A UI sound is a tiny file with strict numbers. Most "this sound feels wrong" complaints are a spec miss — too long for its animation, too loud next to speech, or ten milliseconds of silence before the hit — not a taste miss. Fix the spec first.

Duration

Category	Duration	Rule
Tick / toggle / snap	40–80 ms	Finishes before the eye has registered the state change
Tap / press	80–150 ms	Only in tactile products — see sound-decision-framework
Hover	0 ms	Hover is silent. If a design insists, 120–200 ms and off by default
Send / save / confirm	150–250 ms	One or two notes
Notification / receive	200–600 ms	Longer because attention is being requested
Error	100–200 ms	Short and low; the shake carries the rest
Transition (video / marketing)	300–1000 ms	Product UI never gets these
Brand stinger	1–3 s	Launch video, onboarding hero, once

The Toptal rule ties duration to motion: a sound should not last more than ~300 ms longer than the animation it accompanies. A 120 ms press with an 800 ms tail is a bell, not feedback. Match the duration-table.

Loudness

Sound	Integrated loudness	Notes
Taps, ticks, toggles	−18 to −14 LUFS	Below speech, above silence
Notifications	≈ −12 LUFS	The one class allowed to be louder
Launch-video master	−1 dBTP true peak; integrated loudness stated for the register (medians ≈ −18 LUFS; beat-cut sizzles median ≈ −13, 3 of 4 at −12 to −13; the three quietest films, Linear Agent, Cursor 2.0 and Claude Cowork, sit at −33 to −36)	Loudness-normalizing players (YouTube-style) turn loud masters down and do not raise quiet ones — launch-video-sound

Peak every file at −3 dBFS (−1 dBTP for delivered video). Set the design level in the file and the user level in the mixer — never bake "a bit quieter" into the asset. Interface sounds stay subordinate to speech and media; convey urgency with timbre and rhythm, not volume.

Integrated LUFS is unstable on files under ~400 ms — for ticks and taps, match by ear against a reference tick at −16 LUFS and check the peak, rather than trusting the meter.

Format

Mono. Phones, laptops, and Bluetooth speakers sum to mono anyway; stereo UI sounds phase-smear and double the bytes.
44.1 kHz, 16-bit WAV as the source of truth. Ship MP3 (128 kbps) for universal playback or Opus/OGG for smaller web bundles; keep WAV for native and for video timelines.
Zero leading silence. Trim to the first sample above −60 dBFS. Five milliseconds of pre-roll is a visible sync error — see sound-motion-sync.
Short tail, then cut. Fade the last 10 ms to avoid a click; do not let reverb ride 500 ms past the event.
Sprite when there are many. One decoded buffer, offsets per sound; use-sound and Howler support sprite maps.

Frequency shaping

High-pass at 150–200 Hz. Nothing in that band survives a laptop speaker; it only eats headroom.
Tame 3–6 kHz by a few dB if the sound is "needly" — that is where small speakers resonate.
Keep the body in the mid-range (500 Hz–4 kHz), where every device is honest and where the voice lives.

When to apply

Post-processing every generated or downloaded file, and reviewing any PR that adds an audio asset. scripts/sound-family.mjs applies the trim and peak steps automatically; the LUFS check is yours.

Gotcha

Loudness normalization tools (loudnorm, streaming platforms) measure integrated loudness across the whole file. A sound that is 60 ms of hit and 600 ms of quiet tail will be normalized up until the hit clips. Trim the tail first, normalize second.

Sources

Envato, UI sound design with AI — LUFS targets by class, duration bands, mono, the 0–5 ms trim.
Toptal, A Quick Guide to Designing UX Sounds — the 300 ms-over-animation rule; mid-range guidance.
uisfx.com, UI Sound Design — subordinate to speech, urgency by timbre not volume, one-shots vs loops.
EBU R 128 (−23 LUFS, −1 dBTP max) and streaming practice (≈ −14 LUFS): platform reference levels, not what launch films ship at (medians −18.1 LUFS for 28 Skale client films and −18.4 for 18 acclaimed films, measured by HKTITAN 2026-09-28, docs/research/launch-films/).
Related: duration-table, sound-palette.