(Georgia Institute of Technology, 2009-07-06)
Stanley, Raymond M.
Virtual three-dimensional auditory displays (V3DADs) use digital signal processing to deliver sounds (typically through headphones) that seem to originate from specific external spatial locations. This set of studies investigates the delivery of V3DADs through bone-conduction transducers (BCTs) in addition to conventional headphones. Although previous research has shown that spatial separation can be induced through BCTs, some additional signal adjustments are required for optimization of V3DADs, due to the difference in hearing pathways. The present studies tested a bone-conduction adjustment function (BAF) derived from equal-loudness judgments on pure tones whose frequencies were spaced one critical band apart. Localization performance was assessed through conventional air-conduction headphones, BCTs with only transducer correction, and BCTs with a BAF. The results showed that in the elevation plane, the BAF was effective in restoring the spectral cues altered by the bone-conduction pathway. No evidence for increased percept variability or decreased lateralization in the bone-conduction conditions was found. These findings indicate that a V3DAD can be implemented on a BCT and that a BAF will improve performance, but that there is an apparent performance cost that cannot be addressed with BAFs measured using the methodology in the present studies.
(Georgia Institute of Technology, 2006-11-03)
Stanley, Raymond M.
Virtual three-dimensional (3D) auditory displays utilize signal-processing techniques to
alter sounds presented through headphones so that they seem to originate from specific
spatial locations around the listener. In some circumstances bone-conduction headsets
(bonephones) can provide an alternative sound presentation mechanism. However,
existing 3D audio rendering algorithms need to be adjusted to use bonephones rather than
headphones. This study provided anchor points for a function of shift values that could be
used to adapt virtual 3D auditory displays for use with bonephones. The shift values were
established by having participants adjust phase and amplitude of two waves in order to
cancel out the signal and thus produce silence. These adjustments occurred in a listening
environment consisting of air-conducted and bone-conducted tones, as well as air-
conducted masking. Performance in the calibration condition suggested that participants
understood the task, and could do this task with reasonable accuracy. In the bone-to-air
listening conditions, the data produced a clear set of anchor points for an amplitude shift
function. The data did not reveal, however, anchor points for a phase shift function the
data for phase were highly variable and inconsistent. Application of shifts, as well as
future research to establish full functions and better understand phase are discussed, in
addition to validation and follow-up studies.