Kriz Flew – Official Homepage

Audio Modem

File transfer over MFSK audio modulation — a browser-based acoustic coupler. Two devices: one plays a sound, the other listens and decodes it back into a file. A homage to the modems that used to hand-shake over the phone line.

Send

Choose File

No file selected

Send rate: 40 ms/symbol

Receive

Idle

Signal level — click/drag to set the threshold

Level: 0.0 Threshold: 0.1

Mic gain: +12 dB

Progress

Information

Error correction / modulation: Hamming(7,4) — automatically corrects 1 bit error per 4-bit block. Multiple Frequency-Shift Keying (MFSK) with 8 tones — 3 bits per symbol.

Keep both devices close together, volume around 70–90%. Set the threshold directly on the level meter in the Receive panel by clicking or dragging — just above the resting noise floor, but clearly below the expected start-tone level. If the level barely moves even close-up (some phone mics run quiet), raise the mic gain below it. A higher baud rate (in the Send panel) is faster but more error-prone. The receiver detects the baud rate automatically from the sync signal at the beginning of the transmission.