<P> Audiograms of human hearing are produced using an audiometer, which presents different frequencies to the subject, usually over calibrated headphones, at specified levels . The levels are weighted with frequency relative to a standard graph known as the minimum audibility curve, which is intended to represent "normal" hearing . The threshold of hearing is set at around 0 phon on the equal - loudness contours (i.e. 20 micropascals, approximately the quietest sound a young healthy human can detect), but is standardised in an ANSI standard to 1 kHz . Standards using different reference levels, give rise to differences in audiograms . The ASA - 1951 standard, for example, used a level of 16.5 dB SPL (sound pressure level) at 1 kHz, whereas the later ANSI - 1969 / ISO - 1963 standard uses 6.5 dB SPL, with a 10 dB correction applied for older people . </P> <P> Several primates, especially small ones, can hear frequencies far into the infrasonic field . Defined at 60 decibels, the hearing range for the Senegal bushbaby is 92 Hz--65 kHz, and 67 Hz--58 kHz for the ring - tailed lemur . Of 19 primates tested, the Japanese macaque had the widest range, 28 Hz--34.5 kHz, compared with 31 Hz--17.6 kHz for humans . </P> <P> Cats have excellent hearing and can detect an extremely broad range of frequencies . They can hear higher - pitched sounds than humans or most dogs, detecting frequencies from 55 Hz up to 79 kHz . Cats do not use this ability to hear ultrasound for communication but it is probably important in hunting, since many species of rodents make ultrasonic calls . Cat hearing is also extremely sensitive and is among the best of any mammal, being most acute in the range of 500 Hz to 32 kHz . This sensitivity is further enhanced by the cat's large movable outer ears (their pinnae), which both amplify sounds and help a cat sense the direction from which a noise is coming . </P> <P> The hearing ability of a dog is dependent on breed and age, though the range of hearing is usually around 67 Hz to 45 kHz . As with humans, some dog breeds' hearing ranges narrow with age, such as the German shepherd and miniature poodle . When dogs hear a sound, they will move their ears towards it in order to maximise reception . In order to achieve this, the ears of a dog are controlled by at least 18 muscles, which allow the ears to tilt and rotate . The ear's shape also allows the sound to be heard more accurately . Many breeds often have upright and curved ears, which direct and amplify sounds . </P>

How much more can a dog hear than a human