An electronic fitness device comprises first and second optical transmitters, an optical receiver, and a processing element. The first optical transmitter is configured to transmit a first optical signal having a first wavelength. The second optical transmitter is configured to transmit a first optical signal having a second wavelength. The optical receiver is configured to receive the first and second optical signals and to generate first and second photoplethysmogram (PPG) signals respectively resulting from the received optical signals. The processing element is configured to control the first and second optical transmitters to transmit the first and second optical signals, receive the first and second PPG signals, and utilize the second PPG signal to reduce a noise component from the first PPG signal.
