Chirp is a small GitHub project by solst-ice that sends text from one device to another as sound. One browser plays a series of beeps through its speaker, and another listens with its microphone and turns the beeps back into text. The two devices do not need Wi-Fi or Bluetooth to talk to each other. You can try it on the demo site after allowing microphone access, ideally with two devices in the same room.

Chirp website showing a message being received on a live frequency spectrum

How it turns text into sound

The code shows exactly what the beeps are, and the scheme is simple. Every character has its own pitch:

  • A space is 900 Hz.
  • Punctuation and symbols sit between 1,300 and 4,600 Hz.
  • The digits 0 to 9 run from 4,700 to 5,600 Hz.
  • The letters A to Z run from 5,700 to 8,200 Hz.

The pitches are 100 Hz apart, which gives the receiver enough room to tell neighbouring characters apart. Lowercase text is converted to uppercase before sending, which keeps the alphabet down to 26 tones.

A message starts with a 2,500 Hz tone and ends with a 2,700 Hz tone, so the listener knows when to start and stop recording characters. Each character plays for 70 milliseconds followed by a 30 millisecond gap. That works out at about ten characters a second. It is very slow compared to a normal network, but a short message still only takes a couple of seconds.

On the receiving side, the Web Audio API breaks the microphone input into its frequencies, the same thing the spectrum on screen is showing you. The decoder looks for the loudest tone, matches it to the nearest character within a small tolerance, and ignores repeats that arrive too quickly. To make the signal easier to pick out, each character is sent as two tones played together, 35 Hz apart.

Getting a clean transmission

Background noise easily gets in the way, so a few things help:

  • Use a quiet room. Talking, music or a fan adds frequencies that confuse the decoder.
  • Turn the sending device's volume up and keep the two devices fairly close.
  • Allow microphone access when the browser asks, otherwise the receiver hears nothing.

The README describes it as a proof of concept with a simplified encoding scheme. There is no error correction, so if the receiver misses a beep, that letter is lost.

Why I like it

Sending data over sound has been done before. A startup that was also called Chirp built a business on it, and Sonos bought its technology in 2020, and dial-up modems did something similar long before that. What I like about this project is how easy it is to follow. It is a React and TypeScript app built with Vite, and the whole codec fits in one file. If you want to understand what encoding data means in practice, you can change the frequency table and hear the difference.

The project has also been popular. The repository was created in February 2025, and within about five months it had nearly 600 stars. One of them caught my eye: jackjackbits, Jack Dorsey's GitHub account.

Jack Dorsey's GitHub account starring the Chirp repository

Try it

Open the demo site on two devices, or on one device with the volume up, and send yourself a message. The code is on GitHub if you want to see how it works.