Psychoacoustics
Psychoacoustics is an interdisciplinary field including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science.
Hence, in many problems in acoustics, such as for audio processing, it is advantageous to take into account not just the mechanics of the environment, but also the fact that both the ear and the brain are involved in a person's listening experience.
Telephone networks and audio noise reduction systems make use of this fact by nonlinearly compressing data samples before transmission and then expanding them for playback.
[4] Another effect of the ear's nonlinear response is that sounds that are close in frequency produce phantom beat notes, or intermodulation distortion products.
A more rigorous exploration of the lower limits of audibility determines that the minimum threshold at which a sound can be heard is frequency dependent.
By measuring this minimum intensity for testing tones of various frequencies, a frequency-dependent absolute threshold of hearing (ATH) curve may be derived.
Equal-loudness contours indicate the sound pressure level (dB SPL), over the range of audible frequencies, that are perceived as being of equal loudness.
Equal-loudness contours were first measured by Fletcher and Munson at Bell Labs in 1933 using pure tones reproduced via headphones, and the data they collected are called Fletcher–Munson curves.
Robinson and Dadson refined the process in 1956 to obtain a new set of equal-loudness curves for a frontal sound source measured in an anechoic chamber.
Some species of owls have their ears placed asymmetrically and can detect sound in all three planes, an adaption to hunt small mammals in the dark.
One can change the level of the masker and measure the threshold, then create a diagram of a psychophysical tuning curve that will reveal similar features.
It can explain how a sharp clap of the hands might seem painfully loud in a quiet library but is hardly noticeable after a car backfires on a busy, urban street.
By carefully shifting bits away from the unimportant components and toward the important ones, the algorithm ensures that the sounds a listener is most likely to perceive are most accurately represented.
[14] Irv Teibel's Environments series LPs (1969–79) are an early example of commercially available sounds released expressly for enhancing psychological abilities.
Internet pioneers J. C. R. Licklider and Bob Taylor both completed graduate-level work in psychoacoustics, while BBN Technologies originally specialized in consulting on acoustics issues before it began building the first packet-switched network.
[20] This enables auditory guidance without the need for spatial audio and in sonification computer games[21] and other applications, such as drone flying and image-guided surgery.
