Techniques for implementing digital signal processing (DSP) operations, such as filtering with molecular reactions are discussed. A DSP specification is used to demonstrate how to synthesize molecular reactions that produce time-varying output concentrations of molecules as a function of time-varying input concentrations. The operations are implemented through a 'self-timed' protocol that transfers concentrations between molecular types based on the absence of other types. The methodology is demonstrated with the design of a simple moving average filter along with a more complex biquad filter. A sequential system computes output values in a moving-average filter that are a function of the current input values along with prior input values. It is also demonstrated that delay elements are at the core of digital signal processing, which store signals values temporarily, allowing for iterative processing.