Author: Jonathan Jayanthakumar

1
An Analysis of the Role of the First Reflection
in the Simulation of Distance with Audio
10
Co-supervisor Joseph Paul
Author Jonathan Jayanthakumar
Supervisor Deep Sen
Introduction When was the last time you saw a
film on TV, like Lord of the Rings? If youve
seen it, did you notice that many of the scenes
have Orcs and beasts screaming in the distance,
from over 100m away? Did you also notice that
your TV speakers are much less than 100m away
from you? How do they make the Orcs sound like
they are over 100m away with speakers so close?
They do this by simulating distance with audio
they alter the sound (or the recording method) to
make it sound further away. This is distance
simulation with audio.
A Psychoacoustic Experiment An hearing
experiment was designed to test the role of the
first reflection. Subjects were placed in an
anechoic chamber (no reflections no reverb) and
speakers were placed around the room to simulate
a direct sound, and its reflections (simulated
reverb). A variety of stimuli were chosen,
including unfamiliar sounds (like pure tones and
white noise) and familiar sounds (like speech and
music). In this highly controlled environment,
the subjects heard pairs of sounds, and had to
determine which sound appeared to be closer to
them. The GUI used in the experiment was set up
according to the Two Alternative Forced Choice
(2AFC) model.

• Current Understanding
• In audio distance perception, there are many cues
  that influence our distance judgement. These
  include
• Sound Level
• Reverberation
• Spectral Effects
• Binaural Effects
• Familiarity with Audio

The Objectives The problem statement can be
summarised by saying To find the most effective
way to simulate distance using reverberation. Reve
rberation is an important distance cue that
occurs due to the reflection of sound off
surfaces. An important criteria in considering
reverberation as a cue is the direct-to-indirect
sound ratio. The direct sound is the sound that
travels on the straight line path to the
listener. The indirect sound is the sum of all
the reflections in the room. The first reflection
is the part of the indirect sound that arrives to
the listener first. An experiment was designed to
determine whether the first reflection was (by
itself) sufficient to simulate reverberation, and
whether this first reflection is a distance cue.
The Findings The results showed that, over the
breadth of sounds covered by this experiment, the
first reflection does not play a significant
role. However, when looking at only the familiar
sounds (noting that familiarity is a known
distance cue), a definite trend is observed
changes in distance are perceived when only the
first reflection is simulated. Also, sounds that
are familiar also are perceived much more
accurately from the front of the listener, than
from the side.
Conclusions The first reflection can be
successfully used to simulate distances when
familiar sounds are involved. Also, sounds coming
from the front are perceived more accurately than
sounds from the side. Adding a second reflection
may show a more obvious dependence, and is an
area that should be pursued. Also a significant
area of interest is familiarity with audio it
will be useful to understand what sounds can be
considered familiar, and the way this is
perceived by the brain.