Harman Kardon
In 1959, Harman Kardon marketed the Citation II, an early ultra wideband stereophonic tube amplifier. Designed by Stewart Hegeman, it featured 60 watts/channel output with a frequency response of 18-60,000 Hz at 20 watt output. The company promoted their philosophy of designing high fidelity sound using amplifiers that provided widest possible audio bandwidth. Although the human ear highest audible range is around 20,000 Hz, the full range of sound goes beyond that with harmonics and overtones that may be beyond the hearing range of the human ear. These harmonics interact with other frequencies to produce audible secondary sounds or interference. Harman Kardon promoted the design in audio magazines and product brochures.
Absolute pitch
Scientific study of absolute pitch appears to have commenced in the 19th century, focusing on the phenomenon of musical pitch and methods of measuring it. It would have been difficult for any notion of absolute pitch to have formed earlier because pitch references were not consistent. For example, the note now known as 'A' varied in different local or national musical traditions between what would now be considered as G sharp and B flat before the standardisation of the late 19th century. While the term "absolute pitch", or "absolute ear", was in use by the late 19th century by both British and German researchers, its application was not universal; other terms such as "musical ear", "absolute tone consciousness", or "positive pitch" were also used to refer to the ability. The skill is not exclusively musical, or limited to human perception; absolute pitch has been demonstrated in animals such as bats, wolves, gerbils, and birds, for whom specific pitches facilitate identification of mates or meals.