While measuring heart sound of the fetal by phonocardiographic devices, the heart beat of the mother and background sound cannot be avoided in the input signal. It is especially crucial when the subject is obese and fetal is in the critical condition with very poor cardiac output. In such cases high susceptibility to ambient noise makes the diagnostic evaluation of the phonocardiographic signal erroneous.

Adaptive noise cancellation is a particular application of adaptive filter. This filter tracks the dynamic nature of a system and allows elimination of the unwanted part of signal. In this paper using adaptive filters a noise reducer is developed for fetal heart sound de-noising. Recursive Least Squares (RLS) algorithm is used in the design of the reducer to obtain the most optimum cancellation of the overall noise. The design is implemented by using Digital Signal Processing (DSP) technology and found effective in most practical application. The developed adaptive noise reducer has been tested with various fetal heart sound signals and results show that the proposed technique is suitable and viable for de-noising purpose.