ACOUSTIC LOCALIZATION BY INTERAURAL LEVEL DIFFERENCE

1
ACOUSTIC LOCALIZATION BY INTERAURAL LEVEL
DIFFERENCE STAN BIRCHFIELD AND RAJITHA
GANGISHETTY CLEMSON UNIVERSITY
ILD FORMULATION
ABSTRACT
SIMULATION RESULTS

• N microphones and a source signal s(t), signal
  received by the i th microphone

Interaural level difference (ILD) is an important
cue for acoustic localization. Although its
behavior has been studied extensively in natural
systems, it remains an untapped resource for
computer-based systems. We investigate the
possibility of using ILD for acoustic
localization, deriving constraints on the
location of a sound source given the relative
energy level of the signals received by two
microphones. We then present an algorithm for
computing the sound source location by combining
likelihood functions, one for each microphone
pair. Experimental results show that accurate
acoustic localization can be achieved using ILD
alone.

• The algorithm
• accurately estimates the angle to the sound
  source in some scenarios
• exhibits bias toward far locations (unable to
  reliably estimate the distance to the sound
  source)
• is sensitive to noise and reverberation

• Energy received by i th microphone

• Given E1 and E2 the sound source lies on a
  locus of points (a circle or line) described by

likelihood function computed by horizontal and
vertical microphone pairs
contour plots of likelihood functions (overlaid
and combined)
THE PROBLEM
where
estimated location

• For two microphones the relation between
  energies and distances is

• Acoustic localization
• Determining the location of a sound source by
• comparing signals received by an array of
  microphones
• Issues
• reverberation
• noise

true location
microphones
5m x 5m room, source at 45 degrees, reverberation
0.9, no noise
q
ILD LOCALIZATION
f
sound source
microphone array
Localize sound source by computing likelihood at
a number of candidate locations
5m x 5m room, source at 90 degrees, reverberation
0.9, SNR 0dB

• Define the energy ratio as

TWO SOUND CUES

• Then the estimate for the energy ratio at
  candidate location is

sound source
5m x 5m room, source at 54 degrees, reverberation
0.9, SNR 0dB
where is the location of the ith
microphone
microphones
CONCLUSIONS

• is treated as a Gaussian
  random variable

• Joint probability from multiple microphone pairs
  is computed by combining the individual log
  likelihoods

• ILD is an important cue for acoustic
  localization
• Preliminary results indicate potential for ILD
  (Algorithm yields accurate results for several
  configurations, even with noise and
  reverberation)
• Future work

Interaural Level Difference (ILD) relative
energy level

• Investigate issues (e.g., bias toward distant
  locations, sensitivity to reverberation)
• Experiment in real environments
• Combine with ITD to yield more robust results

Interaural Time Difference (ITD) relative time
shift
The results of ?E estimation using the two
horizontal microphones for the six sound source
locations. From top to bottom, ? 0, 45, 90
degrees from left to right ? 1, 2 m. The
solid line is ground truth.
The simulated room, with four microphones (x) and
six sound source locations (o).
Isocontours for different values of 10 log?E.