Audio & Beat

Modulation

gets its raw signals from two pipelines that run continuously, independent of whatever you’re building in the chain. One is the audio pipeline: it listens to your input, runs an FFT, and reduces the spectrum to six frequency bands you can bind to any parameter. The other is the beat pipeline: it tracks BPM and phase so you can sync any modulation to the tempo.

For the hands-on workflow, see the Audio Reactivity guide and the Beat Sync guide. For how these signals become parameter values, see The Modulation System.

The audio pipeline

audio input → split into six bands → normalise each band to [0, 1] → modulation

Audio input

Lightbridge can listen to any audio device your system exposes: a microphone, a virtual loopback (BlackHole, Loopback, Soundflower, etc.), a USB audio interface, or the system’s default input. The device is selected from the Audio → Input Device submenu in the menu bar. The app remembers your choice across sessions and re-matches by label if device IDs change (which they do on macOS between logins).

From audio to six bands

The audio is split into six musical bands by frequency range:

Band	Frequency range	Design role	What you hear
Sub Bass	20 – 60 Hz	Scale / weight	Deep rumble, sub drops
Kick	60 – 250 Hz	Brightness / pulse	Bass drums, bass guitar
Low Mid	250 – 500 Hz	Texture	Guitar body, low vocals
Mid	500 Hz – 2 kHz	Colour	Snare, vocal presence
Presence	2 – 6 kHz	Detail / edges	Hi-hats, vocal sibilance
Brilliance	6 – 20 kHz	Particles / sparkle	Cymbals, air, shimmer

Each band’s value is normalised so that silence is always 0 and “as loud as it gets” is always 1, no matter what level your audio is running at. That way, a band-driven modulation feels the same on a quiet bedroom mic as on a stadium PA.

Advanced — FFT and dB normalization

The audio is converted to a real-time FFT spectrum (typically 512 bins from a 1024-point FFT). That spectrum is reduced to six bands by averaging the normalized magnitude across each band’s frequency range. The normalization step maps a configurable dbFloor and dbCeil onto [0, 1] — defaults are roughly -60 dB to 0 dB, but the values are tunable in the audio settings.

Three levels of gain

Audio signals pass through three gain stages before reaching a parameter. Each is exposed in a different place in the app, and each has a clearly-labelled control:

Level	What it’s called in the UI	Where to find it	When to set it
Master gain	Master Gain	The audio meters panel (top)	Once per venue — adjust until the band meters bounce in a comfortable range (roughly 30–80% on typical content)
Per-band gain	A gain knob next to each band meter	The audio meters panel, one per band	Once per show — tame or boost specific frequencies to match the source material. Bump Presence if hi-hats are quiet; drop Sub Bass if rumble is drowning the mix
Modulation gain	Gain	Inside the mod panel when the modulation’s source is set to Audio	Per modulation — when one specific modulation needs more swing than the others, without touching global levels

The three stages stack in order:

raw audio → Master Gain → per-band gain → modulation Gain → reactivity → parameter

Start with Master Gain, tune the per-band gains for your source material, and only reach for the per-modulation Gain when one modulation feels limp compared to the others.

The beat pipeline

The beat clock is a single shared timekeeper that every beat-synced modulation reads from. It tracks the current BPM , the current position within a beat, the current beat within a bar, and the total beats elapsed since the session started. When the tempo changes, the current beat position is frozen as a new anchor so phase stays continuous — no jumps, no dropped beats.

The four beat sources

Source	How it works	Pros	Cons
Fixed	You type a BPM value	Reliable. Always stable	Manual; drifts if the track doesn’t match
Tap Tempo	You tap in time with the music; the clock averages up to eight recent taps	Fast to dial in on the fly	You’re the one responsible for accuracy
Auto Sync	Lightbridge listens to the audio input and detects the BPM automatically	Hands-off; adapts to tempo changes	Needs strong beats. Drifts or falls out on sparse material
Ableton Link	Matches tempo and phase with any Link-capable app on the same network automatically	Perfect sync with your DJ software, DAW, or other instruments. Zero configuration	Only works when another Link-capable app is running on the same network

Lightbridge ships them all and lets you switch sources at any time. In most live setups, Ableton Link is the best option when it’s available (because the DJ’s software or your other instruments are already broadcasting a Link session), and Tap Tempo is the best manual fallback.

Bars and phrases

The beat clock tracks more than just individual beats. It also counts bars (four beats each, in 4/4) and phrases (eight bars each — thirty-two beats total). The phrase is a long structural cycle, deliberately chosen to give structural modulations like palette sweeps and long effect ramps something natural to lock to.

Advanced — what the beat clock exposes per frame

Every frame, the beat clock publishes a bundle of state that any modulation can read:

phase — fractional position within the current beat, [0, 1)
bpm — current tempo, clamped to [20, 300]
totalBeats — monotonic count of fractional beats since the session started; modulation reads this for beat-synced LFOs
beat — integer beat within the current bar, [0, 3] (assuming 4/4)
bar — integer bar within the current phrase, [0, 7]
pulse — true on the frame a new beat starts (useful for triggers)
barPulse — true on the frame a new bar starts

The clock uses an “anchor beat + anchor time + tempo” representation, the same pattern Ableton Link uses internally. This is what makes phase continuity across BPM changes possible.

Tap tempo details

Tap tempo sets BPM without resetting phase — the same approach Resolume uses. You’re tapping to tell the clock “this is the tempo,” not “this is the downbeat.” If you want to align phase to a specific beat, use the Resync button (separate from tap) to snap the clock to beat zero.

Up to eight recent taps are averaged to compute BPM. If the gap between taps exceeds three seconds, the tap history resets — you can take a breath between tries without polluting the average.

Phase continuity across BPM changes

When you change the BPM by any means — fixed, tap, link, auto — Lightbridge freezes the current beat position as a new anchor and begins counting forward at the new tempo. Practically, that means your beat-synced modulations don’t jump. If a bell curve was ramping up on a 1-beat modulation at BPM 120 and you drop to BPM 100, it keeps ramping — just more slowly — from wherever it was.

This matters during a live set. Nothing kills a good modulation faster than the whole grid shifting by half a beat because you re-tapped.

How audio and beat come together

The two pipelines feed separate modulation source types — Audio mods read from frequency bands, LFO and Beat mods read from the beat clock — but they end up in the same parameter-overlay stage and combine freely.

A typical live setup has a few audio-reactive modulations (kick → brightness, brilliance → sparkle parameters) and a few beat-synced ones (palette hue on a 16-beat LFO, effect mix on a 4-beat ramp). The audio modulations handle energy and micro-movement; the beat modulations handle structural change. Together they give you a look that responds to the music on a frame-by-frame level and also moves with the music on a bar-by-bar level.

Where to go from here

The Modulation System — how these signals become parameter values, including audio reactivity, response curves, and range mapping.
Audio Reactivity guide — practical walkthrough: adding audio modulation, picking the right band, tuning ranges.
Beat Sync guide — practical walkthrough: picking a beat source, adding beat-synced modulation.
Modulation Curves reference — curve presets for shaping band energy and beat ramps.