A blade monitoring system for calculating average threshold crossings from interpolated threshold crossings of digital waveform samples is disclosed. Each digital waveform sample is converted by an analog-to-digital converter from one of two split analog signals. Each split analog signal is received from a signal splitter that receives each analog signal from an analog signal transmitter. Each analog signal is from a sensed blade passing signal from at least one row of a plurality of blades on a compressor of a turbine.