Hertzio: Spectrum Analyzer

See which frequencies a sound is made of.

Turn on the microphone and the sound it hears is split into frequencies at once: a live spectrum, a spectrogram of the last 10 seconds and octave bands. The strongest frequency is shown with its note and cents, alongside prominent peaks and mains hum. Sound is analysed in memory on this device; it is never recorded.

Live spectrum
A line or bar curve on a logarithmic or linear frequency axis. Touch the chart and slide a finger to read the frequency, note and level at any point; freeze the view to look closer.

Spectrogram and octave bands
The spectrogram shows the last 10 seconds (now at the top, 10 seconds ago at the bottom). The octave view is drawn in 1, 1/3 or 1/6 octave bands (IEC 61260-1).

Strongest frequency and note
The strongest frequency is found with parabolic interpolation and shown with its note (C D E or Do Re Mi), cents and level; the A4 reference is adjustable. Prominent peaks are listed, and 50 and 60 Hz mains hum is marked separately.

Measurement settings
Averaging (off, low, medium, high), peak hold (2 s, 5 s, infinite), Z / A / C weighting (IEC 61672-1), frequency range (all, speech, bass or custom), resolution (FFT 4096 / 8192 / 16384) and window (Hann, Blackman, flat top).

Snapshots and comparison
"Take snapshot" saves the current spectrum. When two or more snapshots are selected, their curves are drawn over the live spectrum and the frequency of the largest difference is shown; for example, a speaker's curve before and after correction.

Audio file analysis
Audio files the device can decode (WAV, MP3, M4A, OGG, FLAC …) are opened on the device; the moment being played or the whole file is analysed. There is playback and a position bar; the file is never uploaded.

Level: dBFS or dB SPL
Enter a correction after comparing with a known sound level meter and levels are shown in dB SPL; without one, they are relative to full digital scale (dBFS).

Export and share
Snapshots are saved as PNG, as CSV (the level at each frequency; optionally the peak list and settings) or as a .hertzio file that can be reopened and compared, and shared with the device's share feature.

Samples
Four sample signals generated on the device: a guitar A string, pink noise, a sweep tone and 50 Hz hum; they play through the speaker only when "Listen" is pressed. Sample snapshots come on first launch (a speaker, before and after; a guitar A string), and "Add samples again" brings them back.

Microphone permission
The microphone listens only when turned on and turns off when the app goes to the background. If permission is refused or no microphone is found, the steps to allow it are shown for the current environment; sample signals and audio files are analysed without permission.

Backup and offline
"Back up…" puts snapshots and settings into a single file, and "Restore from backup…" brings them back on the same or another device. No account is needed; works offline.

Privacy
No account, no ads, no tracking. Your files and data stay on this device; no internet connection is needed.