Level — SPL meter, audience limit and the level protocol

The Level tab is a sound level meter on the measurement channel you picked in Measurement setup. Tap Start listening (on the tab, or at the top) and it reads at once.

dB FS or dB SPL

Until that input and channel are calibrated, every number is in dB FS and the tab says dB FS (uncalibrated) — relative to the input's full scale, useful to compare, meaningless against a limit. Calibrate SPL in Setup (a calibrator, or a reference meter) and the same numbers read dB(A) / dB(C) SPL; the line under the title says which calibration is in force and when it was taken. The calibration belongs to one input and one channel: switch either and you are back to dB FS until that one is calibrated too.

What the meter shows

• LAF (big) — the A-weighted level with the Fast time weighting (125 ms), as a sound level meter's needle. LCF beside it is the same with C weighting.
• LAeq 10 s · 1 min · 15 min and since the start — the energy average over that window. "Since the start" counts from when you started listening or pressed Reset meter; the windows keep up to the last hour.
• LCeq 1 min · 15 min, LCpeak max (the highest C-weighted sample since the start) and LAFmax (the loudest Fast reading).
• C − A over the last minute. Above 10 dB the tab says the low end carries the level — the bass is what to look at for a C limit or the neighbours.
• Clipping: when the input reaches full scale the tab says so. Readings are too low while it clips — turn the input gain down.

Another measurement channel or another input starts the meter over.

How the mic calibration file is applied

The A and C weighting run on the signal as the mic delivers it. When a mic calibration file is loaded, the measurement channel first passes a filter whose response is the file's correction (a 4,096-tap linear-phase FIR), so every band is corrected before it is weighted — not one number for the whole band. The correction is taken relative to 1 kHz, because the SPL calibration with a calibrator already holds the mic's level at 1 kHz; corrections are limited to ±20 dB. After a calibration against a reference meter with pink noise the broadband level can differ by a fraction of a dB from the meter's, as the file then corrects the noise's other bands too.

Audience limit

Pick the Rules: DIN 15905-5 (Germany), V-NISSG (Switzerland), the WHO standard, the Dutch covenant, the French decree, VLAREM (Flanders) or the UK HSE guidance. The default follows your language (German → DIN, French → the decree, Dutch → the covenant, otherwise WHO). The tab shows the rule's window and limit and reads the level the way the rule does:

• DIN 15905-5: LAeq over 30-minute blocks from :00 and :30, and what the running block ends at if the level stays.
• V-NISSG: every 60-minute window, and the loudest one so far.
• WHO, NL, FR, VLAREM: a moving window (15 or 60 minutes); for France the C-weighted Leq limit beside it.
• UK: the whole event.

LCpeak and LAFmax ceilings are checked where the rule has one. Nothing is compared while the reading is in dB FS. While a log runs the limit is judged on the log; otherwise on the live meter. The readouts stay neutral until a value is actually over — a limit is not a target. Rules are as of the date shown; this is not legal advice, check the linked source.

Sent vs heard

While the test tone plays (Setup), the tab shows what is sent (the tone's RMS in dB FS), what is heard (the C-weighted Fast level at the mic) and the difference — the gain from the output to this place. Calibrated, heard is in dB SPL; otherwise in dB FS.

The protocol

1. Start logging records one level per second (A, C, peak and the loudest Fast reading) on the measurement channel. It goes on while you look at another tab, and keeps the screen on where the browser allows. If the input stops (a phone call, a locked screen) the pause shows as a gap.
2. Stop logging. The log keeps the calibration that was in force when it started.
3. Fill in the sheet details: organiser, who wrote the protocol, event, venue, sound engineer, PA, meter / mic, calibrator and its check, the reference place (loudest audience place) and the measuring place.
4. The tab lists the rule's assessment periods (DIN: 30-minute blocks with their LAeq against the limit) and 5-minute rows with LAeq and LCeq.
5. Print (A4) puts the sheet on one page: the fields, the rules and their date, the source and calibration, the whole measurement (LAeq, LCeq, LCpeak, LAFmax), the periods or the loudest window, the 5-minute rows, gaps, a signature line and the SHA-256 of the record — change a number or a name afterwards and the hash no longer matches.

A real meter's log can be the source instead: Import a meter's CSV takes a time column and an LAeq column (LCeq optional), separated by tabs, semicolons or commas, dates as 2026-10-03 or 03.10.2026.

If the page closes while logging, the log stops there and what was logged is kept — the tab says so on the next visit. Starting a new log saves the previous one as a protocol first.

Saved protocols stay on this device

Save on this device keeps the protocol (record, hash and seconds) in this browser — never synced to your account, because a protocol names people and places. On a shared computer another account does not see them. Export file writes all saved protocols as one JSON file; Import file brings them back on any computer, and Open checks the SHA-256 again.

Good to know

• A phone or laptop mic is indicative only: calibrate against a real meter and expect a few dB of error; built-in mics clip above about 115 dB SPL, so LCpeak from them means little. For a record the law asks for, use a class 1 or class 2 meter and import its log.
• LCpeak is the highest sample, not an analogue true peak.