The Effect of Reverberation and Amplification on Sound Localisation

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The Effect of Reverberation and Amplification on
Sound Localisation

• Hadeel al Saleh
• Supervisors Dr.Stefan Bleeck, Prof.Mark Lutman
• 1st July. 2009

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Relation to Audiology

• Localisation is important in
• Quality of Speech perception
• Communication in background noise
• Safety
• Hearing aid and cochlear implant users have
  difficulties with localisation.

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The Coordinate System We Use
What sources of information are available to the
auditory system? Cues for azimuth Cues for
distance Cues for elevation
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Localisation

• Cues for localisation in the horizontal plane
• Interaural time differences (ITD) for low
  frequencies
• Interaural level differences (ILD)
  for high frequencies

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Reverberation

• In reverberant environments, the listener
  receives cues from different directions. The
  sound that arrives to the ear is the combined
  effect of multiple sound reflections within a
  room
• The precedence effect, is our ability to localise
  the sound source in a reverberant environment
  using the first wave that arrives to the ear
  (Yost, 2000)
• Reverberation can be simulated using different
  softwares. Different environments can be
  resembled by changing the reverberation
  parameters.

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The Effect of Reverberation on Sound
Localisation(1)

• As distance between the sound source and
  the listener increases, the amount of direct
  sound energy arriving at the listeners ears
  decreases and the amount of reverberant
  (reflected) energy increases (Mershon et al,1989)

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(2)

• A study by Cunningham (2000) showed that
  listeners adapt to the reverberation in a room
  (broadband noise stimulus).
• Results show that reverberation degrades
  perception of source direction, but with
  experience in a given room, performance improves
• Reverberation enhances distance perception but
  distance accuracy still improves with experience
• Giguere and Abel (1993) found that localisation
  of a third octave noise is worse in the
  reverberant conditions.

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My Research Questions?

• 1- Is there any effect of reverberation on sound
  localisation on normal hearing and hearing
  impaired listeners?
• 2-What is the effect of amplification on sound
  localisation in the reverberant environments?

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The Test Setup

• 21 speakers in anechoic chamber
• Measure average error in degrees (accuracy of
  localisation)

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Stimuli

• For first two experiments, a speech sentence was
  used (where do I speak from?) using a recorded
  male voice.
• The stimulus was modified in each experiment in a
  different way.
• Each sound will be replicated twice from the 21
  loudspeakers in a randomized manner--gtone run
• 2 runs per stimulus
• Reverberation was created using Adobe audition.
  The reverberation components were added to the
  sound files on the right (stereo) channel

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Subjects

• Otologically normal (according to BSA 2004). Must
  have symmetrical hearing(lt10dB)
• Age between 18-30 yrs, and have a normal state of
  health
• Right handed ( to avoid difference in performance
  according to handedness)

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Data Collection

• Subjects need to touch a point on the sensitive
  computer screen that corresponds to the speaker
  position

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1st Experiment

• Is there any effect of reverberation on sound
  localisation on normal listeners?
• To answer the above question, 14 subjects were
  recruited .Three types of stimuli were used
• 1) Speech stimulus
  ? (SPEECH)
• 2) High pass speech (cut off frequency at 1600
  Hz) ? (HPS)
• 3) Low pass speech
  ? (LPS)
• In addition,
• 4) Speech stimulus with reverberation. ?
  (SPEECH-R)
• 5) High pass speech with reverberation ? (HPS-R)
• 6) Low pass speech with reverberation. ? (LPS-R)

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1st Experiment
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1st Experiment

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Results

• Significant effect of reverberation was found on
  localising the lateral speaker positions only.

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2nd Experiment

• What effect does the reverberation length
  have on the ability to localise sound?
• In this experiment each 8 subjects underwent 5
  conditions in the same anechoic chamber. Some
  reverberation was added to resemble 5 different
  environments.
• 1-resembling the rev of large auditorium ?
  (Rev 1)
• 2-resembling the rev of a medium concert hall ?
  (Rev 2)
• 3-resembling the rev of small club ?
  (Rev 3)
• 4-resembling the rev of furnished living room ?
  (Rev 4)
• 5-no reverberation was added ?
  (No Rev)

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2nd Experiment
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Reverberant Room Experiment

• Performing the same localisation experiment in
  the real reverberant room in Rayleigh building.
• Stimuli used are
• Speech
• low-pass speech
• High pass speech
• 4 KHz pure tone
• 500 Hz pure tone

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Reverberant Room Results
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Comparing Simulated Reverberation and Real
Reverberation
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Speech Signals (Anechoic vs. Reverberant)
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Pure tones(Anechoic vs. Reverberant)
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Conclusions for the normal hearing listeners

• No Significant difference was found between the
  real Reverberant room and the simulated
  reverberation.
• Reverberation doesnt seem to have an effect on
  the ability to localise the speech stimulus even
  for longer reverberation times. However, The
  ability to localise pure tones were degraded by
  reverberation.

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Hearing Impaired listeners Experiment

• Performing the same experiment on hearing
  impaired subjects. To investigate the effect of
  hearing aids on utilizing ILD and ITD cues in the
  reverberant conditions. Moreover, compare there
  performance with and without hearing aids.
• This will give us insight into the beneficial and
  the detrimental effects of adding reverberation
  in an auditory display .

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Hearing Impaired Listeners

• Some hearing impaired listeners reported that
  aided localisation is better when compared to
  unaided. On the other hand, experimental results
  revealed that aided localisation is worse than
  unaided in the anechoic conditions. This indicats
  that audibility is important in localisation but
  again there are some disadvantages of hearing
  aids when it comes to localisation. There are a
  number of potential explanations for this
  finding.

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Methodology

• Twenty eight adults with high frequency slopping
  hearing loss were recruited from the Audiology
  department in the Royal South Hants Hospital in
  Southampton.
• Aged between 50 and 80 years.
• No signs of Tinnitus, Conductive hearing loss.
• Symmetrical Hearing loss (no more than 15 dB
  threshold differences across all
• Patients use bilateral Siemens Prisma pro
  hearing aids for 6 months at least.
• Signals used are high pass pink noise, low pass
  pink noise, pink noise and speech.

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Effect of Amplification
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Effect of Reverberation
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Hearing aid wearers and localisation (Results)

• Hearing aid wearers were more accurate in their
  performances without their hearing aids as
  opposed to with their hearing aids. However, this
  difference was the greatest when it come to
  localising the high pass pink noise .
• Significant effect of reverberation on localising
  pink noise , speech and low pass pink noise.
  Greater effect was found for the low pass pink
  noise in both aided and unaided conditions.
• There is a significant decrease in the
  performance of the hearing aid wearers in both
  conditions (Aided and Unaided) when compared to
  normal hearing listeners.

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Future plan

• The effect of reverberation on ITDs and ILDs was
  measured using KEMAR (Knowles Electronics Manikin
  for Acoustic Research).
• Put the data together and write up

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Thank you Q A
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References

• Cunningham, B. (2000, April). Proceedings of the
  2000 International Conference on
• Auditory Display, Atlanta, GA, Learning
  Reverberation Considerations for
• Spatial Auditory Displays.
• Gelfand, S.A. (1998). Hearing An introduction to
  psychological and physiological
• Acoustics. 3rd edition. New York Marcel Dekker.
  pp. 374-381
• Giguere, C. and Abel, S. M. (1993). Sound
  localization Effects of reverberation time,
  speaker array, stimulus frequency, and stimulus
  rise/decay. Journal of the Acoustical Society of
  America, 94, pt 1, 769-776.
• Lutman M, and Payne E, (2002) Investigation of
  localisation abilities of bilateral users of
• Phonak Claro instrument. ISVR Contract Report No.
  02/18, 2002
• Mershon, D.H., W.L. Ballenger, A.D. Little, P.L.
  McMurtry, and J.L. Buchanan, (1989).
• Effects of room reflectance and background noise
  on perceived auditory distance.
• Perception, 18, 403-416.
• Yost, W. A. (2000). Fundamentals of hearing, an
  introduction. 4th edition.

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Reverberant vs. Anechoic room
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Effect of amplification and reverberation on
different stimuli (1)
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(2)