Tetra v1.2 VST
Introduction
Tetra generates a bandlimited quadrature signal, ie. a stereo signal
whose harmonics differ pairwise by 90 degrees. By morphing between
two definable timbres, Tetra can create a wide range of unique sounds.
Tetra was made using Synthedit.
The sound engine isn't based on native Synthedit modules, though, but
newly coded in C++.
Features
- Stereo output of bandlimited quadrature signals with up to
1000 harmonics.
- Morphing between two timbres, controlled by an envelope.
- Copy & Paste buttons for quick storing and restoring of
all control settings.
- Control changes may affect the sound either immediately or
when the next note is played.
- Text field input for all controls.
- Freely selectable polyphony with up to 16 voices. Note
sliding. Adjustable pitch bend range.
- Envelope and key tracking controlled volume.
- Freely adjustable Attack, Decay, and Release slopes.
- MIDI control of all parameters (NRPN).
- 111 presets.
How it works
Feel free to read my article The
Math behind DSF Synthesis if you're interested in knowing how the
synthesis of Tetra works.
How to
use Tetra
Special
Controls
First some words on special controls and general control handling:
- Copy, Paste:
Pressing Copy stores all
control settings, and Paste
restores them. This is useful when you temporarily change some settings
while playing and then want to return to the initial state. Or when you
are creating new presets. In fact, it is possible to copy the settings
of one preset to another preset. Copy
& Paste only works when
the plugin is active and ready to play notes. The leds below the
buttons will flash to indicate a successful storing or restoring.
- Automatable: If
this is active, the Copy and Paste buttons are automatable, ie.
they can be influenced by an extern control like all other knobs and
buttons. However, Copy and Paste will not work properly when
you are recording control events - provided your host is capable of
that. When recording control events, Automatable
should be turned off.
- Change per Note:
When this is turned off, changes of the controls will immediately
affect the sound of all currently playing notes. When turned on,
control changes will only affect the next played note and the notes
after that.
All but the switch controls have text entry fields which you can use to
enter values - just click on them and type. The sliders can be moved
with more precision when you press CTRL while moving them. And to turn
the knobs with more precision, click on them, then move the mouse
pointer away while keeping the mouse button pressed; the farther away
the mouse pointer is, the more precise will be the knob.
Morphing
In the Oscillator section, the two
knob rows marked as Set1 and Set2 define two different timbres.
When a note is played, Tetra will morph between those two timbres as
defined by the envelope generated in the Morph
Control section. If a note is played, morphing will start at the
timbre defined by the lower set, Set2.
The timbre will then change into the timbre defined by the upper set, Set1, at a speed defined by the Attack slider. Morphing will stay
at that level for the time defined by the Hold slider. Then it drops back to Sustain level at the speed defined
by the Decay slider. Finally,
when the note is released, the timbre will change back to the timbre
defined by the lower set. If the LFO
in the Morph Control section
is active, it will add a vibrato to the morphing envelope.
Now, the "lower" parameter set, where the morphing starts, is actually
not always Set2, but it is
freely selectable anywhere between Set1
and Set2. The starting point
of the morphing is defined by the Range
Lower slider in the Morph
Range section. If the slider is in the lowest position, the
starting point is Set2, and
if it is in the highest position, the starting point is Set1. Similarly, the "upper"
parameter set, which is reached after the Attack phase, is defined by
the Range Upper slider.
Oscillator
Settings
The Harmonics knob defines
the amount of harmonics generated by the oscillator. Other than that,
the Oscillator section
defines the parameter sets Set1
and Set2 that determine the
timbre range. The knobs in Set1
and Set2 have the following
meaning:
- FreqRatio: These
two knobs determine the distance between two neighbored harmonics, the
frequency fr.While the fundamental frequency fc is
specified by the currently played note and the Pitch settings, fr
is computed as
fr = fc * left / right +
offset, where "left" is the value of the left knob, "right" is the
value of the right knob, and "offset" is the value of the FreqOffset knob.
- FreqOffset: See
the description of FreqRatio
above. Choosing non-zero values for FreqOffset: usually detunes the
sound but can lead to interesting effects.
- Pitch: Alters
the pitch, measured in octaves. That is, a value of 1 means that the
note is played one octave higher.
- Round: If the Round button under the FreqRatio knobs is turned on, then
the values of the FreqRatio
knobs will be rounded to integers, causing a harmonic spectrum.
Similarly, turning on the Round
button under the Pitch knob
will round the pitch value to an integer, so the pitch will
increase/decrease by full octaves when turning the knob.
- Brightness: This
is the rate by which the magnitude of the harmonics drops off from the
fundamental frequency. Low values make the sound dull, high values make
the sound bright (or even unhearable, unless the overall number of
harmonics is small).
- Color: If this
knob is in its leftmost position, the harmonics will be on the "left"
side of the fundamental frequency only, ie. in the lower frequency
range. If the knob is in its middle position, harmonics will be on both
sides of the fundamental. And if it's in its rightmost position, the
harmonics will be on the right side of the fundamental frequency only.
Turning the knob to intermediate positions will continuously mix
between those states.
- CombFreq and CombPhase: The harmonics'
magnitudes are altered by a comb pattern. CombFreq determines the distance
between notches of the comb, and CombPhase
determines the distance by which the notches are offset.
- FreqMode: In
mode Fixed, the distance
between notches of the comb pattern does not alter when morphing rests
at a certain level. In mode Shift,
however, the distance between notches permanently changes; the CombFreq knob doesn't define the
fixed distance between notches but rather the speed at which the
distance changes. Track is
similar to Shift, but the speed is not only influenced by the knob
value but it also scales with the played note. Either way, the
continuous changes of the notch distance create a flanger-like effect.
- PhaseMode: Fixed, Shift, and Track are analogue to the FreqMode settings, yet they don't
affect the notch distance but the notch offset. Additionally, there is
the setting Effect, which
creates sort of a wah-wah effect that also can be altered by
the FreqMode and PhaseMode knobs. Well, it's hard to
describe, just play around with the settings.
Morph
Control
The Morph Control generates the envelope by which the signal is morphed
between the two parameter sets. The envelope is computed adding the
output of an ADSR and of a low frequency oscillator.
ADSR settings:
- Attack, Hold, Decay, Sustain, Release: Once a note is played,
morphing will basically follow the envelope defined by these sliders.
Hold defines the time the envelope stays at maximum after the attack
phase is finished. Otherwise, nothing special here. Except for:
- Splope controls: Below Attack,
Decay, and Release there are knobs by which
you can change the respective slope of the curve. When the knobs are in
the leftmost position, the slopes start fast and slows down at the end.
Turning the knobs to the rightmost position will result in the opposite
behavior.
- No Release: If
this button is on, the envelope will not drop when the note is released
but it will stay at the current level
LFO settings:
- Speed, Phase, Amount: Speed and Phase define the LFO frequency
and the LFO phase, respectively. Amount
determines how much of the LFO output is mixed with the ADSR output to
create the envelope. The higher the value, the more LFO you will hear.
- Mode: The Mode switches define the method by
which the LFO is mixed with the ADSR.
-
- Normal: In
this mode, the LFO amplitude is not affected by the ADSR envelope but
only determined by Amount.
In the remaining three modes, the LFO amplitude is dynamically scaled
by the ADSR signal.
- Bottom: The
lower bound of the LFO amplitude is constantly zero. The upper bound is
equal to the current value of the ADSR signal.
- Center: The
LFO amplitude is scaled by the ADSR signal. The lower and upper bounds
of the LFO amplitude are not constant but are moving with the ADSR
signal.
- Top: The
upper bound of the LFO amplitude is constant at maximum. The lower
bound is equal to the current value of the ADSR signal.
Volume
Settings
- Attack, Hold, Decay, Sustain, Release: These are working is
usual.
- Level: The
maximum volume level. This control differs from the Volume control in that Level is stored individually with
each preset, while Volume is
not affected by preset changes.
- Slope Controls: Below Attack,
Decay, Release there are knobs to control
the slope of the respective curve.
- Full Attack:
When this button is turned on, the volume envelope will always
complete both the Attack and Hold phase, even when the note is
released meanwhile. This comes in handy when you have a long attack and
hold time but don't want to keep the key pressed so long.
Stereo Settings
Each harmonic pair of the quadrature signal is perfectly balanced in
stereo (in the stereo image, it describes a circle). However, the
overall signal, ie. the sum of the harmonics, may not be balanced. You
can use the stereo controls to change the overall stereo image.
- Width: When this
knob is at the rightmost position, the harmonics are out of phase by 90
degrees (all cosines on the left, all sines on the right, by default).
In the leftmost position, the image is inverted, and in the middle
position, the output is a mono mix of both channels.
- Angle: Angle by
which the stereo image is rotated.
- AngleIncr: The
angle by which the stereo image is rotated further every time a note is
played. At -90 and 90 degrees, left and right channel will be swapped
with every note.
Miscellaneous
Voices: The maximum
amount of voices that can be active at the same time. It can be freely
set between 1 and 16.
Slide: This is the
portamento speed, ie. the speed at which notes slide. To make notes
slide, a key must not be released before the next key is pressed. If
the Slide knob is turned to
the leftmost position, sliding is off.
Bend: This is the pitch
bend range measured in half tones. If you're using a pitch bend wheel,
you may have to alter this parameter to get the desired effect.
Volume: Limits the
overall volume.
MIDI Control
Mapping
This table shows to which MIDI NRPNs the controls are
mapped
| FNum1 (FreqRatio) |
1 |
Harmonics |
21 |
ReleaseAS |
41 |
| FNum2 (FreqRatio) |
2 |
CFMode |
22 |
NoRelease |
42 |
| FDenom1 (FreqRatio) |
3 |
CPMode |
23 |
LfoSpd |
43 |
| FDenom2 (FreqRatio) |
4 |
AttackV (Volume Env) |
24 |
LfoAmt |
44 |
| FOffset1 |
5 |
AttackVS |
25 |
LfoPhase |
45 |
| FOffset2 |
6 |
HoldV |
26 |
LfoMode |
46 |
| Pitch1 |
7 |
DecayV |
27 |
Track |
47 |
| Pitch2 |
8 |
DecayVS |
28 |
Slide |
48 |
| Bright1 |
9 |
SustainV |
29 |
Bend |
49 |
| Bright2 |
10 |
ReleaseV |
30 |
Voices |
50 |
| Color1 |
11 |
ReleaseVS |
31 |
Width |
51 |
| Color2 |
12 |
Level |
32 |
Angle |
52 |
| Fund1 |
13 |
FullAttack |
33 |
AngleIncr |
53 |
| Fund2 |
14 |
AttackA (Morph Env) |
34 |
Volume |
54 |
| CombFreq1 |
15 |
AttackAS |
35 |
RangeL |
55 |
| CombFreq2 |
16 |
HoldA |
36 |
RangeU |
56 |
| CombPhase1 |
17 |
DecayA |
37 |
ChgPerNote |
57 |
| CombPhase2 |
18 |
DecayAS |
38 |
Copy |
58 |
| FRound |
19 |
SustainA |
39 |
Paste |
59 |
| PRound |
20 |
ReleaseA |
40 |
|
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Installation
Put the file Tetra.dll into your VST Plugins folder.
Version History
v1.2:
- Fixed crackling noise when running multiple synth instances
on multi-core systems.
- Added 11 new presets, retuned old presets.
- Minor speed improvements (about 10% less CPU drain).
- Fixed potential pops and sticking notes.
- Limited the maximum generated frequency to 21kHz even at
sample
rates greater than 44.1kHz to avoid volume change at different sample
rates.
- Downward compatible to v1.0/v1.0a.
v1.0a: Fixed the pitch bend knob and another potential
glitch.
v1.0: Initial release.
Contact
Visit "Moppel's
limited synths" for updates and further information.
You can contact me by E-Mail at: moppelsynth@tutututututu.de
(Burkhard Reike).
DISCLAIMER:
This software is provided as is, there is no warranty and nobody is
responsible for any kind of damage. Use it at your own risk.
VST is a trademark of Steinberg Soft- und Hardware GmbH, Germany.
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