This program generates a chirp signal, sweeping over a given frequency range, and drives a given audio output with the signal, while simultaneously analysing the signal coming from an audio input.  This allows electrical spectroscopy and acoustic spectroscopy from ~10Hz-100 kHz to be performed with a £40 sound card.  Note that AC97-channels (such as on-board sound) have lowpass filters built in, restricting the upper limit to around 25 kHz.  Tested with a Creative Audigy 2 ZS, using kX v5.1 drivers.

Download here.