Abstract: This paper presents a scheme for estimating two-band amplitude scale attack within a quantization-based watermarking context.Although quantization-based watermarking schemes achieve the channel capacity in terms of additive noise attacks,these schemes are not robust against linear time invariant filtering attacks.We concentrate on a multi-band amplitude scaling attack that modifies the spectrum of the signal using an analysis/synthesis filter bank.First we derive the probability density function (PDF) of the attacked data.Second, using a simplified approximation of the PDF model,we derive a maximum likelihood (ML) procedure for estimating two-band amplitude scaling factor.Finally,experiments are performed with synthetic audio signals showing the good performance of the proposed estimation technique under realistic conditions.