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Generating the illusion of directional sound using calculated directional transfer functions.

Directional test signal creation

In order to test the accuracy of our calculated HRTFs, we used 5.1 surround sound test files used to calibrate home theater systems. We first had to downsample these files from their original sampling rate of 48000 Hz to our sampling rate of 41000 Hz. Since the files were all meant to be played at the same time, each file only played sound part of the time. Therefore, we had to cut out the unused parts of each file and create new sound files which included only the testing segment of each directional file. After this process was complete, we were left with five signals, each of which specified which direction the sound was supposed to come from.

Directional sound playback

We then simulated these signals coming from particular directions using the equation from the HRTF calculation:

H Channel ( ω ) IN ( ω ) H Directional ( ω ) = OUT ( ω ) size 12{H_ ital "Channel" \( ω \) cdot ital "IN" \( ω \) cdot H_ ital "Directional" \( ω \) = ital "OUT" \( ω \) } {}

In this case H Channel size 12{H_ ital "Channel"} {} is the earbud to ear channel transfer function. Unfortunately, we weren’t able to characterize this channel with our available resources, so in this instance we assumed that H Channel = 1 size 12{H_ ital "Channel"=1} {} . This left us with the following equation:

IN ( ω ) H Directional ( ω ) = OUT ( ω ) size 12{ ital "IN" \( ω \) cdot H_ ital "Directional" \( ω \) = ital "OUT" \( ω \) } {}

By applying this equation to each calculated H Directional ( ω ) size 12{H_ ital "Directional" \( ω \) } {} for both ears we were able to generate a series of synthesized sound files for each ear which when played in stereo would mimic a cound coming from a particular direction by using the following code:

L_OUT=[SYNTH_FL_L, SYNTH_FC_L, SYNTH_FR_L, SYNTH_RR_L, SYNTH_RL_L];

L_OUT=L_OUT';

R_OUT=[SYNTH_FL_R, SYNTH_FC_R, SYNTH_FR_R, SYNTH_RR_R, SYNTH_RL_R];

R_OUT=R_OUT';

FINAL_OUT=[L_OUT, R_OUT];

sound(FINAL_OUT, Fs);

In this code, the SYNTH terms are the vectors corresponding to the filtered test signals for front-left, front-center, front-right, rear-right, and rear-left directions. With the left and right ear outputs arranged as shown in FINAL_OUT, the sound command plays the first set of terms to the left speaker/headphone and the second set of terms to the right speaker/headphone as we desired.

Questions & Answers

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Crow Reply
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RAW Reply
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Damian
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Rafiq
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Damian
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LITNING Reply
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LITNING
scanning tunneling microscope
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Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
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Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
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Adin
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Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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research.net
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Introduction about quantum dots in nanotechnology
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nano basically means 10^(-9). nanometer is a unit to measure length.
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Damian Reply
absolutely yes
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Source:  OpenStax, The science of surround sound. OpenStax CNX. Dec 18, 2010 Download for free at http://cnx.org/content/col11254/1.2
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