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The paper reports on an investigation into some problems relating to the implementation of subband coding systems using nonrecursive quadrature mirror filters. Particular attention is given to the noise resulting from the use of finite-word-length registers for data storage and arithmetic operations. Formulas for the evaluation of the bounds and variances of the errors due to quantisation of the filter coefficients, roundoff in arithmetic computations and the quantisation for compression encoding are derived. The derivations are based on a statistical model of the noise sources. An extensive simulation has been carried out and the results of the simulation have been found to be in excellent agreement with the theoretically predicted results.