Characterization of a fitness monitor based on its operation enables a processor to account for variations in device operating modes and biometric characteristics of the user. The fitness monitor includes an emitter (e.g., LED) for transmitting light toward skin of the user, a receiver (e.g., photodiode) for receiving a reflection of the transmitted light, a photometric front end for generating a photoplethysmogram (PPG) signal based on the received reflection, and a processor configured to select an intensity level for the emitter based on a comparison of a determined component of the PPG signal and a reference value. The reference value, which may characterize the fitness monitor based on a determined variability or range of the PPG signal, may be utilized by the processor to improve or maintain the signal quality of the PPG signal to enable determination of a cardiac component and/or reduction of power consumption by the fitness device.