention of thousands of persons in the VCV
Rack community that use them as mainly drivers to
create their sounds.
Quick Theory of Filters
Filters are one of the main tools in subtractive
synthesis to transform the sounds. The analog
filters found in most vintage synthesizers can be
classified by two main parameters: Filter type and
Slope.
The Filter type refers to which kind of frequencies
it lets pass e.g. Low Pass (LP) keeps low
frequencies and removes high frequencies. High
Pass (HP) is exactly the opposite; it keeps high
frequencies and removes low frequencies. A Band
Pass (BP) is a combination of a LP and HP. It
removes low and high frequencies letting pass only
a ’band’ of frequencies. Using combinations of LP
and HP stages is possible to obtain other filter types
e.g. the Notch filter.
The Slope of a filter defines how good is at
removing unwanted frequencies. The analog filters
used in synthesizers do not have a very steep slope.
The slope is measured in dB of attenuation. The
simplest of the filters (one pole) has an attenuation
of 6dB per octave, which means that if we input
a sine wave of 1V the signal will be reduced to
1

approximately 1/2V if we double the frequency
(make it one octave higher). A slope of 12dB of
attenuation results in approximately 1/4 of the input
voltage. Every 6dB of attenuation that we add will
reduce the amplitude of the signal by the half. In
principle, it is not possible to have a perfect filter
because it will require an infinite attenuation slope.
Filters have what is called the Cutoff frequency.
This frequency is the point at which the signal
is attenuated 3dB (approximately 0.7 of gain).
Most analog filters used for sound design allow
you to control the Cutoff frequency. In modular
synthesizers the Cutoff frequency is controlled in
Volts per Octave. Similarly to controlling the pitch
in oscillators, the Cutoff frequency will double every
volt.
Most filters have a feedback control that is
better know by the name Resonance. The
feedback (Resonance) has the effect of boosting
the frequencies around the Cutoff frequency. This
effect is a very important part of the sound of
analog filters.
Increasing the Resonance will increase the boost
around the Cutoff frequency. But this boost cannot
be infinite. An analog filter cannot produce an
output voltage larger than its power supply voltage.
The output voltage will be clipped. This clipping
is a form of distortion or nonlinearity; and thanks
to this nonlinearity analog filters could present
self-oscillation. When self-oscillating, the filter will
behave as a Voltage Controller Oscillator (VCO) and
it will produce an output signal even when no audio
input is present.
Nonlinear effects can occur in many of the stages
of analog filters. These nonlinearities are what
give the character to the filters. In order to exploit
these distortions we need to drive the filter to its
limits. Many filters have the Drive control which is
basically an attenuator that limits the input signal.
If the input signal is large, the filter can produce
distortion that can spice up the sound.
Some parameters that are not very often
controlled in analog filters are the Slope and the
Quality. Slope tends to be fixed in analog filters
however it is possible to have variable slope filters.
The Quality is basically the bandwidth of the
Resonance. You can find filters that vary the Slope
and Quality in Serge Tcherepnin designs.
Figure 1: Summary of all controls of the Freak module
2 v2.6

The Freak Module
The Freak module is a digital filter that simulates
the sound of a variety of analog filters. It consists
of two individual channels that can be operated in
Stereo, Dual or Duplex mode.
Each simulated filter contains one or more
operation modes, e.g. low pass, high pass notch
etc. All the parameters can be modulated through
the provided inputs and attenuverters.
A summary of the controls and inputs is shown
in Figure 1.
As of version 2.0 of the firmware, the Freak filter
includes distortions and other wave shapers.
In version 2.4 we introduce a builtin VCA mode.
In version 3.0 a new operation mode called
Duplex is included.
Selecting Filters and Modes
You can change the filter models by pressing the
FILTER button. Quick presses will iterate the
models incrementally. Long presses of the FILTER
button will iterate backwards.
Each filter model has different modes. You can
iterate them by using the MODE button. Check
figure 2to discover all the functions of the buttons.
A full list of all the available mode is shown in
section “List of Available Models”.
Common Filter Parameters
The majority of the filter models provided in Freak
have the following parameters to control: Cutoff
frequency, Resonance level and Drive level. These
FILTER
MODE
MODE
FILTER
FILTER
STEREO
LONG
PRESS
+
MODE
FILTER
MODE
MODE
FILTER
FILTER
DUAL/ DUPLEX
LONG
PRESS
LONG
PRESS
+
MODE
FILTER
MODE
FILTER
MENU
+
Next lter
Previous lter
Next mode
Show menu
Next lter
Previous lter
Switch channel
Next option
Select option
Go back
Next mode
Show menu
Figure 2: Functions of the buttons depending on the
operation mode
parameters are directly controlled by the knobs
with the same name in the panel. Other special
filters and distortion models do not have these
specific parameter names but the same knobs are
used to control them. Check the section “List of
Available Models” in order to know how these
controls behave for an specific filter.
You can see in the panel of the Freak module
that each control provides an input jack and an
attenuverter with the same name. In general, these
pairs are used to control the modulation applied to
the parameters. This is the common case in Stereo
mode. In Dual and Duplex mode the attenuverters
control the right channel filter. Check the sections
3 v2.6

“Dual Mode” and “Duplex Mode” to get all the
details on how the module is operated this way.
The attenuverters and control values mix as
defined by the formula:
parameter =knob +attenuverter ·input
Where the values from knobs go from 0→1
attenuverters and inputs go from −1→1. The
equation above is represented in Figure 3.
Figure 3: General case of signal mixing involving knobs
attenuverters and inputs
Audio Routing
The two channels of the Freak filter are
independent and can receive separate audio
inputs. However, the right channel input has a
hardware switch that when unconnected it will
receive the audio input of the left channel. Figure 4
shows the audio routing of the channels.
Navigating the Menus
The FILTER and MODE buttons are used to navigate
all menus and options of the module. There is a set
of actions that are commonly used in all the menus:
Left push (FILTER button), right push (MODE button)
and double push (FILTER and MODE buttons at the
same time).
Figure 4: Audio routing a) when the right input is
unconnected, the left audio goes to both channels. b)
when both inputs are connected, each signal goes into
its corresponding channel.
In general, the left button (FILTER) will iterate
among the displayed menu options. Right button
(MODE) will select the highlighted option. Pressing
both buttons will take you one level up in the
hierarchy of menus. Refer to figure 2to learn the
functions of the buttons.
Operation Modes
The module has three operation modes: Stereo,
Dual and Duplex. Dual mode was introduced in
v2.0 of the firmware. In order to use it you need to
have at least v2.0 of the firmware. Duplex mode
was introduced in v3.0. The version number is
displayed when the module starts. To learn how to
update your firmware check the section “Updating
the Firmware”.
To switch between modes, navigate to the Main
menu by pressing at the same time Left and Right
buttons as many times as needed. There you
should see the option to select either Stereo, Dual
or Duplex mode.
4 v2.6

Stereo Mode
In Stereo mode the left and right channel run the
same filter model and share most of the controls.
The screen will show the current filter, the
operating mode and description (as shown in
Figure 5). You can use the left button (FILTER) to
iterate through the available filter models and the
right button (MODE) to iterate through the modes.
Check the section “List of Available Models” to get
more information about each of the filter models.
Figure 5: Main screen when working in Stereo mode. It
shows the name, mode and description of the filter
In Stereo mode, all controls, attenuverters
and inputs (marked with CUTOFF, RES and
DRIVE), have effect on both filter channels. The
modulations A and B are applied to the left and
right channels correspondingly. You can see the
signal routing of the controls in Figures 6,7and 8.
Figure 6: Left channel signal routing for the Cutoff in
Stereo mode
When processing stereo signals, it is possible to
create interesting effects by modulating the Cutoff
of the channels independently through the A and B
inputs.
Note: Since version 2.5, there is a setting that
Figure 7: Right channel signal routing for the Cutoff in
Stereo mode
Figure 8: Signal routing for the Resonance and Drive
(Left and Right channels) in Stereo mode
will allow you to select different ways of controlling
the Cutoff of the left and right filters. See section
“Stereo Modulation”.
Dual Mode
Dual mode allows selecting a different filter model
on every channel and control them independently.
When entering Dual mode you have to select which
channel is focused, either the left or right (Figure
9). When a channel is focused you can change
the filter and mode (of that channel only) using the
buttons. The focused channel is marked in the top
of the screen as shown in Figure 10. To switch
the focused channel, you can either press and hold
the MODE button or go one level up (by pressing
the two buttons) and select the other channel. See
the section “Navigating the Menus” to find more
information.
5 v2.6

Figure 9: Channel selection menu for Dual mode
Figure 10: Dual mode. The focused channel is
highlighted. Each channel shows the filter and selected
mode. Buttons only affect the focused channel
In Dual mode the attenuverters CUT, RES and
DRIVE become the main controls for the Right
channel. Attenuverters A and B control the Cutoff
for the Left and Right channels correspondingly.
The inputs CUT, RES and DRIVE have direct
control (not attenuated) over the parameters of
both channels. In the Figures 11 to 14 you can see
the signal routing diagrams used in Dual mode.
Figure 11: Signal routing for the Left channel Cutoff in
Dual mode
Dual mode is great of you want to process two
independent signals. But you can also create
interesting effects by connecting the two channels
either in series or parallel.
Figure 12: Signal routing for the Right channel Cutoff in
Dual mode
Figure 13: Signal routing for the Resonance in Dual
mode (both channels)
Figure 14: Signal routing for the Drive in Dual mode
(both channels)
Duplex Mode
Added in v3.0.
The Duplex mode consists of 4 filters (two
per channel) which can be configured into two
arrangements: serial or parallel. Since this mode
is effectively running 4 filters, only a few of all the
filter models can be selected.
6 v2.6

PRE
FILTER
MAIN
FILTER
L
R
L
R
LEFT CHANNEL
PRE
FILTER
MAIN
FILTER
RIGHT CHANNEL
Figure 15: Duplex-S (Serial) mode
The audio routing of the Duplex-S (serial) mode
is shown in figure 15. In this mode, we have
a ”Main” and a ”Pre” (preprocessing) filter. Both
Main filters (L and R channels) are controlled
by the principal controls: Cutoff, Resonance and
Drive knobs. The Pre filter is controlled by
the corresponding attenuverters. The modulation
inputs and attenuverters A and B behave similar to
Dual mode.
TOP
FILTER
BOTTOM
FILTER
LL
LEFT CHANNEL
TOP
FILTER
BOTTOM
FILTER
RR
RIGHT CHANNEL
Figure 16: Duplex-P (Parallel) mode
The routing for Duplex-P mode is shown in figure
16. The filters are referred as ”Top” and ”Bottom”.
Main controls set the parameters for the Top filter.
Settings
In the Settings menu you will find the different
options to change the behavior of the module.
VCA
Since v2.4 you can change the function of the Res
and Drive inputs of the module and turn them into
control signals for a builtin VCAs. The VCAs are
located at the output of every channel as show in
figures 17 and 18.
LEFT
CHANNEL
RIGHT
CHANNEL
DRIVE
L
R
L
R
Figure 17: Builtin VCA. Drive controls both channels:
”DR->L&R”
LEFT
CHANNEL
RIGHT
CHANNEL
DRIVE RES
L
R
L
R
Figure 18: Builtin VCA. Drive controls the R channel and
Res controls the L channel: ”RES->L DR->R”
VCA NO VCA
DR- L R
&
NO VCA
DR- L R
RES- L DR- R
&
Figure 19: VCA menu items
It is possible to configure the VCAs in three ways
(shown in figure 19):
•NO VCA: the VCAs are removed and the filter
works in the normal mode.
•DR->L&R: Drive input controls both channels
(figure 17).
7 v2.6

•RES->L DR->L: Res input controls the left
channel while Drive controls the right (figure
18).
When enabled, the screen displays small
triangles in the bottom representing the different
VCA modes. For mode DR->L&R, you will see one
triangle in the bottom right (near the Drive input).
In RES->L DR->L you will see two triangles, one
on each side of the screen. You can see how they
look in figure 20.
TANGENTS
LOW PASS
STEINER-PARKER FILTER
TANGENTS
LOW PASS
STEINER-PARKER FILTER
a)
b)
Figure 20: Indicators used when the VCAs are enabled.
a) DR->L&R b) RES->L DR->L
The VCA configuration affects both Stereo and
Dual modes.
If there are no signals connected to the VCA
control signals, there will be no output audio from
the module.
Modulation Range
By default, the Freak module expects a signal in the
0-10V range in order to fully modulate a parameter.
Since many Eurorack modules do not output signals
in that range, now it is possible to select a range of
0-5V.
•10V: the modulations are expected in the -10
to 10V range.
•5V: the modulations are expected in the -5 to
5V range.
Output Range
The Freak module outputs can output audio signals
in the -10 to 10V. This level can be very high for
some Eurorack modules. Now it is possible to
attenuate the output signal in three levels:
•100%: Full range -10 to 10V.
•75%: -7.5 to 7.5V.
•50%: -5 to 5V.
Stereo Modulation
The Cutoff input, in most modes, will modulate the
Left and Right filter in the same direction (either
opening or closing the filter). A voltage of 1V
in the Cutoff input will be sent to both Left and
Right filters. The Stereo Modulation option allows
changing this behavior.
•NORMAL: both channels receive the same
voltage. e.g. a 1V Cutoff input is received by
the Left and Right channel.
•INVERTED: the Right channel received the
signal inverted. e.g. a 1V Cutoff input
is received by the Left channel and -1V is
received by the Right channel.
•SUMMED: both channels receive all
modulations. This provides three inputs to
control the cutoff.
Output Mix
In general, both channels act independently. If you
want to save space in your rack and directly mix the
8 v2.6

Left and Right outputs inside the Freak module you
can do it with this setting:
•STEREO 0%: the outputs are independent.
•10%: 10% of the Left signal is sent to the Right
and vice versa.
•25%, 50%, 75%: the different levels of the
signal are mixed.
•MONO 100%: both L and R jacks output the
same signal which is the mix of Left and Right
channels.
Updating the Firmware
We are constantly working on adding new features,
filters and effects to the Freak module. For that
reason we recommend you to track the updates
by subscribing to the Vult mail list or checking the
Freak product page.
We recommend you to check the video Vult Freak:
Firmware Update Mode where you can see a demo
of the whole process.
To update the module you require a way of
playing back a Wave file with a sufficiently high
level. Playing back the file with a laptop or a phone
(through the headphone jack) in most cases is not
enough. You can use a specialized audio card (like
the Expert Sleepers) or run the headphone signal
through a Eurorack module capable of amplifying
the level. A mixer can be used to amplify the signal.
Just connect the signal to two inputs of the mixer.
IMPORTANT: having low audio signal level or
low quality audio can lead the update process to
fail. You need to make sure that the playback is
as raw as possible. We strongly recommend using
Audacity to playback the file because other music
players or DAWs add effects (without telling you)
that can destroy the modulated signal making the
process fail. Low quality sound cards also pose a
problem.
To enter the update mode, press both buttons
and hold them while you press the Reset button
in the back of the module. Alternatively, you can
completely turn off the module, hold the buttons
and power the module. When entering the update
mode you should see the screen in Figure 21.a.
Figure 21: Firmware update screens. a) welcome screen
b) audio level test
Once you are in update mode, you will see a
screen where you can test the audio level of your
signal. Disconnect all the cables from the module
except the audio input and play back the file to
check if the level of the signal is good. A level
around the middle (as shown in figure 21.b) should
be good to update.
Once you are ready, press the right button
(marked by START in the screen). If you want to
abort the mission, press the left one to exit.
Once you start the update process the module
will be waiting for the audio signal. Playback the file
to start receiving data. You should see the screen
shown in Figure 22.a.
IMPORTANT: Once the update process starts
receiving data, the old firmware will be overwritten
and will not be usable anymore.
If the update fails you will the the error screen
show in figure 22.b. Here you will be able to check
the signal level one more time. In order to retry the
update press the right button (marked in the screen
9 v2.6

Figure 22: Firmware update screens. a) receiving data
b) error in the update
as RETRY).
If the update process fails, you should be able to
enter the update mode again to retry the process
as many times as necessary.
List of Available Models
The Freak module provides a variety of filters
that share the same control parameters: Cutoff,
Resonance and Drive. However some of the
models use other parameters mapped to the same
controls, for example, the distortions or the Comb
filter.
In this section you will find a short description of
each model, starting with the common filters and
continuing with the special models.
Models with Common Controls
Tangents - Steiner-Parker Filter
The Tangents filter models the Steiner-Parker filter
circuit. This model comes in three variations:
• TANGENTS (original)
• TANGENTS-MS
• TANGENTS-XX.
The original version is based on the first Eurorack
filter I built. It is derived from the Yusynth design
published by Ives Usson. The main changes in
my model are that the feedback signal is more
controllable in order to avoid the sudden jump to
self oscillation in this filter. The MS and XX versions
are variations on this principle. The XX goes on the
other direction and makes it more aggressive than
the others.
All the Tangents versions feature LP, HP and BP
modes of the filter.
Lateralus - Ladder Filter
Lateralus is a model of the diode/transistor ladder
filter. It’s a hybrid model because I could not pick
which version I liked the most. The initial version
was based on a breadboard circuit I made. This
filter features outputs at every stage of the ladder
providing 6dB, 12dB, 18dB and 24dB slope options.
This kind of sound can be found in filters from
Moog and Roland.
Nurage - Low Pass Gate/Borg Filter
Improved in v2.5
Nurage is a special version of the filter found in
the low pass gate designed by Buchla. Some of the
variations in my model are that the circuit features
a high resonance mode and it features multiple
vactrol models.
The Nurage-VCA model features the ”both”
mode which acts as a VCA and LP filter together. In
the original circuit, this mode does not have a very
exciting resonance. For that reason I have turned it
off. The Resonance knob controls the tail/decay of
the vactrol.
10 v2.6

Ferox - CMOS Filter
Ferox is a model of a CMOS filter. This kind
of filter uses a “not” logic gate which is typically
used in digital electronics. I this case, the logic
gate is used as an inverting amplifier. One of the
variations found in my model is that the filter is more
stable than the original circuit, which makes it more
usable. The Wasp synthesizer used a CMOS filter.
Ferox is a filter that presents some distortion. But
to spice it a bit more, the Drive control after 50%
blend in extra CMOS distortion.
Ferox provides LP, HP, BP and Notch modes.
Vortex - Russian Filter
Vortex, is based on the circuit found in the Polivoks
synthesizer. This circuit uses a special kind of
OPAMPs that allow you to control their bandwidth.
The original circuit is very minimal, but modeling it
proved to be a challenge.
Vortex provides LP and BP modes.
Stabile - State Variable Filter
Stabile is a well-behaved State-Variable filter.
Stabile presents a very clean sound and a nice soft
resonance. Sometimes you want the sound to be
as clean as possible, for those occasions Stabile is
the best.
Stabile provides LP, BP and HP modes.
If you like Stabile, but want a bit more crunch, you
can try Unstabile.
Unstabile - Bent State Variable Filter
Unstabile is the circuit-bent version of the Stabile.
This model is based on the idea of starving
the circuit until the electronic components start
behaving strange. In this case, the OPAMPs are
running with low voltage providing an interesting
distorted sound.
Unstabile has LP, BP and HP modes.
Vorg - MS-20 Style Filter
Vorg is modelled after the OTA (Operational
Transconductance Amplifier) version of the MS-20
filter. More specifically, Vorg was modelled based
on the circuit used found in my Vorg Eurorack
module.
One of the differences between the real analog
Vorg and the modelled Vorg (included in Freak) is
that the modelled version provides a better Drive
control that makes it possible to go further into the
distortion mode.
Vorg provides LP and HP modes.
Boomstick - Sallen-Key Filter
Boomstick is modelled after the basic Sallen-Key
filter architecture. The original circuit I built was
very minimalist; just a couple of capacitors, vactrols
and operational amplifiers. However, one thing I
removed from this model was the vactrol behavior
since I was aiming to get the simplest and best
sounding filter model.
Boomstick provides LP and HP modes.
11 v2.6

Disjoint - DJ style filter
Disjoint combines a LP and a HP filter controlled
in a configuration common in DJ mixers. When
the Cutoff control is turned to the left, the cutoff
frequency of the LP filter is decreased. When
moved to the right, the cutoff frequency of the HP is
increased.
The first mode (48 dB) provides the combined
LP+HP version. Since version 2.3, Disjoint has extra
modes: low pass section only (LP 48 dB and LP 96
dB) and high pass section only (HP 48 dB and HP
96 dB).
Nitrous - Acid filter
Added in v3.0
Nitrous is based on the TB-303 filter. Even when
this filter effectively a ladder (Moog) filter, it has
it’s own personality. Nitrous has 4 poles, which
should make it a 24dB filter. However, one of
the poles is located at a higher frequency which
makes Nitrous to behave as a 18dB filter. With
low levels of resonance, this filter provides a very
smooth sound. When pushing the resonance to the
maximum you get the classic acid sound. This filter
does not self-oscillate.
This model is based on my replica with the same
name.
Special Models
Rescomb - Resonant Comb Filter
Rescomb is a resonant Comb filter. Comb filters
are a special kind of filters that can be obtained by
adding to the original signal a delayed copy of the
same. The resulting effect is the cancellation some
of the frequencies according to the length of the
delay. In addition to the basic Comb filter, Rescomb
allows you to control the level of feedback inserted
in the filter.
Rescomb provides two modes, Comb++ and
Comb- -. The Comb mode defines the direction of
the Comb. The result can resemble either a group
of Notch filters or a group of Peak filters.
The following table shows the mapping of the
filter parameters to the Rescomb parameters:
Filter Parameter Rescomb Parameter
Cutoff Comb Frequency
Resonance Feedback Level
Drive Input Gain
Debriatus - Wave Destructor
Debriatus is a chain of wave-shapers that will help
you destroy your input signal. Debriatus features:
• Wave Folder
• Bit Crusher
• Asymmetric Distortion
• Saturation
The four effects can be operated in two modes:
DIST+FOLD+SAT (Distortion →Wave Folding →
Saturation) of CRUSH+FOLD+SAT (Bit Crush →
Wave Folding →Saturation). Each effect is
controlled with a single parameter.
The following table shows the mapping in
DIST+FOLD+SAT mode:
Filter Parameter Debriatus Parameter
Cutoff Wave Folder
Resonance Asymmetric Distortion
Drive Saturation
In the CRUSH+FOLD+SAT mode the parameters
are the following:
12 v2.6

Filter Parameter Debriatus Parameter
Cutoff Wave Folder
Resonance Bit Crushing
Drive Saturation
It is important to mention that these distortions
are not analog models and can introduce some
aliasing, especially the Bit Crusher.
Nopskate - Flip-Flop Octaver
Added in v2.1
Nopskate is an effect inspired by the Boss OC-2
guitar pedal. It uses a comparator to try to detect
the fundamental frequency of the signal, then two
flip-flops are used as clock divider in order to derive
two signals that are one and two octaves below the
fundamental. This method of obtaining a pitched
down signal is not optimal but it can produce very
interesting effects.
Nopskate allows blending the pitched down
signals in two ways: adding the signals (SUM) of
multiplying them (AM).
There are three modes: 1 octave down, 2 octaves
down and 1&2 octaves down. In all modes the
controls behave as following.
Filter Parameter Nopskate Parameter
Cutoff Dry/Wet
Resonance Sum/AM
Drive Input Gain
The Cutoff knob acts as a Dry/Wet control that
allows you to combine the input signal with the
generated pitch down signals. The Resonance
knob gradually changes from adding the signals
(SUM) to multiplying them (AM).
Flame - Analog Distortion
Added in v2.3
Flame models distortion circuits found in guitar
pedals. Currently it includes the CYLINDER and
RODENT version. These are adapted versions of
the Tube and Rat distortions. The circuits have
been modified to fit better in the Eurorack range of
voltages.
The following table summarizes the control
mapping for the model.
Filter Parameter Flame Parameter
Cutoff Fuel
Resonance Dry/Wet
Drive Volume
In Flame, the Fuel parameter defines the level of
distortion. Depending on the model, it can go from
a gentle warming of the signal to full destruction.
The Dry/Wet parameter can be used to blend
the original signal with the distorted signal. The
Volume parameter controls the level of the output
signal. It can be used to bring back the output to a
reasonable level.
In order to avoid generating lots of noise due to
the high gain of the circuit, Flame include a noise
gate that will silence the input if the level is not
sufficiently high.
Phonok - Vowel Resonator
Added in v2.5
Phonok is a kind of formant filter that can be used
to add a vowel-like sound to your inputs. It consists
of a combination of LP and BP filters tuned to the
vowel frequencies. The Cutoff control allows you to
morph between different vowel combinations.
13 v2.6

Wolv - Wave Shaper
Added in v3.0
Wolv is a wave folder/shaper based on the
original design by Ian Fritz. I modeled Wolv out of
the module I created with the same name.
Wolv module capable of producing very
interesting timbres out of basic waveforms. It
is an unique wave folder/shaper but it is lesser
known than other modules in the same category.
Wolv provides two modes that allow you to
control three out of the four parameters of the
module. The PULSE mode provides the following
mapping.
Filter Parameter Wolv Parameter
Cutoff Pulse Width
Resonance Fold-Mix
Drive Pulse-Mix
The second mode has the following
configuration.
Filter Parameter Wolv Parameter
Cutoff Pulse Width
Resonance Fold-Mix
Drive Offset
The main difference between the analog version
of Wolv and this model is that, since Wolv produces
very high frequency harmonics, the Freak version
can introduce aliasing. In addition, the analog
version can be used with low frequency signals
while this version only supports audio rate signals.
Summary of Models
The following tables summarize all the available
filter models and their corresponding operation
modes as displayed in the module:
Filter Model Operation Modes
TANGENTS LOW PASS
HIGH PASS
BAND PASS
TANGENTS-MS LOW PASS
HIGH PASS
BAND PASS
TANGENTS-XX LOW PASS
HIGH PASS
BAND PASS
LATERALUS LOW PASS 24dB
LOW PASS 18dB
LOW PASS 12dB
LOW PASS 6dB
NURAGE VACTROL S
VACTROL M
VACTROL L
NURAGE-VCA FLEX VACTROL
FEROX LOW PASS
HIGH PASS
BAND PASS
NOTCH
VORTEX LOW PASS
BAND PASS
UNSTABILE LOW PASS
HIGH PASS
BAND PASS
STABILE LOW PASS
HIGH PASS
BAND PASS
RESCOMB COMB++
COMB- -
VORG LOW PASS
HIGH PASS
BOOMSTICK LOW PASS
HIGH PASS
DEBRIATUS DIST+FOLD+SAT
CRUSH+FOLD+SAT
NOPSKATE 1 DOWN
2 DOWN
1+2 DOWN
14 v2.6

Filter Model Operation Modes
DISJOINT 48 dB
LP 48 dB
LP 96 dB
HP 48 dB
HP 96 dB
FLAME CYLINDER
RODENT
PHONOK U-O-A-E-I
U/O/A/E/I
A-I
O-E
U-I
O-A
NITROUS 18dB
WOLV PULSE
OFFSET
Licenses
The Freak firmware is property of Leonardo Laguna
Ruiz. All rights reserved. Owners of a Vult Freak
Hardware module are granted a license to run it
in their Vult Freak Hardware. Any other use is not
allowed by this license.
This project uses the following third-party
sources:
• The Freak Bootloader is a modified version of
the bootloader code, Copyright 2014 Emilie
Gillet released under MIT license.
• Lua VM is included, Copyright 1994–2019
Lua.org, PUC-Rio released under MIT license.
Technical Specifications
• Audio sampling rate: 96 kHz
• Modulation sampling rate: 6 KHz
• Power consumption:
–+12V: 110 mA
–-12V: 13 mA
–5V: 0 mA
• Depth: 50 mm
• Width: 12 HP
Release Notes
• v3.1 Fixes screen initialization problem.
• v3.0 New filters less noise
–Adds Duplex mode
–Adds Nitrous
–Adds Wolv
–Allows to mix all the modulation signals
with the SUMMED mode
–reduces the noise by turning off the HP
filter of the CODEC
–Integrates a screensaver based on the
Wolfram cellular automata
–Many internal improvements and fixes
• v2.6 UI improvements
–Shows the parameter names when
moving the knobs
–In Dual mode, long press the ”Mode”
button switched channels
–Many under-the-hood improvements
• v2.5 Stability and UI improvements
–Models: Adds Boomstick HP
–Models: Adds Nurage-VCA (LPG + VCA)
mode with variable vactrol “decay”
–Models: Adds vactrols with different
“decay” for Nurage
–Models: Adds Phonok, a vowel resonator
15 v2.6

–Avoids pops when changing filters and
models
–Makes easier to press both buttons
–Implements long press to go one filter
back
–Many optimisations to avoid hanging the
module
–Settings are previewed while changing
them
–Setting: modulation input ranges
–Setting: audio output levels
–Setting: stereo modulations
–Setting: output mix
• v2.4 Adds builtin VCA
• v2.3: Adds Flame distortions and extra modes
for Disjoint
• v2.2: Fixes small bug fixes
• v2.1: Added Disjoint and Nopskate
• v2.0: Added Dual mode and Debriatus
Concluding Remarks
I am proud to say that all the filter models were
developed from scratch and that all the DSP code
was written in Vult Language.
16 v2.6