fullbucket scrooo Software Synthesizer PlugIn User Guide
- June 9, 2024
- FULLBUCKET
Table of Contents
fullbucket scrooo Software Synthesizer PlugIn
Introduction
The scrooo is a polyphonic software synthesizer plug-in for Microsoft Windows (VST2/VST3/CLAP) and Apple macOS (VST2/VST3/CLAP/AU) based on a spectral formant synthesis architecture and written in native C++ code for high performance. The main features are:
- Up to 64 voices polyphony including Unison mode portamento
- Two band-limited carrier oscillators
- Three fully independent formant generator sections
- Three formant generation modes
- Two amplifiers with volume and panorama control
- Three envelopes (ADSR) with exponential slopes
- Three low frequency oscillators (LFOs) with tempo synchronization
- MIDI Learn ‒ all parameters can be controlled by MIDI CC
- MTS-ESP (https://oddsound.com/) dynamic micro-tuning support
- Plug-in supports Windows and macOS (32 bit and 64 bit)
The scrooo is based on the new iPlug2 framework maintained by Oli Larkin and
the iPlug2 team. Big thanks, guys!!! Without your work it would not have been
possible to create a resizable scrooo user interface.
To resize the plug-in you just grab the yellow triangle at the bottom right of
the window and drag it. You can save the current window size using the menu
entry
“Save Window Size” in the Options Menu. If you have trouble with the standard
version of the scrooo, please grab the (sound-wise identical) “N” version of
the plug-in which is based on the original iPlug framework.
What’s New With Version 2.0?
Version 2.0 of the scrooo is fully compatible with the previous version 1.x;
it should be safe to replace the old plug-in with the new one.
The scrooo now supports MTS-ESP (https://oddsound.com/) dynamic micro-
tuning.
Besides the new user interface I added two new features to the scrooo: Unison
mode and optional Single trigger mode of the envelopes. I also did a lot of
refactoring to the original code but I guess you will not notice much of it.
Architecture
Each voice of the scrooo features two oscillators feeding three separate
formant generators. The outputs of the formant generators are routed to two
individual amplifiers with panorama control which are connected to the main
stereo output bus.
Aside from the audio modules, the scrooo has three envelopes and three LFOs for modulation purposes.
Oscillators
Each oscillator of the scrooo produces a sinusoid waveform feeding the three
formant generators to create more complex signal spectra. The frequencies of
both oscillators can be modulated independently by two different modulation
sources (unipolar or bipolar).
On a new note event, digital oscillators typically start at the same initial
phase angle of the waveform (e.g. the zero-crossing of a sine’s rising slope)
while classic analog oscillators do not; they are “running free” (which means
they are still oscillating even if no note is played). The scrooo will emulate
this behavior if the Free parameter in the Global section is turned on.
Formant Generators
The scrooo features three formant generators with individual center
frequencies and bandwidths. Furthermore, the center frequency and amplitude of
each formant can be modulated by various modulation sources.
There are three modes of formant generation:
-
Fixed
The center frequency of the formant is independent of the oscillator’s base frequency; the generated spectrum will contain only integer multiples of the base frequency (i.e. harmonics). -
Partial
The center frequency of the formant is a fractional multiple of the oscillator’s base frequency; the generated spectrum will contain only integer multiples of the base frequency (i.e. harmonics). -
Ring
The center frequency of the formant is a fractional multiple of the oscillator frequency; the generated spectrum typically will contain inharmonic frequencies.
Thus, Fixed and Partial modes result in the generation of a pure harmonic
formant spectrum while Ring mode allows the creation of inharmonic spectra
(similar to the output of a Ring modulator; hence the name). On the other
hand, Partial and Ring modes generate formant spectra that are “shifted” along
the frequency scale with respect to the base frequency while they are “fixed”
in Fixed mode (which is a typical characteristic of “acoustic” instruments).
Each formant generator can be applied to only one or both of the oscillators;
the resulting output can be sent individually to the two amplifiers.
Version 2 of the scrooo now generously provides an “oscilloscope screen” for
each formant displaying rough sketches of the resulting wave form (Partial
mode), wave shape (Ring mode) or frequency spectrum (Fixed mode).
Amplifiers
Both amplifier sections offer a stereo panorama control which can be modulated by any unipolar or bipolar source. The output volume is controlled by the Level parameter, the output signal of Envelope 1, and two optional unipolar modulation sources. Note that Envelope 1 is hard-wired to both amplifiers.
Modulation Sources
The scrooo’s oscillator and formant center frequencies, amplitudes etc. can be
modulated by various modulation sources. Sources that produce a control signal
of positive values only (including zero) are called unipolar while sources
producing either positive or negative values are called bipolar. The following
table lists the available modulation sources and their polarity.
| source | polarity | description |
|---|---|---|
| Off | unipolar | constant value 0 |
| On | unipolar | constant value 1 |
| LFO1+ | unipolar | output of LFO1 ranging from 0 to 1 |
| LFO2+ | unipolar | output of LFO2 ranging from 0 to 1 |
| LFO3+ | unipolar | output of LFO3 ranging from 0 to 1 |
| Env1 | unipolar | output of envelope 1 ranging from 0 to 1 |
| Env2 | unipolar | output of envelope 2 ranging from 0 to 1 |
| Env3 | unipolar | output of envelope 3 ranging from 0 to 1 |
| Velo | unipolar | MIDI note velocity |
| Note+ | unipolar | MIDI note value |
| Rnd+ | unipolar | constant random value (for current note) |
| PBnd+ | unipolar | MIDI pitch bend wheel (value at center is 0.5) |
| Wheel | unipolar | MIDI modulation wheel |
| LFO1 | bipolar | output of LFO1 ranging from -1 to 1 |
| LFO2 | bipolar | output of LFO2 ranging from -1 to 1 |
| LFO3 | bipolar | output of LFO3 ranging from -1 to 1 |
| Note | bipolar | MIDI note (value at C3 is 0) |
| Rnd | bipolar | constant random value (for current note) |
| PBend | bipolar | MIDI pitch bend wheel (value at center is 0) |
Envelopes
The three envelopes of the scrooo are standard ADSR generators with
exponential slopes as featured in classic analog synthesizers. Envelopes 2 and
3 also feature an initial delay parameter. Envelope 1 is hard-wired to the
amplifiers and directly controls the overall amplitude contour. It is possible
to switch from Multiple to Single trigger mode using the designated Trig
switch.
LFOs
The three low frequency oscillators (LFOs) generate a periodic control signal
from 0 to 100 Hz and/or can be tempo-synchronized to the host. Seven waveforms
are available: Sine, Triangle, Square, Saw Up (rising sawtooth), Saw Down
(falling sawtooth), S/H (Sample and Hold, i.e. random values), and 3-Step
(“stair”-shaped waveform with three steps). The Retrig parameter controls
whether the LFO is restarted for each new note or is “running free” (similar
to the Free Run mode of the oscillators).
It is possible to modulate the magnitude of the LFO’s output by any unipolar
modulation source (even by the LFO itself). This can be used to control the
LFO via the modulation wheel or to create complex modulation signals, “magic
vibrato” effects, etc.
Control Section
Besides selecting programs, setting the Free parameter (see section
Oscillators) and the Voice Mode as well as Pitch Bend intensity and Portamento
time, this section of the scrooo provides some handy utility functions.
Options Menu
When clicking on the MENU button, a context menu opens with the following
options:
| Copy Program | Copy current program to internal clipboard |
|---|---|
| Paste Program | Paste internal clipboard to current program |
| Init Program | Initialize the current program |
| Load Program | Load a program file containing a patch to the scrooo’s |
current program
Save Program| Save the scrooo’s current program to a program file
Load Bank| Load a bank file containing 64 patches into the scrooo
Save Bank| Save the scrooo’s 64 patches to a bank file
Select Startup Bank| Select the bank file that should always be loaded
when the scrooo is started
Load Startup Bank| Load the Startup bank file; can also be used to check
what the current Startup bank is
Unselect Startup Bank| Unselect the current Startup bank
Default Path for Program Files| Sets the default path for program and
bank files
MIDI Thru| Set globally if MIDI data sent to the scrooo should be sent
through to its MIDI output
Ignore Program Change| Set globally if MIDI Program Change data sent to
the
scrooo should be ignored
Reload Configuration| Reload the scrooo’s configuration file (see
section The scrooo.ini Configuration File)
Save Configuration| Save the scrooo’s configuration file (see section
The scrooo.ini Configuration File)
Check Online for Update| When connected to the Internet, this function
will check if a newer version of the scrooo is available at fullbucket.de
Window Size…| Change the window size of the scrooo
Save Window Size| Stores the current window size to the configuration
file so that it will be restored next time you load the scrooo
Visit fullbucket.de| Open fullbucket.de in your standard browser
Voice Mode
The number of voices in standard Poly mode ranges from 1 to 64. The new Unison
mode allows up to 8 slightly detuned voices stacked on top of each other for
various polyphonic modes. Clicking on the digital display opens a menu where
you can select the desired Unison/Poly mode.
MIDI Learn
Every parameter of the scrooo can be controlled by one MIDI controller. If you
want to change the assignment of MIDI controller (CC; MIDI Control Change) to
scrooo parameter the MIDI Learn function comes in quite handy: Just click the
Learn button on the scrooo’s control panel (caption turns red) and wiggle both
the MIDI controller and the parameter you want to assign (you can abort Learn
by clicking the red button again). To save the controller assignments use
“Save Configuration” in the Options menu (see previous section).
If you want to unlearn the assignment, right-click the Learn button (the label
now reads “Unlearn”) and activate it. Now wiggle the MIDI controller or the
parameter that you want to unlearn.
The scrooo.ini Configuration File
The scrooo is able to read some settings from a configuration file
(scrooo.ini). The exact location of this file depends on your operating system
and will be displayed when you click on “Reload” or “Save Configuration”.
Parameters
Global
| parameter | description |
|---|---|
| Voices | number of polyphonic voices (up to 32) |
| Unison | Switches from Poly to Unison mode |
| PBend | maximum pitch bend amount (± 24 semitones) of the oscillators |
| Porta | portamento time (0 to 5 seconds) |
| Volume | the overall volume |
| Free | controls whether the oscillators are restarted or are “running free” |
(like classic analog oscillators) if a new note event occurs
Clip| controls if the overall output is unlimited or clipped to unity
Note: The clipping LED will light as soon as the signal clips; thus, you can
use Clip to create a distortion effect while attenuating the overall output
using the Volume control.
Oscillators
| parameter | description |
|---|---|
| Pitch | the relative pitch (± 24 semitones) |
| Tune | fine tuning of the oscillator (± 1 semitone) |
| FM1 / FM2 | amount of frequency modulation |
FM1 / FM2
Source
| the source of the frequency modulation; this can be any modulation source (see Modulation Sources above)
Formants
| parameter | description |
|---|---|
| Mode | Fixed : the center frequency is fixed i.e. independent of the |
base frequency; only harmonics of the base frequency are generated
Partial : the center frequency is a fractional multiple of the base frequency; only harmonics of the base frequency are generated
Ring : the center frequency is a fractional multiple of the base frequency; typically, inharmonics of the base frequency are generated
Range| center frequency of the formant
Spread| bandwidth of the formant
FM1 / FM2| amount of center frequency modulation
FM1 / FM2
Source
| the source of the center frequency modulation; this can be any modulation
source (see Modulation Sources above)
Volume| initial amplitude of the formant
Osc 1 / Osc 2| enable / disable formant generation for Oscillator 1 and 2
Osc 1 / Osc 2 Send| balance of formant output sent to Amplifiers 1 and 2
AM| amount of amplitude modulation
AM Source| the source of the amplitude modulation; this can be any
unipolar modulation source (see Modulation Sources above)
Amplifiers
| parameter | description |
|---|---|
| Pan | stereo position (panorama) |
| Pan Mod. | amount of panorama modulation |
| Pan Source | the source of the panorama modulation; this can be any |
modulation source (see Modulation Sources above)
AM1 / AM2| amount of amplitude modulation
AM1 / AM2
Source
| the source of the amplitude modulation; this can be any unipolar modulation
source (see Modulation Sources above)
Level| output level
Envelopes
| parameter | description |
|---|---|
| Single | switches from Multiple to Single trigger mode |
| Delay | initial delay time in seconds (Envelopes 2 and 3 only) |
| Attack | attack time |
| Decay | decay time |
| Sustain | sustain level |
| Release | release time |
LFOs
| parameter | description |
|---|---|
| Waveform | seven types are available: Sine , Triangle , Square , _Saw |
Up_ (rising sawtooth), Saw Down (falling sawtooth), S/H (Sample and Hold,
i.e. random values), and 3-Step (“stair”-shaped waveform with three steps)
Retrig| when a new note event occurs, Retrig controls whether the LFO
starts at the beginning of the wave form or is “running free” (similar to the
Free control for the audio oscillators)
Rate| rate or speed of the LFO (in Hertz or note lengths)
Sync| controls whether the LFO is synchronized to the host tempo
AM| amount of amplitude (output level) modulation
AM Source| the source of the amplitude modulation; this can be any
unipolar modulation source (see Modulation Sources below)
Frequently Asked Questions
How do I install the scrooo (Windows VST2 32 bit version)?
Just copy the files scrooo.dll from the ZIP archive you have downloaded to
your system’s or favorite DAW’s VST2 plug-in folder. Your DAW should
automatically register the scrooo VST2 plug-in the next time you start it.
How do I install the scrooo (Windows VST2 64 bit version)?
Just copy the file scrooo64.dll from the ZIP archive you have downloaded to
your system’s or favorite DAW’s VST2 plug-in folder. Your DAW should
automatically register the scrooo VST2 plug-in the next time you start it.
Note: You may have to remove any existing (32 bit) scrooo.dll from your
VST2 plug-in folder or else your DAW may screw the versions up…
How do I install the scrooo (Windows VST3 64 bit version)?
Just copy the files scrooo.vst3 from the ZIP archive you have downloaded to
your system’s or favorite DAW’s VST3 plug-in folder. Your DAW should
automatically register the scrooo VST3 plug-in the next time you start it.
How do I install the scrooo (Mac VST2/VST3/AU 64 bit)?
Locate the downloaded PKG package file scrooo_2_0_0_mac.pkg in Finder (!) and
do a right- or control-click on it. In the context menu, click on “Open”. You
will be asked if you really want to install the package because it comes from
an “unidentified developer” (me J). Click “OK” and follow the installation
instructions.
What is this “Formant Synthesis” thing?
There are two major approaches to waveform generation: Subtractive Synthesis,
where a complex waveform is reduced to a less complex one using filters, and
Additive Synthesis, where a complex waveform is constructed using a large
number of simple (sinusoid) waveforms1. Formant Synthesis (as implemented in
the scrooo) is more on the latter side but works slightly different: A
“carrier” waveform is created from a sinusoid using a non-linear transform
(Wave Shaping) and “tuned” to a specific frequency (the center frequency of
the formant). Thus, the spectrum of the formant is generated by shifting the
(more or less controllable) spectrum of the carrier waveform to the formant’s
frequency domain. Since the scrooo supports the addition of up to three
formants (or even up to six if the oscillators and formants are adjusted in a
twisted way) the overall spectrum can get quite complex.
If you want to learn more I highly recommend a visit at
http://www.puredata.org/ . Here you can download the Pure Data application,
a great audio (and graphics) processing tool including many examples and
background information.
1 Apart from that, many other paradigms such as Frequency or Phase Modulation
etc. exist.
Hey, no filters in the scrooo?
Yes, that’s true, there is no filter inside the scrooo… well, to be honest
there is a DC blocker right before the overall output but that doesn’t count,
right?
No filters? Then it’s just a piece of crap!
If you do think so, I strongly recommend not to install the scrooo. If not,
you may ask yourself…
What is the plug-in ID of the scrooo?
The ID is 3315.
How can I decrease the scrooo’s CPU load?
Always try this:
- If you don’t need a formant to be generated for one or both oscillators, switch off the respective Osc 1 or Osc 2 button of the formant.
Whenever it does not degrade the sound you need, try this:
- Reduce polyphony, i.e. the number of voices.
- Turn of Free Run mode of the oscillators.
- Turn of tempo-synchronization of the LFOs.
How can I prevent output clipping?
Decrease the formants’ and/or the amplifiers’ Level parameters. Alternatively,
switch on the Clip parameter in the Global section but that might lead to
distortion effects. Hey, maybe that’s exactly what you need? 😉
How can I fine-tune the Parameters in the scrooo editor? Especially the
Range knob…?
Press the Shift key while moving a knob to increase it’s resolution.
Hint: If you double click on a knob, the corresponding parameter will be
reset to it’s default value.