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Re: Sound Spectrum Lab ideas needed




You can do a number of quick and interesting experiments with sound
software which can display an FFT.

1. Show that telephone tone signals consist of two frequencies mixed
in roughly equal amplitude. (Puzzle for you: which digit corresponds
to a mixture of about 760 and 1325 Hz?) How many frequencies are used
to create the digits 0-9 plus * and #? (Please don't bill me for
inadvertent calls to Australia.)

2. Take a paper towel cardboard tube. Predict the resonance
frequencies for a tube with two open ends. Thump the tube near the
mic. Take the FFT of the resulting sound. The lowest major
frequency component is the fundamental resonance of the tube. Find
the speed of sound from this frequency (which for shorter tubes will
be off a bit due to end effects) Try for longer tubes as well. Try
closing one end. Predict effects.

3. Take a 4 foot packing tube. Snap fingers at one end, see this
click in the waveform, see reflection from open (or closed) end. Note
whether or not click waveform is inverted. Why? Find speed of sound
from data.

4. Beats from tuning forks that are maybe 10Hz apart.


In any of these experiments it will be important to play with the
triggering of the sound collection. If you trigger on too low an
amplitude, you'll only see noise. If you set the trigger too high,
you'll not gather any data. My experience with the ULI and microphone
has been that poor triggering is responsible for half of all
experimental troubles, and poor data collection rates or lengths for the
other half.

On 12 Jan 97 at 10:41, Tony Wayne wrote:

I have a piece of sound spectrum software for the Macintosh. What
kind of experiemtns/activities could I use it for. Here are some
ideas I have; show the appearance sine waves for different pitches,
show the effect of crossover componants one an audio signal by
feeding white or pink noise through different value capacitors to a
speaker. -tony


--
John E. Gastineau
900 B Ridgeway Ave.
Morgantown, WV 26505
(304) 296-1966
http://www.badgerden.com/~gastineau
gastineau@badgerden.com