Like other whales, males make long, loud, low-frequency sounds. The vocalizations of blue and fin whales are the lowest-frequency sounds made by any animal. Most sounds are frequency-modulated (FM) down-swept infrasonic pulses from 16 to 40 hertz frequency (the range of sounds that most humans can hear falls between 20 hertz and 20 kilohertz). Each sound lasts one to two seconds, and various sound combinations occur in patterned sequences lasting 7 to 15 minutes each. The whale then repeats the sequences in bouts lasting up to many days. The vocal sequences have source levels of up to 184–186 decibels relative to 1 micropascal at a reference distance of one metre and can be detected hundreds of miles from their source.