Lindsay Smith (l) assists in demo of practical FFT techniques at PNW January 2012 meeting. James jj Johnston stands, Bob Smith sits at right, Dan Mortensen in foreground.
The PNW Section held a free, all-day Saturday workshop/seminar about the FFT and the practical use thereof, with breaks interspersed and a no-host lunch. Attendance was about 30 in the morning (about 15 AES members). The event was held at the Redmond WA Teen Center.
In the morning session, James "JJ" Johnston explained what a Fourier Transform is and what it's for, in non-mathematical terms. Then he explained some of the ways that an FFT (Fast Fourier Transform) can be used to measure, characterize, and correct for various kinds of audio system issues, audio testing, and the like.
JJ's demos made use of "Octave" which is a freeware signal analysis software package available from sourceforge.net, and runs on Windows, Linux, and OSX. Steve Hastings showed attendees how to get this freeware and install it, as well as providing some suitable test signals.
An acoustic measurement system was demonstrated showing the Octave commands that can be used to run an actual room probe in near-real-time by using the combination of the freeware Audacity (for capture) and Octave (for analysis).
Also discussed were issues like windowing, time resolution vs. frequency resolution, and what "smoothing" in the frequency domain means in the time domain.
Attendees were then free to find their own lunch in downtown Redmond.
Door prize winners:
Fluke volt light (courtesy Rick Rodriguez/Fluke) - Bruce Brown
Meterman DMM meter (courtesy Rick Rodriguez/Fluke) - Bob Gudgel
JJ personal photo posters - Mark Rogers, Evan Diehl
In the afternoon, Bob Smith and Dan Mortensen presented an overview of popular acoustic measurement systems. This included the basic signal flow for single and dual channel systems, system calibration and a more detailed comparison of measurement microphones. Commercial and free analysis systems were compared. Differences were highlighted between dedicated hardware, pre-integrated, DIY-integrated and complete DIY systems. Following the slide presentation, several analysis systems were demonstrated in action including Meyer Sound SIM and SmaartLive v7.
Media materials, including meeting Powerpoints, audio, and the instructional materials, are available at http://www.aes.org/sections/pnw/pnwrecaps/2012/jj_jan/
