In this work, we investigate the generalized overlap add and overlap-save methods (GenOLA and GenOLS) using discrete sine and cosine transforms (DST's & DCT's). Compared to the GenOLA and GenOLS using discrete Fourier Transform (DFT), the merit of the DST & DCT approach is that the filtering can be implemented by real-valued operations. It is shown that the computational complexity can be minimized when the transform size of DST or DCT is chosen optimally, and a good tradeoff between the computational complexity and system delay can be achieved.