An electronic fitness device comprises a first optical transmitter array, a first optical receiver, a second optical receiver, and a processing element. The first optical transmitter array includes first optical transmitter operable to transmit a first optical signal having a first wavelength and a second optical transmitter operable to transmit a second optical signal having a second wavelength. The first optical receiver is operable to receive modulated optical signals and generate a first photoplethysmogram (PPG) signal resulting from the first optical signal and a second PPG signal resulting from the second optical signal. The second optical receiver is operable to receive modulated optical signals and generate a third PPG signal resulting from the first optical signal and a fourth PPG signal resulting from the second optical signal. The processing element is operable to determine cardiac information of the user based on the received PPG signals.