SOUND SOURCE LOCALIZATIONSIS PROJECT – EPFL BA6

Marco Vieira Ruas, Clara Barret & Nathalie Camplani

Supervisor Bahar Haghighat

Professor Alcheiro Martinoli

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

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)

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

• 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

• 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

• 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

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

• Use IR sensors

• Webots: 𝐼𝑅0 or 𝐼𝑅1 > 200

• E-pucks: less sensible, use also the 𝐼𝑅6 and 𝐼𝑅7

STEP 6Goal

reached

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

DEMONSTRATION: WEBOTS

DEMONSTRATION: E-PUCKS«Sound source» «Searcher»

← ↓

15 cm 30 cm

«Sound source» «Searcher»

↓ →

15 cm 30 cm

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?