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SOUND SOURCE LOCALIZATIONSIS PROJECT – EPFL BA6
Marco Vieira Ruas, Clara Barret & Nathalie Camplani
Supervisor Bahar Haghighat
Professor Alcheiro Martinoli
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E-PUCKS
• Invented by EPFL in 2004 (first edition) and performed until 2006 (third edition)
• A robot Designed for Education in Engineering
• Equipped with sensors interaction with the environment
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BASIC THEORY
• Sound source localization using a “sound source” and a “searcher”
• “searcher” receives the signal at its microphones with different phases 𝑝 𝑑, 𝑡 = 𝐴0 cos(𝑘𝑑 − 𝜔𝑡 + 𝜑)
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METHODSSTEP 1
Analysis of the signal
STEP 2Determination of 𝜑
and cos 𝜃
STEP 3Turn to the right
direction
STEP 4Stop rotation
STEP 5Go forward
STEP 6Goal
reached
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• FFT (already given) looking for the maximum peak
• Obtain the corresponding coefficients 𝐹𝑖 = 𝐴𝑖2 + 𝐵𝑖
2
• Maximal frequency: 𝑓𝑝𝑒𝑎𝑘 =𝑓𝑠∙𝑖
3∙𝐿
STEP 1Analysis of the signal
Property Webots E-pucks
Sampling frequency [Hz] 33’000 16’384
Signal length [-] 128 256
Index of maximum magnitude (FFT) [-] 4 15 or 7
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• Phase for each microphone: 𝜑 = tan−1 −𝐵𝑖/𝐴𝑖
• Time shifts: ∆𝑇 =∆𝜑
𝜔=
∆𝜑
2𝜋∙𝑓𝑝𝑒𝑎𝑘
• cos 𝜃 =𝑐∙∆𝑇
𝑑
STEP 2Determination of 𝜑
and cos 𝜃
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• Based on ∆𝜑21 − ∆𝜑20
• Webots
• E-pucks not as expected
• Definition of the boundaries after trials
• ∆𝜑21 − ∆𝜑20 < −0.2 turn clockwise
• ∆𝜑21 − ∆𝜑20 > 0.2 turn counter clockwise
STEP 3Turn to the right
direction
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Webots
• Is in front when: cos 𝜃01 < 0.15
STEP 4Stop rotation
E-pucks
If −0.2 < ∆𝜑21 − ∆𝜑20 < 0.2
• When 0 < cos 𝜃12 < 4 e-puck is in front of the
«sound source» : can go straight
• When cos 𝜃12 > 4 or cos 𝜃12 < 0 e-puck is behind the «sound source» :
before going forward it has to make a turn of 180°
STEP 5Go forward
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• Use IR sensors
• Webots: 𝐼𝑅0 or 𝐼𝑅1 > 200
• E-pucks: less sensible, use also the 𝐼𝑅6 and 𝐼𝑅7
STEP 6Goal
reached
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DIFFICULTIES
• E-pucks sensible to noises and limitations of memory
• Frequencies recorded by the e-puck don’t have a constant index of the maximum peak• Chose the most common one
• Wheels change the sound characteristics• Again look at the real values recorded
• Too far from “sound source”, “searcher” recorded only NaN values• Implementation of a new condition: U-turn and go forward
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DEMONSTRATION: WEBOTS
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DEMONSTRATION: E-PUCKS«Sound source» «Searcher»
← ↓
15 cm 30 cm
«Sound source» «Searcher»
↓ →
15 cm 30 cm
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REFERENCES
• SR, SIS Project, Project: E-puck sound source localization, Distributed Intelligent Systems and Algorithms Laboratory, EPFL, accessed on April 2017.
• Xavier Raemy, Introduction to the e-puck robot, SWIS group, EPFL, Lausanne, 28 november 2006, project web page: http://www.e-puck.org.
• Alcherio Martinoli, Signals, Instrumental and System, Course for SIE BA6, EPFL, Lausanne, 2017.
• EPFL, e-puck education robot, http://www.e-puck.org., consulted the 28.05.2017.
THANK YOU, QUESTIONS?