Fourm Modulation Bus Explained

The Modulation section on the Fourm is a powerful way to build complex sounds quickly. Modulation works by routing one parameter to another with control voltage. Instead of patch cables like on a modular synth, routing is shown with color-coding: red sources connect to red destinations, and blue sources connect to blue destinations. When a destination is set to purple, it receives modulation from both red and blue sources. Blue routings are further scaled by the mod wheel, letting you shape and perform modulation in real time. 

This quick guide introduces the Modulation section and shows you how to use it as a tool for exploring the wide range of sonic possibilities available on the Fourm. For a more detailed overview, please reference page 32 of the Fourm User Guide.

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Bus Types

The modulation section uses color-coded LEDs to indicate internal connections between sources and destinations. A connection can be as simple as one source modulating one destination, or as complex as multiple sources modulating multiple destinations.

A modulation connection is established when the source and destination LEDs share the same color.

OFF: Inactive

RED: Direct bus

BLUE: Mod Wheel

PURPLE: Direct Bus and Mod Wheel (only applicable to DESTINATIONS)

Direct Bus (RED)

To have the LFO modulate the filter Cutoff, toggle the LFO ROUTE button until it turns RED, and do the same for the CUTOFF destination button. The modulation depth is controlled by the LFO AMOUNT knob, which allows both positive and negative values—zero modulation is at the 12 o'clock position. You can also route the LFO to any of the other seven destinations by toggling their buttons to RED as well.

For additional complexity, you can introduce other modulation sources in the same way. For example, toggling FILTER ENV or OSC B to RED will combine their control signals with the LFO, so all selected sources contribute modulation CV to the chosen destinations.

Mod Wheel Bus (BLUE)

You can use the mod wheel to control the LFO modulation amount on both oscillators to create a vibrato effect. Toggle the LFO ROUTE button until it turns BLUE, and do the same for both FREQ A and FREQ B. Use the LFO AMOUNT knob to set the maximum modulation depth—positive or negative.

Now, as you raise the mod wheel while playing, the LFO will modulate both oscillator frequencies, producing vibrato.

Direct Bus and Mod Wheel Bus (PURPLE)

When toggling a modulation destination to PURPLE, both DIRECT (RED) and MOD WHEEL (BLUE) modulation sources are applied. In the example below, both FILTER ENV and LFO are routed to PW A; however, only PW B is receives modulation CV from FILT ENV.