A PC with sound card as an audio waveform generator, a two-channel digital oscilloscope and a spectrum analyzer

The availability of inexpensive PC sound cards that can simultaneously play and record stereo digital audio files permits a single PC to function as both a signal generator and as a dual-channel recording digital oscilloscope. When the input and output of a linear analog circuit are recorded, for example, free or inexpensive software permits display of the input and output waveforms and spectra, as well as calculation of the magnitude and phase of the transfer function. Thus, students can perform measurements and calculations on simple signal processing circuits with their own PCs. The result is expanded utility of hardware homework, which before, despite popularity among students, was severely limited in applications beyond DC circuits