The relationship between perceived volume (loudness) and power output in watts of an amplifier is not a linear relationship: The human ear perceives a 50-watt amplifier as only twice as loud as a five-watt amplifier, despite a tenfold increase in power in watts. Doubling the power of an amplifier results in a "just noticeable" increase in volume, so a 100-watt amplifier is only slightly louder than a 50-watt amplifier. In addition is the human ear's tendency to behave as a natural audio compressor at high volumes.