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Special Topic 1

Special Topic 1. Processing Sound Files The most interesting sounds are those which have sine tones. Record Sound with Your Device. 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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Special Topic 1

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  1. Special Topic 1 Processing Sound Files The most interesting sounds are those which have sine tones

  2. Record Sound with Your Device

  3. For Android Users Allows sound recordings to be transferred in *.ogg format via Email. Similar apps appear to be available to iPhone & Apple Devices

  4. 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

  5. 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/

  6. Matlab Utility vibrationdata > Miscellaneous > Sound File Editor > Read wav File Read wav file then Export to Matlab (one or two channels)

  7. CRJ-900 – Cabin Noise Example

  8. Sample Sound File, Two Channels Read into Matlab. Then Export to Workspace File: crj900.wav - noise inside aircraft cabin due to engines, etc.

  9. 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 > FFT - input one of the sound channels

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