soundpost

send

ctrl+enter plays too. uppercase gets lowercased before sending.

receive

hit start listening, then play the chirps on this or another device

how it works

each char gets its own chirp — two tones at the same time, 80ms long. the decoder watches the mic for a pattern of 3 leader chirps (above every letter frequency on purpose) and only starts reading once it sees them. end marker is even higher so it can never be confused with a real char. one checksum chirp at the end so the decoder can tell you it misheard instead of just giving you garbage. that's the whole thing.

if you want to see what the chirps look like, turn your mic on and play something — the spectrogram below shows what the mic picks up in real time

known issues (yes i know about all of these):

• needs a quiet room. the mic picks up everything — fan noise, typing, breathing
• repeated letters (ll, ss) sometimes merge into one. 90ms gap helps but doesn't fully fix it — 2x mode doesn't have this problem since doubles are intentional there
• checksum catches bad chirps but can't fix them. it just says "send again." 2x mode is the closest thing to error correction right now
• wav decode only reads files the save wav button wrote. feed it an mp3 and you get nothing useful back
• only a-z, 0-9 and basic punctuation. anything else gets dropped silently before encoding
• if nothing decodes, turn your volume up first — check the mic level readout below the spectrogram
• the tone table has a gap after 's' because i changed the spacing halfway through building it and fixing it would break the decoder. it stays.