The invention provides spectroscopic systems and spectrometers employing an optical interference filter module having a plurality of bandpass regions. In certain embodiments, the systems include a mechanism for wavelength tuning/scanning and wavelength band decoding based on an angular motion of one or more filters. A spectral processing algorithm separates the multiplexed wavelength-scanned bandpass regions and quantifies the concentrations of the analyzed chemical and/or biological species. The spectroscopic system allows for compact, multi-compound analysis, employing a single-element detector for maximum performance-to-cost ratio. The spectroscopic system also allows for high-sensitivity measurement and robust interference compensation.