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

# Distortion vs noise vs interference

Communication Systems · Chapter 1: Introduction

- Asked in: 2080 Chaitra (CS I), 6 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/distortion-noise-interference-diff
- Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1

## Question

Discuss the difference between distortion, noise and interference.

## Short answer

Distortion arises from non-ideal channel or amplifier response and is deterministic, correctable by equalization; it disappears when the signal is absent. Noise is random, always present, and only reduceable by filtering and coding. Interference is structured unwanted energy from other transmitters, managed by filtering and frequency planning.

## Answer

A received signal can be written as $r(t) = f\{s(t)\} + i(t) + n(t)$: the channel **distorts** the signal $s(t)$, unwanted signals from other sources add **interference** $i(t)$, and random **noise** $n(t)$ is added. These three impairments differ as follows.

#### Distortion
Alteration of the waveform shape by the system or channel itself, so that the output is not $K\,s(t - t_d)$.
- **Linear distortion:** amplitude distortion (non-flat $|H(f)|$) and phase/delay distortion (non-linear phase), e.g. ISI in data channels, multipath.
- **Non-linear distortion:** caused by non-linear devices (amplifier saturation), producing harmonics and intermodulation.
- It exists only while the signal is present and is deterministic, so it can be corrected by **equalization** or by improving linearity.

#### Noise
Random, unpredictable unwanted electrical energy from natural sources.
- **External:** atmospheric (lightning), solar and cosmic, industrial (ignition, motors).
- **Internal:** thermal noise $P_n = kTB$, shot noise, partition and flicker noise.
- Always present, even with no signal. Cannot be removed fully; reduced by limiting bandwidth, low-noise amplifiers, higher transmit power, wideband modulation (FM) and error-correcting codes.

#### Interference
Unwanted signals from **other communication sources** that fall in the receiver band.
- Examples: co-channel and adjacent-channel interference, crosstalk between cables, image-frequency interference in superheterodyne receivers, power-line hum.
- Usually has a definite form and frequency, so it can be reduced by good filtering, shielding, frequency planning, directional antennas.

| Basis | Distortion | Noise | Interference |
|---|---|---|---|
| Cause | Imperfect system response | Natural random processes | Other transmitters/systems |
| Character | Deterministic | Random | Structured, man-made |
| Needs signal to exist | Yes | No | No |
| Effect on signal | Changes shape | Adds random variation | Adds unwanted signal |
| Remedy | Equalizer, linearization | Filtering, LNA, coding | Filtering, shielding, planning |
| Example | Rounded pulses, ISI | Radio hiss | Crosstalk, adjacent station |

## Check yourself

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

1. In r(t) = f{s(t)} + i(t) + n(t), what do f{s(t)}, i(t) and n(t) represent?
   A. Noise, interference, distortion
   B. Interference, noise, distortion
   C. Distortion of the signal, interference, and noise
   D. Signal, noise, interference
   Answer: C. The channel distorts s(t), other sources add interference i(t), and random noise n(t) is added. (Key point: Received signal model)

2. Which is an example of non-linear distortion?
   A. Non-flat amplitude response
   B. Non-linear phase response
   C. Multipath delay spread
   D. Amplifier saturation producing harmonics and intermodulation
   Answer: D. Amplitude and phase distortion are linear distortions; non-linear devices create new frequencies. (Key point: Types of distortion)

3. Internal thermal noise power in a bandwidth B at temperature T is:
   A. kTB
   B. kT/B
   C. k B / T
   D. T B^2
   Answer: A. P_n = kTB, so limiting bandwidth reduces noise power. (Key point: Thermal noise)

## Related in Communication Systems

- [Noise vs interference vs distortion](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-distortion) — 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
- [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
- [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 vs interference; minimizing effects; need for modulation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-minimize-modulation-need) — 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