PURPOSE: To determine the Fourier spectrum of complex waves.

DESCRIPTION: This experiment uses a digital oscilloscope with a fast Fourier transform module to determine the Fourier spectrum, simultaneously displaying the wave shape and the Fourier spectrum on its CRT. Any periodic wave from a wave generator or sound, such as a musical instrument or the singing voice, can be analyzed. A variety of waves can be input from wave generators, such as the standard wave shapes, and a microphone, such as steady-state instrumental or vocal sounds.

The photographs above show a 200 Hz square wave (left) and a clarinet playing the note G ~ 200 Hz. For the electronic sounds a loudspeaker is provided so that you can hear the sound of each electronically generated wave. The loudspeaker is buffered by an audio amplifier so that the signal input into the oscilloscope is not distorted by having a speaker attached.

Click on any of the wave shapes displayed below to see and hear an mpeg video analyzing the sound of an instrumental wave and its comparable electronically generated wave.

sine wave and recorder	sawtooth wave and horn
pulse train wave and crumhorn	square wave and clarinet

SUGGESTIONS: Because most people have not actually heard a crumhorn played, we have provided an example of fine crumhorn music that can be accessed by clicking: Crumhorn music, please!

REFERENCES: (PIRA unknown.)

EQUIPMENT: Tektronix TDS digital oscilloscope with FFT module, wave generator with amplifier and loudspeaker, and microphone with high-level output for instrumental and vocal sounds.

SETUP TIME: 5 min.