1. NOISE

2. NOISE AND DISTORTION NOISE : Noise can be defined as an unwanted signal that interferes with the communication of another signal. A noise itself is an information-bearing signal that conveys information regarding the sources of the noise and the environment in which it propagates. For example, the noise from a car engine conveys information regarding the state of the engine and how smoothly it is running. Background speech conversations in a crowded venue can constitute interference with the hearing of a desired conversation or speech.

3. NOISE AND DISTORTION DISTORTION : Signal distortion is the term often used to describe a systematic undesirable change in a signal and refers to changes in a signal due to the non-ideal characteristics of the communication channel, signal reverberation, echo, multipath reflections and missing samples.

4. NOISE AND DISTORTION ACOUSTIC NOISE : Acoustic noise emanates from moving, vibrating, or colliding sources and is the most familiar type of noise present in various degrees in everyday environments. Acoustic noise is generated by such sources as moving vehicles, air-conditioners, computer fans, people talking in the background, wind, rain, etc. ACOUSTIC ECHO NOISE : Due to the reflections of sounds from the walls of a room or due to the coupling between microphones and speakers, for example in mobile phones.

5. NOISE AND DISTORTION ELECTRONIC DEVICE NOISE : It includes the following noises. THERMAL NOISE : Thermal noise is generated by the accidental movements of thermally energized particles in an electric conductor. Thermal noise is essential to all conductors and is present without any applied voltage. BURST NOISE : Rush noise consists of step transitions of as high as several hundred mill volts, at random times and durations.

6. NOISE AND DISTORTION SHOT NOISE : Shot noise consists of random fluctuations(up down) of the electric current in an electrical conductor and is central to current flow. Shot noise is caused by the fact that the current is carried by disconnected charges (i.e. electrons) with random rise and fall and random arrival times.

7. NOISE AND DISTORTION ELECTRO MAGNETIC NOISE : Electro magnetic noise is present at all frequencies and in particular at the radio frequency range (kHz to GHz range) where telecommunication systems operate. Electromagnetic noise is composed of a combination of man- made noise sources from electrical devices and natural noise sources due to atmospheric noise and cosmic(space) noise.

8. NOISE AND DISTORTION ELECTROSTATIC NOISE: Electrostatic noise: generated by the presence of a voltage with or without current flow. Fluorescent lighting is one of the more common sources of electrostatic noise. PROCESSING NOISE: Processing noise the noise that results from the digital and analog processing of signals. EXAMPLE : Quantization noise in digital coding of speech or image signals, or lost data packets in digital data communication systems.

9. Noise and distortion DIFFERENT CLASSES AND SPECTRAL/ TEMPORAL SHAPES OF NOISE : Depending on its frequency range or time characteristics, a noise process can be further classified into one of several categories as follows: WHITE NOISE : White noise is defined as an uncorrelated random noise process with equal power at all frequencies. A random noise that has the same power at all frequencies in the range of ±∞ would necessarily need to have infinite power, and is therefore only a theoretical concept.

10. Noise and distortion EXAMPLE : For an audio system with a bandwidth of 10 kHz, any flat- spectrum audio noise with a bandwidth of equal to or greater than 10 kHz looks like a white noise.

11. Noise and distortion COLOURED NOISE; PINK NOISE AND BROWN NOISE : The term colored noise refers to any broadband noise with a non-white spectrum. EXAMPLE : Most audio-frequency noise, such as the noise from moving cars, noise from computer fans, electric drill noise and people talking in the background, have a non-white mainly low- frequency spectrum. Furthermore, a white noise passing through a channel is ‘colored’ by the shape of the frequency response of the channel. Two classic varieties of colored noise are the so-called pink noise and brown noise.

12. Noise and distortion PINK NOISE SIGNALBROWN NOISE SIGNAL

13. Noise and distortion IMPULSIVE AND CLICK NOISE : Impulsive noise consists of random short-duration ‘on/off’ noise pulses, caused by a variety of sources, such as switching noise, electromagnetic interference, unfavorable channel environments in a communication system, drop-outs or surface degradation of audio recordings, clicks from computer keyboards, etc.