Developing a model to explain and stimulate the perception

of sounds in three dimensions

David Kraljevich and Chris Dove

Experimental Goal

• Create a model describing how sound waves recorded at the position of the eardrum change depending on the location of their source.

• Test the model by attempting to synthesize “directional” sounds and evaluate them subjectively.

Sound, the Listener, and the Environment

• Pressure waves• Diffraction and

Reflection• Interference• Reverberation :

Direct Field vs. Indirect Field

                 

               

From “A 3D Sound Primer” http://www.northwestern.edu/musicschool/classes/3D/pages/sndPrmGK.html#anchor509080

Pressure waves

Two researchers, Headphones, and a Brain:

Winter experimentsA sound arriving at the near ear is more intense and arrives earlier than the sound at the far ear.

• The speed of sound at room temperature and 1atm is 343 m/s

• At most, there will be a 0.7 to 0.8 ms difference between the time it takes to reach one ear and the other.

• We also predict that they will usually arrive at different phases.

Out of Phase Experiment

Right channel: slightly out of phase

Results: perceived sound coming from the right!

Soundforge 4.5. 60 Hz stereo. 44100 samples/sec

Zen Clock Experiment

1. Record “silence”

2. Record Bar Resonating

3. Spectral Analysis

http://www.serenityhealth.com/zclok_burg.html

Amplitude (dB) vs. time (samples)

Amplitude (dB) vs. Frequency (Hz) (FFT)

Signal vs Noise

Frequency spectrum of “silent” recording. Computed with a Fast Fourier Transform using 4096 samples. No smoothing windows applied. RMS power = -52.30 dB

silence

clock

Time-domain to frequency-domain

Spectrum of 6500Hz sine wave

Frequency spectra of piano and violin

Our Model

Will Include• Phase differences • Time differences• Intensity differences

May Include• Spectral differences

Won’t Include• Psychological

factors• Head movement• Moving sources• Environmental cues

-Reverberation

Spring Research

• Use of Binaural Head

• Deeper exploration of Fourier analysis

• Quantitative treatment of elevation