Called volume, level, amplitude, loudness, sound pressure, or intensity.
- Professional term: Sound Pressure Level (dB SPL)
- Measured in decibels (dB)
- The vertical dimension of a sound waveform when shown in an editing application
- An increase of approximately 10 dB represents a doubling of perceived loudness (note that this is technically about nine times louder, but that most human ears are not very sensitive to small changes)
- An increase of 6 dB requires doubles the wattage required from an amplifier to represent the signal through speakers
- An increase of 3 dB doubles the sound pressure applied to objects (the technical loudness)
- Whisper: 20 dB
- Conversation: about 55 dB
- Rock Concert: above 100 dB (typically 115 dB at the back row, as specified in tech riders)
- Gunshot: 140 dB
- Threshold of pain starts at around 120 dB
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- Sound levels (amplitude) fall off according to the *inverse square law*. When the distance to a sound source doubles, the size of the disturbance (level) diminishes to one quarter of its original size.
- This is only a theoretical reality for DIRECT SOUND (sound that travels by way of the shortest path from source to receiver). In reality it doesn't work this way because reflective surfaces in an environment can keep the sound levels from falling off according to the inverse square law.
