Special Topic 1

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Special Topic 1

• Processing Sound Files
• The most interesting sounds are those which have
  sine tones

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Record Sound with Your Device
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For Android Users
Allows sound recordings to be transferred in
.ogg format via Email. Similar apps appear to
be available to iPhone Apple Devices
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Audio File Formats
There are many types of formats. Common ones
are .mp3 - MPEG Layer III Audio - compressed
format - popular for CDs .ogg - Ogg Vorbis -
open source - compressed format - Archos and
Samsung .wav - large file sizes, convenient
for conversion to ASCII text
http//en.wikipedia.org/wiki/Audio_file_format
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Conversion
Need data in .wav format for digital
post-processing Use conversion utility such as

• Online conversion
• http//www.zamzar.com/
• Download freeware audio editor
• http//audacity.sourceforge.net/

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Matlab Utility
vibrationdata gt Miscellaneous gt Sound File Editor
gt Read wav File Read wav file then Export to
Matlab (one or two channels)
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CRJ-900 Cabin Noise Example
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Sample Sound File, Two Channels
Read into Matlab. Then Export to Workspace
File crj900.wav - noise inside aircraft cabin
due to engines, etc.
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Fast Fourier Transform
Each turbofan engine has two rotors. N1 Fan -
104 Hz N2 Core - 252 Hz Engines were at 85
power for this recording.
vibrationdata gt FFT - input one of the sound
channels