Audio Transfer — Receive
Listen for the sender's control beacon, synchronize by sound, receive the selected FSK band, reconstruct the file, and verify it locally.
Important
Acoustic transfer is intentionally much slower than the visual mode. It is intended for small files and demonstrations. Speaker and microphone frequency response varies heavily by device, so this revision restricts automatic data-band selection to 2.8–10.6 kHz.
A control beacon contains 42 FSK symbols. If raw tone detections increase but accepted symbols stay near zero, the microphone hears the sender but timing/SNR is poor. If accepted symbols approach 42 but preamble hits remain zero, symbols are being misclassified. If a preamble is found but no packet decodes, the packet is reaching the receiver with symbol errors and failing CRC.