An analog input signal is digitized by first sampling the analog signal to produce a first sequence of analog samples representing successive magnitudes and de-interleaving the first sequence into a set of two or more second sequences. A parallel processing, sigma-delta modulator then processes the set of second sequences to produce a set of two or more third sequences of digital data elements which are then interleaved to produce a fourth sequence of digital data elements. The fourth sequence is then digitally filtered and decimated to produce a fifth sequence of digital data elements representing successive magnitudes of the analog input signal.