where does the sound of a burp come from
Burping Burping is generally caused by swallowing air when eating or drinking and subsequently expelling it, so in this case the expelled gas is mainly a mixture of nitrogen and oxygen. Burps can also be caused by drinking carbonated beverages, such as beer, soft drinks, energy drinks, and wine in which case the expelled gas is primarily carbon dioxide from the drink itself. Common diabetes drugs metformin[1] and Byetta[2] can cause burping, especially at higher doses. This often resolves in a few weeks. Burping combined with other symptoms such as dyspepsia, nausea and heartburn may be a sign of an ulcer or hiatal hernia, and should be reviewed by a physician.[3] Other causes of burping include: food allergy, gallbladder problems, acid reflux disease, H. pylori, and gastritis.
Loudness The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound. The human auditory system averages the effects of SPL over a 600–1000 ms interval. A sound of constant SPL will be perceived to increase in loudness as samples of duration 20, 50, 100, 200 ms are heard, up to a duration of about 1 second at which point the perception of loudness will stabilize. For sounds of duration greater than 1 second, the moment-by-moment perception of loudness will be related to the average loudness during the preceding 600–1000 ms.[citation needed]