In the context of vibration, a signal is basically some information somehow encoded as a wave. Everything travels as a wave. Figure 6 represents a basic sine wave. The vertical axis is the volume, or air pressure, or strength, or energy, or amplitude etc. For example this is an ocean wave, and then the vertical axis may be the wave height. If this is a sound wave in the air, then it is the air pressure. If it is a sound wave in a wire, then it is the voltage. The horizontal axis often represents the time or distance that the wave traverses in. waves generally have a period, which can be viewed as a time or distance of when the wave repeats itself starts the next iteration. In figure 6 the period is 2. A closely related property of the period is the frequency. Frequency is the speed at which the wave cycle is periods, and is always expressed in proper units, as cycles per second and kilo-cycles per seconds.

Figure 6: Analog sine wave
1.52 Time Domain Figure 7: Time Domain …show more content…
Horizontal axis is now time, and is expressed in seconds. To given the frequency, can easily find the wave period. For example, if the wave cycle it is 4 times per second, then the period is ¼ seconds, or simply 1/f frequency. Similarly, knowing the period, can find the frequency. Another closely related value is the wavelength, which is basically the distance occupied by the wave period. Given the speed of propagation, can calculate that too. For example light or electricity travel around 3E8 meters per second. Let’s imagine that figure 7 represents electricity in a wire, and then the wave length is just 3E8/4 or just 7.5*10E7 meters, or simply velocity/frequency. Obviously can find the velocity if you know the wavelength and frequency. Continuing on with the discussion, figure 8 shows a wave of 12Hz, and with 1/3 amplitude. Notice how the period got smaller as the frequency