This technique allows discrimination between dullness to percussion from pleural effusion and that from consolidation. It again reflects the properties of normal and abnormal lung for transmitting and filtering sound. Auscultate over the chest in a systematic fashion while the patient says “ninety nine” repeatedly. As previously mentioned, normal lung transmits lower and filters higher frequency sound leading to the numbers being indistinct and reverberating in quality. Consolidated lung will transmit the higher frequencies and the numbers will sound far more distinct and with a vague buzzing quality, like speech after the inhalation of helium. In the case of pleural disease such as effusion the vocal resonance will simply be much reduced in intensity or absent.