SoundDrop
Transfer a small file directly from one nearby device to another using audible sound. The page never uploads the selected file and its Content Security Policy forbids network connections.
● Local bytes → sound → local bytes · decoder build 1.1
Receive
Start listening first, keep this page visible, then start the sender. Put the devices 10–40 cm apart with the sender at roughly 60–80% volume.
ReceiverIdle
Packets recovered0
File progressWaiting for manifest
File verified
Browsers require a tap before placing a received file in Downloads or the mobile Files app.
Diagnostics
Microphone not started.
Send
Best for text, keys, small documents, and other files of a few kilobytes. Audible transmission is deliberately slow because reliability matters more than headline bitrate.
Selected fileNone
Estimated acoustic time—
Packet plan—
Do not use maximum speaker volume: clipping creates harmonics that can be worse than a quieter signal. Keep notifications silent and avoid moving either device during a packet.
SenderIdle
Current packet0 / 0
How the modem resists real mobile audio problems
- Each symbol is a two-tone DTMF-style signal in the normal voice band, not fragile ultrasound.
- Every packet has its own long leader, synchronization word, convolutional error correction, interleaving, and CRC-32.
- The file is split into 128-byte blocks. One XOR parity packet is sent for every four blocks, allowing one missing block in each group to be reconstructed.
- The receiver stores only packets that pass CRC, ignores duplicates, and verifies the CRC of the complete file before enabling Save.