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GENERATORS
Sytrus - Basics of FM Synthesis and the Modulation Matrix Cottage rental
Basics of FM Synthesis
Most of the software synths nowadays use subtraction synthesis -
a spectrum rich oscillator (saw, square, triangle etc.) is
processed with a low-pass, band-pass or high-pass resonant filter
to produce the final sound.
FM (Frequency Modulation) uses another approach: additive
synthesis. Pure tones (sine waves) are mixed and processed in such
a way that additional harmonics are created and added to the signal
to produce the final sound.
Unlike subsynths, the basic module of the FM synth is called an
"operator". An operator includes a pure tone oscillator (sine wave)
and an articulation section (at the basic level the articulation
section is at least a simple ADSR volume envelope):
FM Synths contain 2 or more operators (Sytrus supports 6
operators). When an operator is connected to the input of another
(see the modulator input in the diagram above), a pitch (frequency)
modulation occurs. The modulating operator is called "modulator"
while the modulated operator is called "carrier" (in Sytrus a
single operator can act both as a carrier and modulator):
If the modulator has an extremely low frequency (as in the
example on the left), the result is simply a vibrato effect on the
carrier. High modulating frequencies however produce complex, rich
sounds. The arrangement which defines how each operator interacts
with the other (modulate, be modulated or simple mix) is called an
FM synthesis algorithm. In Sytrus, the creation of an algorithm is
made easy with the modulation matrix interface (see
Modulation Matrix below).
Sytrus Implementation
Sytrus offers everything found in classic FM synthesizers and
supports 6 operators and a modulation matrix where you can define
the synthesis algorithm. Sytrus also includes a set of advanced
features which allow you to create many unique sounds:
- Custom Oscillator Shape - The oscillator shape
of each operator can be tweaked in various ways, such as adding
harmonics, morphing to other shapes than sine (square, triangle),
pulse width, add noise etc. An operator can also be set to generate
plucked string tones with fully customizable damping envelope,
which can be indispensable for string and pads patches.
- Ring Modulation - Besides FM (frequency
modulation) and additive mixing, Sytrus operators can interact in
RM (Ring Modulation) mode. Ring Modulation is the process where
input signals are multiplied together to produce a new sound, often
having characteristics qualitatively different than the input
signals.
- Support for Subtractive Synthesis - Sytrus
includes 3 full-featured SVF (filter) modules which can be used to
filter the operators' output. By combining both additive (FM/RM)
and subtractive (SVF) synthesis techniques into a single product,
Sytrus is extremely flexible and can produce a wide range of sounds
without additional plugins and processing.
- Effects Module - The Effects module in Sytrus
offers a range of effects to touch-up the patch sound. Included are
3 delay lines (which can process in parallel or in serial mode) and
a high-quality chorus effect to add depth to your Sytrus patches.
Additionally the signal from the effects module can be sent to a
mixer send
track for additional processing.
- Fully Customizable Articulation - The mapping
diagrams, LFO and envelopes in Sytrus extend far beyond the simple
ADSR volume envelope support. Each diagram and envelope state can
be comprised of unlimited number of curve segments, and allow you
to control pitch, volume, panning, velocity mapping, unison
settings etc., thus allowing complex patch structure, including
even programming whole drum and synth loops into a single
patch/voice.
- Programmable Unison Mode - Sytrus provides
unison mode which supports sub-level voices, variable pitch, pan,
volume and envelope variation. Uniquely, each property which can be
targeted in the articulation sections of the modules can be mapped
by the patch creator to the unison voices following 100%
customizable mapping graphs, which allows practically every voice
in the unison to have different properties (for more information,
see the main module).
Note: If you intend to author your own Sytrus
patches or modify the existing ones, it's recommended to check the
Sytrus processing diagram. It describes in detail how the Sytrus
modules are processed and mixed:
The same diagram is quickly accessible from a button on the
Sytrus interface:
Modulation Matrix
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 The modulation matrix of Sytrus is where
you setup the FM synthesis algorithm. Additionally the matrix
contains the necessary controls to adjust the operator send levels
to the effects and filter modules, panning and "dry" output
level.
Each knob controls a certain function or mapping controlled by
its value (explained below). The neutral position for each knob is
the middle (Alt + left click to reset a knob to its neutral
position). You can also right-click a knob for a quick mute/unmute
while preserving the knob value (this feature is useful while you
are testing and tuning a patch):
The matrix comprises of several discrete parts. Below we take a
deeper look into each section and explain its usage:
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Modulation Setup
 The FM/RM section
sets up the modulation algorithm of Sytrus.
Each row represents an operator and sets up which operators
modulate it and how much. The knobs determine the amount of
modulation, where if the value set is negative (turn the wheel on
left) the modulation phase will be inverted. At the neutral level
(Alt + left click a knob) no modulation occurs.
It is not required for an operator to be modulated to produce
output.
Note: if you hesitate for the purpose of a knob
in the matrix, simply rollover it with the mouse and check out the
FL Studio hint bar.
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Here are few very basic algorithms and their representation in
the Sytrus matrix:
In these examples operator 1 is used as a carrier and the rest
of the active operators are modulators. You can modulate an
operator by itself (in example 3, row 2, column 2 - modulating
operator 2 by itself) thus creating a feedback effect.
Notice that the carrier must be assigned an output, either a
direct (as in the examples) or via the filter modules. For more
information on the filters and output assignment, check the other
two matrix sections covered below.
Sytrus also supports RM (ring modulation) interaction between
the operators. To see and adjust the RM setup, click the FM/RM
switch at the bottom of the matrix:
Please keep in mind the switch only affects the modulation setup
section of the matrix, as the rest of the settings (pan, FX send,
filter send etc.) are shared among the FM/RM setups.
Filter Send Levels
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 This section
adjusts the amount of signal sent from each operator to the filter
modules. Negative values will send inverted signal to the filter
modules.
Sytrus includes 3 filter modules, and each row in the section
represents one of them. If you want to send 50% of the operator 3
and 4 output to filter section 2, adjust the knobs as follow: in
row F2 (filter section 2), adjust the knob in column 3 (operator 3)
to 50%; in the same row adjust the knob in column 4 (operator 4) to
50%.
To reset a knob to a neutral position, hold Alt and left-click
it.
Note that to hear the output of the filter sections, they need
to be assigned an output. To learn more about this check the
Pan, FX Send and Output section covered below.
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Pan, FX Send and Output
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 In this matrix
section you can define the panning, effects send amount, and output
amount for each of the operators and the three filter sections.
The first column sets the panning of its corresponding module
(operator or filter). The default position is centered.
The second column defines the amount of signal sent to the
effects module. If you set this knob to a negative value, the
signal sent to the effects module will be inverted. The default
neutral position (middle) sends no signal to the effects
module.
The third column defines the output amount for its corresponding
module (operator or filter). Negative value sends inverted signal
to the output.
IMPORTANT: Neither the operators or the filter
modules in Sytrus make their output automatically audible. Instead,
you have these choices to make the output audible:
1. Assign an output level for the module from this matrix
section
2. Assign an effects send level for the module (the effects
module is automatically send to the output).
3. (operators only) Assign the operator a filter send level via
the Filter Send Levels matrix section (see above).
The filter module you send to needs to "reach" an output on its
own.
4. (filters only) Use the Send to Next knob
level (please check the filter
module page for more info).
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