Click Start Capture, then choose a tab/screen and enable “Share audio”.
MODE—RATE—FFT—RES—
SPECTRUM · WAITING FOR SIGNALCLIP ≥ 0 dBFS
SAMPLE PEAK
—
dBFS · sample peak (time-domain)
SESSION HOLD
—
dBFS
RMS
—
dBFS · time-domain
CREST FACTOR
—
dB · peak−RMS
CLIP EVENTS
0
0.00/s · 60s window
PEAK HISTORY · LAST 60swaiting…
BAND ENERGY · —normalized · autosens · 48 bands
Capture chain: Global Capture uses the browser's tab/system audio share (getDisplayMedia). This path is not guaranteed bit-transparent — the OS/browser may resample or apply internal gain staging before LabCast ever sees the signal. Treat readings as a reliable relative/trending measure, not a calibrated lab reference, unless verified against known-good source material.
Peak & RMS: computed from raw time-domain samples (getFloatTimeDomainData), independent of the FFT display — these numbers do not depend on FFT window size or smoothing. This is a sample peak, not an oversampled/inter-sample true-peak measurement — a signal that clips only between samples (common after lossy encoding) can read slightly under 0 dBFS here while still clipping on playback elsewhere.
Spectrum & clip: derived from getFloatFrequencyData (dBFS). Web Audio applies an internal Blackman window; wider FFT sizes trade time resolution for frequency resolution — see RES above.
SETTINGS · BELMONT LABS · BL-013
Theme
Analyzer
Teal
Amber
Rose
Blue
Purple
Mono
Phosphor
Windows XP
Windows 3.11
Windows 11
Synthwave
Abyss
Starfield
Old Glory
Composition
CGA
EGA
HyperCard
UI Scale
Size
Channels
Mode
Band Energy Smoothing
Style
Affects only the Band Energy strip below the spectrum (a CAVA-style visual aid). Peak / RMS / Clip readings are unsmoothed and unaffected by this setting.
FFT Size (Global Capture)
Bins
Larger FFT = finer frequency resolution (narrower Hz-per-bin) at the cost of time resolution — transients smear across more analysis frames. 8192 @ 48kHz ≈ 5.9 Hz/bin, a reasonable default for general-purpose measurement. Use 16384 for detailed low-frequency work; use 4096 if you need faster transient response.
Clip Threshold
Reference
0 dBFS is true digital full-scale on the time-domain Sample Peak reading. This is a sample-value peak, not an oversampled/inter-sample true-peak measurement. The −1 dBFS option flags material that's getting close, which is useful if you want early warning before an intersample/lossy-encode overshoot could clip downstream.
LabCast Analyzer
BL-013 — Belmont Labs.
LabCast was originally a multi-source audio player; that role now lives at Intercom19. LabCast has been reoriented around its one genuinely distinct capability: a full-spectrum, dual-channel audio analyzer built for real measurement work, not just visualization.
See the Measurement Notes panel on the main view for an honest account of the capture chain's accuracy characteristics and limits.