A decibel (dB) level is measured in each octave band at a known distance, the decibel levels are combined logarithmically on an energy basis to give an overall level. The decibel level is typically measured in sound pressure level – (SPL), or sound power level – (PWL).

Sound Power Level (PWL) is a measure of total acoustic power or potential, similar to the watt rating of a light bulb.Sound Pressure Level (SPL) is a measure of the actual acoustic effect due to distance and other mitigating factors. Sound Pressure (SPL) is what we hear, caused by Sound Power (PWL) emitted from the source. 

31.5 Hz
63 Hz
125 Hz
250 Hz
500 Hz
1000 Hz
2000 Hz
4000 Hz
8000 Hz

Noise is any unwanted sound. Noise may be continuous or intermittent based on the source.

Noise measurements are taken in the audible sound spectrum and defined as center octave bands consisting of:

Jet Engine 160 Hearing Damage
Threshold of Pain 140
Threshold of Feeling 120
OSHA Limit 90 8 Hour Exposure
Normal Conversation 60
Whisper 40

Sound amplification or loudness is measured in decibels (dB). The threshold of human hearing is approximately 6 dB at 1000 Hz and increases with decreasing frequency. (approximately 25 dB at 63Hz)