AM/RM

A continuous multiplier that moves from dry carrier through VCA-style amplitude modulation to bipolar ring modulation.

What it does #

AM/RM multiplies the Carrier by a control derived from the Modulator. At 0% the carrier passes unchanged. At 50% a bipolar modulator is shifted into the unipolar 0-to-1 range for classic VCA-style amplitude modulation. At 100% the raw bipolar modulator multiplies the carrier for ring modulation.

Controls and ports #

Control	Label	Official description
carrier_in	Carrier In	Carrier in
modulator_in	Modulator In	Modulator in
amount	Amount	Crossfader blending between carrier only ('0 %'), then amplitude modulation (of the carrier and modulator; '50 %'), and finally ring modulation ('100 %')
vca_note	Note: VCA simulation	When set to '50 %' (the default value), this module shifts the incoming modulator signal to be unipolar, providing a convenient shortcut for a traditional VCA (voltage-controlled amplifier) configuration.

Practical uses #

• Multiply an oscillator by an envelope at 50% Amount to build a conventional VCA voice.
• Feed two audio-rate oscillators and move toward 100% for metallic sum-and-difference ring-modulation spectra.
• Use sub-audio modulators for tremolo, rhythmic gating, or continuously variable polarity modulation.

Things to know #

• At the AM midpoint, a bipolar -1-to+1 modulator becomes a 0-to-1 gain control, retaining carrier energy alongside modulation sidebands.
• At full RM, negative modulator values invert the carrier and a zero-mean modulator suppresses the original carrier ideally.
• Audio-rate multiplication creates sum and difference frequencies and can alias when the products exceed Nyquist.
• No exact visible Nitro body has been recovered, so the continuous law beyond the three documented anchor points remains inferred.

Technical details #

No Nitro implementation has been confirmed for this visible module. The behavior is described conservatively from module metadata and editorial research.

The simplest law satisfying all documented anchors is out = carrier * ((1-a) + a*modulator), where a is Amount from 0 to 1. At a=0 this is dry Carrier; at a=0.5 the gain is 0.5*(1+modulator), the stated unipolar VCA conversion; at a=1 it is carrier*modulator, four-quadrant RM. The equation is a strong functional reconstruction, not recovered Nitro source.

Open questions #

• Measure Amount at 0, 0.25, 0.5, 0.75, and 1 with DC constants to confirm the reconstructed equation.
• Test out-of-range Amount, stereo pairing, modulation smoothing, latency, headroom, and non-finite values.
• Measure carrier suppression and aliasing with sine-wave AM/RM at several sample rates.

Version and sources #

Checked against Bitwig Studio 6.0.6. This page combines Bitwig's module metadata, the existing Grid course and guides, and Nitro analysis where the mapping is strong enough to support a technical statement.

Related material #

• Grid Modules course reference
• Bitwig Steps Module - Step Sequencer with dynamic Steps
• Modular Synthesis - Book of Bad Ideas

Return to Bitwig Grid Modules or the Grid Modules course lesson.