Researchers at the German Aerospace Center (DLR), working at Turbomeca’s test facilities in Bordes, France, have managed to measure the noise inside a helicopter engine. They used new hot-gas microphone probes in an environment of high pressure (up to 12 bar) and high temperature (up to 1,200 degrees C). The microphones were installed at various places inside the engine and around the exhaust. Their signals were recorded simultaneously. Analysis of the noise field enabled the DLR to explain how noise is generated and how sound propagates.