Fransys is software for accurately measuring the frequency response of audio equipment using a computer's sound card. Fransys can be used to measure all sorts of devices – speakers, headphones, sound cards, amplifiers, electronic circuits, etc. Fransys is free for non-commercial use. A sweep of sine waves is produced and played through the equipment under test. The equipment's output is then recorded and measured. Fransys measures both the amplitude and phase of the tones as the frequency varies. Experiments show that an old PC running Fransys can match expensive lab equipment to within 0.2% average error. For more information please take a look at the manual.