This paper presents a novel algorithm of a scalable and efficient Pseudo-Quadrature Mirror Filters (PQMF), which is employed for partial decoding a single-layer audio bitstream such as MP3, typically coded in joint/MS mode. The proposed algorithm is a new extension to our previous work on scalable audio decoding and is designed for asymmetric partial spectrum reconstruction (APSR), where perceptually irrelevant computations are removed. Furthermore, an efficient up-sampling operation is introduced for right channel output. The slight distortions introduced by our simple up-sampling method are inaudible according to a set of perceptual evaluations. Simulation results show that 64.6% energy savings can be achieved for a typical configuration in comparison to the standard PQMF algorithm employed by MPEG-1 audio.