Methods and apparatus are provided for determining the concentration of an analyte in a sample, such as an analyte in a sample of bodily fluid. Some embodiments use a synchronous demodulator and digital filter to reduce microphonic signal content. Some embodiments monitor the microphonic signal content and “hold off” on making a measurement until vibrations subside. Monitoring can be performed using an accelerometer or other vibration sensor. An algorithm can be used to examine the detector output signal and detect excessive microphonic components, making an accelerometer unnecessary.