Binaural Technique — Basic Methods for Recording, Synthesis, and Reproduction

Abstract

Summary. The term "binaural technique" is used as a cover label here for methods of sound recording, synthesis and reproduction, where the signals in focus are the acoustic signals at the eardrums. If these are presented authentically to listeners, the listeners will obtain acoustic cues which are deemed sufficient for authentic auditory experience -including its spatial aspects. This chapter reviews the basic principles of binaural technique -putting a special focus on results of investigations which have been performed at Aalborg University. These basic principles form the foundation for current utilization of binaural technique at large. They include basic theory, investigations on sound transmission in the ear canal, measurements and post-processing of head-related transfer functions, HRTFs, transfer functions of headphones and their adequate equalization, and results from localization experiments in real life as well as with binaural recordings from real heads and artificial heads. Numerous applications to these methods exist. Some of them will be introduced exemplarily.

Crowdsourcing vs. laboratory experiments – QoE evaluation of binaural playback in a teleconference scenario

“…As mentioned in [24] there are numerous applications for binaural synthesis such as surround sound by headphones, 3-D auditory displays or virtual reality. Another interesting area of application, where users can benefit from binaural playback, is communication systems.…”

“…Filtering an audio signal with the corresponding HRTFs for the left and right ear can therefore make the sound source virtually appear at any position where HRTFs were measured. An in depth review of the state of the art methods for HRTF measurement as well as binaural synthesis and playback can be found in [24].…”

On the distortion of binaural localization cues using headphones

“…A sufficient model for the latter effects is encompassed in the Headphone Transfer Function (HpTF), which describes the filtering from headphone input to the output of a microphone placed at the entrance of the ear canal. There is a general consensus in the literature that HpTF equalisation is necessary to improve the performance of binaural synthesis [1,2]. It has been shown that the HpTF varies significantly from individual to individual, from one headphone type to another, and also on the positioning of the headphone on the ears [3].…”

A Survey on Hardware and Software Solutions for Multimodal Wearable Assistive Devices Targeting the Visually Impaired

“…For all of these phenomena, the hearing system uses the filtering effects of the outer ears, head, and torso. These response characteristics are called Head-Related Transfer Functions (HRTFs) and they can be measured, stored, and used for reverse engineering usually in the form of digital IIR and/or FIR filters [15][16][17][18].…”