Leak locates are carried out by the use of a leak correlator or sonic leak detector. The correlator consists of a microprocessor, which is located in the van, as well as radio transmitters, which amplify and send the noise or vibration signals to the correlator. Sensors for the radio transmitters contact the pipeline and pick up the noise from the pipe wall or water. The correlator's sensitivity, speed and convenience make it a superior leak detection instrument. Sonic leak detectors detect noise by contacting the pipeline and listening for leak. Once a noise is detected, a ground microphone is used above the pipeline to determine the location. External noises will affect the efficiency of this instrument.