A system and methods for synchronizing quantized sampled data in a monitoring device. A variable frequency output signal is coupled to an analog to digital converter. A fixed frequency clock is coupled to the analog to digital converter. The analog to digital converter samples the output signal at a fixed frequency to produce high speed samples. A group of initial high speed samples is stored from the analog to digital converter over a fixed window of time. The group of initial high speed samples is interpolated to produce a group of fewer low speed samples from the initial group of high speed samples over the fixed window of time. The group of low speed samples is stored as a representation of the variable frequency output signal.