Signal types:

• Deterministic
  Can be described analytically and can be repeated

Periodic
     In the simplest form are sinusoidal, that is, consisting of a single sine wave (pure tone).
     Complex periodic signals (also known as complex tones) are composed of multiple sinusoidal components.
     All these frequencies are multiples of some fundamental frequency

Pseudo-random signal

• Particular type of periodic signal
• Sometimes used to simulate random signals
• Periodic time is very long
• Can be reproduced exactly - benefit in testing

Non-periodic

Quasi-periodic
     Frequencies of the various sinusoids are not harmonically related.

Transient
      Occur only once or very infrequently. Their starts and terminate at a value equal to 0.

      Examples
          Slamming a door
          Shock wave generated from an impact test

• Random

Stationary
     Average properties do not vary with time - independent of the particular sample record

     Examples
          Thermal noise at constant temperature

Non-stationary
     Statistical properties change significantly over the observation window

     Examples
          Jet engine noise
          Machine tool vibrations
          Earthquake motions
          Speech