the scrooo
Software Synthesizer Plug-In
Version 1.2
© 2011-2018 by Björn Arlt @ Full Bucket Music
http://www.fullbucket.de/music
VST is a trademark of Steinberg Media Technologies GmbH
Windows is a registered trademark of Microsoft Corporation
The Audio Units logo is a trademark of Apple Computer, Inc.
the scrooo Manual Page 2
Table of Contents
Introduction................................2
What's New With Version 1.2?........2
Architecture.................................3
Oscillators...................................3
Formant Generators......................3
Amplifiers....................................4
Modulation Sources......................5
Envelopes.....................................5
LFOs............................................5
Program and File Menu..................6
MIDI Learn...................................7
The scrooo.ini Configuration File.....7
Parameters..................................8
Global..........................................8
Oscillators.....................................8
Formants......................................9
Amplifiers.....................................9
Envelopes...................................10
LFOs..........................................10
Frequently Asked Questions.........11
Introduction
The scrooo is a polyphonic software synthesizer plug-in for Microsoft Windows (VST)
and Apple macOS (VST/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 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
● Double precision audio processing
● Plug-in supports Windows and macOS (32 bit and 64 bit)
What's New With Version 1.2?
Version 1.2 of the scrooo is fully compatible with the previous version 1.0; it should be
safe to replace the old plug-in with the new one.
the scrooo Manual Page 3
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.
Partial amplitudes for a given center frequency and bandwidth.
The bell-shaped area shows the formant spectrum's “hull”.
1 2 3 4 5 6 7 8 9
Osc 2
Osc 1
Formant 1
Amp 1
Amp 2
L
R
Formant 2
Formant 3
center frequency
bandwidth
the scrooo Manual Page 4
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.
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 Volume
parameter, the output signal of Envelope 1, and two optional unipolar modulation
sources. Note that Envelope 1 is hard-wired to both amplifiers.
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