An efficient method of detecting engine knock using spectral analysis is presented. Multiple single-point DFTs are used to condition the measured knock signal. Using multiple frequencies in the detection algorithm provides a better signature of the combustion process and enhances the ability to detect low-level knock across the entire operating range of the engine. The detection strategy compares the DFT outputs to a variable reference to determine a knock intensity metric. Unlike currently used techniques, the algorithm adapts the reference (no-knock condition) to varying engine speeds and loads. An overview of the knock detection problem and current technology is presented.