According to an example aspect of the present invention, there is provided a Method for regularizing the inversion of a stereo headphone transfer function for headphone equalization, characterized by using the equation for the equalization: H S ⁢ ⁢ 1 - 1 ⁡ ( ω ) = H * ⁡ ( ω )  H ⁡ ( ω )  2 + β ^ ⁡ ( ω ) ⁢ D ⁡ ( ω ) = H * ⁡ ( ω )  H ⁡ ( ω )  2 + [ α ⁡ ( ω ) + σ 2 ⁡ ( ω ) ] ⁢ D ⁡ ( ω ) . in which equation HSI−1(ω) is sigma inversion H*(ω) is complex conjugate of a response D(ω) is a delay filter introduced to produce a causal inverse HRI−1(ω) H*(ω) a response α(ω) is headphone reproduction bandwidth, σ(ω) an estimation of the regularization needed inside that bandwidth.