WaveByte (Python edition)

Send text and small files between two laptops with sound only (near-ultrasonic, ~17-20 kHz). No Wi-Fi, Bluetooth, pairing, server or return channel.

pip install numpy scipy sounddevice        # Linux also: sudo apt install libportaudio2
python -m wavebyte selftest                # simulated-channel sweep (no hardware)
python -m unittest discover -s tests       # 9 tests

Step 0 - find out whether your hardware can do it (do this first!)

laptop B:  python -m wavebyte probe-rx     # records 10 s
laptop A:  python -m wavebyte probe-tx     # plays a 14-22 kHz sweep

probe-rx prints the response and recommends --profile and --f-lo. If it says no usable band, that speaker/mic pair cannot carry near-ultrasound; try closer, louder, or a lower --f-lo. Also disable "audio enhancements / noise suppression / AGC" for the microphone in the OS.

Transfer

B: python -m wavebyte receive --profile standard
A: python -m wavebyte send report.pdf --profile standard      (or --text "hello")

Both sides must use the same profile / --f-lo / --guard-ms. Echoey room: --guard-ms 15. No laptops handy: send --wav out.wav, play it on any phone, record, receive --wav rec.wav (record at 48 kHz).

Profiles (net throughput)

robust 8 tones ~4 B/s - standard 16 tones ~7.5 B/s - fast 32 tones ~12.8 B/s. A 100 KB file takes hours; this is for text and small files.