Noise is unwanted disturbance that interferes with signals. It comes from many sources. Thermal noise from electrons. Interference from other signals. Impulse noise from motors and lightning. Noise degrades signal quality. It limits how far a signal can travel and how fast data can flow.

Noise is measured as a power ratio. The signal-to-noise ratio compares signal strength to noise. A high SNR means a clean signal. A low SNR means the signal is buried in noise. Digital systems can tolerate some noise. Error correction recovers data. But beyond a threshold, the signal is lost.

Types of noise

• Thermal: random electron motion
• Shot: discrete nature of electrons
• Interference: other signals
• Impulse: sudden spikes
• Quantization: from analog-to-digital conversion

Noise is the enemy of communication. Engineers fight it with shielding, filtering, amplification, and error correction. They design modulation schemes that are robust to noise. They add redundancy so errors can be corrected. The battle against noise never ends. It is the fundamental limit of communication.