Audio spectrogram and SSTV decoder
View a WAV as a spectrogram to find text drawn in frequency space, decode Morse and SSTV, and extract LSB data from audio samples.
Open in ctfpalAudio challenges come in a small number of shapes, and the spectrogram distinguishes them at a glance. Open it first, before doing anything else with the file.
The reason to look before listening is that most audio steganography is inaudible by design but visually obvious. A file that sounds like ten seconds of hiss can have a flag drawn across its frequency plot in letters a centimetre tall. Listening tells you almost nothing; the picture tells you which of five techniques you are facing.
Reading the spectrogram
| What you see | What it is |
|---|---|
| Letters drawn in the frequency plot | Text painted into the spectrum - read it directly |
| Short and long bursts at one tone | Morse - measure the ratio |
| Dense diagonal sweeps in bands | SSTV - an image transmitted as audio |
| Pairs of simultaneous tones | DTMF - telephone keypad digits |
| Noise that looks like ordinary audio | Probably LSB in the samples, not the spectrum |
Part of a module
8. Steganography
Sweep an image, audio file, or paragraph for hidden data across the whole technique space rather than guessing one method.
Practise on real challenges
Related tools
Morse code translator
Translate Morse code to text and back, tolerating any dot/dash characters and any word separator. Also decodes Morse recovered from audio.
DTMF tone decoder
Decode telephone keypad tones from audio - the dual-frequency pairs that encode digits 0-9, *, #, and A-D.
Automatic steganography solver
Throw every applicable steganography technique at a file at once - image, audio, archive, text, and document - recursively unpack what falls out, and surface flag matches.
LSB steganography extractor
Extract least-significant-bit data from images across every channel, bit order, and traversal direction, with bit-plane visualisation.