A PC based audio measurement system made by Audiomatica. Includes a calibrated microphone and software. This system can measure impedance, component values of inductors and capacitors. Most important, the time-domain and frequency response, both amplitude and phase, of drivers and systems can be measured. It also measures room reverberation time, SPL sound levels, and sundry other stuff. This was an absolutely essential tool in developing my system, and I highly recommend it to anyone serious about building sound systems