20 10 School of Electrical Engineering &Telecommunications UNSW UNSW 10 Author: Jonathan Jayanthakumar An Analysis of the Role of the First Reflection in the Simulation of Distance with Audio Introduction When was the last time you saw a film on TV, like ‘Lord of the Rings?’ If you’ve 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. Supervisor: Deep Sen Co-supervisor: Joseph Paul Current Understanding In audio distance perception, there are many cues that influence our distance judgement. These include: 1.Sound Level 2.Reverberation 3.Spectral Effects 4.Binaural Effects 5.Familiarity with Audio The Objectives The problem statement can be summarised by saying: To find the most effective way to simulate distance using reverberation. Reverberation 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. Ideal Psychometric CurveExperimental Psychometric Curve 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.