Estimating the number of sources impinging on an array of sensors is a well known and well investigated problem .A common approach for solving this problem is to use an information theoretic criterion, such as Minimum Description Length (MDL) . MDL technique is very important in many application , but its response degrades under low signal-to-noise ratio (SNR) conditions. This paper proposes a new system to estimate the number of sources by applying MDL to the output of the filter bank consisting quadrature mirror filters (QMF) . Some numerical experiments show that the proposed method can estimate the number of sources under low signal-to-noise ratio(SNR).