Audio Systems Laboratory
Kevin D. Donohue,
Department of
The following links are to audio,
image, and video files related to experiments and demonstrations with
microphone array systems. The lab
equipment consists of a cage
(13’x13’x7’) on which speakers and microphones can be mounted for collecting or
rendering acoustic energy over an array system.
The cage was built with components from 80/20
Inc. The Industrial
Erector Set. In addition, acoustic treatments can be
mounted on the wall of the cage to realize various noise and reflectively
properties of a variety of rooms. The
data collection and processing is driven by 2 dual AMD processor computers
running Linux. The data recording
computer is connected to 2 Delta 1010 cards by M-Audio with 8 analog input channels each sampled up
to 96kHz (24 bit) and 8 analog outputs each.
Pictures of Audio Cage:
Cage side
with Linear Microphone array, a couple of speakers, and absorptive acoustic
treatment
Pictures of Electronic Interface (for 8 speakers and 8
microphones):
Preamps, Delta1010, Output Amp
Acoustic image (steered response power (SRP)) from a
20 ms audio frame:
Sound Source Location movie of a walking guitar:
This is a quick-time format movie of SRP
images of a guitar playing in front of an 8 element linear microphone
array. The microphones are 40 cm apart
and are located at the bottom of the movie frame. The field of view (FOV) is 3 meters wide and
2 meters deep. At 2 points the guitar
steps out of the FOV; however because the coherence length of the tonal sounds
is so long and the wavelength are as large as 2 to 3 meters, the sound will
bleed into the FOV. In addition, with a 40 cm spacing, aliasing (for frequencies higher than about
430 Hz) and strong sidelobes can be observed in this image. No processing is done to reduce these
artifacts: (Walking
Guitar)
Video and Acoustic SRP movie together:
In these examples a perimeter
array is used, consisting of 8 microphones, 2 on each wall arranged on vertices
of an equilateral octagon with a spacing of 1.35 Meters at a height about equal
to mouths of the speakers in the cage. A
fisheye lens was mounted to the ceiling about 7.5’ above the floor and an angle
of 185 degrees. So the audio SRP data
was collected with the video so that the activity in the cage could be viewed
while watching the SRP movie. The
fisheye lens distorts the image nonlinearly over the acoustic imaging plane, so
a one-to-one correspondence between the video and SRP image is not observed
(except when the speaker was directly under the lens). For all movies the FOV was 3.225m by 3.225m.
This movie is a single
speaker talking and moving around, the video image is on top and the SRP image
on the bottom: Single
Speaker Split
This movie is the same as above
except images are overlaid: Single
Speaker Overlay
This movie has two speakers talking simultaneously and moving around, the video image is on top and the SRP image on the bottom: Two Speakers Split
This movie is the same as
above except images are overlaid: Two
Speakers Overlay
