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We use magnetic Barkhausen noise to assess the microstructure, hardness, and residual stresses in hardened surface layers. We performed measurements on induction surface-hardened specimens, the thickness of hardened layers being different in each case. A change in the microstructure of the hardened surface layer produces changes in specific electric conductivity and relative permeability μr. The two parameters and chosen analyzing frequencies influence the depth sensing of micromagnetic changes. The most commonly chosen characteristic of Barkhausen noise is the VRMS2 value of a captured signal. The choice of frequency determines the depth at which the Barkhausen noise will be analyzed to determine microhardness or residual stresses. [ABSTRACT FROM AUTHOR]