---
title: "Noise vs interference vs distortion"
subject: "Communication Systems"
chapter: 1
key: "semester_6/communication_systems:noise-interference-distortion"
source: https://www.bctengineer.com/q/semester_6/communication_systems/noise-interference-distortion
site: BCT Engineering
---

# Noise vs interference vs distortion

Communication Systems · Chapter 1: Introduction

- Asked in: 2078 Chaitra, 5 marks
- Video: [1.2 Noise, distortion and interference | Communication System IOE](https://www.youtube.com/watch?v=kTfHdgxg5QY) — Saurab Poudel
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/communication_systems/noise-interference-distortion
- Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1

## Question

Differentiate among noise, interference and distortion.

## Short answer

Noise is random, additive, always present, from thermal and natural sources, and cannot be removed completely. Interference is structured, man-made signals from other transmitters, reducible by filtering. Distortion is deterministic waveform change due to the system, vanishes without signal, and can be colected by equalisation.

## Answer

**Noise**, **interference** and **distortion** all degrade a received signal, but they differ in origin and in how they can be reduced.

- **Noise:** unwanted, random electrical signals that add to the wanted signal. Sources: thermal (Johnson) noise in resistors, shot noise in devices, atmospheric, cosmic and man-made noise. Example: hiss in a radio, snow on a TV screen.
- **Interference:** contamination by unwanted signals from other **man-made transmitters or systems**, usually having a definite structure and frequency. Example: a neighbouring radio station heard in the background, crosstalk between telephone lines.
- **Distortion:** change in the **shape** of the signal caused by the imperfect response of the system itself (non-flat amplitude, non-linear phase, non-linearity). Example: a square pulse becoming rounded after a band-limited channel.

| Basis | Noise | Interference | Distortion |
|---|---|---|---|
| Nature | Random, unpredictable | Signals from other sources, structured | Deterministic alteration |
| Source | Natural and device physics | Other transmitters, crosstalk | System/channel response |
| Present without signal? | Yes | Yes | No, disappears with signal |
| Spectrum | Wideband (white) | Narrow, at specific frequencies | Within/around signal band |
| Mathematical effect | Additive $n(t)$ | Additive $i(t)$ | $y = f\{x(t)\}$, not $Kx(t-t_d)$ |
| Reduction | Filtering, low-noise amps, more power, coding | Filtering, shielding, frequency planning | Equalizers, linear design, pre-distortion |

Key point: distortion can in principle be undone by an inverse system (equalizer), because it is a deterministic function of the signal; noise cannot be removed completely, only reduced, because it is random.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What best distinguishes interference from noise?
   A. Interference comes from natural random processes, noise from other transmitters
   B. Interference comes from other man-made transmitters or systems and has a definite structure, while noise is random
   C. Interference only exists when the signal is present
   D. Noise has a definite frequency, interference is wideband
   Answer: B. Noise is random (thermal, shot, atmospheric); interference is structured, like a neighbouring station or crosstalk. (Key point: Noise vs interference origin)

2. Which impairment disappears when the signal is switched off?
   A. Noise
   B. Interference
   C. Distortion
   D. All three
   Answer: C. Distortion is the system's alteration of the signal shape, so no signal means no distortion; noise and interference persist. (Key point: Distortion needs the signal)

3. Why can distortion be undone while noise cannot be removed completely?
   A. Distortion is a deterministic function of the signal, so an inverse system (equalizer) can reverse it; noise is random
   B. Distortion is random, noise is deterministic
   C. Noise can be removed by equalizers
   D. Both can be fully removed by filtering
   Answer: A. An equalizer inverts a known deterministic response, but random noise can only be reduced. (Key point: Remedy difference)

## Related in Communication Systems

- [Distortion vs noise vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-diff) — Communication Systems, chapter 1
- [Reasons for modulation; noise vs distortion vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Amodulation-reasons-noise-distortion-compare) — Communication Systems, chapter 1
- [Distortion, noise, interference; four types of noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-four-noise) — Communication Systems, chapter 1
- [Noise, distortion, interference; internal and external noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-types-internal-external) — Communication Systems, chapter 1
- [Noise, interference, distortion; thermal and high frequency noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-effects-thermal-hf) — Communication Systems, chapter 1
- [Noise vs interference and their limitations](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-limitations) — Communication Systems, chapter 1

## Related in other subjects

- [Noise, thermal noise, delay distortion](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Anoise-types-thermal) — Data Communication, chapter 1