Remember this?

When loading was fun

Who am I?

What is data?

0110100001100101011011000110110001101111001000000110101001110011011000110110111101101110011001100111010101111001

How do we get data into audio?

01011

+

An Encoding Problem!

Humans are good at encoding data.

Communication breaks down when you don't speak the language

How do we do this?

Communication Needed

• Fast transmission.
• Something Easy to use.
• Something Cheap to implement.

Telegraphy

Coded Signals Line of Sight

Optical Telegraph 

Both sides need to know the code

Claude Chappe

1792 - 1837~

Morse Code

Pioneered by Samuel Morse

1836

Electrical Signals over a wire.

Both sides needed to be trained in morse code.

Baudot Code

Invented by Émile Baudot

1874

5 bit code to send letters

Multiplexed transmissions

Chorded Keyboard

"Baud" Comes from Baudot

Multiplex like it is 1855

🔥240 baud

🎷🔥

Alexander Bell

Harmonic Telegraph / 

Audible Telegraphy 

1876~

Allowed 10 signals on a 1 telegram line.

Audible Multiplexing

How is data encoded into audio?

FSK

By Frequency Shifting a Key we can encode state.

AFSK

Audio Frequency Shift

Keying

Demo

TTY

~1908

Non-Skilled operators on both ends, uses Baudot Murray encoding. Enabled typing and receiving on both ends.

Existing Medium

• Intended to carry speech
• "hacked" to carry data
• AFSK work(s)(ed) on existing infrastructure.

Modem

~1942

Connect teleprinters over regular phone lines.

Demodulates and Modulates data to be sent over standard lines.

Recreating a Modem in the Browser with JavaScript!

The  Oscillator Node

Allows us to change the frequency over time.

Demo

ScriptProcessorNode

Process chunks of audio JIT with a given bin size and sampling rate

JavaScriptNode

WaveTableNode

AudioWorkerNode

Converting Data

String => Binary

Demo

Bits to Audio

Demo

Data Extraction

The hard part

Extracting Bits From the Waveform

How do we get from a wave to frequency Intensity?

Goertzel Algorithm

Goertzel tldr;

It allows us to extract a (single) target frequency intensity over time

Goertzel Results in:

Goertzel filter is not quite perfect.

We want it to be as close to "binary" as we can get it.

Hamming Window

Frequency Intensity 

Demo

All Together now.

Demo

What if there was noise on the line?

Noisy Signals

Demo

What if we wanted more speed?

Multiplexed

Demo

What is next?

• Air-gapped communications.
• Dynamic JS Injection.
• WebRTC Modem?
• ✨✨✨✨✨✨✨✨✨?

github.com/samccone/noise

Thanks!

@samccone