AES San Francisco 2008
Poster Session P8
Friday, October 3, 11:30 am — 1:00 pm
P8 - Room Acoustics and Binaural Audio
P8-1 On the Minimum-Phase Nature of Head-Related Transfer Functions
—Juhan Nam, Miriam A. Kolar, Jonathan S. Abel
, Stanford University - Stanford, CA, USA
For binaural synthesis, head-related transfer functions (HRTFs) are commonly implemented as pure delays followed by minimum-phase systems. Here, the minimum-phase nature of HRTFs is studied. The cross-coherence between minimum-phase and unprocessed measured HRTFs was seen to be greater than 0.9 for a vast majority of the HRTFs, and was rarely below 0.8. Non-minimum-phase filter components resulting in reduced cross-coherence appeared in frontal and ipsilateral directions. The excess group delay indicates that these non-minimum-phase components are associated with regions of moderate HRTF energy. Other regions of excess phase correspond to high-frequency spectral nulls, and have little effect on cross-coherence.
Convention Paper 7546 (Purchase now)P8-2 Apparatus Comparison for the Characterization of Spaces
—Adam Kestian, Agnieszka Roginska
, New York University - NY, NY, USA
This work presents an extension of the Acoustic Pulse Reflectometry (APR) methodology that was previously used to obtain the characteristics of smaller acoustic spaces. Upon reconstructing larger spaces, the geometric configuration and characteristics of the measurement apparatus can be directly related to the clarity of the results. This paper describes and compares three measurement setups and apparatus configurations. The advantages and disadvantages of each methodology are discussed.
Convention Paper 7547 (Purchase now)P8-3 Quantifying the Effect of Room Response on Automatic Speech Recognition Systems
—Jeremy Anderson, John Harris
, University of Florida - Gainesville, FL, USA
It has been demonstrated that the acoustic environment has an impact on timbre and speech intelligibility. Automatic speech recognition is an established area that suffers from the negative effects of mismatch between different room impulse responses (RIR). To better understand the changes imparted by the RIR, we have created synthetic responses to simulate utterances recorded in different locations. Using speech recognition techniques to quantify our results, we then looked for trends in performance to connect with impulse response changes.
Convention Paper 7548 (Purchase now)P8-4 In Situ Determination of Acoustic Absorption Coefficients
, University of Waterloo - Waterloo, Ontario, Canada
The determination of absorption characteristics for a given material is developed for in situ measurements. Experiments utilize maximum length sequences and a single microphone. The sound pressure is modeled using the compact source approximation. Emphasis is placed on low frequency resolution that is dependent on the geometry of both the loudspeaker-microphone-sample configuration and the room in which the measurement is performed. Methods used to overcome this limitation are discussed. The concept of the acoustic center is applied in the low frequency region, modifying the calculation of the absorption coefficient.
Convention Paper 7549 (Purchase now)P8-5 Head-Related Transfer Function Customization by Frequency Scaling and Rotation Shift Based on a New Morphological Matching Method
, Laboratoire d’Acoustique de l’Université du Maine - Le Mans, France, and Orange Labs, Lannion, France; Thomas Guignard, Rozenn Nicol
, Orange Labs - Lannion, France
Head-Related Transfer Functions (HRTFs) individualization is required to achieve high quality Virtual Auditory Spaces. An alternative to acoustic measurements is the customization of non-individual HRTFs. To transform HRTF data, we propose a combination of frequency scaling and rotation shifts, whose parameters are predicted by a new morphological matching method. Mesh models of head and pinnae are acquired, and differences in size and orientation of pinnae are evaluated with a modified Iterative Closest Point (ICP) algorithm. Optimal HRTF transformations are computed in parallel. A relatively good correlation between morphological and transformation parameters is found and allows one to predict the customization parameters from the registration of pinna shapes. The resulting model achieves better customization than frequency scaling only, which shows that adding the rotation degree of freedom improves HRTF individualization.
Convention Paper 7550 (Purchase now)