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.
Ernst Terhardt
According to Terhardt’s theory of pitch perception, pitch perception can be divided into two separate stages: auditory spectral analysis and harmonic pitch pattern recognition. In the first stage, the inner ear (cochlea and basilar membrane) performs a running spectral analysis of the incoming signal. The parameters of this analysis (e.g. the effective length and shape of the analysis window) depend directly on physiology and indirectly on the co-evolution of ear and voice as our human and prehuman ancestors interacted with their social and physical environments. The output of this first stage is called a spectral pitch pattern, when it is determined by psychoacoustic experiments in which listeners make subjective judgments, matching the perceived pitch of a pure reference tone to that of a successively presented complex tone. The spectral pitches differ in perceptual salience since their sound pressure levels differ physically, they lie at different distances above the threshold of hearing, they mask each other (and therefore lie at different distances above the masked threshold), and may or may not lie in a region to which the ear is particularly sensitive (a dominance region of pitch perception). A cornerstone of Terhardt’s is approach is the idea that because spectral pitches are subjective, we must not jump to conclusions about the relationship between them and their physiological (physical) foundations in the ear and brain.