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By introducing a fictitious signal yo if necessary we define a transform of a given linear control system which generalizes the passage from the scattering to the chain formalism in circuit theory. Given a factorization b = 0 R of $where R is a block matrix function with a certain key block equal to a minimal phase (or outer) matrix function, we show that a given compensator U = Ky is internally stabilizing for the system B if and only if a related compensator K' is stabilizing for 0. Factorizations 9'= 0 R with 0 having a certain block upper triangular form lead to an alternative derivation of the Youla parametrization of stabilizing compensators. Factorizations with 0 equal to a J-inner matrix function (in a precise weak sense) lead to a parametrization of all solutions K of the H" problem associated with 9. This gives a new solution of the H" problem completely in the transfer function domain. Computation of the needed factorization B= 0 R in terms of a state-space realization of 9 ' leads to the state-space formulas for the solution of the H" problem recently obtained in the literature. KEY WORDS Feedback stabilization H" control J-inner-outer factorization J-spectral factorization 0. INTRODUCTION A standard general feedback configuration in terms of which many problems of interest in

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