I wanted an answer to a boringly practical question: what if the network is gone, but the speakers and microphones still work?

SignalHop is an acoustic modem and mesh prototype that moves tiny messages over ultrasound instead of Wi‑Fi or Bluetooth.

What it actually does

The current build uses:

FSK tones at 18 kHz and 20 kHz

48 kHz sample rate

a 4 up-chirp sync preamble

frames with payloads up to 255 bytes

a WAV/audio runtime for encode/decode and round-trip testing

That makes it useful for emergency text, sensor payloads, and low-bandwidth status updates. Not glamorous. Very useful.

The measured part

From the current proof pack:

Metric Value

Encode latency 16.634 ms mean

Decode latency 713.028 ms mean

Round-trip true

Payload tested 77 bytes

Max payload 255 bytes

The decode path is slower because it scans the full signal with correlation. That is fine for v1.…