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Project design by: Jennifer Murdoch University of Victoria, Canada

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Two items stolen: Worthless vase. Over $100,000 CDN from a bank vault. QUESTION: Who stole which loot? The Case Under Investigation: The Evidence ... – PowerPoint PPT presentation

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Title: Project design by: Jennifer Murdoch University of Victoria, Canada


1
CSI Computer Science Investigations(Learn Java
and Solve a Crime in the Same Day!)
  • Project design by Jennifer Murdoch (University
    of Victoria, Canada)
  • Lecturer - IEEE Member since 2004

2
CSI Computer Science Investigations(Learn Java
and Solve a Crime in the Same Day!)
  • SUMMARY

3
Computer Science and ForensicsA Real World
Application
  • Acoustical gunshot analysis,
  • audio enhancement,
  • voiceprint analysis,
  • voice elimination,
  • aural steganography,
  • evidence authentication, and
  • Acoustic Simulation for Scene Reconstruction

4
The Case Under Investigation...
  • Bank of Good Cents (Toronto, Canada) has been
    robbed!!
  • YOU have been hired to crack the case.
  • 2 security guards are the prime suspects
  • Alice (day shift)
  • Bob (night shift)
  • Two items stolen
  • Worthless vase
  • Over 100,000 CDN from a bank vault
  • QUESTION Who stole which loot?

5
The Case Under InvestigationThe Evidence
  • Simultaneous recordings from 5 microphones with
    known coordinates around the periphery of the
    bank vault room where the crime took place.
  • 5 audio recordings from the day shift
  • 5 audio recordings from the night shift

6
The Case Under Investigation...
7
Sound in the Real World
8
Sound in the Digital World
Time (seconds)
Amplitude ( -1 to 1 )
double samples 0.0029602954191717277,
0.002838221381267739, 0.00271614734336375,
0.0025025177770317698, 0.0023194067201757866,
0.0025025177770317698, 0.0027466658528397473,
0.00271614734336375, 0.0025025177770317698,
0.0024414807580797754, 0.0023194067201757866,
0.002380443739127781, 0.002227851191747795,
0.002349925229651784, -0.0016174810022278
512, 0.002533036286507767, -0.0010376293221839045,
-0.00173955504013184, -0.017364501953125,
0.05694753868221076
9
The Case Under Investigation Analyzing the
Evidence
  • Analyze the audio recordings to determine TDOA
    between pairs of microphones.
  • Use TDOA values to derive position of the
    perpetrator in the bank.
  • Repeat this process over time to plot a
    trajectory (path) of the perpetrators movements
    over time in order to reconstruct the crime.

10
The Case Under Investigation Snapshot of 4
Footsteps Recorded by 2 Mics
11
(1) Computing TDOA between a Pair of Audio
Recordings
  • You explored two different approaches for
    computing TDOA between a pair of microphones
  • Threshold-Based Approach
  • Cross-Correlation Approach
  • Compare these algorithms in terms of the
    following key criteria
  • Accuracy of computed TDOA values,
  • Robustness of the algorithm (does it work for
    any set of audio recordings, or only audio
    recorded under ideal conditions),
  • How fast it executes (relate this to the
    complexity of the source code), and
  • How easy it is to implement.
  • Note that the Threshold-Based Approach uses a
    single for loop, while the Cross-Correlation
    Approach uses a pair of nested for loops

12
(2) Use TDOA Values to Derive Position of the
Perpetrator in the Bank
  • You learned how to use API documentation in order
    to make use of new Java classes that provided you
    with new tools for solving the crime!

13
(3) Explore the Trade-Off Between Noise Level and
Computed Coordinate Accuracy
  • You used experimental observations regarding the
    robustness of your algorithm to signal noise in
    order to provide evidence of the guilt or
    innocence of the perpetrators!

14
You also Learned !!!
  • Create 1-dimensional arrays Read from/write to
    array elements using both explicit and computed
    index values
  • Create 2-dimensional arrays Read from/write to
    array elements using both explicit and computed
    index values
  • Use provided Java classes and an API reference
  • Compare the source code complexity, running time,
    and accuracy of two different solutions to a
    problem
  • Create a hypothesis and collect empirical data to
    analyse and support that hypothesis
  • Perform effectively as part of a programming pair

15
CONGRATULATIONS !!!
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