Cochlea
(Duplex Theory, Haas Effect)
This paper gives a brief description of the binaural cues in sound localization, exploring the difference between Interaural Time Differences and Interaural Level diferences and briefly touching on intermediate frequencies that are hard to localize.
The paper extends into the auditory pathways of the left and right cochlea, how sound is introduced at the level of the superior olive complex and how ITDs and ILDs are combined in the inferior colliculus.
It also explores masking tones, unmasking tones and signal to noise ratio, allowing the listener to distinguish a voice in a noisy environment.
- "a sound that is 90 degrees to the right will create an ITD of about 0.7ms"
- "stimuli in the intermediate region fall in a gray area and may be hard to localize"
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Binaural Source Localization by Joint Estimation of ILD and ITD, Matin Raspaud, Harald Viste and Gianpaolo Evangelista, senior member, IEEE, January, 2010
(Duplex Theory, Haas effect, Precedence effect, HRTF)
This paper gives a description of ITD and ILD, computes the two cues from a two-channel time-frequency representation and are combined to estimate the azimuthal angle of sources in binaural space.
A parametric model for ITD and ILD is used
An average parametric for HRIR's is used
Several experiments that validate this approach are conducted to show how models are favoured in available techniques.
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Additive Versus Multiplicative Combination of Differences of Interaural Time and Intensity, Samuel H. Tao, Carnegie Mellon University, Pittsburgh, Pennsylvania, May 1992
Additive versus multiplicative
This paper uses the position-variable model to describe the subjective lateralization of tones and bandpass noise.
Experiments include:
- A tone that covers a wide range of frequencies that give a small ITD and no ILD.
- A 500Hz tone over a range of ITD's and ILD's
- Warble tones with a 500Hz center frequency over a range of different bandwidths and ILD's using one of four combinations of ITD's and IPD's
Better results were obtained from the warble tones using additive intensity weighting - the predicted position with an intensity difference is a proportional offset of the ILD from the predicted position with no IID.
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Introduction to Head-Related Transfer Functions (HRTF's): Representation of HRTF's in Time, Frequency and Space, Corey I.Cheng, Gregory H. Wakefield, University of Michigan, USA, April, 2001
In this paper, head related transfer functions are introduced and treated with respect to their role in the synthesis of spatial sound over headphones. It describes frequencies localized along the azimuthal plane and ambiguity around 1500Hz, where the wavelength becomes comparable to the diameter of the observers head. Head shadowing effects are explained above this frequency that give rise to interaural intensity differences
The paper notes the 'cone of confusion' from the work of Hornbostel and Wertheimer (1920), where unique spatial positions are not given by ITDS and ILDs as there is ambiguity of an infinite number of equi-distant points from the observer.
Typical HRTF measurement strategies are described, and simple applications of HRTFs to headphone-based spatialized sound synthesis are given.
By comparing and contrasting respresentations of HRTFs in the time, frequency and spatial domains, different analytic and signal processing techniques used to investigate the structure of HRTFs are highlighted.
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Computational Auditory Scene Analysis, Chapter 5, Binaural Sound Localization, DeLiang Wang and Guy J. Brown (eds.) ISBN 0-471-45435-4, 2005
SternWangBrownChapter Binaural Sound Localization
This paper is useful for providing a good solid background to Binaural Sound Localization.
Physical cues and physiological mechanisms that are involved in auditory localization are explain in depth, defining the lateralization of a binaural signal as a periodic function of the ITD with a period equal to the reciprocal of the center frequency.
"If a low-frequency tone and a broadband masker are presented monaurally, the threshold SNR that is obtained will generally depend on various stimulus presented such as target duration and frequency, and the masker bandwidth" (5.4.2 - classical binaural detection)
Includes a great amount of information on the various models of Binaural perception, starting with the Jeffress hypothesis model (picture on home page), the equalization-cancellation model, cross correlation-based models of binaural interaction, Lindermann's model and Breebaart's model stating any extensions added by other researchers.
- "since the maximum possible ITD is about 0.66ms for a human head of typical size"
This paper explores doppler effect of mechanical waves when the relative velocity is along the wave vector and when it is not. The geometric relationship described in this paper is necessary for explaining the frequency change of the source traveling parallel to the wave vector and the mathematics, for creating this effect in Csound.
It demonstrates the frequency ratio as a function of time and plots this result. This is necessary for predicting the small changes in frequency as the source passes the observer and can be easily plotted with respect to change in angle instead to provide a more suitable representation.
BOOKS
Doppler Effect
Kinsler, E. Lawrence, Austin. R. Frey, Alan. B. Coppens and James. V. Sanders. Fundamentals of Acoustics. Fourth Edition. 2000. USA. John Wiley and Sons. pp 453-455
Chapter 15, pages 453 to 455 gives a mathematical representation of doppler effect and describes briefly, the physics behind it's derivation.
Kuttruff, Heinrich. Acoustics - An Introduction. 2004. Albingdox, Oxon. Taylor and Francis. pp 74,75
Chapter 5, page 74 explains the Doppler effect as a change in frequency that occurs when either the source, observer or both are moving relative to one another.
It describes a source moving away from an observer and an observer moving towards a resting source, as expansion or contraction of the sound's frequency. (the mathematical relationship for doppler effect was adapted from this chapter)
Wood, Alexander. Acoustics. 1940. Scotland, Glasgow. Blackie and Sons, Ltd. pp324-328
Alexander Wood defines Doppler's principal in chapter 12, pages 324 to 328, beginning with the history of it's applications, the effect of motion of the medium, motion of the source and motion of the observer.
The effect of a sound source that is traveling in a straight line, which does not pass through the observer is described mathematically and the change in frequency for this event is plotted, frequency ratio against time. (this plot is useful, frequency ratio with respect to angle instead)
Binaural Localization
Kuttruff, Heinrich. Acoustics - An Introduction. 2004. Albingdox, Oxon. Taylor and Francis. pp 252-256
Everest, Alton. F and Ken. C. Pohlmann. Master handbook of Acoustics. 2001. USA. The McGraw Hill Companies. pp 64-69
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