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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 ??r . The two parameters and chosen analyzing frequencies influence the depth sensing of micromagnetic changes. The most commonly chosen characteristic of Barkhausen noise is the V2 RMS 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.