How to use Noisecatcher

Open the Meter page

Tap Meter in the navigation bar (or the mic icon on mobile). This is where all measurements happen.

Allow microphone access

When you tap Start Measuring, your browser will ask for microphone permission. Tap Allow — the app cannot function without this. Your audio is never recorded or sent anywhere; only the computed volume level is used.

Hold your phone steady

For consistent readings, hold the device at chest height with the microphone facing the noise source. Avoid covering the mic with your hand or case.

Wait for stabilisation

The gauge takes 2–3 seconds to stabilise. The ● LEVEL indicator turns green once the reading has been steady for at least 1.5 seconds — this is the best moment to drop a pin.

Stop measuring or generate a report

Tap Stop to end the session, or — after at least 5 readings — tap Stop & Report to save a full session summary and navigate directly to your noise report.

Start measuring

Begin a session on the Meter page as normal.

Tap 'Stop & Report'

Once at least 5 readings have been recorded, the Stop & Report button appears next to the Stop button. Tap it to save the session and open the report.

Review the report

The report shows Leq, peak, L10/L50/L90 percentiles, EU and OSHA noise dose, psychoacoustic metrics (loudness, sharpness, roughness, annoyance), ACI, and HF deterrent scan results.

Add a voice note

Tap Add voice note to attach an audio commentary — useful for describing the noise context, source, or impact.

Print or save as PDF

Tap Print / Save PDF. Your browser's native print dialog opens; choose 'Save as PDF' to keep a file, or send to a printer.

Start measuring

You must be actively measuring to drop a pin. The microphone must be running.

Wait for a stable reading

Watch the ● LEVEL indicator. When it turns green, the reading has stabilised and is ready to save.

Tap 'Pin this reading'

Press the Pin this reading on map button below the gauge. This navigates you to the Map page. Once there, tap the spot on the map where you were standing — the pin form opens at that location. Choose a noise category and confirm to save.

View your pin on the map

Your pin appears as a coloured dot — green for safe, yellow for caution, orange for dangerous, red for critical. An arrow inside the dot shows the bearing you were facing.

Find the voice recorder

Voice note recorders appear on the Report page (after generating a session report) and inside each Notebookunder the "Add note" section.

Start recording

Tap the microphone button. Your browser will request microphone access if not already granted. Recording begins immediately — a pulsing red dot and a live timer confirm it is active.

Stop recording

Tap Release to stop, or recording stops automatically at 60 seconds.

Play or delete

After saving, tap Play to listen back, or the trash icon to delete and re-record. The audio is stored as a base64 data URL in IndexedDB — it never leaves your device.

Create a notebook

Navigate to Notebooks, tap + New notebook, give it a name, optional notes, and a colour. Tap Create.

Open the notebook

Tap the notebook card to open the detail view. You will see sections for pins, reports, and voice notes that belong to this notebook, plus the voice recorder to add a new note instantly.

Link future recordings

When generating a noise report with Stop & Report, you will be able to assign it to a notebook. Pins dropped from the map can also be linked via the pin form.

Use as a dossier

A well-built notebook — spanning multiple days, times of day, and noise events — is a strong basis for a formal complaint to your local authority, an ombudsman, or a noise pollution legal aid service.

Go to the Map page

Navigate to Map.

Tap '↓ Export GeoJSON'

The button appears in the toolbar above the map. A .geojson file will be downloaded to your device.

Use your data

Open the file in QGIS, Google Maps, ArcGIS, or any GIS platform. Each feature includes properties: db, timestamp, category, bearing.

Position the microphone correctly

Hold the device at chest height, microphone facing the sound source. Most smartphones have their microphone at the bottom edge. On iPhones, the primary mic is at the bottom; a second mic for noise cancellation is at the top or rear — this one is not used by the Web Audio API. Avoid covering the mic grille with your palm or case material.

Stabilise before you read

The Leq (energy average) takes 2–3 seconds to stabilise. Wait for the ● LEVEL indicator to turn green before dropping a pin. Transient sounds in the first second (traffic passing, a door closing) will skew the reading if you measure too quickly.

Keep the device still

Movement creates handling noise. Rest the device on a surface, use a small tripod, or brace it against your body. If you are measuring a stationary source (HVAC unit, transformer, construction site), a fixed position gives more reproducible results. Note your exact position in the pin description for future reference.

Manage wind noise

Wind across the microphone generates low-frequency turbulence that inflates readings by 5–15 dB. Outdoors: shield the mic with a foam windscreen (any lavalier foam works), a piece of fabric, or by pointing the device slightly away from the wind. Note wind conditions in your pin description. Readings taken in wind above Beaufort 3 should be flagged as unreliable.

Enable Airplane mode

Incoming calls, SMS, and cellular radio events cause electromagnetic interference that appears as brief spikes or a rhythmic buzzing at ~217 Hz (GSM) in recordings. Switch to Airplane mode — then re-enable Wi-Fi only if you need maps or federation data. This eliminates RF artefacts from your measurements.

Avoid Active Noise Cancellation

Never use earphones with Active Noise Cancellation (ANC) when measuring. ANC earphones include a pass-through microphone whose input has been electronically modified. The signal Noisecatcher receives will not reflect the actual acoustic environment. See the About page for the full ethos argument.

Use an external microphone when possible

An omnidirectional lavalier (worn at chest height) gives a more consistent, body-referenced measurement of personal noise exposure than the phone microphone. A USB-C or Lightning stereo microphone (e.g. Shure MV88, Rode VideoMic Me-L/Me-C) gives spatial information. See the Microphones guide for hardware recommendations aligned with Noisecatcher's ethos.

Calibrate at the start of each session

Use the Calibration tool (tap the sliders icon on the Meter screen) to anchor your device against a known quiet environment or a reference sound level meter. A single calibration offset applies to the entire session. If you change location or device orientation significantly, re-calibrate. Log your offset value in the Notebook notes for the session.

Document what you hear, not just what you measure

The most powerful Noisecatcher record combines: the dB reading (objective), a voice note (subjective description), a pin category (contextual), and GPS coordinates (spatial). Describe what you hear in the voice note immediately after recording — the smell of exhaust, the vibration through the floor, the emotional state it produces. These details cannot be recovered later from numbers alone.

Get a reference reading

Use a calibrated sound level meter (or a certified app) to measure the level of a stable sound source — e.g. a pink noise generator, a fan, or road traffic from a fixed position.

Measure the same source in Noisecatcher

Start measuring and wait for the reading to stabilise.

Apply the offset

Tap Calibrateon the Meter page. Enter the difference between the reference reading and Noisecatcher's reading. For example: if reference = 65 dB and Noisecatcher shows 59 dB, enter +6.