The invention provides a method for improving efficiency of a filter bank. The filter bank includes multiple filters implemented by a firmware program. Each of the filters has a corresponding filter equation with a plurality of variables including a plurality of input samples and output samples of the corresponding filter. The variables of the filters are first stored in a specific order, wherein the variables of the same filter are stored together and the input samples and the output samples are stored separately and sorted according to a time index thereof. A starting pointer is then pointed to a first variable of a first filter of the filters. A plurality of current output samples of the filters is then generated according to the filter equations, the variables stored in the specific order, and a plurality of current input samples of the filters. The variables of the filter equations are then updated with the current input samples and the current output samples according to the specific order. Finally, the starting pointer is moved to a next variable of the first variable along a variable update direction for identifying the variables corresponding to a plurality of next samples of the filters.