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A novel approach to the realization of fast and efficient IIR digital filters is presented. The realization is based on recently introduced state-space structures and retains and enhances their low noise and sensitivity properties while reducing the number-of-required multiplications. This permits the implementation of higher order optimal forms requiring only 1.34 to 1.65 times the number of multiplications used in the direct form (well known for 'its poor coefficient sensitivity and high output noise levels). The high inherent parallelism of the state-space structure is also further enhanced by the proposed fast digital filter (FDF). The resulting block-processing algorithm is suitable for high speed implementation of digital filters on parallel processing systems. These systems employ fast and efficient techniques, such as distributed arithmetic or multimicroprocessor techniques, to perform the required computation of the long-independent inner products. In addition to low quantization noise, the FDF structure has other desirable properties including low sensitivity and improved limit cycle behavior. For output decimating IIR filters additional savings in the number of multiplications is achieved with the proposed structure.