Tornadoes also produce identifiable inaudible infrasonic signatures. The frequencies of sonars range from infrasonic to above a megahertz. Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively. Since infrasonic bass is felt, sub-bass can be augmented using tactile transducers. In addition, the vocals of northern elephant seals may produce infrasonic vibrations. In contrast, earplugs can provide some attenuation to infrasonic sounds. The entire spectrum can be divided into three sections&colon; audio, ultrasonic, and infrasonic. Rumbles are produced during mild arousal and some appear to be infrasonic. Long range infrasonic waves are difficult to differentiate (e.g. chemical explosion and a nuclear explosion). Megasound has been best remembered for its infrasonic rumble capability. One of his experiments was an infrasonic whistle, an oversized organ pipe. One of the pioneers in infrasonic research was French scientist Vladimir Gavreau. At Amboseli, several different infrasonic calls have been identified. Infrasonic frequency response measurements include earthquakes and electroencephalography (brain waves). The Torus Infrasonic Generator was brought into this product line in 2016.