Soundmark: Sound Collection

A nocturnal field-recording notebook.

Record whatever you can hear right now — rain on a balcony awning, the wind a train pushes out of a tunnel, a convenience-store freezer at two in the morning. Trim the ends off, give it a title and a place, attach a photo if the moment needs one. Then let your iPhone take it apart.

ANALYSED ON THE DEVICE

Every recording is analysed in full the moment you save it: FFT and short-time Fourier transform, on the phone. You get the waveform, the spectrum, a spectrogram, and a Fourier-series view that draws the five strongest components as sine curves — alongside dominant frequency, loudness in RMS dB, spectral centroid, zero-crossing rate and sample rate. No queue, no upload; it finishes just the same in airplane mode.

THREE STEPS INTO THE LIBRARY

• Record — 48 kHz, with the live waveform and the dominant frequency moving with whatever is in front of you. Choose the back, front or bottom microphone; for ambience, the one facing the world is usually the right one.

• Trim — drag the two handles until only the part worth keeping is left. Trimming writes a new file and re-runs the analysis.

• Note — add a title, a place and a description, and attach photos or a video if the moment needs them.

EVERY SOUND GETS ITS OWN COLOUR

The dominant frequency, 60 Hz to 4 kHz, is taken on a log scale and mapped onto hues from amber to violet. The low hum of a freezer runs warm; the fine hiss of a mountain stream runs cold. The colour isn't decoration — it's a reading, and it follows the audio when you re-trim it.

WHILE IT PLAYS

Scrub the waveform with your finger and the spectrum follows the playhead, reading the real STFT column underneath it rather than a decorative shimmer.

NOTHING LEAVES THE PHONE

No accounts, no servers, no analytics, no third-party SDKs, and not a single network request anywhere in the code. Recordings, attachments and the index are written into the app's own Documents directory and synced nowhere. The place is a line of text you type — the app never reads your location. Photos and video arrive through the iOS picker, so Soundmark never gets access to your photo library. Delete a recording and its audio and attachments go with it; delete the app and everything is gone.

FREE

No in-app purchases, no subscription, no ads.

iOS 17 or later. iPhone. Dark by design — it was made for the hours when the world is quiet enough to hear.