The present invention relates to a system for calculating a digital quality index (DQI), which provides a rating on a predetermined scale, indicative of the impairments in a received quadrature amplitude modulated (QAM) signal in a CATV cable system. The DQI system utilizes bit error rates prior to and after forward error correction to calculate the DQI value. To increase the calculation rate, the bit error rates can be estimated using voltage errors, signal to noise ratios and/or average corner error metrics.