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.
Scientific pitch
In the 19th century, Italian composer Giuseppe Verdi tried to stop the increase in pitch to which orchestras were tuned. In 1874 he wrote his "Requiem" using the official French standard "diapason normal" pitch of A4 tuned to 435 Hz. Later, he indicated that 432 Hz would be slightly better for orchestras. One solution he proposed was scientific pitch. He had little success.