Type: Module

Category: Source

Updated: Nov 24, 2019

Manufacturer: MRB

Contact Manufacturer


Listen to the demo on the bundle page.

Video Manual:


The Voltage Modular version of the Zeroscillator is a software clone of the very popular hardware module I designed in 2005. It was manufactured and sold by Cyndustries in a wide variety of formats. If you Google Zeroscillator images, you can see what they all looked like.

The Zeroscillator (ZO) is a VCO with a wide variety of features and modulations. It's main purpose is to do linear, through-zero frequency modulation (TZFM) synthesis. That may sound like a mouthful, but the ZO's purpose is to make TZFM easy while leaving full creativity up to the user like a good module should. TZFM differs from traditional subtractive synthesis in a very fundamental way and sounds completely different. TZFM was the method used in the wildly successful Yamaha DX-7, but rest assured, the ZO sounds nothing like a DX-7.

Rather than start with a waveform rich in harmonics, such as a sawtooth wave and sweeping a filter to select or reject those harmonics, TZFM usually begins with a sine wave, the "carrier". This is the wave you hear. That carrier wave is then frequency modulated at audio rates by a "modulator" to create sidebands which the ear hears as harmonics or overtones. When the depth or "index" of modulation is varied, sidebands appear and disappear much to the ear's delight, creating both complex sounds evocative of the real world and sounds new to mankind. The entire variety of sounds results from the ratio of carrier to modulator frequencies (their relative tunings) and the depth of modulation. If the modulation gets too deep, the frequency will actually go through zero.

Through zero? The modulation is linear which means when the modulation signal falls to zero volts, the oscillator stops at zero Hz -- it flatlines wherever it happens to be in its cycle. If the modulation goes negative, a typical oscillator would still be stopped, but a VCO that can go through zero stops at zero Hz and then runs backwards, or reverses. Think of it like a wheel slowing, stopping, and then reversing. When it runs backwards, the oscillator is said to be producing so called "negative frequencies". The ear can't hear the difference, and positive and negative frequencies look the same on a scope, but the waveform reversals at audio rates give it all its character. The ZO has a toggle switch which allows you to turn the through-zero feature on and off so you can hear how the 2 styles of modulation differ.

(( Please do not confuse waveform reversals with inversions. When you invert a waveform (change its sign), it's being flipped around the X-axis -- bottom becomes top and vice versa. A waveform reversal looks like a flip around the Y-axis -- left becomes right. ))

With the Zeroscillator, you don't have to start with just a sine wave. Saw, square with PWM, and triangle are available too. There are also 2 voltage controlled wave morphers provided which continuously go from triangle through sine to square. Taking outputs from these and modulating the shapes differently creates great stereo effects. The 4 morph outputs are also in quadrature, meaning each output is 90 degrees apart. This is great for LFO use to make things sound swirly and for simulating panning around a room.

Don't worry if you don't understand all of the above, a quick play with the presets will get you up and running. Once you get the basic concept which is really quite easy, experimentation becomes intuitive.


  1. Traditional exponential FM (1V/OCT)
  2. Pulse width modulation
  3. Through-zero linear FM
  4. FM index (depth)
  5. Variable strength sync
  6. Time reversal
  7. Dual waveform morphs


The top row of jacks from edge to edge are all the module outputs.

The big knob in the center is the coarse TUNING control. The QUANT switch, when on, quantizes this knob to semitones (half steps) making tuning very easy. Below to the left is the FINE tuning knob, and below it is the octave RANGE switch. The BIAS knob is explained below.

Starting halfway down on the right side, you find the usual 1V/oct keyboard input with variable tracking and 2 exponential FM inputs with attenuverters. Below that is the pulse width modulation (PWM) input with the initial PULSE WIDTH control to its left. These control the main square wave output and do not affect the MORPH waveforms.

Halfway down on the left side you find the VARI-SYNCH input with strength knob. The sync effect in the ZO sounds very different from what you may be used to, so please experiment. Slowly sweeping an oscillator at this input while playing with the strength knob reveals all you need to know (It's the king of ~glitch~).

Below that are the 3 linear FM inputs which are at the heart of the ZO's function. LINEAR FM takes a modulation signal straight to the core. You can change the modulation depth with the knob. But more fun, and more to the spirit of the ZO is dynamic depth FM. This is created when you plug the modulating oscillator (or whatever) into the MODULATOR input and plug an envelope (or whatever) into the FM INDEX (depth) input. These 2 inputs form a VCA whose output is summed with the LINEAR FM input (if used). The resulting modulating signal linearly modulates the core. The higher the FM INDEX signal, the deeper the modulation. This modulation signal sum is available at the MOD OUT jack. You could use this to modulate something else, like maybe another ZO.

When an envelope patched to the FM INDEX falls, the modulation goes to zero. This means that the sound decays into a pure sine wave, or whatever output you're listening to. This may not be the desired effect. Therefore, a new knob, INITIAL INDEX, (not featured on the original hardware ZO), is provided. By turning this knob up, a modulation "floor" is created, so when the envelope decays to zero, the modulation doesn't completely disappear. The FM INDEX attenuverter must be above (or below) zero to hear the effect of the INITIAL INDEX knob.

The BIAS knob is also tied in with all this as follows. Without modulation, the ZO runs at its "natural" frequency. The BIAS setting defines an internal voltage where this occurs and around which the modulation occurs. In other words, the BIAS voltage is the center of the modulation. If the BIAS is high, a strong modulation voltage (downward) is required before the oscillator reaches zero. If the BIAS is low, zero is nearby, and a much weaker modulation is required to hit zero and below. Therefore, lower BIAS results in the modulation sounding much stronger. If the BIAS is zero, the ZO's natural frequency is zero Hz.

At the bottom you find the TIME REVERSAL jack. A signal here forces the ZO to reverse as if the linear modulation has passed through zero. Its sound is similar to sync, but not at all the same as the VARI-SYNCH feature.

The 2 LEDs show you when the linear modulation changes sign. Due to the nature of LEDs in Voltage Modular, they can only track slow modulations accurately, but they still show you if you're going through zero.

The quadrature waveform MORPHs occupy the 2 boxes in the upper left and right corners. The initial waveform is controlled by the black knob and a signal at the INPUT modulates the shape. This is a true waveform morph just like in the hardware version and not a crossfade. Each pair of jacks output the same waveform 180 degrees apart with the different pairs in quadrature (90 degrees shifted as explained). If you patch the same modulating signal into both INPUT A and INPUT B and then set the attenuverters to opposite signs, the 2 MORPHs change shape opposite one another. Listening to the 2 sides in stereo makes for a stunning panning timbre effect.

I am very pleased with how the Zeroscillator has ported over to software. The sound is faithful to the original. I am also very happy that it lives again through Voltage Modular, and this time nobody needs to go without meals to afford it. Have fun creating sounds ranging from gnarly to sublime.


May 28, 20


Mark Barton's Zeroscillator module is simply fabulous. Please feel free to explore the many dimensions inside of this eco system. There's a sonic universe inside of this generator that leads to many abstract, beautiful, and unique timbres. Not only can it be a sound generator, it can also be an excellent source of control voltage, waveshaping, effects systems, and prototyping advanced realms of sound creation. The wild thing is just by plugging in one of the varied waveforms with no processing, you know that you're on to something because it sounds deep, powerful, and rich. I'm glad that Mark's incredible work is on this side of the pond with Cherry Audio's Voltage Modular. The wild thing is that there's a poly Zeroscillaor as well. This is a great time to be in this wonderful, deep, and fascinating universe of sound. The possibilites are endless, it's just our imagination, experimentation, and willingness to deeply connect with these tools.