Nature & Duration

Sound can also be characterized by nature and duration. The nature of noise can be considered as either:

• Steady-state/continuous: an on-going sound that does not typically change. Examples include engine noise, running equipment (pumps, conveyors, fans, etc.)
• Impulse: a sound with a sharp increase followed by a rapid decrease; the sound can repeat or occur just once. Examples include vehicle back-up alarms, horns, bells, sirens, fireworks, etc.
• Impact: a sound typically created by an object striking another object or surface. It is short in duration but can produce a delayed sound (echo, ringing, etc.). Examples: jack hammers, stamping machines, etc.
• Intermittent: a sound where higher and lower levels alternate at irregular intervals.
• Varying: a sound where the level constantly change in substantial ways.
• Ambient: background sound in a given environment. Examples include air conditioning, traffic, etc.

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