Tetra v1.2 VST
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
- Stereo output of bandlimited quadrature signals with
- Morphing between two timbres, controlled by an
- Copy & Paste buttons for quick storing and
all control settings.
- Control changes may affect the sound either
when the next note is played.
- Text field input for all controls.
- Freely selectable polyphony with up to 16 voices.
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.
Feel free to read my article The
Math behind DSF Synthesis if you're interested in knowing how
synthesis of Tetra works.
First some words on special controls and general control
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.
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.
is active, the Copy
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.
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.
In the Oscillator
section, the two
knob rows marked as Set1
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
will then change into the timbre defined by the upper set, Set1, at a speed
by the Attack
Morphing will stay at that level for the time defined by the Hold slider. Then
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
the Morph Control
will add a vibrato to the morphing envelope.
Now, the "lower" parameter set, where the morphing starts, is
actually not always Set2,
it is freely selectable
anywhere between Set1
point of the morphing is defined by the Range Lower slider
in the Morph Range
the slider is in the lowest position, the starting point is Set2, and if it is
the highest position, the starting point is Set1. Similarly,
parameter set, which is reached after the Attack phase, is
defined by the Range
defines the amount of harmonics generated by the oscillator.
Other than that, the Oscillator
section defines the
parameter sets Set1
that determine the
timbre range. The knobs in Set1
have the following
knobs determine the distance between two neighbored
harmonics, the frequency fr.While the
frequency fc is specified by the
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
description of FreqRatio
non-zero values for FreqOffset:
usually detunes the
sound but can lead to interesting effects.
pitch, measured in octaves. That is, a value of 1 means that
the note is played one octave higher.
If the Round
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
will round the pitch
value to an integer, so the pitch will increase/decrease by
full octaves when turning the knob.
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).
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
harmonics' magnitudes are altered by a comb pattern. CombFreq determines
the distance between notches of the comb, and CombPhase
distance by which the notches are offset.
between notches of the comb pattern does not alter when
morphing rests at a certain level. In mode Shift, however, the
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.
Fixed, Shift, and Track are analogue
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
Well, it's hard to describe, just play around with the
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
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.
button is on, the envelope will not drop when the note is
released but it will stay at the current level
and Phase define
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.
the method by which the LFO is mixed with the ADSR.
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.
lower bound of the LFO amplitude is constantly zero. The
upper bound is equal to the current value of the ADSR
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.
bound of the LFO amplitude is constant at maximum. The
lower bound is equal to the current value of the ADSR
These are working is
volume level. This control differs from the Volume control in
individually with each preset, while Volume
is not affected by preset
- Slope Controls: Below Attack, Decay, Release there are
knobs to control
the slope of the respective curve.
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.
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.
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.
which the stereo image is rotated.
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.
amount of voices that can be active at the same time. It can be
freely set between 1 and 16.
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.
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
This table shows to which MIDI NRPNs the controls are
| FNum1 (FreqRatio)
| FNum2 (FreqRatio)
| FDenom1 (FreqRatio)
| FDenom2 (FreqRatio)
|| AttackV (Volume Env)
|| AttackA (Morph Env)
Put the file Tetra.dll into your VST Plugins folder.
v1.0a: Fixed the pitch bend knob and another potential
- Fixed crackling noise when running multiple synth
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
rates greater than 44.1kHz to avoid volume change at different sample
- Downward compatible to v1.0/v1.0a.
v1.0: Initial release.
You can contact me by E-Mail at: firstname.lastname@example.org
This software is provided as is, there is no warranty and
nobody is responsible for any kind of damage. Use it at your own
VST is a trademark of Steinberg Soft- und Hardware GmbH,
Older Versions: Tetra_1_0a.zip
This synth is free. If you like it, feel free to leave a donation.