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∇
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
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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
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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.
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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.
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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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The last control of the EG is the infamous Trigger Mode switch. Since there is only one
VCF, VCA, and EG, what should happen if you press more than one key? You have two
options: The EG is re-triggered for each additional key pressed (Multiple Trigger), or it
is not re-triggered until all keys have been released and a new key is pressed (Single
Trigger).
The Strings Section
In the 70s, it was not uncommon to put multiple sections, e.g. Strings, Brass,
Synthesizer, and Organ, into one box sharing a common keyboard controller;
examples are the ARP Quadra, the Moog Opus, but also the Siel Trilogy, or the
Yamaha SK series. The Delta is a modest instrument that only features two section
different sections, the Synthesizer and the Strings.
Sound Generation
The Nabla's string sound is based on two sawtooth-like signals (16' and 8'). Note that
both “saws” are derived from the same source as the Signal Generators of the
Synthesizer section: A fixed, hard-wired mixer combines the four square waves (16',
8', 4', 2') “under the hood” to form the rough approximations of a 16' and an 8'
sawtooth. Using the Octave Balance control, one can continuously fade between both
“saws”, and the result is run through an (again fixed & hard-wired) Ensemble effect.
Envelope Generator, Amplifier, Equalizer
The Strings section again is paraphonic, i.e. for all voices there is only one amplifier
controlled by an even simpler Attack/Release envelope. This envelope also features a
Trigger Mode selector which has a slightly different effect than for the EG of the
Synthesizer: Re-triggering in Multiple mode causes the envelope to reset the output to
Zero, and then re-starts it from the very beginning of the Attack phase.
The Strings' last processing stage is the Equalizer with a low- and a high-shelf band.
Nothing special here except that it may have quite an impact on the sound.
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Common Sections
This chapter describes the features and controls common to both the Synthesizer and
the Strings sections.
From Joystick To Wheels
The original Delta features a joystick for modulation purposes: The horizontal axis
directly controls pitch and/or VCF cutoff frequency while the vertical axis controls the
amount of modulation of the LFO (when pushing the joystick “up”) or the Noise (when
pulling the joystick “down”).
However, joysticks are pretty out of fashion theses days (which is a pity) and modern
controllers almost all have the classic Pitch and Modulation wheels instead. Thus, for
the Nabla I decided to map the horizontal joystick axis to the Pitch wheel and the
vertical axis to the Modulation wheel. Unfortunately, you now have to select what
modulation source (LFO or Noise) is controlled by the Modulation wheel; this is what
the Wheel switch is for.
LFO and Noise
Apart from the Pitch wheel there are two (!) other modulation sources
available: The global LFO and the Noise. The LFO features a triangular wave
ranging from 0.001Hz to 25Hz. This signal can be used directly to apply a
Vibrato effect. Note that the Vibrato affects both the Synthesizer and the
Strings section because both share the same generator bank!
Noise provides a continuous random signal, unlike the classic Sample & Hold which is
a stepwise signal. There is no way to control it except for modulation depth.
Destinations
Pitch and VCF cutoff frequency are the only destinations of modulation. The amount of
pitch or Frequency Modulation (FM) and VCF or Cutoff Frequency Modulation (FcM)
can be set separately. It's also possible to switch FM and/or FcM on or off.
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General Pitch and Mixer
The master tune is controlled by the Tune parameter, and the whole instrument can
be “transposed” one octave up.
Finally, the volume of the Synthesizer and the Strings section as well as the overall
Volume can be set individually.
Tweaks
Up to now the Nabla recreates all the features known from the Delta. Apart from the
trivial ability to store and recall the programmed sound patches, I added some new
features which I think are quite useful. However, I call them tweaks because 1) they
are somehow tweaking the original design of the Delta and 2) “tweak” sounds cooler
than “enhancement” or “improvement”.
Panorama Controls
The Delta features a general mono “Mix” output and two additional mono outputs for
the Synthesizer and the Strings section. In the Nabla VSTi, these outputs are merged
into a stereo output pair where both sections have their own Panorama control. I think
this setup suits more the typical use case of today's music production, while the
original output configuration is still available (just pan the two sections to opposite
directions and handle the Left/Right outputs accordingly).
GOD Mode
A debatable tweak. I struggled long with myself whether I should include it or not. But
what if one could play the Delta in full polyphonic glory? So I added a simple switch,
applied my amazing Generative Object Duplication technology (which is even capable
of modifying the color of LEDs), and turned the Nabla into a true polyphonic
instrument. Huzzah!
Note that in GOD Mode the Trigger Mode control of the Synthesizer section has no
effect.
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Wheel Source
As explained in the section From Joystick To Wheels the modulation source controlled
by the Modulation wheel has to be chosen by the Wheel switch. This is because there
exists no proper mapping between the two segments of the vertical joystick axis and
the single dimension of the Modulation wheel.
Phaser
I love phasers, and it looks as if others love them too, at least in the context of string
machines. The phaser of the Nabla is a straight forward four stage zero-delay allpass
filter with Speed, Feedback and Mix controls. Of course you can deactivate it.
Delay
I love delays, and it looks as if others love them too, at least in the context of
electronic music. The delay of the Nabla simulates a classic Bucket Brigade Delay
(BBD) with delay times from 62ms to 500ms.
Technical note: The delay consists of a fixed number of sample memory cells (the
buckets, not to be confused with the Full Buckets) like a pipeline that the signal has to
pass before it reoccurs at the output. The “speed” of transferring the signal through
these cells determines the delay time, and since there is a “maximum speed” and a
fixed number of cells, the minimum delay time is not 0 but 62ms.
Program and File Menu
Not really a tweak but still something that the Delta did not have: A way of storing
programs or patches and even giving them names! To select one of the 64 patches
just click on the program number, and edit its' name by clicking in the text field.
When clicking on the File 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
Load Program Load a VST program file containing a patch to the Nabla's
current program
Save Program Save the Nabla's current program to a VST program file
Load Bank Load a VST bank file containing 64 patches into the Nabla
Save Bank Save the Nabla's 64 patches to a VST bank file
Init Program Initialize the current program
Reload Configuration Reload the Nabla's configuration file (see section The
nabla.ini Configuration File)
Visit fullbucket.de Open fullbucket.de in your standard browser
Note: Depending on your VST host (for example Reaper) the Load/Save may not
work. In this case use the respective commands of your host.
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The nabla.ini Configuration File
The Nabla is able to read some settings from a configuration file (nabla.ini) located
in the same directory as the Nabla VST DLL (nabla.dll or nabla64.dll) itself. After
you have edited this INI file in a text editor, you have to reload it using the Reload
Configuration command from the File menu (see section Program and File Menu).
Force GOD Mode
This setting configures whether GOD mode is forced to be “always on”, regardless of
what the GOD Mode switch is set to. This might be useful if you are annoyed by the
Nabla's Curse of Paraphony and want to enjoy the full capabilities of today's digital
wonders without tweaking the current patch. Just add or modify the
following section to/in nabla.ini:
[Nabla]
ForceGODMode = true
If you want to disable ForceGODMode, just change true to false. If it is
active then a virtual duct tape will be pasted over the GOD Mode switch.
Use Linear Knob Mode In Editor
Some folks prefer the Linear over the default Circular Knob Mode when twiddling the
knobs in the editor; you can configure this by setting the UseLinearKnobMode in the
Editor section from false to true:
[Editor]
UseLinearKnobMode = true
MIDI Control Change Messages
All parameters of the Nabla can be controlled by MIDI controllers, or more precise:
Each MIDI controller (except Modulation Wheel and Sustain Pedal) can control one of
Nabla's parameters. The mapping is defined in the nabla.ini for example like this:
[MIDI Control]
# General Purpose controllers
CC16 = 2 # Synth Volume
CC17 = 4 # Strings Volume
CC18 = 44 # Delay Time
CC19 = 45 # Delay Feedback
# trying to follow GM2 definitions here ;-)
CC7 = 1 # Volume
CC8 = 3 # Synth Pan
CC10 = 5 # Strings Pan
...
The syntax is straight forward:
CC<controller number> = <parameter ID>
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Given the above example, controller 7 directly controls the overall Volume parameter,
controller 44 the Delay Time etc. As you can see, comments are introduced by the
Pound sign (#); they are here just for description purposes and completely optional.
The parameter ID of one of the Nabla's parameters is given in the section Parameters
below. Note that the controller number can run from 0 to 119, with the exception of 1
(Modulation Wheel) and 64 (Sustain Pedal); the latter two are simply ignored.
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Parameters
Synthesizer
parameter ID description
16' 15 volume of the 16' rectangle wave
8' 16 volume of the 8' rectangle wave
4' 17 volume of the 4' rectangle wave
2' 18 volume of the 2' rectangle wave
Noise 19 volume of the Noise
Attack 20 attack time of the Synthesizer EG
Decay 21 decay time of the Synthesizer EG
Sustain 22 sustain level of the Synthesizer EG
Release 23 release time of the Synthesizer EG
VCA EG
Mode
24 selects whether the amplitude contour is controlled by the
EG or by a simple gated envelope
Trigger Mode 25 selects if the EG will be re-triggered only after all keys have
been released (Single) or for each key pressed (Multiple)
Cutoff Freq. 26 cutoff frequency
Resonance 27 resonance level
EG Depth 28 amount of cutoff frequency modulation by the EG
Filter Mode 29 filter mode: Bandpass or Lowpass
Key Follower 30 selects whether the cutoff frequency increases along with
the highest key pressed or not
Strings
parameter ID description
Oct Balance 31 mix between 16' and 8' wave
Attack 32 attack time of the Strings envelope
Release 33 release time of the Strings envelope
Trigger Mode 34 selects whether the Strings envelope will be re-triggered
only after all keys have been released (Single) or for each
key pressed (Multiple)
Equalizer
Low
35 gain of the low equalizer band
Equalizer
High
36 gain of the high equalizer band
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Joywheels
parameter ID description
FM SG 8 enable or disable pitch modulation
FM Depth SG 9 maximum amount of pitch modulation
fcM SG 10 enable or disable VCF modulation
fcM Depth
SG
11 maximum amount of VCF modulation
Modulation Generator (MG) and Tune
parameter ID description
Vibrato
Depth
13 amount of pitch modulation
Speed 14 rate of the MG (0 to 25Hz)
Tune 6 master tune
Octave 7 switches the overall pitch one octave up
Volume
parameter ID description
Volume 1 master volume
Synthesizer 2 volume of the Synthesizer section
Strings 4 volume of the Strings section
Pan, Mode, Wheel
parameter ID description
Synthesizer 3 panorama of the Synthesizer section
Strings 5 panorama of the Strings section
GOD Mode 0 switches the GOD mode (true polyphony) on or off
Wheel
Source
12 selects the source for the pitch/VCF modulation (MG or
Noise)
Phaser
parameter ID description
Enable 37 switches the phaser on or off
Speed 38 rate of the phaser frequency modulation (0 to 25Hz)
Feedback 39 amount of feedback
Mix 40 mix between dry and wet signal
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Delay
parameter ID description
Enable 43 switches the delay on or off
Time 44 delay time (62 to 500ms)
Feedback 45 amount of feedback
Mix 46 mix between dry and wet signal
Hidden Parameters
parameter ID description
Phaser
Frequency
41 center frequency of the phaser
Phaser
Modulation
42 modulation amount of the phaser
Ensemble
Delay 1
47 delay time of delay line 1 of the Ensemble effect
Ensemble
Delay 2
48 delay time of delay line 2 of the Ensemble effect
Ensemble
LFO 1 Speed
49 speed of the LFO 1 of the Ensemble effect
Ensemble
LFO 2 Speed
50 speed of the LFO 2 of the Ensemble effect
Ensemble
LFO 1 to
Delay 1
51 modulation amount of LFO 1 to delay line 1 of the
Ensemble effect
Ensemble
LFO 1 to
Delay 2
52 modulation amount of LFO 1 to delay line 2 of the
Ensemble effect
Ensemble
LFO 2 to
Delay 1
53 modulation amount of LFO 2 to delay line 1 of the
Ensemble effect
Ensemble
LFO 2 to
Delay 2
54 modulation amount of LFO 2 to delay line 2 of the
Ensemble effect
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Frequently Asked Questions
How do I install the Nabla (32 bit version)?
Just copy the files nabla.dll and nabla.ini from the ZIP archive you have
downloaded to your system's or favorite DAW's VST plug-in folder. Your DAW should
automatically register the Nabla VST plug-in the next time you start it.
How do I install the Nabla (64 bit version)?
Just copy the files nabla64.dll and nabla.ini from the ZIP archive you have
downloaded to your system's or favorite DAW's VST plug-in folder. Your DAW should
automatically register the Nabla VST plug-in the next time you start it.
Note: You may have to remove any existing (32 bit) nabla.dll from your VST plug-in
folder or else your DAW may screw the versions up...
How do I install the Nabla on the V-Machine?
1. Make sure that you have installed the latest V-Machine firmware and VFX software
(available from www.smproaudio.com). The Nabla is known to work with version
2.0.20101204. :-)
2. I will not take any responsibility if the following install procedure does not work for
you, corrupts or damages your V-Machine, or bores you! :-P
I do have a V-Machine and tested the Nabla against it. Have faith! ;-)
3. Export the files nabla.dll, nabla.ini, and nabla.vfxwizard from the ZIP archive
to a temporary folder on your PC/Mac. Run the VFX software and import the
nabla.dll plug-in from this folder; select the nabla.vfxwizard under the Wizard
File option (this will ensure that the nabla.ini is copied to the V-Machine as well).
4. Create a preset for your V-Machine using the Nabla and you're done!
What is the VST plug-in ID of the Nabla?
The ID is D L 5 0 .
How can I decrease the Nabla's CPU load?
Whenever it does not degrade the sound you need, try this:
• Switch GOD Mode off.
• Deactivate the Phaser or the Delay.
• If you don't need the Synthesizer or Strings section, set the respective volume
slider to zero.
There is no sound when I play a key below C-0?
This is by design. Sorry.
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