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Understanding Audio Reactivity in Lyric Videos

2026-04-12•By Threnic Team

Audio reactivity is the feature that separates Threnic from static lyric video generators. Instead of manually keyframing visual changes, you connect audio frequency data directly to visual parameters, creating videos that breathe, pulse, and react to every beat in your music. This guide explains how audio reactivity works under the hood and how to use it effectively.

How Audio Reactivity Works

When you load an audio file into Threnic, the Web Audio API creates an AnalyserNode that performs a Fast Fourier Transform (FFT) on the audio signal in real time. This converts the raw audio waveform into frequency domain data — a snapshot of how much energy exists at each frequency at any given moment.

Threnic divides this frequency spectrum into three bands:

| Band | Frequency Range | Typical Sources | | -------- | ----------------- | --------------------------------------------------------------- | | Bass | 20 – 250 Hz | Kick drums, bass guitar, sub-bass synths, floor toms | | Mid | 250 – 4,000 Hz | Vocals, guitars, snare body, piano, most melodic instruments | | High | 4,000 – 20,000 Hz | Hi-hats, cymbals, vocal sibilance, synth sparkle, breath sounds |

Each band produces a normalized amplitude value between 0.0 and 1.0, updated every frame. When you enable audio reactivity on a visual effect, Threnic maps this amplitude value to the effect's parameter range.

The Mapping Formula

The relationship is simple:

effectValue = minValue + (maxValue - minValue) × amplitude

For example, if you set a Bloom effect's intensity to react to Bass with Min: 10 and Max: 80:

  • During a quiet passage (amplitude ≈ 0.1): Bloom intensity = 10 + (80 - 10) × 0.1 = 17
  • During a bass drop (amplitude ≈ 0.9): Bloom intensity = 10 + (80 - 10) × 0.9 = 73

This creates smooth, natural transitions that feel perfectly synchronized because they literally are driven by the music's physics.

Setting Up Audio Reactivity

Step 1: Enable on an Effect

Open any effect panel (Distortion, Bloom, Chromatic Aberration, etc.) and toggle Audio Reactivity to On. Additional controls will appear.

Step 2: Choose Your Frequency Band

Select Bass, Mid, or High based on what element of the music you want the visual to follow. As a rule of thumb:

  • Use Bass for rhythmic, beat-driven pulsing (most common)
  • Use Mid for melodic, vocal-following movement
  • Use High for sparkly, textural shimmer

Step 3: Set Min and Max Values

The Min value is the effect's baseline when the audio is quiet. The Max value is the peak when the audio hits maximum amplitude in that band. A wider gap between Min and Max creates more dramatic visual swings.

Step 4: Fine-Tune with Sensitivity

Some effects expose a Sensitivity or Threshold slider. This controls how much of the audio signal is required before the effect starts responding. A high threshold means only loud transients (like a snare hit) trigger the effect; a low threshold means even subtle background instruments cause visible changes.

Creative Strategies

Layer Different Bands Across Effects

The most professional-looking lyric videos use multiple effects, each driven by a different frequency band. This creates rich, multi-dimensional reactivity where different visual layers respond to different aspects of the music simultaneously.

Example setup for a hip-hop track:

  • Distortion → Bass (kick drum drives the warp)
  • Bloom → Mid (vocals make the glow breathe)
  • Chromatic Aberration → High (hi-hats trigger color splits)

This approach prevents the "everything pulses together" look that makes audio-reactive visuals feel amateur.

Match Visual Intensity to Genre Energy

Different genres have radically different frequency profiles:

| Genre | Dominant Band | Suggested Primary Effect | | ----------------- | -------------------- | ---------------------------------- | | Trap / Bass Music | Heavy Bass | Distortion with wide range | | Acoustic / Folk | Strong Mids | Subtle Bloom on vocals | | EDM / House | Balanced Bass + High | Chromatic Aberration on drops | | Metal | Full spectrum | Multiple effects, high sensitivity | | Lo-fi / Ambient | Gentle Mids | Very subtle film grain movement |

Use Inverted Reactivity

Some effects support an Invert toggle that flips the mapping — the effect is strongest during quiet moments and weakest during loud ones. This creates a "breathing" effect where visuals expand in the silence between beats, which works beautifully for atmospheric and ambient genres.

Create Tension with Delayed Reactivity

If you set a very high Min value and a slightly higher Max value (e.g., Min: 60, Max: 75), the effect will appear almost constant with subtle variation. This creates visual tension — the viewer subconsciously senses the movement without it being obvious. Use this technique on background elements while keeping foreground lyrics clean and readable.

Common Mistakes

Over-Reactive Everything

The biggest mistake is enabling audio reactivity on every effect at maximum range. This creates an overwhelming, visually noisy result where nothing has focus. Be selective — pick 1-2 effects for strong reactivity and keep others static or very subtly reactive.

Wrong Band Selection

Mapping a visual effect to the wrong frequency band creates disconnected-feeling results. If you see the distortion pulsing but it doesn't feel synchronized with what you're hearing, you probably have the wrong band selected. The most common fix is switching to Bass for rhythmic effects.

Ignoring the Min Value

Setting Min to 0 means the effect completely disappears during quiet passages, which can look jarring — like the effect is broken. Unless you specifically want that on/off behavior, set the Min to at least 15-20% of your Max value for smooth visual continuity.

Not Previewing with Audio

Always preview your audio reactivity settings with the actual audio playing. The real-time preview in Threnic shows you exactly how the final export will look. Adjusting parameters while paused gives you no feedback on how the reactivity feels in motion.

Technical Details

FFT Size and Smoothing

Threnic uses an FFT size of 2048 samples, which provides a good balance between frequency resolution and time resolution. The analyser node applies time-domain smoothing (smoothingTimeConstant = 0.8) to prevent jittery, frame-to-frame noise in the frequency data.

Performance Impact

Audio analysis itself is very lightweight — the Web Audio API handles FFT processing on a separate thread. The performance cost of audio reactivity comes from the visual effects being updated every frame, not from the audio processing. If you're experiencing performance issues, reducing effect complexity will help more than disabling audio reactivity.

Frame-Perfect Sync in Export

During real-time preview, audio reactivity is driven by the live audio playback. During export, Threnic processes audio frame-by-frame at the exact timestamp of each video frame, ensuring perfect synchronization in the final output even if your computer can't maintain real-time playback speeds.

Next Steps

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