Basics
Modulation is the process of changing parameters over time using a control signal.
Modular synthesis uses a signal modulator to change different aspects of another carrier signal like amplitude, frequency or timbre/tone color.
Good question to ask is: which principle of modulation is used in this step?
Basic terminology
Modulation
Using a signal(the modulator) to affect/change another signal (the carrier). Some types of modulation are: - frequency modulation - amplitude modulation - phase modulation - ring modulation - pulse with modulation
Voltage span
All Eurorack/VCVrack modules work with Voltage in a maximum value span of 10 Volt. - -5V to 5V - 0 to 10V - 0 to 1V
Amplitude
Level/strength of an audio or control voltage(CV) signal. For audio the amplitude controls the loudness of a sound.
For control voltage signal(CV) the amplitude controls the intensity of modulation that gets applied to a signal.
Frequency
The rate a signal oscillates. Measured in Hertz(hz). Mainly used to control the pitch of a tone although it can control many aspect of a module. E.g. can be used to control the cutoff frequency of a filter.
Clock
The clock signal is a steady stream of triggers/pulses which are used to synchronize other modules. The synchronizing is essential to produce precise and complex rhythms and patterns that align with tempo.
To create a clock signal there are a lot of clock modules available.
Trigger
Short burst signal of voltage that goes HIGH and directly goes back to LOW state.
Triggers get used for example for envelopes that control percussive sounds which lack sustain phase.
Gate
Voltage signal that is used to control the duration of an event. Unlike triggers gates are longer, sustained signals that remain high for the duration of the event - could be a note being played.
LFO
A Low Frequency Oscillator generates a low frequency waveform that is typically used to modulate other modules. The typical waveforms available in an LFO are sine, triangle, sawtooth and square. The output of a LFO is a control voltage that we can use for modulation.
VCO
Voltage Controlled Oscillator generate audio-frequency signal that can create wide range of sounds. It creates a continously running tone. To shape a single sound we can create a substractive synthesizer voice
Bipolar
A control voltage signal that can have positive and negative values. For example a LFO signal with its center at 0V and its peaks and trophs at 5. and -5V.
Unipolar
Control voltage signal that is only positive. Usually in between 0 and max 10V.
Envelope Generator
Envelope generator can shape the amplitude or the timbre of a sound over time. Most commonly used is ADSR. ADSR stands for Attack,Decay,Sustain and Release. Other envelopes are AR, ADR or AD which have less stages as the ADSR.
V/OCT
Volt per Octave is a standard way of controlling musical pitch with voltage where: - one octave equals 1 volt difference. Going from C4 to c5 requires 1 volt increase. - one semitone equals 1/12 volt(approximately 0.0833 volts). A semitone is the smallest step between notes in Western music. Each semitone requires adding or subtracting 0.0833 Volts.
VCA
A Voltage Controlled Amplifier allows a CV signal to control the amplitude of an audio signal. This works similar to a volume control which can be modified by for example a LFO signal.
VCF
Voltage Controlled Filter allows a CV signal to control the frequency response of an audio signal that passes through module.
The typical filter are: - low-pass - band-pass - high-pass
We use filter for emphasis or reduction of certain frequencies in a sound/signal.
Substractive Synthesizer Voice
To create a substractive synth voice patch we substract with modules parts of the source signal. For example we can use Envelope or Filter modules to modulate the output signal of a VCO.
The first thing you want to substract from a continuous sound is volume information with a VCA to control the amplitude and an ADSR envelope(Envelope Generator) to control the shape of the signal that controls the amplitude.
In the VCA we have to plug in a control voltage signal that shapes our volume.
The ADSR need to be triggered so the Envelope gets executed. For ADSR we use a gate signal.
With filter modules we can further manipulate our signal. For that we can use a VCF with a lowpass or highpass filter. Often filter have their own envelopes to control the cutoff.