Dynamic computation of the ratio between two bitstreams representing slowly varying quantities and Dolby Pro Logic decoder

摘要

The ratio y(n) of two digital values, respectively a(n) and b(n), representing the nth elements of two respective sequences of digital input data representing two quantities slowly varying in time, is obtained by computing y(n)=y(n-1)+g*[a(n)-b(n)*y(n-1)]wherein g represents a multiplying factor. Within the domain of the z transform, the expression becomes: Y(z)=z-1*Y(z)+g[A(z)-B(z)conv Y(z)*z-1 where conv indicates an operation of convolution and which, for input sequences corresponding to signals filtered through a lowpass filter with a time constant greater than or equal to 3 msec is simplified to: The approximation is exceptionally good and computation thereof may be achieved by the use of relatively simple hardware, without severely burdening the workload of a microprocessor.