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Human Differential Sound Intensity Sensitivity

April 4th Fact-of-the-Day

How much must the RF output of a CW or SSB transmitter be increased for a loudness change to be perceived by an average listener using a receiver without automatic volume control? Extensive psychoacoustical testing has established that under laboratory conditions an average human listener can perceive sound level changes as small as 1/4 dB with fast A/B comparisons between two loud 1000 Hz tones. However, sensitivity to change varies with both audio level and sound frequency such that under real-world point-to-point groundwave radio communication conditions the smallest change that typically can be perceived with fast A/B comparisons is about 1dB. Therefore, doubling transmitter power (3dB) under ideal radio conditions with no signal fading and automatic volume control switched off increases the received sound level about three of the smallest loudness steps a human can perceive. ©2005 Martek International All rights reserved.

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