"A digital adaptive noise-canceller based on a stabilized version of the widrow L.M.S. algorithm"

A powerful digital adaptive noise-canceller which has recently been constructed at RSRE is described. The processor is based on a number of identical adaptive filter modules. Each module functions as a 255-stage tapped delay line which operates with 12 bit data and coefficient words and can be clocked at any sample rate up to 14 kHz providing a maximum signal bandwidth of 6 kHz. Up to 16 modules may be connected in series to generate a long filter so it is possible to construct a 4080 stage device operating at full sample rate. The coefficients are updated using a modified version of the Widrow L.M.S. algorithm which greatly improves the stability of the filter and this important factor has had considerable impact on the overall design. The results of some noise cancellation experiments are also described.