Improvement of Audibility for Multi Speakers

1
Improvement of Audibility for Multi Speakers with
the Head Related Transfer Function Takanori
Nishino, Kazuhiro Uchida, Naoya Inoue, Kazuya
Takeda and Fumitada Itakura Center for
Information Media Studies/CIAIR, Nagoya University
Experiment 2
Introduction
If two speakers talk at same time, it is
difficult to distinguish the speaker and the
details of the speech when the listener uses the
headphone. However, the listener can hear the
target speech when there are many speakers its
called the cocktail party effect. It is
considered that the sound localization
contributes to the cocktail party effect. When
using the headphones, it is necessary to control
the directions of the speakers for hearing. Sound
localization can be controlled by the head
related transfer function (HRTF) with the
headphones. The HRTF is the acoustical transfer
function that exists between the sound source and
the entrance of the ear canal, and since the HRTF
is characterized by the subjects and the source
directions, it is necessary to measure the HRTFs
of all subjects and directions. Because it is
computationally expensive and time consuming to
measure the HRTFs, it is necessary to estimate
the HRTFs for the listener. In this study, we
investigate the audible angle when there are two
speakers using the auditory masking, and estimate
suitable HRTFs for the listener.
Purpose
HRTF
The relation between the HRTFs and physical sizes
of the head and the ear is investigated by the
multiple regression analysis. The suitable HRTFs
are estimated with the multiple regression model.
A sound wave is reflected and diffracted with the
head and the ears.
Physical size of the head and the ear
Method
The Analysis of the Magnitude Response
Measurement
Measurement Conditions
The Analysis of the Initial Delay
Anthropometric Measures (Burkhard and Sachs,
1975)
Generating the HRTFs
Experimental Conditions
Results
Magnitude Response

• HRTFs and anthropometric measures of right ear
• Evaluated bandwidth
• 0.0 4.0 kHz, 8.0 kHz, 12.0 kHz, 16.0 kHz, 20.0
  kHz, 22.0 kHz, 24.0 kHz
• Using from the first PC weight to the fifth
• Multiple regression model is made by 70 subjects
  data (Measured)
• 8 subjects HRTFs are estimated by the
  anthropometric measures and the multiple
  regression model (Unmeasured)
• Experiments are performed 71 mutually different
  conditions
• Evaluation by objective measure
• (Spectral Distortion)
• If the small SD is obtained, the estimated
  HRTF is similar to the measured HRTF.

Experiment 1
Purpose
It is more audible when the speakers are in the
different direction.
It is not audible when the many speakers talk at
the same time.

• No significant difference
• (Nishino et al. 1999)

Initial Delay
To investigate the audible performances when the
direction of the speakers is changed.
Method
Results

• The Method of the limits for measuring the
  masking level(2up-2down).
• The subjects answer the recognizable or not when
  the stimuli are listened with the earphones.
• The stimuli are convolution of the speech and
  the HRTFs or the interaural level/time
  difference.
• If the higher level is obtained, it is easier to
  hear the maskee at that angle.

• Imperceptible (Toole and Sayers 1965)

Conclusions
In this study, it is investigated to the
improvement of the audibility for the multi
speakers. As the results, it is more effective
for audibility at the intervals of 45 degrees and
the suitable HRTFs for the listeners can be
estimated. The communication system for multi
speakers can be designed with these results.
Experimental Conditions
HRTF Database http//www.itakura.nuee.nagoya-u.ac.
jp/HRTF/ -Contents HRTFs used in this
experiments HRTFs measured for 72 azimuths and
28 elevations

• It is more effective at the intervals of 45
  degrees.