Project design by: Jennifer Murdoch University of Victoria, Canada

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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

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

• SUMMARY

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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

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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?

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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

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The Case Under Investigation...
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Sound in the Real World
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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
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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.

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The Case Under Investigation Snapshot of 4
Footsteps Recorded by 2 Mics
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(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

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(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!

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(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!

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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

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CONGRATULATIONS !!!