lab5 - 1 Physics 198 PHYSICS OF MUSIC Laboratory 5 Name _...

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1 Physics 198 PHYSICS OF MUSIC Laboratory 5 Name ________________________________ Partner(s) ___________________________________ This laboratory is an introduction to computer-based spectral analysis of sound. Goals : I. To learn to measure Fourier spectra of sound waves. II. To measure the spectrum of a tuning fork and think about its normal modes. III. To gain understanding of how resonances in a speaker distort the sound it produces. IV. To investigate a virtual fundamental. Apparatus : Dell Optiplex 620 Computer equipped with SpectraPlus sound analysis software, USB audio interface box (M-Audio, FastTrack) with a connected microphone (Shure MD58), microphone stand, speaker (Realistic) and audio amplifier, sound level meter (Realistic) and 440 Hz tuning forks. The microphone should be connected to the computer through the USB interface, and the speaker connected through an amplifier to the output of the internal computer sound card. The “mic-input” level knob should be all way CW and the “mix” knob should be all the way CCW (“input”) and the “input-monitor” knob should be pushed in (mono). There is a wiring diagram as an appendix. SpectraPlus Settings : Under “options”, “Device” input should be set to “FastTrack” and output should be set “SoundMAX”. The vertical scaling should be linear and the horizontal also linear, and the “Settings” (again under the “options” menu) should be default, and the mode should be real time. These are also in the appendix. ( Note for instructor: The USB audio interface sometimes enters into a strange mode in which frequencies in the spectrum are off by a multiplicative factor, for example a 440 Hz tuning fork peak might appear at 480 Hz. If this happens: (1) hit the stop button in the SpectraPlus package to stop data acquisition, (2) unplug the USB cable from the interface and (3) plug the USB cable back in. This eliminates the problem. A similar problem is that SpectraPlus sometimes forgets that Fastrack exists. (This is very rare.) the solution is to proceed (1) exit SpectraPlus, unplug FastTrack and plug it back in, (2) restart SpectraPlus and set the input device to FastTrack. You may also need to reset scaling when you do this.) PART I. Measuring Fourier Spectra In this part of the lab, you will learn how to measure spectra using the SpectraPlus package. We will also use function generators implemented in software on the computers. Make sure that the “mic input” level all the way up (clockwise) in the “FastTRACK” interface. The “mix” should be on all the way counterclockwise (“input”). Start the SpectraPLUS package, turn on the “Time Series” view as in the last lab, press the “Run” button on the second row on the screen and speak, hum whistle or sing into the microphone. You should see the waveform of the sound displayed as in the last lab. Now turn on the “Spectrum” view. (You may want to turn off the “Time Series” view if it is distracting.)
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lab5 - 1 Physics 198 PHYSICS OF MUSIC Laboratory 5 Name _...

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