1. A device for determining a physiological parameter, the device comprising: a processor capable of: transforming an input signal at least in part using a wavelet transform to generate a transformed signal; generating a first wavelet scalogram based at least in part on the transformed signal; detecting ridges within a region of the first wavelet scalogram; determining one or more parameters for the detected ridges; determining a ridge density distribution function based at least in part on the one or more parameters; and selecting a ridge based at least in part on the ridge having a scale corresponding to a maximum value of the ridge density distribution function.