concept

Error-correcting code

The practical way to beat noise. Instead of just sending the message, the transmitter sends extra, carefully structured bits alongside it, so the receiver can detect corruption and mathematically reconstruct what was damaged. This is the trick that lets a scratched disc still play, and lets a spacecraft billions of kilometres away send back a clean photo through a sea of static. But the redundancy is not free: every error-correcting bit is one NOT spent on the message. On a noisy channel, guaranteeing perfect fidelity can eat most of the capacity.