Purpose:Compare and analyze the frequency spectra of various modulated sounds such as tremolo, vibrato, and beats.
Description:Using the Pasco Dual Function Generator, a 1000 Hz sine wave is modulated by a 100 Hz sine wave and the spectrum of the modulated signal displayed using the spectrum analyzer. The photograph at the center shows the original 1000 Hz sine wave and the photograph at the right shows the case where that wave is amplitude modulated by a 100 Hz sine wave, producing a beat-like wave and a spectrum that has two sidebands around the 1000 Hz carrier. Amplitude modulation, frequency modulation, or double sideband modulation (sometimes called balanced modulation, or ring modulation with synthesizers) can be used. Two sine waves can be added together using the Dual Function Generator to produce beats, and the spectrum of the beats obtained and compared with that of double sideband modulation. The waveform is displayed on one trace and the spectrum on the other.
Try out some frequency combinations ahead of time, then have students predict the results.