Above is an audio demonstration of decibels. What is a decibel? You can see from the Acoustics FAQ that the decibel is a logarithmic unit which is used in a number of scientific disciplines. The program is intended to show the relative change in audible sound with the change in decibels. The sounds should be heard as continuous tones. However there may be a slight 'click' as the sound buttons are changed which could mislead. Switch buttons back and forth a few times to get an idea of the steady levels. Most people will find the change of 3dB just perceptible.
FULL STORY @ MEASURE (http://www.measure.demon.co.uk/Acoustics_Software/db_demo.html)