∇
NABLA
VST™ String Synthesizer
Version 1.0
© 2014 by Björn Arlt @ Full Bucket Music
http://www.fullbucket.de/music
VST is a trademark of Steinberg Media Technologies GmbH
NABLA Manual Page 2
Table of Contents
Introduction....................................................3
Turning The Δ Upside Down..............................3
The Synthesizer Section....................................5
Signal Generators (SG)....................................5
Voltage Controlled Filter (VCF)..........................5
Envelope Generator (EG) and Voltage Controlled
Amplifier (VCA)...............................................5
The Strings Section..........................................6
Sound Generation............................................6
Envelope Generator, Amplifier, Equalizer.............6
Common Sections............................................7
From Joystick To Wheels...................................7
LFO and Noise.................................................7
Destinations....................................................7
General Pitch and Mixer....................................8
Tweaks...........................................................8
Panorama Controls..........................................8
GOD Mode......................................................8
Wheel Source..................................................9
Phaser...........................................................9
Delay.............................................................9
Program and File Menu.....................................9
The nabla.ini Configuration File........................10
Force GOD Mode............................................10
Use Linear Knob Mode In Editor.......................10
MIDI Control Change Messages........................10
Parameters...................................................12
Synthesizer...................................................12
Strings.........................................................12
Joywheels.....................................................13
Modulation Generator (MG) and Tune...............13
Volume.........................................................13
Pan, Mode, Wheel..........................................13
Phaser..........................................................13
Delay...........................................................14
Hidden Parameters.........................................14
Frequently Asked Questions.............................15
NABLA Manual Page 3
Introduction
The NABLA is a VST™2.4 software instrument for Microsoft® Windows® simulating the
KORG® Delta DL-50 Strings Synthesizer from 1979. It is written in native C++ code
for high performance and low CPU consumption. The main features are:
● Paraphonic Synthesizer and Strings sections
● Up to 64 voices polyphony
● Synthesizer section:
○ Four band-limited frequency divider-driven signal generators
○ Additional noise generator
○ 4-pole zero-delay feedback bandpass/lowpass filter
● Strings section:
○ Two band-limited frequency divider-driven signal generators
○ 2-band equalizer
○ Ensemble effect
● Flexible pitch/filter modulation by LFO or noise
● Tweaks (not to be found in the original Delta):
○ “GOD Mode” to provide true polyphony
○ Panning for Synthesizer/Strings sections
○ Built-in phaser and delay effects
● Double precision audio processing
● All parameters can be controlled by MIDI controllers
● Plug-in comes in 32 bit and 64 bit versions
● Fully compatible with SM Pro Audio's V-Machine™
Turning The Δ Upside Down
Once upon a time I promised myself not to create a VSTi simulation of an existing
piece of hardware that I do not own by myself. Well, as you can see, I broke my
promise: I never owned a Delta nor is it very likely that I ever will. But due to the
internet – or better: due to gentle folks uploading material there for free – I was able
to get the PDF of the original Delta service handbook including its' schematics, and
tons of videos featuring this neat little instrument. At a first glance I thought “Well,
you can use your own deputy Mark II to simulate the Delta!”, but then I found out that
this not exactly true.
The Delta follows a very clever (some would say “cheap”) technical design of a
polyphonic frequency divider-driven signal generator that is able to simultaneously
create square waves in four footages (16', 8', 4', 2'). These waves – called Signal
Generators – are nothing else than choirs of an electronic organ and can be mixed to
produce other wave shapes. While the mixed generator signal is fed into one single
Voltage Controlled Filter (VCF) and used for the Delta's Synthesizer section, a second,
hard-wired mixer section combines the four signals to generate the rough equivalent
of a 16' and an 8' sawtooth wave. These two “saws”, running through a fixed
Ensemble effect, are the basis for the Strings section.
The rest of the sound processing is paraphonic, meaning that there is only one VCF,
ADSR envelope, and amplifier for the Synthesizer, and only one AR envelope and amp
for the Strings section. Why? Well, just to save money – hardware is expensive.
NABLA Manual Page 4
Then what is so striking about the Delta besides the mystic “It's one of these good old
analog thingies”? The Delta is very usable: Obviously, the Korg engineers, driven by
the reckless forces of cost reduction, did a great job on selecting those controls that
really make sense to lay one's hands on, and made them available for the user.
“Limitation is the friend of Creativity”, and within it's limits the Delta is damned
efficient to use.
OK, as of today's standards, the Delta is indeed pretty limited, so I asked myself:
“What would you almost always add to the Delta if you played it?”
First – a Phaser: The Delta contains a String Ensemble, and Monsieur Jarre
somehow established the phaser as the natural companion to it.
Second – a Delay: Here I would like to give Klaus Schulze and Tangerine Dream
the credit of making delays the standard effects of electronic music.
Third – a “GOD Mode”: Hardware is expensive, software is cheap, so why not
turn the Delta into a true polyphonic instrument? Thanks to the innovative
Generative Object Duplication technology you can now relieve this fine
instrument from the Curse of Paraphony!
All decisions were made except for one: I needed a name for the VSTi version of the
Delta. From Physics we know that there is a symbol like the Greek letter ∆ (Delta)
rotated by 180° (turned upside down), i.e. ∇, and this symbol is called Nabla.
“You cannot name a VSTi Nabla!” I thought. Yes, I can.
NABLA Manual Page 5
The Synthesizer Section
This somehow is the heart of the Nabla: A polyphonic oscillator followed by a filter and
an amplifier. An ADSR envelope to control the filter cutoff and/or the amplitude, plus a
LFO for vibrato or cutoff modulation. The classic design of a JUNO 6. Or not?
Signal Generators (SG)
The Synthesizer section is equipped with four Signal Generators providing square
waves in four different octaves (16', 8', 4', 2') plus an additional Noise generator. The
level of each signal is set by a dedicated fader. Note that the Signal Generators are
realized by using only one Master oscillator and a “Top-Octave Synthesizer”, followed
by a cascade of frequency dividers. This means that the four square wave signals are
totally correlated! For example the rising edge of the 16' square wave always falls
together with the rising edge of the 8' square wave. The same is true for the 4' and 2'
waves as well as for keys (i.e. C to B) of different octaves.
Until now the Synthesizer section is fully polyphonic – even more than a JUNO 6! But
here comes the...
Voltage Controlled Filter (VCF)
Yes, the filter, not the filters: The whole polyphonic signal pathway now becomes
paraphonic (unless you switch to “real” polyphony, but that's a different story; see
section GOD Mode). The VCF can be run in two modes: Lowpass and Bandpass. It
features a Resonance parameter (like in the Delta without self-oscillation), a control
for positive or negative modulation by the ADSR envelope, and a Key Follower switch,
tracking the highest key that is currently pressed. Oh, by the way, you can of course
set the Cutoff Frequency, too.
Do I have to mention that I am using a Zero-Delay Feedback design for the filter?
Envelope Generator (EG) and Voltage Controlled Amplifier (VCA)
The EG has the standard controls for Attack, Decay, Sustain, and Release; it can be
used to control the VCF and/or the VCA. For the latter, one can instead select a simple
“gated” envelope, resulting in a organ-like amplitude contour.
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