Modembin – A pastebin that encodes your text into real FSK modem audio
A fun weekend project: https://www.modembin.com It's a pastebin, except text/files are encoded into .wav files using real FSK modem audio. Image sharing is supported via Slow-Scan Television (SSTV), a method of transmitting images as FM audio originally used by ham radio operators. Everything runs in the browser with zero audio libraries and the encoding is vanilla TypeScript sine wave math: phase-continuous FSK with proper 8-N-1 framing, fractional bit accumulation for non-integer sample rates, and a quadrature FM discriminator on the decode side (no FFT windowing or…
In plain words
Modembin is a pastebin that encodes text and files into FSK modem audio files playable as .wav format. It supports multiple encoding standards including Bell 103 and 1200-baud formats, plus image sharing via Slow-Scan Television (SSTV) and a chat mode that transmits messages as actual modem audio. The tool runs entirely in the browser using TypeScript sine wave mathematics with no external audio libraries, making it suitable for users interested in retro communication protocols and hobbyist radio transmission methods.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
A fun weekend project: https://www.modembin.com It's a pastebin, except text/files are encoded into .wav files using real FSK modem audio. Image sharing is supported via Slow-Scan Television (SSTV), a method of transmitting images as FM audio originally used by ham radio operators. Everything runs in the browser with zero audio libraries and the encoding is vanilla TypeScript sine wave math: phase-continuous FSK with proper 8-N-1 framing, fractional bit accumulation for non-integer sample rates, and a quadrature FM discriminator on the decode side (no FFT windowing or Goertzel), The only dependency is lz-string for URL sharing compression. It supports Bell 103 (300 baud), Bell 202 (1200 baud), V.21, RTTY/Baudot, Caller ID (Bellcore MDMF), DTMF, Blue Box MF tones, and SSTV image encoding. There's also a chat mode where messages are transmitted as actual Bell 103 audio over WebSocket... or use the acoustic mode for speaker-to-mic coupling for in-room local chat.
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