Web Audio API · FFT Analysis · Psychoacoustics
Live Tool
Spectra Stamp
Drop any audio file and get its real psychoacoustic fingerprint —
dominant perceptual zone, spectral centroid, and masking risk calculated from
actual FFT data. Tell it what kind of sound it is, and it will tell you
what it will conflict with in a mix.
Export the result as structured metadata to attach to stems, sample packs, or any deliverable.
◈ Real FFT — no fake bars
◈ Nothing leaves your device
◈ WAV · MP3 · FLAC · OGG · AIFF
◈ JSON export
◈ How to Use
- Drop or browse an audio file — WAV, MP3, FLAC, OGG or AIFF. The file never leaves your browser. Analysis runs entirely in memory
- Select the source type — this matters. A kick drum and a bass synth can share the same dominant frequency zone, but their masking thresholds are completely different
- Add a label — name it exactly as you'd name it in your session. This identifies the stamp when you hand it to someone else
- Click Analyse & Stamp — a 4096-point FFT runs on the file, the spectrum renders from real data, and a unique stamp ID is generated
- Export JSON — download the metadata. Drop it next to the audio file or bundle it with a sample pack
◈ Who This Is For
- Sound designers handing off stems — a stamp tells the developer exactly where the asset lives spectrally, without them needing to open a DAW
- Mixing engineers — document spectral decisions at the moment you make them, not after the fact
- Game audio teams — catch masking conflicts before they reach the mix
- Sample pack creators — give buyers spectral context per sample, not just a genre tag
- Researchers — exportable per-file acoustic metadata for listening studies or content analysis
02 — Reading the Output
Every value in the stamp is derived from real spectral data — not defaults, not guesses.
Here is what each metric means and what to do with it.
◈ Metric Breakdown
- Dominant Zone — the perceptual band carrying the most energy, mapped to Bark-scale boundaries. Sub, Bass, Low-Mid, Mid, Presence, or Air. This is the zone most likely to cause conflict when layering
- Spectral Centroid — the frequency centre of mass. High centroid = bright or airy. Low centroid = warm or heavy. The pink dashed line marks it on the spectrum
- Peak Frequency — the single loudest bin in the analysis. Useful for spotting resonances, identifying fundamentals, or finding the exact frequency a notch filter should target
- Masking Risk — calculated from the dominant zone, energy density, and source type. Source type shifts the threshold so the risk rating reflects actual mix context, not just raw numbers
- Zone Energy Profile — all six zones scored individually in the exported JSON. Load two stamps side by side and see exactly where they'll fight
03 — Technical Implementation
Spectra Stamp uses the Web Audio API's OfflineAudioContext
to run a 4096-point FFT on the file without playing it back. Audio is decoded entirely in browser memory,
frequency bins are mapped on a logarithmic scale to match how the ear distributes resolution,
and zone boundaries follow Bark-scale conventions rather than equal-width octaves.
◈ Why OfflineAudioContext
- No playback required — analysis runs faster than real-time on the full file without touching your audio interface
- Nothing leaves your device — the file is processed in memory and discarded. No server, no upload, no network request
- Repeatable results — file-based FFT gives a stable measurement. Stamp the same file twice and you get the same stamp
04 — Technology Stack
Web Audio API
OfflineAudioContext, FFT analysis
Canvas 2D
Log-scale spectrum rendering
Vanilla JS
Zero dependencies
Bark Scale
Perceptual zone mapping
JSON Export
Portable structured metadata
OfflineAudioContext
Silent analysis, no playback needed