Noise and Distortion

Noise

An electronic signal made up of many random frequencies at many amplitudes added to a radio or information signal during transmission or processing.

Noise on oscilloscope

Appears as a random AC voltage regardless of the noise source.

Difference between noise and interference

Noise is random and non-informational, while interference comes from unwanted information signals added to the original signal.

Signal noise

Unwanted interference that degrades a communication signal and affects both analog and digital signals.

Noise in digital vs. analog signals

Digital signals require a higher amount of noise to be affected because they use binary pulses.

Effect of noise on a signal

Adds or detracts from the expected value, leading to unpredictable and possibly damaging results.

Example of noise in radio

The hiss or static heard when tuning between AM or FM stations.

Example of noise in television

Appears as “snow” on black-and-white TVs or “confetti” on colored screens.

When noise is too high or signal too weak

The noise can completely overshadow the original signal.

Classifications of noise

External Noise and Internal Noise.

External Noise

Caused by sources that cannot be controlled by humans, such as industrial, atmospheric, or space.

Industrial Noise

Produced by manufacturing equipment like ignition systems, generators, and electric motors that cause transients or bursts of energy.

Atmospheric Noise

Natural electrical disturbances (static) caused by lightning that affect signals with frequencies below 30 MHz.

Extraterrestrial Noise

Noise coming from the sun (solar) or stars (cosmic) in space.

Solar Noise

Noise from the sun, which radiates a wide range of signals and follows an 11-year noise cycle causing strong interference.

Cosmic Noise

Noise from stars outside the solar system, causing disruptions in the 10 MHz to 1.5 GHz range, mainly between 15–150 MHz.

Internal Noise

Caused by electronic components inside a receiver, such as resistors, diodes, and transistors.

Common internal noise types

Thermal noise, semiconductor noise, and intermodulation distortion.

Thermal Noise

Caused by thermal agitation, which is the random motion of free electrons in a conductor due to heat.

Other names for Thermal Noise

Also called White Noise or Johnson Noise after John B. Johnson (1928).

Reason it’s called White Noise

Believed to contain all frequencies randomly, similar to how white light contains all colors.

Pink Noise

Filtered or band-limited version of white noise.

Semiconductor Noise

Produced by components like diodes and transistors due to random current flow.

Types of Semiconductor Noise

Shot noise, transit-time noise, and flicker noise.

Shot Noise

Caused by random movement of current carriers like electrons from source to destination.

Transit-Time Noise

Occurs when the signal frequency period equals the time an electron takes to move from input to output.

Flicker Noise

Results from random variations in resistance in semiconductors; inversely proportional to frequency (1/f noise).

Intermodulation Distortion

Caused by non-linear circuits that generate new signals or harmonics when two or more signals are combined.

When intermodulation distortion occurs

When two or more signals are used in a non-linear circuit.

Signal-to-Noise Ratio (SNR)

Establishes the relative strengths of the signal and noise in a communication system.

High S/N ratio

The signal is strong and the noise is weak, resulting in good quality.

Low S/N ratio

The signal is weak and the noise is strong, resulting in unreliable reception.

Noise Factor (NR)

Ratio between S/N at the input and S/N at the output.

Purpose of noise factor and noise figure

Used to express the quality of noise performance in a receiver.

Distortion

Unwanted change in the waveform of an audio or video signal in a device or communication channel.

Causes of distortion

Environmental factors, channel properties, and distance between transmitting and receiving devices.

Difference between distortion and noise

Distortion alters the waveform but does not fully affect the signal, while noise completely interferes.

Effect of distortion on voice transmission

Results in garbled, harsh, or unnatural sounds.

Desirable distortion

In Dolby systems, audio signals are purposely distorted to emphasize certain aspects and reduce noise.

Example of desirable distortion

Used as a musical effect on electric guitars to create unique tones.