An overview of analog and digital torsional vibration measurement methods is presented. Significant sources of digital measurement error are discussed in detail. Methods to minimize measurement errors are explored. A method to use multi-bit A/D data acquisition of a magnetic pickup signal to accurately measure tooth passing frequency with low sample rates is proposed. A frequency domain correction window is proposed which improves the frequency response of the standard digital demodulation technique. The proposed improvements enable accurate torsional vibration measurement with inexpensive A/D data acquisition equipment.