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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 |