This paper presents a multiple-voltage high-level synthesis methodology for low power DSP applications using algorithmic transformation techniques. Our approach is motivated by maximization of task mobilities in that the increase of mobilities may raise the possibility of assigning tasks to low-voltage components. The mobility means the ability to schedule the starting time of a task. It is defined as the distance between its as-late-as-possible (ALAP) schedule time and its as-soon-as-possible (ASAP) schedule time. To earn task-mobilities, we use loop shrinking, retiming and unfolding techniques. The loop shrinking can first reduce the iteration period bound (IPB) and, then, the others are employed for shortening the minimum achieved sample period (MASP) as much as possible. The minimization of MASP results in high task mobilities. Thereafter, we can assign tasks with high mobilities to low-voltage components and minimize energy dissipation under resource and latency constraints. With considering the overhead of level conversion, our approach can achieve significant power reduction. For instance, as the experimental results, we can save the power consumption up to 54.77% for the case of the third-order IIR filter.