Membrane less optical microphones show a huge potential in industrial applications due to their excellent robustness to electromagnetic interference and temperature. A key element of such an optical microphone is a digital controller which stabilizes the DC operating point and cancels low frequency interference as the microphone is also sensitive to static pressure changes, e.g. by temperature, altitude, etc. SILA Embedded Solutions has developed a suitable low noise digital controller, which can operate in real-time up to 200 kHz using a Cortex M4/DSP with fixed point floating point. The implemented solution includes multi-rate signal processing where sample rate up/down conversion is employed to implement low frequency control loops. For high frequency interference rejection, the digital controllers operate at the maximum sampling frequency. In addition, a suitable design flow using MATLAB has been developed which allows the simulation of the open and closed control loop including code generation for the embedded systems. Our customer benefited from our combined expertise in audio and control engineering.