We consider the problem of representing timing information associated with functions in a dataflow graph used to represent a signal processing system in the context of high-level hardware (architectural) synthesis. This information is used for synthesis of appropriate architectures for implementing the graph. Conventional models for timing suffer from shortcomings that make it difficult to represent timing information in a hierarchical manner, especially for multirate signal processing systems.We identify some of these shortcomings, and provide an alternate model that does not have these problems. We show that with some reasonable assumptions on the way hardware implementations of multirate systems operate, we can derive general hierarchical descriptions.of multirate systems similarly to single rate systems. Several analytical results such as the computation of the iteration period bound, that previously applied only to single rate systems can also easily be extended to multirate systems under the n e w assumptions.We have applied our model to several multirate signal processing applications, and obtained favorable results. We present results of the timing information computed for several multirate DSP applications that show how the new treatment can streamline the problem of performance analysis and synthesis of such systems.