---
title: "Distortion and its types"
subject: "Communication Systems"
chapter: 1
key: "semester_6/communication_systems:distortion-types"
source: https://www.bctengineer.com/q/semester_6/communication_systems/distortion-types
site: BCT Engineering
---

# Distortion and its types

Communication Systems · Chapter 1: Introduction

- Asked in: 2081 Baisakh (CS II), 3 marks
- Video: [Communication Distortion](https://www.youtube.com/watch?v=-A0vo2jscY8) — Sonal Mahadik
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/communication_systems/distortion-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1

## Question

Define distortion and explain its types.

## Short answer

Distortion is the unwanted deterministic change in signal shape due to imperfect system characteristics. Linear distortion includes amplitude distortion (non-constant |H(f)|) and phase (delay) distortion (non-linear phase); nonlinear distortion produces harmonics and intermodulation products.

## Answer

**Distortion** is the unwanted change in the shape of a signal caused by the imperfect characteristics of the system (channel, amplifier, filter) through which it passes. Unlike noise, it is deterministic and disappears when the signal is removed.

#### Types
1. **Linear distortion** – caused by a linear system that is not distortionless:
   - **Amplitude distortion:** $\lvert H(f)\rvert$ is not constant over the signal band, so different frequencies are attenuated differently (e.g. a cable cutting high frequencies, making pulses rounded).
   - **Phase (delay) distortion:** phase is not linear in $f$, so different frequencies are delayed by different times; pulses spread and cause ISI in data links.
2. **Non-linear distortion** – caused when the output is a non-linear function of input, $y=a_1x+a_2x^2+a_3x^3+\dots$ (e.g. an overdriven amplifier):
   - **Harmonic distortion:** new components at $2f,3f,\dots$.
   - **Intermodulation distortion:** with two inputs $f_1,f_2$, new components at $f_1\pm f_2$, $2f_1-f_2$, etc., causing crosstalk in multichannel systems.

Linear distortion is corrected by **equalizers**; non-linear distortion is reduced by operating devices in their linear region, pre-distortion or companding.

## Check yourself

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

1. Distortion is best defined as
   A. Random unwanted energy
   B. Unwanted change in signal shape caused by the system's imperfect characteristics
   C. Signals from other transmitters
   D. Loss of signal power only
   Answer: B. Distortion is deterministic and caused by the system itself. (Key point: Definition of distortion)

2. Phase (delay) distortion occurs when
   A. |H(f)| is not constant
   B. Phase is not linear in f, so frequencies are delayed differently
   C. The amplifier clips
   D. Noise is added
   Answer: B. Different components arrive at different times, spreading pulses and causing ISI. (Key point: Phase distortion)

3. With two inputs f1 and f2, a non-linear system produces components at
   A. Only 2f1 and 2f2
   B. f1 ± f2 and 2f1 - f2 (intermodulation)
   C. Only f1 and f2
   D. No new frequencies
   Answer: B. Non-linearity creates intermodulation products causing crosstalk, besides harmonics. (Key point: Intermodulation vs harmonic)