Multiphonics Concepts
In a hardware modular synth, the patch cables transmit analog electrical signals from one module to another. These signals are measured in volts. Multiphonics works the same way. You can see it for yourself by connecting any output jack to a level module: it will either show the signal’s current voltage, or give an idea of its range if you are measuring a high frequency signal (the refresh rate of a computer monitor is too slow to show a precise value passed a certain frequency).
The signals produced by modules can be bipolar, meaning that they oscillate between negative and positive voltages, or unipolar, meaning that they are strictly positive.
Examples of bipolar signals are VCOs, LFOs or noise generators. Examples of unipolar signals are envelope generators (ADSR), gates, or clocks.
A nice feature of Multiphonics is that all modules were designed so that their inputs and outputs work with a signal range of 10V peak-to-peak. This can either be from -5V to +5V for so-called bipolar signals, or 0V to +10V for unipolar signals. Because all inputs and outputs operate with roughly the same voltage range, anything can be freely connected to anything else.
Types of Signals ⚓︎
Audio Signals ⚓︎
Audio signals oscillate at a frequency in the hearing range, between 20 Hz and 20 kHz. A patch will normally have at least one module that produces audio signals, and it will be connected to the Output module either directly or through various filters, mixers and other sound processors.
Examples of modules that produce or process audio signals are the Classic VCO, the State Variable Filter, the Objeq Filter, the VCA and the various mixers.
Connecting an audio-rate signal into a module’s modulation input will work, but might not always behave exactly like it would on an analog synthesizer. This is explained in the Audio Rate and CV Rate section further down this page.
Many modules that process audio signals have stereo input and output jacks. You can tell the left and right channels apart by looking for a small dot on the top-left or top right of the jack. The stereo jacks can be placed vertically or horizontally, as shown in the next image.
Stereo modules can be used in mono by connecting only to one channel. By convention in the audio world, we will generally connect to the left channel for mono.
CV Signals ⚓︎
Any signal meant to control a module rather than to produce a sound is called a control voltage (CV) signal. They come in many flavors.
Gate and Trigger
Gate and trigger signals are the simplest kinds of CV signals. They have only two states: low and high, at 0V and 10V respectively.
Outputs labeled Gate will stay high for the duration of an event. For example, in the Keyboard module, the Gate output will be high for as long as a note is pressed on a MIDI keyboard.
Outputs labeled Trig only generate a very short pulse at 10V when an event happens. Trigger pulses are also generated by output jacks with different names, like End in the ADSR and Start of Cycle in the LFO.
In Multiphonics, the trigger pulse length is approximately 0.5 millisecond.
Some inputs are designed to process gates and triggers. Obviously, inputs labeled Gate expect a gate signal. Other inputs only look for a rising edge in the signal. A rising edge happens when the signal goes from 0V to 10V. These inputs will work with either gate or trigger signals. Any input labeled Trig, Reset or Clock operates that way.
Inputs that expect gate or trigger signals will also work with any kind of CV signal. In Multiphonics, the threshold between a low and a high signal is 2V. Therefore, gate inputs will be active for as long as their input is above 2V, while inputs that are triggered on a rising edge will look for the signal to go from below 2V to above 2V.
Pitch
Inputs and outputs labeled Pitch work with the 1 volt per octave rule (1V/oct) found in most modular synths. This means that a variation of +1V will increase the pitch by one octave, and -1V will decrease the pitch by as much.
A special attribute of Multiphonics is that its pitch signals are bipolar and cover the whole range of MIDI notes. 0V represents middle C (MIDI 60, 261.63 Hz), -1V is the C one octave below, 1V is the C one octave above, and so on. This allows the pitch to have approximately a 10V range (MIDI 0 is -5V and MIDI 127 is 5.58V), and to be used like any other modulation signal anywhere in the patch.
Pitch signals corresponding to the twelve-tone equal temperament tuning are produced by the Keyboard module and the Gate+CV Sequencer, but any kind of CV signal can be connected to a pitch input. The Quantizer module can even be used to convert any random CV to the scale of your choice.
Envelope
Envelopes are unipolar signals that change over time in a certain shape. The most popular envelope generator is the ADSR, although envelopes can be produced by other means, such as processing a gate signal through a Slew Limiter.
In many patches, an envelope signal will be used to shape the volume of the sound when a note is played. This is done by patching the envelope into the CV input of a VCA.
Envelopes signals are also good modulation sources for any knob that has modulation inputs.
Clock
Clock signals are special gates that alternate between high and low (10V and 0V) at a given rate. In the Master Clock module found in the top row, the clock rate is set by the current tempo, the Clock Div setting and the Swing knob.
It can be patched in the Clock input of a sequencer, or anywhere a gate or trig signal is expected. Conversely, a module with a Clock input will also work with any kind of trigger signal; it does not absolutely need to be connected to an actual clock.
Tempo
The Tempo signal found in the Master Clock and Clock modules is a unique feature of Multiphonics that makes the synchronization of any time-based parameter possible.
For an in-depth explanation of how such synchronization works, read the section titled Synchronizing Rates and Times in the Master Clock manual page.
For a concrete example of how to synchronize modules to the tempo, take a look at the Sync to Tempo patch in the Basics folder of the Factory collection.
Velocity ⚓︎
Velocity is another place where Multiphonics improves on most other modular synthesizers. Like with the pitch signals, we decided to make our velocity signals bipolar with a range of ±5V.
The main velocity source is the Vel output on the Keyboard module. It converts the MIDI velocity value into a CV signal: -5V will be MIDI velocity 1, 0V will be velocity 64, and +5V will be velocity 127.
A Gate+CV Sequencer’s CV output can also be used as a velocity signal source.
Some modules have inputs labeled Vel, designed to be connected to a velocity CV signal. Vel inputs will control an amplitude using an exponential curve, where 0V will have no effect (0dB). These inputs have an attenuator to adjust the velocity curve. When it is fully clockwise, each increase of 1V on the velocity signal will double the volume (+6.02dB) and each decrease of 1V will halve the volume (-6.02dB).
When a Vel input signal has a range of ±5V and the attenuator is turned fully clockwise, the full dynamic range will be a whopping 60dB. For a more manageable dynamic range, try setting the attenuator somewhere betweeen 10% and 30%.
Modulation ⚓︎
Modulation is a fundamental aspect of modular synthesis. Nearly all parameter knobs on Multiphonics modules have modulation inputs that react swiftly to incoming signals and that can withstand deep and quick modulation without unwanted artefacts.
Modulation inputs are easily recognizable as the unlabeled jacks with small attenuverter knobs located near parameter knobs. The following image shows different possible layouts for modulation inputs (highlighted in yellow).
Think of modulation as a way to turn a knob automatically. When a CV signal is applied to a modulation input, the effect will be the same as if you turned the knob by an amount proportional to the signal’s amplitude.
The small attenuverter knob next to the modulation input jack controls the modulation depth. The effect of the modulation is inverted if the modulation depth is negative.
The following video shows that modulating the Cutoff parameter on a µLP with an ADSR has the same effect as turning the Cutoff knob with the mouse.
Modulation Range ⚓︎
As a rule of the thumb, when the modulation depth is at 100%, then a modulation signal with a 10V range will cover the parameter knob’s range. For example, in the previous video, the Cutoff knob is fully counterclockwise, the modulation depth is at 100%, and the modulation signal from the ADSR goes from 0V to 10V. This has the same effect as turning the Cutoff knob fully clockwise.
Likewise, setting a parameter knob to its middle position and applying a bipolar modulation signal, such as the output of a LFO, will also cover the whole range of the knob.
This rule may not always be exact, but we followed it whenever possible while we were designing the module library to ensure a consistent patching experience.
Modulation Bounds ⚓︎
When a deep modulation is applied, it might go beyond the parameter knob’s range. Depending on the type of parameter, Multiphonics can handle this situation in three different ways.
Unbounded Modulation
For some parameters, it is possible for a modulation signal to make the internal parameter value go beyond the knob’s minimum or maximum values. For example, the Cutoff knob on the State Variable Filter module has a minimum value of 16 Hz, but it’s possible to go below that frequency with a deep negative modulation.
Clipped Modulation
Some parameters have hard limits that can’t be crossed. For example, the Noise Density can’t go above 100%, and the Mix 5 input volume can’t go below 0% (-∞dB). In those cases, applying a deeper modulation will have no effect.
Folding Modulation
Instead of clipping, some parameters have an innovative way to handle modulations that go beyond the parameter’s limit: when the limit is reached, the effect of the modulation signal folds back, so it sounds as if the modulated parameter had bounced on the limit and started going the other way. We call this a folding modulation.
For example, if you center the Compact VCO Sub FM knob and apply a slow rising envelope with a modulation depth of 100%, you will hear the FM effect increasing up to the maximum, and then decreasing even though the envelope is still rising.
This behaviour only applies to a few chosen parameters to ensure that modulation signals always have an effect no matter what kind of modulation is applied, and no matter what the parameter knob position is.
Audio Rate and CV Rate ⚓︎
To find a good balance between reasonable CPU consumption and the freedom to connect anything anywhere, we decided to run modules at two different rates.
The rate at which the audio signals are processed is called the audio rate. It is always equal to the sampling rate at which your DAW or audio interface is running.
Multiphonics is designed to operate properly at sampling rates of 44.1 kHz or higher. Its oscillator modules don’t produce audible aliasing under normal operation and with reasonable amounts of modulation. For the vast majority of patches, increasing the sampling rate will not improve the sound quality.
The rate at which CV signals are processed is called the CV rate. It is fixed at 2000 Hz, meaning that CV signals are processed 2000 times per second. While this is not as fast as the audio rate, it is still well within the hearing range and is quick enough for crazy modulations.
Modulation inputs attached to parameter knobs generally run at CV rate, as do most other inputs designed for CV signals (Pitch, Vel, Env, Gate, Trig, Reset, etc).
Any audio signal connected to an input that runs at CV rate will be mercilessly downsampled to the CV rate. The aliasing artefacts caused by that downsampling may introduce unexpected glitches in your patch, but it may also produce some amazing noises.